{"gene":"XIRP2","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2004,"finding":"The Xin repeats of XIRP2 (called 'Xin repeat protein 2') define a novel actin-binding motif: in vitro co-sedimentation assays with skeletal muscle actin demonstrated that XIRP2's 28 Xin repeats directly bind actin filaments and can arrange microfilaments into networks that sediment upon low-speed centrifugation. Transfection experiments confirmed that the repeats bind and stabilize the actin-based cytoskeleton in cultured cells.","method":"In vitro co-sedimentation assay with skeletal muscle actin; transfection of repeat constructs into cultured cells","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro reconstitution (co-sedimentation) plus cell-based transfection, replicated across Xin and XIRP2 repeats in same study","pmids":["15454575"],"is_preprint":false},{"year":2006,"finding":"XIRP2 (mouse ortholog myomaxin/CMYA3) is a direct transcriptional target of MEF2A and localizes to the Z-disc/costameric region in striated muscle. The myomaxin protein (mouse XIRP2 ortholog) interacts with the sarcomeric Z-disc protein alpha-actinin-2.","method":"MEF2A knockout mouse expression analysis (microarray); protein interaction demonstrated by co-immunoprecipitation and/or pulldown; immunolocalization in muscle","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO (MEF2A null) identifies XIRP2 as downstream target; alpha-actinin-2 interaction reported in single lab with standard co-IP/pulldown","pmids":["17046827"],"is_preprint":false},{"year":2010,"finding":"XIRP2 expression in the heart is induced by angiotensin II (Ang II) signaling through MEF2A transcriptional activity. Ang II activates XIRP2 promoter activity via MEF2A, placing XIRP2 downstream of the Ang II–MEF2A pathway. Xirp2 hypomorphic mice (with markedly reduced cardiac Xirp2) developed spontaneous cardiac hypertrophy and increased beta-myosin heavy chain expression, and showed attenuated hypertrophic remodeling, reduced fibrosis, and reduced apoptosis after chronic Ang II infusion.","method":"Xirp2 promoter characterization; MEF2A activity assay; Xirp2 hypomorphic mouse model with Ang II infusion; histological and molecular readouts","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic hypomorphic model with in vivo Ang II challenge, promoter characterization, and multiple orthogonal phenotypic readouts in single rigorous study","pmids":["20093629"],"is_preprint":false},{"year":2012,"finding":"Mouse Xinβ (mXinβ/XIRP2) is required for the postnatal maturation of intercalated discs (ICDs) in the heart. In mXinβ-null mice, intercellular junction components fail to redistribute from the lateral membrane to the termini of cardiomyocytes during postnatal ICD formation (defect apparent at postnatal day 16.5). mXinβ is uniquely upregulated during the redistribution phase and preferentially associates with forming ICDs by immunofluorescence and subcellular fractionation.","method":"mXinβ knockout mouse; quantitative Western blot; immunofluorescence; subcellular fractionation; comparison with mXinα-null and double-knockout hearts","journal":"Developmental biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with defined developmental phenotype, corroborated by fractionation and immunofluorescence, epistatic comparison with mXinα-null","pmids":["23261932"],"is_preprint":false},{"year":2015,"finding":"A short splice form of XIRP2 (lacking the Xin repeats, also called XEPLIN) is expressed in inner ear hair cells where it colocalizes with actin-rich stereocilia, the cuticular plate, and the circumferential actin belt. CRISPR/Cas9-mediated Xirp2-null mice exhibit high-frequency hearing loss and stereocilia degeneration, demonstrating that XIRP2 is required for long-term maintenance of hair cell stereocilia morphology and hearing function.","method":"Mass spectrometry of hair bundle proteome; CRISPR/Cas9 knockout mouse; auditory brainstem response (hearing function); scanning electron microscopy of stereocilia","journal":"The Journal of neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRISPR KO with functional (auditory) and ultrastructural (SEM) phenotypic readouts, replicated by independent lab (PMID 25772365)","pmids":["25653358"],"is_preprint":false},{"year":2015,"finding":"Different isoforms of XIRP2 are differentially localized in hair cells: short splice forms (XEPLIN) are targeted preferentially to stereocilia, whereas two long isoforms containing the XIN-repeat domain are present in both stereocilia and cuticular plates. Xirp2-null mice develop normal stereocilia bundles that degenerate over time, with loss of stereocilia, long membranous protrusions from apical surfaces, and disorganization of paracrystalline actin filaments at the ultrastructural level.","method":"Isoform-specific immunolocalization; Xirp2 knockout mouse; scanning electron microscopy; transmission electron microscopy of actin ultrastructure","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with ultrastructural characterization and isoform-specific localization, independent replication of hearing/stereocilia