{"gene":"ATXN3","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":1999,"finding":"The 26S proteasome complex redistributes into polyglutamine aggregates in SCA3/MJD; in neurons from SCA3/MJD brain, the proteasome localizes to intranuclear inclusions containing mutant ataxin-3. Proteasome inhibitors caused a repeat length-dependent increase in aggregate formation, implying the proteasome directly suppresses polyglutamine aggregation. Inclusion formation by full-length mutant ataxin-3 required nuclear localization of the protein and occurred within PML oncogenic domains.","method":"Immunohistochemistry of human SCA3/MJD brain tissue, transfected cell models with proteasome inhibitors, subcellular fractionation/localization studies","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell and tissue localization with functional pharmacological perturbation; single lab, multiple orthogonal approaches","pmids":["10072437"],"is_preprint":false},{"year":2007,"finding":"Loss of Atxn3 in knockout mice increased levels of ubiquitinated proteins in vivo, providing direct evidence for ATXN3's deubiquitinating activity in a physiological context. Atxn3 ko mice showed no overt neurological abnormality on rotarod but displayed reduced exploratory behavior.","method":"Targeted gene knockout in mice; western blot for ubiquitinated proteins; behavioral testing (rotarod, open field)","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean in vivo knockout with direct biochemical readout; provides in vivo evidence for DUB activity","pmids":["17764659"],"is_preprint":false},{"year":2010,"finding":"CK2 and GSK3 phosphorylate ATXN3 on serine 29 within the Josephin domain, and this phosphorylation promotes nuclear uptake of ATXN3. Site-directed mutagenesis of S29 to alanine strongly reduced nuclear localization, while phospho-mimic S29D restored wild-type nuclear localization. Treatment with CK2 and GSK3 inhibitors prevented S29 phosphorylation and inhibited nuclear uptake.","method":"In vitro kinase assay on purified ATXN3, MS analysis of phosphorylation sites, site-directed mutagenesis (S29A and S29D), CK2/GSK3 inhibitor treatment in COS-7 cells, subcellular localization by transfection","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis plus cell-based localization validation, single lab with multiple orthogonal methods","pmids":["20347968"],"is_preprint":false},{"year":2012,"finding":"Calpain-2 cleaves ataxin-3 in vitro and in mouse brain homogenates, and polyglutamine-expanded ataxin-3 is more sensitive to calpain-mediated degradation than wild-type. In vivo, enhancing calpain activity (via calpastatin knockout in SCA3 transgenic mice) aggravated neurological phenotype, increased nuclear aggregate number, and accelerated cerebellar neurodegeneration.","method":"In vitro calpain cleavage assay, mouse brain homogenate cleavage experiments, double-mutant mouse model (SCA3 transgenic × calpastatin KO), immunohistochemistry for nuclear aggregates, behavioral assessment","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro cleavage assay combined with in vivo genetic epistasis model with defined phenotypic readout","pmids":["23100324"],"is_preprint":false},{"year":2009,"finding":"Ataxin-3 protein cleavage (likely caspase-dependent) is conserved in Drosophila models of SCA3, and preventing cleavage by mutating caspase cleavage sites reduces neuronal loss in vivo, demonstrating that ataxin-3 cleavage enhances neurotoxicity.","method":"Drosophila transgenic models expressing wild-type vs. caspase-site mutant ataxin-3; quantification of neuronal loss in vivo; cell-based SL2 cleavage assay","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic in vivo approach in Drosophila with cleavage-site mutagenesis, single lab","pmids":["19783548"],"is_preprint":false},{"year":2015,"finding":"Mutant ATXN3 (polyQ-expanded) physically interacts with and inactivates the DNA repair enzyme PNKP, resulting in inefficient DNA strand break repair, persistent DNA damage accumulation, and chronic ATM activation leading to p53 and PKC-δ pro-apoptotic signaling and neuronal death in SCA3. PNKP overexpression or ATM inhibition blocked mutant ATXN3-mediated cell death.","method":"Co-immunoprecipitation of ATXN3 with PNKP, PNKP enzyme activity assays, DNA damage assays (comet assay, γH2AX), ATM pathway activation assays, PNKP overexpression rescue, ATM inhibitor pharmacology in cell and mouse models","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP plus functional enzyme assay plus genetic rescue, multiple orthogonal methods with defined phenotypic readout","pmids":["25590633"],"is_preprint":false},{"year":2019,"finding":"Mutant HTT impairs a transcription-coupled DNA repair (TCR) complex that includes ATXN3, POLR2A, PNKP, and CBP. Within this complex, ATXN3 activity prevents CBP ubiquitination and degradation; loss of ATXN3 function in HD leads to CBP degradation, impairing transcription and DNA repair. Wild-type ATXN3 thus protects CBP from ubiquitin-mediated degradation as part of the TCR complex.","method":"Co-immunoprecipitation (ATXN3 with POLR2A, PNKP, CBP), PNKP and ATXN3 activity assays, CBP ubiquitination and stability assays, chromatin immunoprecipitation, HD transgenic mouse models","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple reciprocal Co-IPs, enzyme activity assays, and ubiquitination assays across cell and animal models","pmids":["30994454"],"is_preprint":false},{"year":2020,"finding":"ATXN3 associates with RNA polymerase II (RNAP II) and classical non-homologous end-joining (C-NHEJ) proteins including PNKP along with nascent RNAs under physiological conditions. ATXN3 depletion significantly decreases global transcription, repair of transcribed genes, and error-free double-strand break repair. Brain extracts from SCA3 patients show lower PNKP activity, elevated 53BP1, more DNA strand breaks in transcribed genes, and degradation of RNAP II. PNKP complementation completely rescues SCA3 phenotype in Drosophila.","method":"Co-immunoprecipitation of ATXN3 with RNAP II and C-NHEJ proteins, nascent RNA capture, transcription assays, DSB repair reporter assay, ATXN3 knockdown studies, brain extracts from SCA3 patients and mice, Drosophila genetic rescue with PNKP","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple Co-IPs, biochemical activity assays in patient tissue and animal models, genetic complementation in Drosophila","pmids":["32205441"],"is_preprint":false},{"year":2018,"finding":"ATXN3 physically interacts with HDAC3, deubiquitinates HDAC3, and thereby stabilizes HDAC3 protein. This ATXN3/HDAC3 interaction increases during viral infection and promotes IFN-I-mediated signaling pathway (not IFN-I production itself) to enhance antiviral response in murine primary lung cells and human cell lines.","method":"Co-immunoprecipitation of ATXN3 with HDAC3, ubiquitination assays of HDAC3 with and without ATXN3, ATXN3 knockdown/knockout studies, IFN-I signaling assays, viral infection models","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus deubiquitination assay plus functional signaling readout; single lab","pmids":["29802126"],"is_preprint":false},{"year":2019,"finding":"ATXN3 binds to KLF4 via immunoprecipitation and acts as a deubiquitinating enzyme for KLF4, mediating its deubiquitination and stabilization, thereby promoting breast cancer cell metastasis in vitro and in vivo.","method":"DUB library screen (65 enzymes), co-immunoprecipitation of ATXN3 with KLF4, ubiquitination assays, ATXN3 knockdown with KLF4 rescue, in vitro migration/invasion assays, mouse xenograft models","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus deubiquitination assay plus in vivo xenograft model; single lab","pmids":["31563563"],"is_preprint":false},{"year":2023,"finding":"CRISPR screen identified ATXN3 as a positive regulator of PD-L1 transcription. ATXN3 deubiquitinates the AP-1 transcription factor JunB and also stabilizes IRF1, STAT3, and HIF-2α, transcription factors that drive PD-L1 expression in response to IFN-γ and hypoxia. ATXN3 deletion abolished IFN-γ- and hypoxia-induced PD-L1 expression.","method":"CRISPR-based screen, co-immunoprecipitation of ATXN3 with JunB, ubiquitination assays, ATXN3 knockdown with PD-L1 reconstitution, mouse tumor models, IFN-γ/hypoxia stimulation assays","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR screen validated by Co-IP and deubiquitination assays and in vivo models; single lab","pmids":["38038129"],"is_preprint":false},{"year":2023,"finding":"ATXN3 acts as a deubiquitinase for YAP in prostate cancer: the Josephin domain of ATXN3 interacts with the WW domain of YAP, deubiquitylates YAP (specifically inhibiting K48-linked polyubiquitination), and stabilizes YAP protein, thereby promoting YAP/TEAD target gene expression (CTGF, ANKRD1, CYR61) and prostate cancer cell proliferation and invasion.","method":"Co-immunoprecipitation (Josephin domain mapping), K48-specific ubiquitination assays, protein stability (cycloheximide chase), ATXN3 depletion with YAP overexpression rescue, xenograft mouse model, real-time PCR of YAP target genes","journal":"Cell communication and signaling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with domain mapping, K48-specific ubiquitination assay, in vivo rescue; single lab","pmids":["37349820"],"is_preprint":false},{"year":2021,"finding":"ATXN3 promotes anaplastic thyroid carcinoma progression by directly binding to EIF5A2 and reducing its K48-linked ubiquitination and proteasomal degradation, thereby stabilizing EIF5A2 expression.","method":"Co-immunoprecipitation of ATXN3 with EIF5A2, ubiquitination assays, protein stability assays, ATXN3 gain/loss-of-function cellular assays","journal":"Molecular and cellular endocrinology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP and ubiquitination assay from one