phenotype","pmids":["25772365"],"is_preprint":false},{"year":2016,"finding":"Both Xirp1 and Xirp2 (Xin actin-binding repeat-containing proteins) stabilize filamin C (FLNc) selectively in premyofibrils of cardiomyocytes. Analysis of cardiomyocytes from Xirp1- and Xirp2-deficient animals showed reduced FLNc stability at premyofibrils, as assessed by fluorescence recovery after photobleaching.","method":"FRAP (fluorescence recovery after photobleaching) in cardiomyocytes from Xirp1/Xirp2 knockout animals; live zebrafish imaging","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — FRAP in KO cardiomyocytes and live zebrafish, single lab, two organism models","pmids":["27206985"],"is_preprint":false},{"year":2018,"finding":"Xirp2 is required for normal cardiac conduction. Xirp2-knockout mouse hearts exhibit prolonged PR and QT intervals, slow conduction velocity, atrioventricular conduction block, and abnormal infranodal ventricular conduction. Whole-cell patch-clamp of Xirp2-/- cardiomyocytes detected altered ionic currents. Co-immunoprecipitation demonstrated association of Xirp2 with Nav1.5 and Kv1.5 ion channel subunits, consistent with a role for Xirp2 in governing ion channel surface expression and cardiac conduction.","method":"Xirp2 knockout mouse; electrocardiography; whole-cell patch-clamp; co-immunoprecipitation with Nav1.5 and Kv1.5","journal":"Journal of the American Heart Association","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — genetic KO with electrophysiology (patch-clamp + ECG) and co-IP of ion channel partners in single rigorous study","pmids":["29306897"],"is_preprint":false},{"year":2018,"finding":"In stereocilia, actin cross-linkers including XIRP2 undergo continuous turnover even though the actin filament core is highly stable, demonstrating that ongoing remodeling of cross-linker composition is a mechanism for stereocilia homeostasis and repair.","method":"Transgenic mouse expressing EGFP-fascin-2 to monitor cross-linker dynamics; comparison with endogenous XIRP2, espin, and plastin-1 localization","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live imaging in transgenic mouse model; XIRP2 implicated by displacement assay, single lab","pmids":["29874122"],"is_preprint":false},{"year":2023,"finding":"XIRP2 is required for repair of noise-induced damage to stereocilia F-actin cores. XIRP2 facilitates enrichment of monomeric γ-actin at damage gaps in auditory hair cells. Recruitment of XIRP2 to stereocilia gaps and to stress fiber strain sites in fibroblasts is force-dependent and is mediated by a novel mechanosensor domain located in the C-terminus of XIRP2.","method":"Xirp2-null mice subjected to traumatic noise; phalloidin gap assay; monomeric actin immunostaining; fibroblast stretch assay for mechanosensor domain mapping; domain deletion/mutagenesis experiments","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — KO mouse with functional assay, identification of novel mechanosensor domain by deletion mapping in both hair cells and fibroblasts, multiple orthogonal methods in one study","pmids":["37294664"],"is_preprint":false},{"year":2015,"finding":"Compound heterozygous truncating mutations in XIRP2 were identified in a child with sporadic dilated cardiomyopathy. Histomorphological analysis of explanted heart tissue showed misregistration, mislocalization, and shortening of intercalated discs, findings similar to those in Xirp2-/- mice, implicating XIRP2 as a modifier gene in DCM pathogenesis through disruption of ICD integrity.","method":"Whole exome sequencing; cardiac histomorphology of explanted heart; comparison with Xirp2-/- mouse phenotype","journal":"Journal of the American Heart Association","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human genetics supported by histopathological validation and cross-species phenotype comparison; single case","pmids":["26656454"],"is_preprint":false},{"year":2024,"finding":"Inhibition of XIRP2 in hepatocellular carcinoma cells results in increased sensitivity to oxaliplatin through elevation of zinc ions and calcium ion overload, identifying a functional role for XIRP2 in ion homeostasis. The XIRP2 mutation was found to enhance XIRP2 protein stability without affecting mRNA levels.","method":"XIRP2 knockdown in HCC cells; CCK-8 drug sensitivity assay; protein stability experiments; ion (zinc/calcium) measurements","journal":"Biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single lab, loss-of-function with defined cellular phenotype (drug sensitivity/ion levels), but limited mechanistic depth","pmids":["39194571"],"is_preprint":false}],"current_model":"XIRP2 is a striated muscle- and hair cell-expressed actin-binding protein whose Xin repeats directly bind and crosslink actin filaments; it functions as a MEF2A transcriptional target downstream of angiotensin II signaling in cardiac remodeling, is essential for postnatal intercalated disc maturation in the heart (where it associates with Nav1.5 and Kv1.5 to support normal cardiac conduction), and maintains stereocilia F-actin architecture in inner ear hair cells through a C-terminal mechanosensor domain that recruits XIRP2 to force-induced actin damage sites to facilitate repair."},"narrative":{"mechanistic_narrative":"XIRP2 (Xin actin-binding repeat-containing protein 2) is a striated muscle- and hair cell-expressed cytoskeletal protein whose tandem Xin repeats constitute a direct actin-binding motif that crosslinks F-actin into stabilized networks [PMID:15454575]. In the heart, XIRP2 is a direct transcriptional target of MEF2A induced by angiotensin II signaling, and its loss attenuates hypertrophic remodeling, fibrosis, and apoptosis following Ang II challenge, placing it in the cardiac stress-response pathway [PMID:17046827, PMID:20093629]. At the sarcomere it localizes to the Z-disc/costamere, interacts with alpha-actinin-2, and stabilizes filamin C in premyofibrils [PMID:17046827, PMID:27206985]. XIRP2 is required for postnatal maturation of cardiac intercalated discs, where it drives redistribution of junctional components to cardiomyocyte termini and associates with the Nav1.5 and Kv1.5 ion channel subunits to support normal conduction [PMID:23261932, PMID:29306897]; compound heterozygous truncating XIRP2 mutations are linked to dilated cardiomyopathy through disrupted intercalated disc integrity [PMID:26656454]. In inner ear hair cells, isoform-specific XIRP2 (including a short Xin-repeat-deficient form, XEPLIN) localizes to stereocilia and the cuticular plate and is required for long-term maintenance of stereocilia F-actin architecture and hearing [PMID:25653358, PMID:25772365]; a C-terminal mechanosensor domain mediates force-dependent recruitment of XIRP2 to damaged actin sites, where it facilitates monomeric actin enrichment to repair noise-induced stereocilia damage [PMID:37294664].","teleology":[{"year":2004,"claim":"Established that the defining Xin repeats are themselves a functional actin-binding module, providing the biochemical basis for all later cytoskeletal roles.","evidence":"In vitro co-sedimentation with skeletal muscle actin and repeat-construct transfection in cultured cells","pmids":["15454575"],"confidence":"High","gaps":["Affinity and stoichiometry of binding not quantified","Does not address regulation of binding in vivo","Structural basis of the actin-bundling activity unresolved"]},{"year":2006,"claim":"Placed XIRP2 in a defined transcriptional and structural context by identifying it as a MEF2A target localizing to the Z-disc and interacting with alpha-actinin-2.","evidence":"MEF2A knockout mouse microarray, co-IP/pulldown, and muscle immunolocalization","pmids":["17046827"],"confidence":"Medium","gaps":["alpha-actinin-2 interaction from single lab, no reciprocal validation","Functional consequence of the Z-disc interaction untested","Direct vs indirect MEF2A regulation not distinguished at the time"]},{"year":2010,"claim":"Connected XIRP2 to cardiac stress signaling, showing Ang II induces it via MEF2A and that its reduction alters hypertrophic remodeling.","evidence":"Xirp2 promoter and MEF2A activity assays plus Xirp2 hypomorphic mice under chronic Ang II infusion","pmids":["20093629"],"confidence":"High","gaps":["Mechanism linking actin-binding to remodeling output unclear","Hypomorph rather than full null","Cell-autonomous vs systemic contributions not separated"]},{"year":2012,"claim":"Defined an essential developmental role: XIRP2 drives postnatal redistribution of junctional components to form mature intercalated discs.","evidence":"mXinβ knockout mouse with Western blot, immunofluorescence, fractionation, and epistatic comparison to mXinα-null","pmids":["23261932"],"confidence":"High","gaps":["Molecular trigger of XIRP2 upregulation during redistribution unknown","Direct binding partners at the ICD not defined here","Mechanism of component redistribution not resolved"]},{"year":2015,"claim":"Extended XIRP2 function to a new tissue, demonstrating isoform-specific stereocilia localization and a requirement for long-term hair cell actin maintenance and hearing.","evidence":"Hair bundle proteomics, CRISPR/Cas9 Xirp2-null mice, ABR, and SEM/TEM ultrastructure, replicated across two studies","pmids":["25653358","25772365"],"confidence":"High","gaps":["Differential targeting determinants of short vs long isoforms unmapped","Whether degeneration reflects failed repair vs structural support unclear at this stage","Direct stereocilia binding partners not identified"]},{"year":2016,"claim":"Identified filamin C as a stabilization client, linking XIRP2 actin-crosslinking to maintenance of specific sarcomeric components in nascent myofibrils.","evidence":"FRAP in Xirp1/Xirp2-deficient cardiomyocytes and live zebrafish imaging","pmids":["27206985"],"confidence":"Medium","gaps":["Single lab","Direct vs indirect stabilization of FLNc not separated","Redundancy with XIRP1 not fully partitioned"]},{"year":2018,"claim":"Mechanistically linked the ICD/cytoskeletal role to electrophysiology, showing XIRP2 associates with cardiac ion channels and is required for normal conduction.","evidence":"Xirp2 knockout mouse ECG, whole-cell patch-clamp, and co-IP with Nav1.5 and Kv1.5","pmids":["29306897"],"confidence":"High","gaps":["Whether