lab, limited mechanistic depth in abstract","pmids":["34428509"],"is_preprint":false},{"year":2013,"finding":"The type II iodothyronine deiodinase (D2) undergoes retrotranslocation from the ER to the cytoplasm via a p97-ATPase complex, and during this process, Ataxin-3 (Atx3) deubiquitinates ubiquitinated D2 (UbD2). Inhibiting Atx3 with eeyarestatin-I did not affect D2:p97 binding but decreased UbD2 retrotranslocation and caused ER accumulation of high-molecular-weight UbD2.","method":"Co-immunoprecipitation of D2 with p97 and Atx3, eeyarestatin-I pharmacological inhibition of Atx3, ubiquitination assays, subcellular fractionation, colocalization with 20S/19S proteasome subunits","journal":"Molecular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, pharmacological inhibition, and biochemical retrotranslocation assay in D2-expressing cell models; single lab","pmids":["24196352"],"is_preprint":false},{"year":2018,"finding":"Loss of ATXN3 in null mouse embryonic fibroblasts altered transcription of multiple signal transduction pathways, including depressed Wnt and BMP4 and elevated Prolactin, TGF-β, and Ephrin pathways. The most upregulated gene was Efna3 (Ephrin receptor A3), associated with hyperacetylation of histones H3 and H4 at the Efna3 promoter and decreased HDAC3 and NCoR levels in ATXN3-null cells. Overexpression of normal or expanded ATXN3 suppressed Efna3 expression.","method":"RNA-seq transcriptomics in Atxn3 null vs. WT MEFs, chromatin immunoprecipitation for histone acetylation at Efna3 promoter, HDAC3/NCoR western blots, ATXN3 overexpression rescue in cells, qRT-PCR validation in knockout mouse brainstem","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP plus transcriptomics plus KO rescue across two cell types; single lab","pmids":["30231063"],"is_preprint":false},{"year":2023,"finding":"ATXN3 regulates chromatin organization in a catalytic-independent (deubiquitinase-independent) manner. Loss of ATXN3 leads to abnormal nuclear and nucleolar morphology, altered DNA replication timing, increased global transcription, increased histone H1 mobility, changes in epigenetic marks, and higher chromatin sensitivity to MNase digestion. ATXN3 controls the subcellular localization of HDAC3 (its interaction partner), and absence of ATXN3 decreases HDAC3 chromatin recruitment. PolyQ-expanded ATXN3 behaves as a null mutant in these assays, altering DNA replication parameters, epigenetic marks, and HDAC3 subcellular distribution.","method":"ATXN3 KO cell lines; DNA replication timing assays; FRAP for histone H1 mobility; ChIP for epigenetic marks; MNase sensitivity; HDAC3 localization by fractionation/imaging; comparison of catalytic mutant vs. null vs. PolyQ-expanded ATXN3","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (replication timing, FRAP, ChIP, MNase, fractionation) with mechanistic dissection of HDAC3 interaction and catalytic independence","pmids":["36971114"],"is_preprint":false},{"year":2004,"finding":"The misfolding propensity and ubiquitination of ataxin-3 are directly proportional to the length of the polyglutamine repeat and inversely dependent on the size of the protein. Normal-repeat ataxin-3 (full-length and truncated) is not ubiquitinated, whereas expanded-polyQ ataxin-3 is ubiquitinated in proportion to its misfolding propensity.","method":"Cell-based ubiquitination assays with varying polyQ-length ataxin-3 constructs, immunoprecipitation, 1C2 antibody binding assays for misfolding assessment","journal":"Neurotoxicity research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based ubiquitination assay with multiple constructs; single lab","pmids":["15639784"],"is_preprint":false},{"year":2013,"finding":"In Drosophila SCA3 models, Hsp104 suppressed toxicity of a C-terminal ataxin-3 fragment containing the expanded polyQ tract but unexpectedly enhanced aggregation and toxicity of full-length pathogenic ataxin-3. Hsp104 suppressed toxicity of MJD variants lacking part of the N-terminal deubiquitylase domain and variants unable to engage polyubiquitin, indicating that MJD-ubiquitin interactions hinder protective Hsp104 function. This demonstrates that the ubiquitin-binding capacity of ataxin-3 is functionally important for its behavior in protein disaggregation contexts.","method":"Drosophila transgenic models with various ataxin-3 constructs (full-length, truncated, ubiquitin-binding mutants), eye degeneration scoring, aggregation quantification, staging experiments with post-onset Hsp104 expression","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic dissection in Drosophila with multiple domain mutants and staging; single lab","pmids":["24039611"],"is_preprint":false},{"year":2017,"finding":"The truncated C-terminal fragment of mutant ATXN3 causes more mitochondrial fission, decreases expression of mitochondrial fusion markers Mfn-1 and Mfn-2, reduces mitochondrial membrane potential, increases reactive oxygen species, and leads to higher cell death than full-length mutant ATXN3 in neuroblastoma cells and transgenic mice.","method":"Neuroblastoma cell models and transgenic mouse models expressing truncated vs. full-length mutant ATXN3, mitochondrial morphology imaging, Mfn-1/Mfn-2 western blots, MMP assay, ROS measurement, cell death assays","journal":"Frontiers in molecular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell and mouse model comparison with multiple mitochondrial readouts; single lab","pmids":["28676741"],"is_preprint":false},{"year":2006,"finding":"Neuronally differentiated PC12 cells expressing expanded ataxin-3 showed significantly reduced resting membrane potential and a hyperpolarizing shift of the delayed rectifier potassium current activation curve, prior to neuronal cell death, indicating that mutant ataxin-3 causes potassium channel dysfunction.","method":"Stable inducible PC12 cell model with normal vs. expanded ataxin-3; patch-clamp electrophysiology; cell viability assay; ultrastructural analysis","journal":"Experimental neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — patch-clamp in defined cell model with inducible expression; single lab","pmids":["16765348"],"is_preprint":false},{"year":2022,"finding":"Oligodendrocyte maturation is impaired early in SCA3 disease in selectively vulnerable brain regions (cerebellum and brainstem) of SCA3 transgenic mice. This impairment is a cell-autonomous toxic gain-of-function of mutant ATXN3, as ATXN3 KO mice show no oligodendrocyte maturation defects. Ultrastructural microscopy confirmed abnormalities in axonal myelination in SCA3 mice.","method":"Weighted gene coexpression network analysis of longitudinal transcriptomics in SCA3 mouse brain, reporter mouse crosses to quantify mature oligodendrocytes, electron microscopy for axonal myelination, isolation and culture of oligodendrocyte precursor cells from SCA3 mice","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO comparison plus cell-autonomous OPC culture plus ultrastructural confirmation; multiple orthogonal methods, peer-reviewed","pmids":["35042771"],"is_preprint":false},{"year":2005,"finding":"Ribosomal frameshifting occurs at the expanded CAG repeat in ATXN3 mRNA, specifically by -1 slippage, generating polyalanine-containing proteins. This frameshifting is dependent on long CAG tract length. PolyQ-encoding CAA repeats (which cannot frameshift) were not toxic, while expanded CAG ATXN3 was toxic, indicating that frameshifting (not the polyQ per se) contributes to toxicity. Anisomycin reduced -1 frameshifting and also reduced toxicity.","method":"Cell-based ribosomal frameshifting reporter assay, comparison of CAG vs. CAA repeat ATXN3 constructs, anisomycin pharmacology, toxicity assays","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cellular reporter plus pharmacological validation plus CAA control; single lab","pmids":["16087686"],"is_preprint":false},{"year":2012,"finding":"Frameshifting events occurring at the expanded CAG repeat in ATXN3 are toxic in Drosophila and mammalian neurons. Transgenic expression of expanded CAG ATXN3 led to -1 frameshifting, whereas expression of polyglutamine-encoding expanded CAA ATXN3 (which cannot frameshift) was not toxic, demonstrating that expanded CAG-derived frameshifting (not polyQ per se) is necessary for toxicity in these models.","method":"Drosophila transgenic models and mouse neuron models expressing CAG vs. CAA repeat ATXN3 constructs, neurodegeneration scoring, frameshifting detection","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic dissection with CAG vs. CAA controls in two model systems; single lab","pmids":["22337953"],"is_preprint":false},{"year":2015,"finding":"ATXN3 does not interact with the ubiquitin-binding protein UBQLN2 (tested by Co-IP via UBA domain), in contrast to mutant HTT which does interact with UBQLN2. Consequently, UBQLN2 is not recruited to inclusions in SCA3 (neither in mouse models nor human SCA3 brain), distinguishing SCA3 inclusions from HD inclusions.","method":"Co-immunoprecipitation in cell-based system testing ATXN3 vs. HTT interaction with UBQLN2, immunohistochemistry of SCA3 and HD mouse and human brain for UBQLN2 localization","journal":"Neurobiology of disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — negative result confirmed by Co-IP and IHC across multiple models; single lab; negative finding is itself mechanistically informative","pmids":["26141599"],"is_preprint":false}],"current_model":"ATXN3 is a deubiquitinating enzyme (DUB) of the Josephin family that regulates protein homeostasis via the ubiquitin-proteasome pathway, participates in transcription-coupled DNA repair as part of a complex with RNAP II, PNKP, and CBP, controls chromatin organization (in a catalytic-independent manner) by regulating HDAC3 subcellular localization, is activated for nuclear entry by CK2/GSK3 phosphorylation on S29, and is cleaved by calpains to generate toxic fragments; polyQ expansion of ATXN3 inactivates PNKP leading to DNA damage accumulation and ATM-mediated apoptosis, impairs oligodendrocyte maturation through a cell-autonomous toxic gain-of-function, and causes potassium channel dysfunction, while wild-type ATXN3 deubiquitinates substrates including HDAC3, KLF4, YAP, and EIF5A2 in contexts ranging from antiviral signaling to cancer progression."