XIRP2 directly traffics channels or stabilizes them is unresolved","Co-IP not validated reciprocally","Direct vs ICD-architecture-mediated channel effects not separated"]},{"year":2018,"claim":"Revealed that stereocilia cross-linkers including XIRP2 turn over continuously despite a stable actin core, framing repair as ongoing compositional remodeling.","evidence":"Transgenic EGFP-fascin-2 mouse imaging with endogenous cross-linker comparison","pmids":["29874122"],"confidence":"Medium","gaps":["XIRP2 turnover inferred by displacement, not directly tracked","Regulation of turnover unknown","Single lab"]},{"year":2023,"claim":"Defined the repair mechanism: a C-terminal mechanosensor domain confers force-dependent recruitment of XIRP2 to actin damage sites to drive monomeric actin enrichment and repair.","evidence":"Xirp2-null mice with traumatic noise, phalloidin gap and monomeric actin assays, and fibroblast stretch with domain deletion mapping","pmids":["37294664"],"confidence":"High","gaps":["Molecular nature of the force-sensing conformational change unresolved","How XIRP2 promotes actin monomer delivery mechanistically unclear","Whether the cardiac functions use the same mechanosensor domain untested"]},{"year":2015,"claim":"Provided human disease relevance, linking truncating XIRP2 mutations to dilated cardiomyopathy via the same ICD defect seen in mice.","evidence":"Whole exome sequencing of a DCM child with cardiac histomorphology and cross-species phenotype comparison","pmids":["26656454"],"confidence":"Medium","gaps":["Single case","Modifier vs primary causative role not established","Functional consequence of the specific truncations not tested in vitro"]},{"year":2024,"claim":"Implicated XIRP2 in cancer-cell ion homeostasis and chemosensitivity, suggesting a role beyond cytoskeletal architecture.","evidence":"XIRP2 knockdown in hepatocellular carcinoma cells with drug sensitivity, ion measurements, and protein stability assays","pmids":["39194571"],"confidence":"Medium","gaps":["Mechanism linking XIRP2 to zinc/calcium regulation undefined","Single lab with limited mechanistic depth","Relationship to the cytoskeletal/ion-channel roles unclear"]},{"year":null,"claim":"How XIRP2's single actin-crosslinking and mechanosensing biochemistry is deployed across such divergent contexts — cardiac ICD/channel organization, sarcomeric stabilization, stereocilia repair, and ion homeostasis — remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structure of the actin-binding repeats or mechanosensor domain","Unified model relating tissue-specific isoforms to function lacking","Direct vs scaffolding role in ion channel surface expression not established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[0,6]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[9]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,5]}],"localization":[{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[0,5,9]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[1,3]}],"pathway":[{"term_id":"R-HSA-397014","term_label":"Muscle contraction","supporting_discovery_ids":[1,6]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[2]},{"term_id":"R-HSA-9709957","term_label":"Sensory Perception","supporting_discovery_ids":[4,5,9]}],"complexes":["intercalated disc","stereocilia actin core"],"partners":["ACTN2","FLNC","SCN5A","KCNA5"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"A4UGR9","full_name":"Xin actin-binding repeat-containing protein 2","aliases":["Beta-xin","Cardiomyopathy-associated protein 3","Xeplin"],"length_aa":3374,"mass_kda":382.3,"function":"Protects actin filaments from depolymerization (PubMed:15454575). Required for correct morphology of cell membranes and maturation of intercalated disks of cardiomyocytes via facilitating localization of XIRP1 and CDH2 to the termini of aligned mature cardiomyocytes (By similarity). Thereby required for correct postnatal heart development and growth regulation that is crucial for overall heart morphology and diastolic function (By similarity). Required for normal electrical conduction in the heart including formation of the infranodal ventricular conduction system and normal action potential configuration, as a result of its interaction with the cardiac ion channel components Scn5a/Nav1.5 and Kcna5/Kv1.5 (By similarity). Required for regular actin filament spacing of the paracrystalline array in both inner and outer hair cells of the cochlea, thereby required for maintenance of stereocilia morphology (By similarity)","subcellular_location":"Cell junction","url":"https://www.uniprot.org/uniprotkb/A4UGR9/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/XIRP2","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/XIRP2","total_profiled":1310},"omim":[{"mim_id":"620775","title":"NEUROMUSCULAR DISORDER, CONGENITAL, WITH DYSMORPHIC FACIES; NMDF","url":"https://www.omim.org/entry/620775"},{"mim_id":"615779","title":"CONGENITAL HEART DEFECTS, MULTIPLE TYPES, 4; CHTD4","url":"https://www.omim.org/entry/615779"},{"mim_id":"609778","title":"XIN ACTIN-BINDING REPEAT-CONTAINING PROTEIN 2; XIRP2","url":"https://www.omim.org/entry/609778"},{"mim_id":"171890","title":"PHOSPHODIESTERASE 1A; PDE1A","url":"https://www.omim.org/entry/171890"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Plasma membrane","reliability":"Approved"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"heart muscle","ntpm":180.7},{"tissue":"skeletal muscle","ntpm":962.9},{"tissue":"tongue","ntpm":458.6}],"url":"https://www.proteinatlas.org/search/XIRP2"},"hgnc":{"alias_symbol":[],"prev_symbol":["CMYA3"]},"alphafold":{"accession":"A4UGR9","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/A4UGR9","model_url":"https://alphafold.ebi.ac.uk/files/AF-A4UGR9-7-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-A4UGR9-7-F1-predicted_aligned_error_v6.png","plddt_mean":49.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=XIRP2","jax_strain_url":"https://www.jax.org/strain/search?query=XIRP2"},"sequence":{"accession":"A4UGR9","fasta_url":"https://rest.uniprot.org/uniprotkb/A4UGR9.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/A4UGR9/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/A4UGR9"}},"corpus_meta":[{"pmid":"32657779","id":"PMC_32657779","title":"Genomic landscape of metastatic breast cancer identifies preferentially dysregulated pathways and 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Transfection experiments confirmed that the repeats bind and stabilize the actin-based cytoskeleton in cultured cells.\",\n      \"method\": \"In vitro co-sedimentation assay with skeletal muscle actin; transfection of repeat constructs into cultured cells\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro reconstitution (co-sedimentation) plus cell-based transfection, replicated across Xin and XIRP2 repeats in same study\",\n      \"pmids\": [\"15454575\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"XIRP2 (mouse ortholog myomaxin/CMYA3) is a direct transcriptional target of MEF2A and localizes to the Z-disc/costameric region in striated muscle. The myomaxin protein (mouse XIRP2 ortholog) interacts with the sarcomeric Z-disc protein alpha-actinin-2.\",\n      \"method\": \"MEF2A knockout mouse expression analysis (microarray); protein interaction demonstrated by co-immunoprecipitation and/or pulldown; immunolocalization in muscle\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO (MEF2A null) identifies XIRP2 as downstream target; alpha-actinin-2 interaction reported in single lab with standard co-IP/pulldown\",\n      \"pmids\": [\"17046827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"XIRP2 expression in the heart is induced by angiotensin II (Ang II) signaling through MEF2A transcriptional activity. Ang II activates XIRP2 promoter activity via MEF2A, placing XIRP2 downstream of the Ang II–MEF2A pathway. Xirp2 hypomorphic mice (with markedly reduced cardiac Xirp2) developed spontaneous cardiac hypertrophy and increased beta-myosin heavy chain expression, and showed attenuated hypertrophic remodeling, reduced fibrosis, and reduced apoptosis after chronic Ang II infusion.\",\n      \"method\": \"Xirp2 promoter characterization; MEF2A activity assay; Xirp2 hypomorphic mouse model with Ang II infusion; histological and molecular readouts\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic hypomorphic model with in vivo Ang II challenge, promoter characterization, and multiple orthogonal phenotypic readouts in single rigorous study\",\n      \"pmids\": [\"20093629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Mouse Xinβ (mXinβ/XIRP2) is required for the postnatal maturation of intercalated discs (ICDs) in the heart. In mXinβ-null mice, intercellular junction components fail to redistribute from the lateral membrane to the termini of cardiomyocytes during postnatal ICD formation (defect apparent at postnatal day 16.5). mXinβ is uniquely upregulated during the redistribution phase and preferentially associates with forming ICDs by immunofluorescence and subcellular fractionation.\",\n      \"method\": \"mXinβ knockout mouse; quantitative Western blot; immunofluorescence; subcellular fractionation; comparison with mXinα-null and double-knockout hearts\",\n      \"journal\": \"Developmental biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with defined developmental phenotype, corroborated by fractionation and immunofluorescence, epistatic comparison with mXinα-null\",\n      \"pmids\": [\"23261932\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A short splice form of XIRP2 (lacking the Xin repeats, also called XEPLIN) is expressed in inner ear hair cells where it colocalizes with actin-rich stereocilia, the cuticular plate, and the circumferential actin belt. CRISPR/Cas9-mediated Xirp2-null mice exhibit high-frequency hearing loss and stereocilia degeneration, demonstrating that XIRP2 is required for long-term maintenance of hair cell stereocilia morphology and hearing function.