},"narrative":{"mechanistic_narrative":"ATXN3 is a Josephin-family deubiquitinating enzyme that maintains protein homeostasis through the ubiquitin-proteasome system, with knockout animals accumulating ubiquitinated proteins in vivo [PMID:17764659]. It removes ubiquitin from a broad range of substrates to control their stability, including HDAC3 during antiviral interferon-I signaling [PMID:29802126], the transcription factors KLF4 [PMID:31563563], YAP via Josephin-domain engagement of the YAP WW domain with K48-linkage specificity [PMID:37349820], and JunB/IRF1/STAT3/HIF-2α to drive PD-L1 expression in tumor cells [PMID:38038129]. Beyond catalysis, ATXN3 operates in genome maintenance as a component of a transcription-coupled DNA repair complex with RNA polymerase II, PNKP and CBP, where its activity protects CBP from ubiquitin-mediated degradation and supports global transcription and error-free double-strand break repair [PMID:30994454, PMID:32205441]. It also functions through a catalytic-independent activity to organize chromatin, controlling HDAC3 subcellular localization and chromatin recruitment, with loss producing abnormal nuclear morphology, altered replication timing and epigenetic marks [PMID:36971114, PMID:30231063]. Nuclear entry of ATXN3 is gated by CK2/GSK3 phosphorylation of serine 29 within the Josephin domain [PMID:20347968], and the protein is processed by calpains and caspases to generate C-terminal fragments [PMID:23100324, PMID:19783548]. ATXN3 also participates in ER-associated retrotranslocation, deubiquitinating type II iodothyronine deiodinase as it is extracted via the p97 ATPase [PMID:24196352]. Polyglutamine expansion causes the SCA3/MJD spinocerebellar ataxia through multiple toxic mechanisms: nuclear inclusion formation that sequesters the proteasome [PMID:10072437], physical inactivation of PNKP leading to persistent DNA damage and ATM-mediated apoptotic signaling [PMID:25590633], cell-autonomous impairment of oligodendrocyte maturation [PMID:35042771], potassium channel dysfunction [PMID:16765348], and toxicity arising from -1 ribosomal frameshifting at the expanded CAG repeat rather than the polyQ tract alone [PMID:16087686, PMID:22337953].","teleology":[{"year":1999,"claim":"Established that mutant ataxin-3 forms nuclear inclusions that sequester the 26S proteasome, linking the proteasome system to polyglutamine aggregation pathology in SCA3.","evidence":"Immunohistochemistry of SCA3 brain and proteasome-inhibitor perturbation in transfected cells","pmids":["10072437"],"confidence":"Medium","gaps":["Does not establish whether proteasome sequestration is cause or consequence of toxicity","Mechanism of proteasome suppression of aggregation not resolved"]},{"year":2004,"claim":"Showed that misfolding and ubiquitination of ataxin-3 scale with polyQ length, defining the biochemical basis of the toxic gain-of-function.","evidence":"Cell-based ubiquitination assays across polyQ-length and truncation constructs","pmids":["15639784"],"confidence":"Medium","gaps":["Ubiquitin ligase responsible not identified","Cellular consequence of expanded-form ubiquitination not addressed"]},{"year":2005,"claim":"Identified -1 ribosomal frameshifting at the expanded CAG repeat as a toxicity mechanism distinct from polyQ itself, reframing how repeat expansion causes disease.","evidence":"Cell-based frameshifting reporter, CAG vs CAA constructs, anisomycin pharmacology","pmids":["16087686"],"confidence":"Medium","gaps":["Contribution of frameshift products to human disease not quantified","Identity and fate of polyalanine products in neurons not characterized"]},{"year":2006,"claim":"Demonstrated that expanded ataxin-3 disrupts potassium channel function before cell death, identifying an early electrophysiological deficit.","evidence":"Patch-clamp electrophysiology in inducible PC12 model","pmids":["16765348"],"confidence":"Medium","gaps":["Molecular link between ATXN3 and the channel not defined","Not confirmed in neurons of patients or animal models"]},{"year":2007,"claim":"Provided the first in vivo evidence that ATXN3 is a functional deubiquitinase, since its loss elevates ubiquitinated proteins.","evidence":"Atxn3 knockout mice with western blot for ubiquitinated proteins and behavioral testing","pmids":["17764659"],"confidence":"High","gaps":["Physiological substrates not identified in this study","Mild phenotype leaves functional redundancy unresolved"]},{"year":2009,"claim":"Established that proteolytic cleavage of ataxin-3 enhances neurotoxicity, since blocking caspase sites reduces neuronal loss.","evidence":"Drosophila transgenics with caspase-site mutants and cell-based cleavage assays","pmids":["19783548"],"confidence":"Medium","gaps":["Specific protease in vivo not definitively assigned","Mechanism by which fragments confer toxicity not addressed here"]},{"year":2010,"claim":"Defined how ATXN3 nuclear entry is regulated, identifying CK2/GSK3 phosphorylation of S29 as the switch controlling nuclear localization.","evidence":"In vitro kinase assay, MS, S29A/S29D mutagenesis and kinase inhibitors with cell localization","pmids":["20347968"],"confidence":"High","gaps":["Consequence of regulated nuclear entry for substrate processing not shown","Whether polyQ expansion alters this regulation not tested"]},{"year":2012,"claim":"Showed that calpain cleavage generates fragments and that enhancing calpain activity worsens SCA3 pathology in vivo, establishing calpain as a disease modifier.","evidence":"In vitro calpain cleavage and SCA3 transgenic x calpastatin-KO epistasis with histology and behavior","pmids":["23100324"],"confidence":"High","gaps":["Precise cleavage sites not mapped","Relative contribution of calpain vs caspase fragments unresolved"]},{"year":2013,"claim":"Connected ATXN3 to ER-associated degradation, showing it deubiquitinates D2 during p97-mediated retrotranslocation.","evidence":"Co-IP of D2 with p97 and Atx3, eeyarestatin-I inhibition, retrotranslocation assays","pmids":["24196352"],"confidence":"Medium","gaps":["Pharmacological inhibitor may have off-target effects","Generality across other ERAD substrates not established"]},{"year":2013,"claim":"Used Drosophila genetic dissection to show ataxin-3's ubiquitin-binding capacity governs its behavior in disaggregation, revealing the UBA domains shape disease-relevant handling.","evidence":"Drosophila models with full-length, truncated and ubiquitin-binding-mutant constructs plus Hsp104 staging","pmids":["24039611"],"confidence":"Medium","gaps":["Human relevance of Hsp104 interplay limited","Endogenous disaggregase partners not identified"]},{"year":2015,"claim":"Identified PNKP inactivation by mutant ATXN3 as a direct mechanism linking the protein to DNA damage accumulation and ATM-driven neuronal apoptosis.","evidence":"Reciprocal Co-IP, PNKP activity assays, DNA damage and ATM pathway readouts, PNKP-overexpression and ATM-inhibitor rescue","pmids":["25590633"],"confidence":"High","gaps":["Whether wild-type ATXN3 normally activates PNKP not fully resolved here","Spatial/temporal sequence of damage vs aggregation in neurons unclear"]},{"year":2015,"claim":"Distinguished SCA3 from Huntington disease at the molecular level by showing ATXN3 does not engage UBQLN2 and UBQLN2 is not recruited to SCA3 inclusions.","evidence":"Co-IP comparing ATXN3 vs HTT with UBQLN2 and IHC of SCA3 and HD brain","pmids":["26141599"],"confidence":"Medium","gaps":["Negative result; does not rule out weak or transient interactions","Functional consequence of absent UBQLN2 recruitment not explored"]},{"year":2017,"claim":"Demonstrated that the truncated C-terminal mutant fragment drives mitochondrial fission and oxidative stress more potently than full-length protein, linking fragmentation to mitochondrial toxicity.","evidence":"Neuroblastoma and transgenic mouse comparison of truncated vs full-length mutant ATXN3 with mitochondrial and ROS readouts","pmids":["28676741"],"confidence":"Medium","gaps":["Direct molecular link to fusion machinery not defined","Single-lab observation"]},{"year":2018,"claim":"Established ATXN3 as a deubiquitinase for HDAC3 that stabilizes it to promote interferon-I-mediated antiviral signaling, defining a physiological substrate.","evidence":"Reciprocal Co-IP, HDAC3 ubiquitination assays, ATXN3 knockdown/KO and IFN-I signaling readouts in viral infection models","pmids":["29802126"],"confidence":"Medium","gaps":["Single-lab finding","Linkage to ATXN3's neuronal roles not made"]},{"year":2018,"claim":"Linked ATXN3 to transcriptional and chromatin control, showing its loss alters signaling-pathway gene expression and histone acetylation at the Efna3 promoter alongside reduced HDAC3/NCoR.","evidence":"RNA-seq, ChIP for histone acetylation, HDAC3/NCoR westerns and ATXN3 rescue in MEFs and KO brainstem","pmids":["30231063"],"confidence":"Medium","gaps":["Direct vs indirect transcriptional effects not separated","Mechanism connecting ATXN3 to HDAC3/NCoR levels not resolved here"]},{"year":2019,"claim":"Placed ATXN3 within a transcription-coupled DNA repair complex (RNAP II, PNKP, CBP) where its activity protects CBP from degradation, bridging transcription and repair functions.","evidence":"Co-IPs, PNKP/ATXN3 activity assays, CBP ubiquitination/stability assays, ChIP and HD mouse models","pmids":["30994454"],"confidence":"High","gaps":["Stoichiometry and assembly order of the complex not defined","Whether