\",\n      \"method\": \"Mass spectrometry of hair bundle proteome; CRISPR/Cas9 knockout mouse; auditory brainstem response (hearing function); scanning electron microscopy of stereocilia\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRISPR KO with functional (auditory) and ultrastructural (SEM) phenotypic readouts, replicated by independent lab (PMID 25772365)\",\n      \"pmids\": [\"25653358\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Different isoforms of XIRP2 are differentially localized in hair cells: short splice forms (XEPLIN) are targeted preferentially to stereocilia, whereas two long isoforms containing the XIN-repeat domain are present in both stereocilia and cuticular plates. Xirp2-null mice develop normal stereocilia bundles that degenerate over time, with loss of stereocilia, long membranous protrusions from apical surfaces, and disorganization of paracrystalline actin filaments at the ultrastructural level.\",\n      \"method\": \"Isoform-specific immunolocalization; Xirp2 knockout mouse; scanning electron microscopy; transmission electron microscopy of actin ultrastructure\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with ultrastructural characterization and isoform-specific localization, independent replication of hearing/stereocilia phenotype\",\n      \"pmids\": [\"25772365\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Both Xirp1 and Xirp2 (Xin actin-binding repeat-containing proteins) stabilize filamin C (FLNc) selectively in premyofibrils of cardiomyocytes. Analysis of cardiomyocytes from Xirp1- and Xirp2-deficient animals showed reduced FLNc stability at premyofibrils, as assessed by fluorescence recovery after photobleaching.\",\n      \"method\": \"FRAP (fluorescence recovery after photobleaching) in cardiomyocytes from Xirp1/Xirp2 knockout animals; live zebrafish imaging\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — FRAP in KO cardiomyocytes and live zebrafish, single lab, two organism models\",\n      \"pmids\": [\"27206985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Xirp2 is required for normal cardiac conduction. Xirp2-knockout mouse hearts exhibit prolonged PR and QT intervals, slow conduction velocity, atrioventricular conduction block, and abnormal infranodal ventricular conduction. Whole-cell patch-clamp of Xirp2-/- cardiomyocytes detected altered ionic currents. Co-immunoprecipitation demonstrated association of Xirp2 with Nav1.5 and Kv1.5 ion channel subunits, consistent with a role for Xirp2 in governing ion channel surface expression and cardiac conduction.\",\n      \"method\": \"Xirp2 knockout mouse; electrocardiography; whole-cell patch-clamp; co-immunoprecipitation with Nav1.5 and Kv1.5\",\n      \"journal\": \"Journal of the American Heart Association\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — genetic KO with electrophysiology (patch-clamp + ECG) and co-IP of ion channel partners in single rigorous study\",\n      \"pmids\": [\"29306897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In stereocilia, actin cross-linkers including XIRP2 undergo continuous turnover even though the actin filament core is highly stable, demonstrating that ongoing remodeling of cross-linker composition is a mechanism for stereocilia homeostasis and repair.\",\n      \"method\": \"Transgenic mouse expressing EGFP-fascin-2 to monitor cross-linker dynamics; comparison with endogenous XIRP2, espin, and plastin-1 localization\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging in transgenic mouse model; XIRP2 implicated by displacement assay, single lab\",\n      \"pmids\": [\"29874122\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"XIRP2 is required for repair of noise-induced damage to stereocilia F-actin cores. XIRP2 facilitates enrichment of monomeric γ-actin at damage gaps in auditory hair cells. Recruitment of XIRP2 to stereocilia gaps and to stress fiber strain sites in fibroblasts is force-dependent and is mediated by a novel mechanosensor domain located in the C-terminus of XIRP2.\",\n      \"method\": \"Xirp2-null mice subjected to traumatic noise; phalloidin gap assay; monomeric actin immunostaining; fibroblast stretch assay for mechanosensor domain mapping; domain deletion/mutagenesis experiments\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — KO mouse with functional assay, identification of novel mechanosensor domain by deletion mapping in both hair cells and fibroblasts, multiple orthogonal methods in one study\",\n      \"pmids\": [\"37294664\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Compound heterozygous truncating mutations in XIRP2 were identified in a child with sporadic dilated cardiomyopathy. Histomorphological analysis of explanted heart tissue showed misregistration, mislocalization, and shortening of intercalated discs, findings similar to those in Xirp2-/- mice, implicating XIRP2 as a modifier gene in DCM pathogenesis through disruption of ICD integrity.\",\n      \"method\": \"Whole exome sequencing; cardiac histomorphology of explanted heart; comparison with Xirp2-/- mouse phenotype\",\n      \"journal\": \"Journal of the American Heart Association\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human genetics supported by histopathological validation and cross-species phenotype comparison; single case\",\n      \"pmids\": [\"26656454\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Inhibition of XIRP2 in hepatocellular carcinoma cells results in increased sensitivity to oxaliplatin through elevation of zinc ions and calcium ion overload, identifying a functional role for XIRP2 in ion homeostasis. The XIRP2 mutation was found to enhance XIRP2 protein stability without affecting mRNA levels.\",\n      \"method\": \"XIRP2 knockdown in HCC cells; CCK-8 drug sensitivity assay; protein stability experiments; ion (zinc/calcium) measurements\",\n      \"journal\": \"Biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single lab, loss-of-function with defined cellular phenotype (drug sensitivity/ion levels), but limited mechanistic depth\",\n      \"pmids\": [\"39194571\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"XIRP2 is a striated muscle- and hair cell-expressed actin-binding protein whose Xin repeats directly bind and crosslink actin filaments; it functions as a MEF2A transcriptional target downstream of angiotensin II signaling in cardiac remodeling, is essential for postnatal intercalated disc maturation in the heart (where it associates with Nav1.5 and Kv1.5 to support normal cardiac conduction), and maintains stereocilia F-actin architecture in inner ear hair cells through a C-terminal mechanosensor domain that recruits XIRP2 to force-induced actin damage sites to facilitate repair.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"XIRP2 (Xin actin-binding repeat-containing protein 2) is a striated muscle- and hair cell-expressed cytoskeletal protein whose tandem Xin repeats constitute a direct actin-binding motif that crosslinks F-actin into stabilized networks [#0]. In the heart, XIRP2 is a direct transcriptional target of MEF2A induced by angiotensin II signaling, and its loss attenuates hypertrophic remodeling, fibrosis, and apoptosis following Ang II challenge, placing it in the cardiac stress-response pathway [#1, #2]. At the sarcomere it localizes to the Z-disc/costamere, interacts with alpha-actinin-2, and stabilizes filamin C in premyofibrils [#1, #6]. XIRP2 is required for postnatal maturation of cardiac intercalated discs, where it drives redistribution of junctional components to cardiomyocyte termini and associates with the Nav1.5 and Kv1.5 ion channel subunits to support normal conduction [#3, #7]; compound heterozygous truncating XIRP2 mutations are linked to dilated cardiomyopathy through disrupted intercalated disc integrity [#10]. In inner ear hair cells, isoform-specific XIRP2 (including a short Xin-repeat-deficient form, XEPLIN) localizes to stereocilia and the cuticular plate and is required for long-term maintenance of stereocilia F-actin architecture and hearing [#4, #5]; a C-terminal mechanosensor domain mediates force-dependent recruitment of XIRP2 to damaged actin sites, where it facilitates monomeric actin enrichment to repair noise-induced stereocilia damage [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established that the defining Xin repeats are themselves a functional actin-binding module, providing the biochemical basis for all later cytoskeletal roles.\",\n      \"evidence\": \"In vitro co-sedimentation with skeletal muscle actin and repeat-construct transfection in cultured cells\",\n      \"pmids\": [\"15454575\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Affinity and stoichiometry of binding not quantified\", \"Does not address regulation of binding in vivo\", \"Structural basis of the actin-bundling activity unresolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Placed XIRP2 in a defined transcriptional and structural context by identifying it as a MEF2A target localizing to the Z-disc and interacting with alpha-actinin-2.\",\n      \"evidence\": \"MEF2A knockout mouse microarray, co-IP/pulldown, and muscle immunolocalization\",\n      \"pmids\": [\"17046827\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"alpha-actinin-2 interaction from single lab, no reciprocal validation\", \"Functional consequence of the Z-disc interaction untested\", \"Direct vs indirect MEF2A regulation not distinguished at the time\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Connected XIRP2 to cardiac stress signaling, showing Ang II induces it via MEF2A and that its reduction alters hypertrophic remodeling.\",\n      \"evidence\": \"Xirp2 promoter and MEF2A activity assays plus Xirp2 hypomorphic mice under chronic Ang II infusion\",\n      \"pmids\": [\"20093629\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking actin-binding to remodeling output unclear\", \"Hypomorph rather than full null\", \"Cell-autonomous vs systemic contributions not separated\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined an essential developmental role: XIRP2 drives postnatal redistribution of junctional components to form mature intercalated discs.\",\n      \"evidence\": \"mXinβ knockout mouse with Western blot, immunofluorescence, fractionation, and epistatic comparison to mXinα-null\",\n      \"pmids\": [\"23261932\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular trigger of XIRP2 upregulation during redistribution unknown\", \"Direct binding partners at the ICD not defined here\", \"Mechanism of component redistribution not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Extended XIRP2 function to a new tissue, demonstrating isoform-specific stereocilia localization and a requirement for long-term hair cell actin maintenance and hearing.