expanded ATXN3 disrupts CBP protection not directly tested here"]},{"year":2019,"claim":"Identified KLF4 as an ATXN3 substrate stabilized via deubiquitination, implicating ATXN3 in breast cancer metastasis.","evidence":"DUB-library screen, Co-IP, ubiquitination assays, knockdown/rescue, migration and xenograft assays","pmids":["31563563"],"confidence":"Medium","gaps":["Ubiquitin linkage type not specified","Single-lab cancer-context finding"]},{"year":2020,"claim":"Showed ATXN3 physiologically associates with RNAP II and C-NHEJ machinery to sustain transcription and error-free DSB repair, and that SCA3 patient brain shows impaired PNKP activity and RNAP II degradation.","evidence":"Co-IPs, nascent-RNA capture, DSB repair reporters, knockdown, patient/mouse brain extracts, Drosophila PNKP rescue","pmids":["32205441"],"confidence":"High","gaps":["Causal order between transcription loss and repair loss not disentangled","Whether PNKP rescue translates to mammals not shown"]},{"year":2021,"claim":"Extended ATXN3 substrate range to EIF5A2 in anaplastic thyroid carcinoma via reduced K48-linked ubiquitination and stabilization.","evidence":"Co-IP, ubiquitination and stability assays, gain/loss-of-function cellular assays","pmids":["34428509"],"confidence":"Low","gaps":["Limited mechanistic depth; single Co-IP and ubiquitination assay from one lab","No in vivo validation reported"]},{"year":2022,"claim":"Demonstrated a cell-autonomous toxic gain-of-function: mutant ATXN3 impairs oligodendrocyte maturation in vulnerable regions while loss of ATXN3 does not, identifying a non-neuronal disease mechanism.","evidence":"Longitudinal transcriptomics, reporter mouse crosses, electron microscopy and SCA3 OPC culture","pmids":["35042771"],"confidence":"High","gaps":["Molecular target of mutant ATXN3 in oligodendrocytes not identified","Contribution to motor phenotype relative to neuronal loss unquantified"]},{"year":2023,"claim":"Defined a catalytic-independent chromatin-organizing role for ATXN3 acting through HDAC3 localization, and showed polyQ-expanded ATXN3 behaves as a null in these assays.","evidence":"ATXN3 KO cells, replication timing, FRAP, ChIP, MNase sensitivity, HDAC3 fractionation/imaging, catalytic-mutant comparison","pmids":["36971114"],"confidence":"High","gaps":["How ATXN3 directs HDAC3 localization mechanistically unresolved","Relationship of chromatin role to disease progression not established"]},{"year":2023,"claim":"Showed ATXN3 deubiquitinates JunB and stabilizes IRF1/STAT3/HIF-2α to drive PD-L1 expression under IFN-γ and hypoxia, implicating it in tumor immune evasion.","evidence":"CRISPR screen, Co-IP, ubiquitination assays, knockdown/reconstitution and mouse tumor models","pmids":["38038129"],"confidence":"Medium","gaps":["Direct vs indirect stabilization of the multiple factors not fully separated","Single-lab finding"]},{"year":2023,"claim":"Established ATXN3 as a YAP deubiquitinase in prostate cancer via Josephin-WW domain interaction and K48-specific deubiquitination, promoting YAP/TEAD target expression.","evidence":"Domain-mapping Co-IP, K48-specific ubiquitination assays, cycloheximide chase, depletion/rescue and xenograft","pmids":["37349820"],"confidence":"Medium","gaps":["Single-lab cancer-context finding","Connection to ATXN3's other substrate networks not explored"]},{"year":null,"claim":"How ATXN3's distinct activities — DUB catalysis, catalytic-independent chromatin organization, transcription-coupled repair, and regulated nuclear trafficking — are integrated, and which are mechanistically central to SCA3 neurodegeneration, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model connecting catalytic and non-catalytic roles","Causal hierarchy among DNA damage, oligodendrocyte defects, fragment toxicity, and frameshifting in disease not established","Endogenous physiological substrate spectrum in neurons not comprehensively defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a 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Binds long polyubiquitin chains and trims them, while it has weak or no activity against chains of 4 or less ubiquitins (PubMed:17696782). Involved in degradation of misfolded chaperone substrates via its interaction with STUB1/CHIP: recruited to monoubiquitinated STUB1/CHIP, and restricts the length of ubiquitin chain attached to STUB1/CHIP substrates and preventing further chain extension (By similarity). Interacts with key regulators of transcription and represses transcription: acts as a histone-binding protein that regulates transcription (PubMed:12297501). Acts as a negative regulator of mTORC1 signaling in response to amino acid deprivation by mediating deubiquitination of RHEB, thereby promoting RHEB inactivation by the TSC-TBC complex (PubMed:33157014). Regulates autophagy via the deubiquitination of 'Lys-402' of BECN1 leading to the stabilization of BECN1 (PubMed:28445460)","subcellular_location":"Nucleus matrix; Nucleus; Lysosome membrane","url":"https://www.uniprot.org/uniprotkb/P54252/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ATXN3","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000066427","cell_line_id":"CID001683","localizations":[{"compartment":"cytoplasmic","grade":3},{"compartment":"nucleoplasm","grade":3},{"compartment":"big_aggregates","grade":2}],"interactors":[{"gene":"GPALPP1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID001683","total_profiled":1310},"omim":[{"mim_id":"615324","title":"JOSEPHIN DOMAIN-CONTAINING PROTEIN 2; JOSD2","url":"https://www.omim.org/entry/615324"},{"mim_id":"615323","title":"JOSEPHIN DOMAIN-CONTAINING PROTEIN 1; JOSD1","url":"https://www.omim.org/entry/615323"},{"mim_id":"612876","title":"SPINOCEREBELLAR ATAXIA 9; SCA9","url":"https://www.omim.org/entry/612876"},{"mim_id":"610150","title":"CHAPERONIN CONTAINING T-COMPLEX POLYPEPTIDE 1, SUBUNIT 5; CCT5","url":"https://www.omim.org/entry/610150"},{"mim_id":"607047","title":"ATAXIN 3; ATXN3","url":"https://www.omim.org/entry/607047"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Nucleoli","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ATXN3"},"hgnc":{"alias_symbol":["ATX3","JOS"],"prev_symbol":["SCA3","MJD"]},"alphafold":{"accession":"P54252","domains":[{"cath_id":"3.90.70.40","chopping":"15-194","consensus_level":"medium","plddt":90.8321,"start":15,"end":194}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P54252","model_url":"https://alphafold.ebi.ac.uk/files/AF-P54252-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P54252-F1-predicted_aligned_error_v6.png","plddt_mean":75.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ATXN3","jax_strain_url":"https://www.jax.org/strain/search?query=ATXN3"},"sequence":{"accession":"P54252","fasta_url":"https://rest.uniprot.org/uniprotkb/P54252.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P54252/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P54252"}},"corpus_meta":[{"pmid":"10072437","id":"PMC_10072437","title":"Evidence for proteasome involvement in polyglutamine disease: localization to nuclear inclusions in SCA3/MJD and suppression of polyglutamine aggregation in vitro.","date":"1999","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/10072437","citation_count":324,"is_preprint":false},{"pmid":"8931575","id":"PMC_8931575","title":"Autosomal dominant cerebellar ataxia type I clinical features and MRI in families with SCA1, SCA2 and SCA3.","date":"1996","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/8931575","citation_count":197,"is_preprint":false},{"pmid":"18418689","id":"PMC_18418689","title":"SCA3: neurological features, pathogenesis and animal models.","date":"2008","source":"Cerebellum (London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/18418689","citation_count":181,"is_preprint":false},{"pmid":"31669734","id":"PMC_31669734","title":"Pathogenesis of SCA3 and implications for other polyglutamine diseases.","date":"2019","source":"Neurobiology of disease","url":"https://pubmed.ncbi.nlm.nih.gov/31669734","citation_count":145,"is_preprint":false},{"pmid":"10768629","id":"PMC_10768629","title":"Frequency of SCA1, SCA2, SCA3/MJD, SCA6, SCA7, and DRPLA CAG trinucleotide repeat expansion in patients with hereditary spinocerebellar ataxia from Chinese kindreds.","date":"2000","source":"Archives of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/10768629","citation_count":141,"is_preprint":false},{"pmid":"17764659","id":"PMC_17764659","title":"Inactivation of the mouse Atxn3 (ataxin-3) gene increases protein ubiquitination.","date":"2007","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/17764659","citation_count":133,"is_preprint":false},{"pmid":"30994454","id":"PMC_30994454","title":"Mutant huntingtin impairs PNKP and ATXN3, disrupting DNA repair and transcription.","date":"2019","source":"eLife","url":"https://pubmed.ncbi.nlm.nih.gov/30994454","citation_count":107,"is_preprint":false},{"pmid":"9448569","id":"PMC_9448569","title":"Autosomal dominant cerebellar ataxia type I. 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(SBMA).","date":"1998","source":"Neurochemical research","url":"https://pubmed.ncbi.nlm.nih.gov/9482263","citation_count":21,"is_preprint":false},{"pmid":"30942397","id":"PMC_30942397","title":"MicroRNA‑25/ATXN3 interaction regulates human colon cancer cell growth and migration.","date":"2019","source":"Molecular medicine reports","url":"https://pubmed.ncbi.nlm.nih.gov/30942397","citation_count":20,"is_preprint":false},{"pmid":"28094059","id":"PMC_28094059","title":"Alteration of methylation status in the ATXN3 gene promoter region is linked to the SCA3/MJD.","date":"2016","source":"Neurobiology of aging","url":"https://pubmed.ncbi.nlm.nih.gov/28094059","citation_count":20,"is_preprint":false},{"pmid":"31783119","id":"PMC_31783119","title":"Druggable genome screen identifies new regulators of the abundance and toxicity of ATXN3, the Spinocerebellar Ataxia type 3 disease protein.","date":"2019","source":"Neurobiology of 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Brain of Young Presymptomatic Ki91 SCA3/MJD Mouse.","date":"2019","source":"Molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/31201651","citation_count":17,"is_preprint":false},{"pmid":"37349820","id":"PMC_37349820","title":"ATXN3 promotes prostate cancer progression by stabilizing YAP.","date":"2023","source":"Cell communication and signaling : CCS","url":"https://pubmed.ncbi.nlm.nih.gov/37349820","citation_count":16,"is_preprint":false},{"pmid":"34428509","id":"PMC_34428509","title":"The deubiquitinating enzyme ATXN3 promotes the progression of anaplastic thyroid carcinoma by stabilizing EIF5A2.","date":"2021","source":"Molecular and cellular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/34428509","citation_count":16,"is_preprint":false},{"pmid":"35025075","id":"PMC_35025075","title":"Inhibition of HDAC3 and ATXN3 by miR-25 prevents neuronal loss and ameliorates neurological recovery in cerebral stroke experimental rats.","date":"2022","source":"Journal of physiology and biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/35025075","citation_count":16,"is_preprint":false},{"pmid":"21334959","id":"PMC_21334959","title":"Relative contribution of SCA2, SCA3 and SCA17 in Korean patients with parkinsonism and ataxia.","date":"2011","source":"Parkinsonism & related disorders","url":"https://pubmed.ncbi.nlm.nih.gov/21334959","citation_count":16,"is_preprint":false},{"pmid":"20079840","id":"PMC_20079840","title":"Polyglutamine-induced neurodegeneration in SCA3 is not mitigated by non-expanded ataxin-3: conclusions from double-transgenic mouse models.","date":"2010","source":"Neurobiology of disease","url":"https://pubmed.ncbi.nlm.nih.gov/20079840","citation_count":16,"is_preprint":false},{"pmid":"39320846","id":"PMC_39320846","title":"ATXN3: a multifunctional protein involved in the polyglutamine disease spinocerebellar ataxia type 3.","date":"2024","source":"Expert reviews in molecular 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Knockdown of ATXN3 Alleviates Molecular Disease Hallmarks in a Mouse Model for Spinocerebellar Ataxia Type 3.","date":"2021","source":"Nucleic acid therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/34878314","citation_count":15,"is_preprint":false},{"pmid":"33106888","id":"PMC_33106888","title":"PolyQ-expanded ataxin-3 protein levels in peripheral blood mononuclear cells correlate with clinical parameters in SCA3: a pilot study.","date":"2020","source":"Journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/33106888","citation_count":14,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":51863,"output_tokens":7012,"usd":0.130384,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":16009,"output_tokens":6569,"usd":0.122135,"stage2_stop_reason":"end_turn"},"total_usd":0.252519,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1999,\n      \"finding\": \"The 26S proteasome complex redistributes into polyglutamine aggregates in SCA3/MJD; in neurons from SCA3/MJD brain, the proteasome localizes to intranuclear inclusions containing mutant ataxin-3. Proteasome inhibitors caused a repeat length-dependent increase in aggregate formation, implying the proteasome directly suppresses polyglutamine aggregation. Inclusion formation by full-length mutant ataxin-3 required nuclear localization of the protein and occurred within PML oncogenic domains.\",\n      \"method\": \"Immunohistochemistry of human SCA3/MJD brain tissue, transfected cell models with proteasome inhibitors, subcellular fractionation/localization studies\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell and tissue localization with functional pharmacological perturbation; single lab, multiple orthogonal approaches\",\n      \"pmids\": [\"10072437\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Loss of Atxn3 in knockout mice increased levels of ubiquitinated proteins in vivo, providing direct evidence for ATXN3's deubiquitinating activity in a physiological context. Atxn3 ko mice showed no overt neurological abnormality on rotarod but displayed reduced exploratory behavior.\",\n      \"method\": \"Targeted gene knockout in mice; western blot for ubiquitinated proteins; behavioral testing (rotarod, open field)\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean in vivo knockout with direct biochemical readout; provides in vivo evidence for DUB activity\",\n      \"pmids\": [\"17764659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"CK2 and GSK3 phosphorylate ATXN3 on serine 29 within the Josephin domain, and this phosphorylation promotes nuclear uptake of ATXN3. Site-directed mutagenesis of S29 to alanine strongly reduced nuclear localization, while phospho-mimic S29D restored wild-type nuclear localization. Treatment with CK2 and GSK3 inhibitors prevented S29 phosphorylation and inhibited nuclear uptake.\",\n      \"method\": \"In vitro kinase assay on purified ATXN3, MS analysis of phosphorylation sites, site-directed mutagenesis (S29A and S29D), CK2/GSK3 inhibitor treatment in COS-7 cells, subcellular localization by transfection\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis plus cell-based localization validation, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"20347968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Calpain-2 cleaves ataxin-3 in vitro and in mouse brain homogenates, and polyglutamine-expanded ataxin-3 is more sensitive to calpain-mediated degradation than wild-type. In vivo, enhancing calpain activity (via calpastatin knockout in SCA3 transgenic mice) aggravated neurological phenotype, increased nuclear aggregate number, and accelerated cerebellar neurodegeneration.\",\n      \"method\": \"In vitro calpain cleavage assay, mouse brain homogenate cleavage experiments, double-mutant mouse model (SCA3 transgenic × calpastatin KO), immunohistochemistry for nuclear aggregates, behavioral assessment\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro cleavage assay combined with in vivo genetic epistasis model with defined phenotypic readout\",\n      \"pmids\": [\"23100324\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Ataxin-3 protein cleavage (likely caspase-dependent) is conserved in Drosophila models of SCA3, and preventing cleavage by mutating caspase cleavage sites reduces neuronal loss in vivo, demonstrating that ataxin-3 cleavage enhances neurotoxicity.\",\n      \"method\": \"Drosophila transgenic models expressing wild-type vs. caspase-site mutant ataxin-3; quantification of neuronal loss in vivo; cell-based SL2 cleavage assay\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic in vivo approach in Drosophila with cleavage-site mutagenesis, single lab\",\n      \"pmids\": [\"19783548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Mutant ATXN3 (polyQ-expanded) physically interacts with and inactivates the DNA repair enzyme PNKP, resulting in inefficient DNA strand break repair, persistent DNA damage accumulation, and chronic ATM activation leading to p53 and PKC-δ pro-apoptotic signaling and neuronal death in SCA3. PNKP overexpression or ATM inhibition blocked mutant ATXN3-mediated cell death.\",\n      \"method\": \"Co-immunoprecipitation of ATXN3 with PNKP, PNKP enzyme activity assays, DNA damage assays (comet assay, γH2AX), ATM pathway activation assays, PNKP overexpression rescue, ATM inhibitor pharmacology in cell and mouse models\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP plus functional enzyme assay plus genetic rescue, multiple orthogonal methods with defined phenotypic readout\",\n      \"pmids\": [\"25590633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Mutant HTT impairs a transcription-coupled DNA repair (TCR) complex that includes ATXN3, POLR2A, PNKP, and CBP. Within this complex, ATXN3 activity prevents CBP ubiquitination and degradation; loss of ATXN3 function in HD leads to CBP degradation, impairing transcription and DNA repair. Wild-type ATXN3 thus protects CBP from ubiquitin-mediated degradation as part of the TCR complex.\",\n      \"method\": \"Co-immunoprecipitation (ATXN3 with POLR2A, PNKP, CBP), PNKP and ATXN3 activity assays, CBP ubiquitination and stability assays, chromatin immunoprecipitation, HD transgenic mouse models\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple reciprocal Co-IPs, enzyme activity assays, and ubiquitination assays across cell and animal models\",\n      \"pmids\": [\"30994454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ATXN3 associates with RNA polymerase II (RNAP II) and classical non-homologous end-joining (C-NHEJ) proteins including PNKP along with nascent RNAs under physiological conditions. ATXN3 depletion significantly decreases global transcription, repair of transcribed genes, and error-free double-strand break repair. Brain extracts from SCA3 patients show lower PNKP activity, elevated 53BP1, more DNA strand breaks in transcribed genes, and degradation of RNAP II. PNKP complementation completely rescues SCA3 phenotype in Drosophila.\",\n      \"method\": \"Co-immunoprecipitation of ATXN3 with RNAP II and C-NHEJ proteins, nascent RNA capture, transcription assays, DSB repair reporter assay, ATXN3 knockdown studies, brain extracts from SCA3 patients and mice, Drosophila genetic rescue with PNKP\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple Co-IPs, biochemical activity assays in patient tissue and animal models, genetic complementation in Drosophila\",\n      \"pmids\": [\"32205441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"ATXN3 physically interacts with HDAC3, deubiquitinates HDAC3, and thereby stabilizes HDAC3 protein. This ATXN3/HDAC3 interaction increases during viral infection and promotes IFN-I-mediated signaling pathway (not IFN-I production itself) to enhance antiviral response in murine primary lung cells and human cell lines.