\",\n      \"evidence\": \"Hair bundle proteomics, CRISPR/Cas9 Xirp2-null mice, ABR, and SEM/TEM ultrastructure, replicated across two studies\",\n      \"pmids\": [\"25653358\", \"25772365\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Differential targeting determinants of short vs long isoforms unmapped\", \"Whether degeneration reflects failed repair vs structural support unclear at this stage\", \"Direct stereocilia binding partners not identified\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified filamin C as a stabilization client, linking XIRP2 actin-crosslinking to maintenance of specific sarcomeric components in nascent myofibrils.\",\n      \"evidence\": \"FRAP in Xirp1/Xirp2-deficient cardiomyocytes and live zebrafish imaging\",\n      \"pmids\": [\"27206985\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct vs indirect stabilization of FLNc not separated\", \"Redundancy with XIRP1 not fully partitioned\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Mechanistically linked the ICD/cytoskeletal role to electrophysiology, showing XIRP2 associates with cardiac ion channels and is required for normal conduction.\",\n      \"evidence\": \"Xirp2 knockout mouse ECG, whole-cell patch-clamp, and co-IP with Nav1.5 and Kv1.5\",\n      \"pmids\": [\"29306897\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether XIRP2 directly traffics channels or stabilizes them is unresolved\", \"Co-IP not validated reciprocally\", \"Direct vs ICD-architecture-mediated channel effects not separated\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Revealed that stereocilia cross-linkers including XIRP2 turn over continuously despite a stable actin core, framing repair as ongoing compositional remodeling.\",\n      \"evidence\": \"Transgenic EGFP-fascin-2 mouse imaging with endogenous cross-linker comparison\",\n      \"pmids\": [\"29874122\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"XIRP2 turnover inferred by displacement, not directly tracked\", \"Regulation of turnover unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defined the repair mechanism: a C-terminal mechanosensor domain confers force-dependent recruitment of XIRP2 to actin damage sites to drive monomeric actin enrichment and repair.\",\n      \"evidence\": \"Xirp2-null mice with traumatic noise, phalloidin gap and monomeric actin assays, and fibroblast stretch with domain deletion mapping\",\n      \"pmids\": [\"37294664\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular nature of the force-sensing conformational change unresolved\", \"How XIRP2 promotes actin monomer delivery mechanistically unclear\", \"Whether the cardiac functions use the same mechanosensor domain untested\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Provided human disease relevance, linking truncating XIRP2 mutations to dilated cardiomyopathy via the same ICD defect seen in mice.\",\n      \"evidence\": \"Whole exome sequencing of a DCM child with cardiac histomorphology and cross-species phenotype comparison\",\n      \"pmids\": [\"26656454\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single case\", \"Modifier vs primary causative role not established\", \"Functional consequence of the specific truncations not tested in vitro\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Implicated XIRP2 in cancer-cell ion homeostasis and chemosensitivity, suggesting a role beyond cytoskeletal architecture.\",\n      \"evidence\": \"XIRP2 knockdown in hepatocellular carcinoma cells with drug sensitivity, ion measurements, and protein stability assays\",\n      \"pmids\": [\"39194571\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking XIRP2 to zinc/calcium regulation undefined\", \"Single lab with limited mechanistic depth\", \"Relationship to the cytoskeletal/ion-channel roles unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How XIRP2's single actin-crosslinking and mechanosensing biochemistry is deployed across such divergent contexts — cardiac ICD/channel organization, sarcomeric stabilization, stereocilia repair, and ion homeostasis — remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structure of the actin-binding repeats or mechanosensor domain\", \"Unified model relating tissue-specific isoforms to function lacking\", \"Direct vs scaffolding role in ion channel surface expression not established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [0, 5, 9]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-397014\", \"supporting_discovery_ids\": [1, 6]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-9709957\", \"supporting_discovery_ids\": [4, 5, 9]}\n    ],\n    \"complexes\": [\"intercalated disc\", \"stereocilia actin core\"],\n    \"partners\": [\"ACTN2\", \"FLNC\", \"SCN5A\", \"KCNA5\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}