\",\n      \"method\": \"Co-immunoprecipitation of ATXN3 with HDAC3, ubiquitination assays of HDAC3 with and without ATXN3, ATXN3 knockdown/knockout studies, IFN-I signaling assays, viral infection models\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus deubiquitination assay plus functional signaling readout; single lab\",\n      \"pmids\": [\"29802126\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ATXN3 binds to KLF4 via immunoprecipitation and acts as a deubiquitinating enzyme for KLF4, mediating its deubiquitination and stabilization, thereby promoting breast cancer cell metastasis in vitro and in vivo.\",\n      \"method\": \"DUB library screen (65 enzymes), co-immunoprecipitation of ATXN3 with KLF4, ubiquitination assays, ATXN3 knockdown with KLF4 rescue, in vitro migration/invasion assays, mouse xenograft models\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus deubiquitination assay plus in vivo xenograft model; single lab\",\n      \"pmids\": [\"31563563\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CRISPR screen identified ATXN3 as a positive regulator of PD-L1 transcription. ATXN3 deubiquitinates the AP-1 transcription factor JunB and also stabilizes IRF1, STAT3, and HIF-2α, transcription factors that drive PD-L1 expression in response to IFN-γ and hypoxia. ATXN3 deletion abolished IFN-γ- and hypoxia-induced PD-L1 expression.\",\n      \"method\": \"CRISPR-based screen, co-immunoprecipitation of ATXN3 with JunB, ubiquitination assays, ATXN3 knockdown with PD-L1 reconstitution, mouse tumor models, IFN-γ/hypoxia stimulation assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR screen validated by Co-IP and deubiquitination assays and in vivo models; single lab\",\n      \"pmids\": [\"38038129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ATXN3 acts as a deubiquitinase for YAP in prostate cancer: the Josephin domain of ATXN3 interacts with the WW domain of YAP, deubiquitylates YAP (specifically inhibiting K48-linked polyubiquitination), and stabilizes YAP protein, thereby promoting YAP/TEAD target gene expression (CTGF, ANKRD1, CYR61) and prostate cancer cell proliferation and invasion.\",\n      \"method\": \"Co-immunoprecipitation (Josephin domain mapping), K48-specific ubiquitination assays, protein stability (cycloheximide chase), ATXN3 depletion with YAP overexpression rescue, xenograft mouse model, real-time PCR of YAP target genes\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with domain mapping, K48-specific ubiquitination assay, in vivo rescue; single lab\",\n      \"pmids\": [\"37349820\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ATXN3 promotes anaplastic thyroid carcinoma progression by directly binding to EIF5A2 and reducing its K48-linked ubiquitination and proteasomal degradation, thereby stabilizing EIF5A2 expression.\",\n      \"method\": \"Co-immunoprecipitation of ATXN3 with EIF5A2, ubiquitination assays, protein stability assays, ATXN3 gain/loss-of-function cellular assays\",\n      \"journal\": \"Molecular and cellular endocrinology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP and ubiquitination assay from one lab, limited mechanistic depth in abstract\",\n      \"pmids\": [\"34428509\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The type II iodothyronine deiodinase (D2) undergoes retrotranslocation from the ER to the cytoplasm via a p97-ATPase complex, and during this process, Ataxin-3 (Atx3) deubiquitinates ubiquitinated D2 (UbD2). Inhibiting Atx3 with eeyarestatin-I did not affect D2:p97 binding but decreased UbD2 retrotranslocation and caused ER accumulation of high-molecular-weight UbD2.\",\n      \"method\": \"Co-immunoprecipitation of D2 with p97 and Atx3, eeyarestatin-I pharmacological inhibition of Atx3, ubiquitination assays, subcellular fractionation, colocalization with 20S/19S proteasome subunits\",\n      \"journal\": \"Molecular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, pharmacological inhibition, and biochemical retrotranslocation assay in D2-expressing cell models; single lab\",\n      \"pmids\": [\"24196352\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Loss of ATXN3 in null mouse embryonic fibroblasts altered transcription of multiple signal transduction pathways, including depressed Wnt and BMP4 and elevated Prolactin, TGF-β, and Ephrin pathways. The most upregulated gene was Efna3 (Ephrin receptor A3), associated with hyperacetylation of histones H3 and H4 at the Efna3 promoter and decreased HDAC3 and NCoR levels in ATXN3-null cells. Overexpression of normal or expanded ATXN3 suppressed Efna3 expression.\",\n      \"method\": \"RNA-seq transcriptomics in Atxn3 null vs. WT MEFs, chromatin immunoprecipitation for histone acetylation at Efna3 promoter, HDAC3/NCoR western blots, ATXN3 overexpression rescue in cells, qRT-PCR validation in knockout mouse brainstem\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP plus transcriptomics plus KO rescue across two cell types; single lab\",\n      \"pmids\": [\"30231063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"ATXN3 regulates chromatin organization in a catalytic-independent (deubiquitinase-independent) manner. Loss of ATXN3 leads to abnormal nuclear and nucleolar morphology, altered DNA replication timing, increased global transcription, increased histone H1 mobility, changes in epigenetic marks, and higher chromatin sensitivity to MNase digestion. ATXN3 controls the subcellular localization of HDAC3 (its interaction partner), and absence of ATXN3 decreases HDAC3 chromatin recruitment. PolyQ-expanded ATXN3 behaves as a null mutant in these assays, altering DNA replication parameters, epigenetic marks, and HDAC3 subcellular distribution.\",\n      \"method\": \"ATXN3 KO cell lines; DNA replication timing assays; FRAP for histone H1 mobility; ChIP for epigenetic marks; MNase sensitivity; HDAC3 localization by fractionation/imaging; comparison of catalytic mutant vs. null vs. PolyQ-expanded ATXN3\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (replication timing, FRAP, ChIP, MNase, fractionation) with mechanistic dissection of HDAC3 interaction and catalytic independence\",\n      \"pmids\": [\"36971114\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The misfolding propensity and ubiquitination of ataxin-3 are directly proportional to the length of the polyglutamine repeat and inversely dependent on the size of the protein. Normal-repeat ataxin-3 (full-length and truncated) is not ubiquitinated, whereas expanded-polyQ ataxin-3 is ubiquitinated in proportion to its misfolding propensity.\",\n      \"method\": \"Cell-based ubiquitination assays with varying polyQ-length ataxin-3 constructs, immunoprecipitation, 1C2 antibody binding assays for misfolding assessment\",\n      \"journal\": \"Neurotoxicity research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based ubiquitination assay with multiple constructs; single lab\",\n      \"pmids\": [\"15639784\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In Drosophila SCA3 models, Hsp104 suppressed toxicity of a C-terminal ataxin-3 fragment containing the expanded polyQ tract but unexpectedly enhanced aggregation and toxicity of full-length pathogenic ataxin-3. Hsp104 suppressed toxicity of MJD variants lacking part of the N-terminal deubiquitylase domain and variants unable to engage polyubiquitin, indicating that MJD-ubiquitin interactions hinder protective Hsp104 function. This demonstrates that the ubiquitin-binding capacity of ataxin-3 is functionally important for its behavior in protein disaggregation contexts.\",\n      \"method\": \"Drosophila transgenic models with various ataxin-3 constructs (full-length, truncated, ubiquitin-binding mutants), eye degeneration scoring, aggregation quantification, staging experiments with post-onset Hsp104 expression\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic dissection in Drosophila with multiple domain mutants and staging; single lab\",\n      \"pmids\": [\"24039611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The truncated C-terminal fragment of mutant ATXN3 causes more mitochondrial fission, decreases expression of mitochondrial fusion markers Mfn-1 and Mfn-2, reduces mitochondrial membrane potential, increases reactive oxygen species, and leads to higher cell death than full-length mutant ATXN3 in neuroblastoma cells and transgenic mice.\",\n      \"method\": \"Neuroblastoma cell models and transgenic mouse models expressing truncated vs. full-length mutant ATXN3, mitochondrial morphology imaging, Mfn-1/Mfn-2 western blots, MMP assay, ROS measurement, cell death assays\",\n      \"journal\": \"Frontiers in molecular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell and mouse model comparison with multiple mitochondrial readouts; single lab\",\n      \"pmids\": [\"28676741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Neuronally differentiated PC12 cells expressing expanded ataxin-3 showed significantly reduced resting membrane potential and a hyperpolarizing shift of the delayed rectifier potassium current activation curve, prior to neuronal cell death, indicating that mutant ataxin-3 causes potassium channel dysfunction.\",\n      \"method\": \"Stable inducible PC12 cell model with normal vs. expanded ataxin-3; patch-clamp electrophysiology; cell viability assay; ultrastructural analysis\",\n      \"journal\": \"Experimental neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — patch-clamp in defined cell model with inducible expression; single lab\",\n      \"pmids\": [\"16765348\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Oligodendrocyte maturation is impaired early in SCA3 disease in selectively vulnerable brain regions (cerebellum and brainstem) of SCA3 transgenic mice. This impairment is a cell-autonomous toxic gain-of-function of mutant ATXN3, as ATXN3 KO mice show no oligodendrocyte maturation defects. Ultrastructural microscopy confirmed abnormalities in axonal myelination in SCA3 mice.\",\n      \"method\": \"Weighted gene coexpression network analysis of longitudinal transcriptomics in SCA3 mouse brain, reporter mouse crosses to quantify mature oligodendrocytes, electron microscopy for axonal myelination, isolation and culture of oligodendrocyte precursor cells from SCA3 mice\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO comparison plus cell-autonomous OPC culture plus ultrastructural confirmation; multiple orthogonal methods, peer-reviewed\",\n      \"pmids\": [\"35042771\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ribosomal frameshifting occurs at the expanded CAG repeat in ATXN3 mRNA, specifically by -1 slippage, generating polyalanine-containing proteins. This frameshifting is dependent on long CAG tract length. PolyQ-encoding CAA repeats (which cannot frameshift) were not toxic, while expanded CAG ATXN3 was toxic, indicating that frameshifting (not the polyQ per se) contributes to toxicity. Anisomycin reduced -1 frameshifting and also reduced toxicity.\",\n      \"method\": \"Cell-based ribosomal frameshifting reporter assay, comparison of CAG vs. CAA repeat ATXN3 constructs, anisomycin pharmacology, toxicity assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cellular reporter plus pharmacological validation plus CAA control; single lab\",\n      \"pmids\": [\"16087686\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Frameshifting events occurring at the expanded CAG repeat in ATXN3 are toxic in Drosophila and mammalian neurons. Transgenic expression of expanded CAG ATXN3 led to -1 frameshifting, whereas expression of polyglutamine-encoding expanded CAA ATXN3 (which cannot frameshift) was not toxic, demonstrating that expanded CAG-derived frameshifting (not polyQ per se) is necessary for toxicity in these models.\",\n      \"method\": \"Drosophila transgenic models and mouse neuron models expressing CAG vs. CAA repeat ATXN3 constructs, neurodegeneration scoring, frameshifting detection\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic dissection with CAG vs. CAA controls in two model systems; single lab\",\n      \"pmids\": [\"22337953\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ATXN3 does not interact with the ubiquitin-binding protein UBQLN2 (tested by Co-IP via UBA domain), in contrast to mutant HTT which does interact with UBQLN2. Consequently, UBQLN2 is not recruited to inclusions in SCA3 (neither in mouse models nor human SCA3 brain), distinguishing SCA3 inclusions from HD inclusions.\",\n      \"method\": \"Co-immunoprecipitation in cell-based system testing ATXN3 vs. HTT interaction with UBQLN2, immunohistochemistry of SCA3 and HD mouse and human brain for UBQLN2 localization\",\n      \"journal\": \"Neurobiology of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — negative result confirmed by Co-IP and IHC across multiple models; single lab; negative finding is itself mechanistically informative\",\n      \"pmids\": [\"26141599\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ATXN3 is a deubiquitinating enzyme (DUB) of the Josephin family that regulates protein homeostasis via the ubiquitin-proteasome pathway, participates in transcription-coupled DNA repair as part of a complex with RNAP II, PNKP, and CBP, controls chromatin organization (in a catalytic-independent manner) by regulating HDAC3 subcellular localization, is activated for nuclear entry by CK2/GSK3 phosphorylation on S29, and is cleaved by calpains to generate toxic fragments; polyQ expansion of ATXN3 inactivates PNKP leading to DNA damage accumulation and ATM-mediated apoptosis, impairs oligodendrocyte maturation through a cell-autonomous toxic gain-of-function, and causes potassium channel dysfunction, while wild-type ATXN3 deubiquitinates substrates including HDAC3, KLF4, YAP, and EIF5A2 in contexts ranging from antiviral signaling to cancer progression.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ATXN3 is a Josephin-family deubiquitinating enzyme that maintains protein homeostasis through the ubiquitin-proteasome system, with knockout animals accumulating ubiquitinated proteins in vivo [#1]. It removes ubiquitin from a broad range of substrates to control their stability, including HDAC3 during antiviral interferon-I signaling [#8], the transcription factors KLF4 [#9], YAP via Josephin-domain engagement of the YAP WW domain with K48-linkage specificity [#11], and JunB/IRF1/STAT3/HIF-2\\u03b1 to drive PD-L1 expression in tumor cells [#10]. Beyond catalysis, ATXN3 operates in genome maintenance as a component of a transcription-coupled DNA repair complex with RNA polymerase II, PNKP and CBP, where its activity protects CBP from ubiquitin-mediated degradation and supports global transcription and error-free double-strand break repair [#6, #7]. It also functions through a catalytic-independent activity to organize chromatin, controlling HDAC3 subcellular localization and chromatin recruitment, with loss producing abnormal nuclear morphology, altered replication timing and epigenetic marks [#15, #14]. Nuclear entry of ATXN3 is gated by CK2/GSK3 phosphorylation of serine 29 within the Josephin domain [#2], and the protein is processed by calpains and caspases to generate C-terminal fragments [#3, #4]. ATXN3 also participates in ER-associated retrotranslocation, deubiquitinating type II iodothyronine deiodinase as it is extracted via the p97 ATPase [#13]. Polyglutamine expansion causes the SCA3/MJD spinocerebellar ataxia through multiple toxic mechanisms: nuclear inclusion formation that sequesters the proteasome [#0], physical inactivation of PNKP leading to persistent DNA damage and ATM-mediated apoptotic signaling [#5], cell-autonomous impairment of oligodendrocyte maturation [#20], potassium channel dysfunction [#19], and toxicity arising from -1 ribosomal frameshifting at the expanded CAG repeat rather than the polyQ tract alone [#21, #22].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that mutant ataxin-3 forms nuclear inclusions that sequester the 26S proteasome, linking the proteasome system to polyglutamine aggregation pathology in SCA3.\",\n      \"evidence\": \"Immunohistochemistry of SCA3 brain and proteasome-inhibitor perturbation in transfected cells\",\n      \"pmids\": [\"10072437\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not establish whether proteasome sequestration is cause or consequence of toxicity\", \"Mechanism of proteasome suppression of aggregation not resolved\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed that misfolding and ubiquitination of ataxin-3 scale with polyQ length, defining the biochemical basis of the toxic gain-of-function.\",\n      \"evidence\": \"Cell-based ubiquitination assays across polyQ-length and truncation constructs\",\n      \"pmids\": [\"15639784\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin ligase responsible not identified\", \"Cellular consequence of expanded-form ubiquitination not addressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified -1 ribosomal frameshifting at the expanded CAG repeat as a toxicity mechanism distinct from polyQ itself, reframing how repeat expansion causes disease.\",\n      \"evidence\": \"Cell-based frameshifting reporter, CAG vs CAA constructs, anisomycin pharmacology\",\n      \"pmids\": [\"16087686\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Contribution of frameshift products to human disease not quantified\", \"Identity and fate of polyalanine products in neurons not characterized\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrated that expanded ataxin-3 disrupts potassium channel function before cell death, identifying an early electrophysiological deficit.\",\n      \"evidence\": \"Patch-clamp electrophysiology in inducible PC12 model\",\n      \"pmids\": [\"16765348\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular link between ATXN3 and the channel not defined\", \"Not confirmed in neurons of patients or animal models\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Provided the first in vivo evidence that ATXN3 is a functional deubiquitinase, since its loss elevates ubiquitinated proteins.\",\n      \"evidence\": \"Atxn3 knockout mice with western blot for ubiquitinated proteins and behavioral testing\",\n      \"pmids\": [\"17764659\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrates not identified in this study\", \"Mild phenotype leaves functional redundancy unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Established that proteolytic cleavage of ataxin-3 enhances neurotoxicity, since blocking caspase sites reduces neuronal loss.\",\n      \"evidence\": \"Drosophila transgenics with caspase-site mutants and cell-based cleavage assays\",\n      \"pmids\": [\"19783548\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific protease in vivo not definitively assigned\", \"Mechanism by which fragments confer toxicity not addressed here\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined how ATXN3 nuclear entry is regulated, identifying CK2/GSK3 phosphorylation of S29 as the switch controlling nuclear localization.\",\n      \"evidence\": \"In vitro kinase assay, MS, S29A/S29D mutagenesis and kinase inhibitors with cell localization\",\n      \"pmids\": [\"20347968\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Consequence of regulated nuclear entry for substrate processing not shown\", \"Whether polyQ expansion alters this regulation not tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed that calpain cleavage generates fragments and that enhancing calpain activity worsens SCA3 pathology in vivo, establishing calpain as a disease modifier.\",\n      \"evidence\": \"In vitro calpain cleavage and SCA3 transgenic x calpastatin-KO epistasis with histology and behavior\",\n      \"pmids\": [\"23100324\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise cleavage sites not mapped\", \"Relative contribution of calpain vs caspase fragments unresolved\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Connected ATXN3 to ER-associated degradation, showing it deubiquitinates D2 during p97-mediated retrotranslocation.\",\n      \"evidence\": \"Co-IP of D2 with p97 and Atx3, eeyarestatin-I inhibition, retrotranslocation assays\",\n      \"pmids\": [\"24196352\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pharmacological inhibitor may have off-target effects\", \"Generality across other ERAD substrates not established\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Used Drosophila genetic dissection to show ataxin-3's ubiquitin-binding capacity governs its behavior in disaggregation, revealing the UBA domains shape disease-relevant handling.\",\n      \"evidence\": \"Drosophila models with full-length, truncated and ubiquitin-binding-mutant constructs plus Hsp104 staging\",\n      \"pmids\": [\"24039611\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Human relevance of Hsp104 interplay limited\", \"Endogenous disaggregase partners not identified\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Identified PNKP inactivation by mutant ATXN3 as a direct mechanism linking the protein to DNA damage accumulation and ATM-driven neuronal apoptosis.\",\n      \"evidence\": \"Reciprocal Co-IP, PNKP activity assays, DNA damage and ATM pathway readouts, PNKP-overexpression and ATM-inhibitor rescue\",\n      \"pmids\": [\"25590633\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether wild-type ATXN3 normally activates PNKP not fully resolved here\", \"Spatial/temporal sequence of damage vs aggregation in neurons unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Distinguished SCA3 from Huntington disease at the molecular level by showing ATXN3 does not engage UBQLN2 and UBQLN2 is not recruited to SCA3 inclusions.\",\n      \"evidence\": \"Co-IP comparing ATXN3 vs HTT with UBQLN2 and IHC of SCA3 and HD brain\",\n      \"pmids\": [\"26141599\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Negative result; does not rule out weak or transient interactions\", \"Functional consequence of absent UBQLN2 recruitment not explored\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated that the truncated C-terminal mutant fragment drives mitochondrial fission and oxidative stress more potently than full-length protein, linking fragmentation to mitochondrial toxicity.\",\n      \"evidence\": \"Neuroblastoma and transgenic mouse comparison of truncated vs full-length mutant ATXN3 with mitochondrial and ROS readouts\",\n      \"pmids\": [\"28676741\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular link to fusion machinery not defined\", \"Single-lab observation\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established ATXN3 as a deubiquitinase for HDAC3 that stabilizes it to promote interferon-I-mediated antiviral signaling, defining a physiological substrate.\",\n      \"evidence\": \"Reciprocal Co-IP, HDAC3 ubiquitination assays, ATXN3 knockdown/KO and IFN-I signaling readouts in viral infection models\",\n      \"pmids\": [\"29802126\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab finding\", \"Linkage to ATXN3's neuronal roles not made\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Linked ATXN3 to transcriptional and chromatin control, showing its loss alters signaling-pathway gene expression and histone acetylation at the Efna3 promoter alongside reduced HDAC3/NCoR.\",\n      \"evidence\": \"RNA-seq, ChIP for histone acetylation, HDAC3/NCoR westerns and ATXN3 rescue in MEFs and KO brainstem\",\n      \"pmids\": [\"30231063\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect transcriptional effects not separated\", \"Mechanism connecting ATXN3 to HDAC3/NCoR levels not resolved here\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Placed ATXN3 within a transcription-coupled DNA repair complex (RNAP II, PNKP, CBP) where its activity protects CBP from degradation, bridging transcription and repair functions.\",\n      \"evidence\": \"Co-IPs, PNKP/ATXN3 activity assays, CBP ubiquitination/stability assays, ChIP and HD mouse models\",\n      \"pmids\": [\"30994454\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and assembly order of the complex not defined\", \"Whether expanded ATXN3 disrupts CBP protection not directly tested here\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified KLF4 as an ATXN3 substrate stabilized via deubiquitination, implicating ATXN3 in breast cancer metastasis.\",\n      \"evidence\": \"DUB-library screen, Co-IP, ubiquitination assays, knockdown/rescue, migration and xenograft assays\",\n      \"pmids\": [\"31563563\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin linkage type not specified\", \"Single-lab cancer-context finding\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed ATXN3 physiologically associates with RNAP II and C-NHEJ machinery to sustain transcription and error-free DSB repair, and that SCA3 patient brain shows impaired PNKP activity and RNAP II degradation.\",\n      \"evidence\": \"Co-IPs, nascent-RNA capture, DSB repair reporters, knockdown, patient/mouse brain extracts, Drosophila PNKP rescue\",\n      \"pmids\": [\"32205441\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal order between transcription loss and repair loss not disentangled\", \"Whether PNKP rescue translates to mammals not shown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Extended ATXN3 substrate range to EIF5A2 in anaplastic thyroid carcinoma via reduced K48-linked ubiquitination and stabilization.\",\n      \"evidence\": \"Co-IP, ubiquitination and stability assays, gain/loss-of-function cellular assays\",\n      \"pmids\": [\"34428509\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Limited mechanistic depth; single Co-IP and ubiquitination assay from one lab\", \"No in vivo validation reported\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated a cell-autonomous toxic gain-of-function: mutant ATXN3 impairs oligodendrocyte maturation in vulnerable regions while loss of ATXN3 does not, identifying a non-neuronal disease mechanism.\",\n      \"evidence\": \"Longitudinal transcriptomics, reporter mouse crosses, electron microscopy and SCA3 OPC culture\",\n      \"pmids\": [\"35042771\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular target of mutant ATXN3 in oligodendrocytes not identified\", \"Contribution to motor phenotype relative to neuronal loss unquantified\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined a catalytic-independent chromatin-organizing role for ATXN3 acting through HDAC3 localization, and showed polyQ-expanded ATXN3 behaves as a null in these assays.\",\n      \"evidence\": \"ATXN3 KO cells, replication timing, FRAP, ChIP, MNase sensitivity, HDAC3 fractionation/imaging, catalytic-mutant comparison\",\n      \"pmids\": [\"36971114\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How ATXN3 directs HDAC3 localization mechanistically unresolved\", \"Relationship of chromatin role to disease progression not established\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed ATXN3 deubiquitinates JunB and stabilizes IRF1/STAT3/HIF-2\\u03b1 to drive PD-L1 expression under IFN-\\u03b3 and hypoxia, implicating it in tumor immune evasion.\",\n      \"evidence\": \"CRISPR screen, Co-IP, ubiquitination assays, knockdown/reconstitution and mouse tumor models\",\n      \"pmids\": [\"38038129\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect stabilization of the multiple factors not fully separated\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established ATXN3 as a YAP deubiquitinase in prostate cancer via Josephin-WW domain interaction and K48-specific deubiquitination, promoting YAP/TEAD target expression.\",\n      \"evidence\": \"Domain-mapping Co-IP, K48-specific ubiquitination assays, cycloheximide chase, depletion/rescue and xenograft\",\n      \"pmids\": [\"37349820\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab cancer-context finding\", \"Connection to ATXN3's other substrate networks not explored\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How ATXN3's distinct activities — DUB catalysis, catalytic-independent chromatin organization, transcription-coupled repair, and regulated nuclear trafficking — are integrated, and which are mechanistically central to SCA3 neurodegeneration, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model connecting catalytic and non-catalytic roles\", \"Causal hierarchy among DNA damage, oligodendrocyte defects, fragment toxicity, and frameshifting in disease not established\", \"Endogenous physiological substrate spectrum in neurons not comprehensively defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 5, 6, 8, 9, 11, 13]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [1, 8, 11, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 2, 15]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [2, 13]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 13]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [5, 6, 7]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [14, 15]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [6, 7]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [8, 10]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 5, 20]}\n    ],\n    \"complexes\": [\"transcription-coupled DNA repair complex (RNAP II / PNKP / CBP)\"],\n    \"partners\": [\"PNKP\", \"HDAC3\", \"POLR2A\", \"CBP\", \"YAP\", \"KLF4\", \"JunB\", \"p97/VCP\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}