{"gene":"IRS4","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":2000,"finding":"IRS-4 mediates PKB/Akt activation and BAD phosphorylation during insulin stimulation in 32D myeloid progenitor cells, but only weakly binds and activates p85-associated PI 3-kinase and fails to activate p70(s6k) or inhibit apoptosis, distinguishing it functionally from IRS-1 and IRS-2. IRS-4 also promotes Grb-2 association and MAPK activation similarly to IRS-1.","method":"Retroviral expression in 32D(IR) cells, co-immunoprecipitation, kinase assays, apoptosis assays, phosphorylation measurements","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (co-IP, kinase assay, apoptosis assay, phosphorylation measurements) with clear functional readouts; functionally compared IRS-1, IRS-2, and IRS-4 side-by-side","pmids":["10594015"],"is_preprint":false},{"year":2001,"finding":"IRS-4 overexpression decreases IRS-2 mRNA and protein levels and impairs IGF-1-stimulated tyrosine phosphorylation of IRS-1 and IRS-2, increases basal PI 3-kinase activity and Akt phosphorylation, but fails to reconstitute the mitogenic response to IGF-1 in IRS-1 KO cells, acting as a negative regulator of IGF-1 signaling.","method":"Retroviral transduction into 3T3 fibroblasts from WT and IRS-1 KO mice, immunoblotting, PI 3-kinase activity assay, MAPK phosphorylation assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods across WT and KO cell backgrounds, replicated signaling pathway analysis","pmids":["11113178"],"is_preprint":false},{"year":1999,"finding":"IRS-4 overexpression in rat adipose cells stimulates GLUT4 translocation to the cell surface in a PI 3-kinase-dependent manner, even in the absence of insulin, demonstrating that IRS-4 can mediate insulin metabolic actions.","method":"Cotransfection of HA-tagged GLUT4 and IRS-4 in rat adipose cells, cell surface GLUT4 measurement, PI 3-kinase inhibitor studies, YXXM motif mutagenesis","journal":"Molecular endocrinology (Baltimore, Md.)","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — direct functional assay with mutagenesis (IRS-3-F4 YXXM mutant confirmed PI3K-dependence), multiple conditions tested in a single study","pmids":["10077007"],"is_preprint":false},{"year":2003,"finding":"IRS-4 expression in INS-1 pancreatic beta-cells compensates for IRS-2 depletion by enhancing glucose/IGF-1-induced mitogenesis and protecting against fatty acid-induced apoptosis via PKB activation and decreased caspase-9 activation.","method":"Adenoviral-mediated overexpression and antisense knockdown in INS-1 cells, PKB phosphorylation assay, caspase-9 activation assay, apoptosis assay","journal":"Molecular and cellular endocrinology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — adenoviral gain/loss of function with multiple signaling readouts in a single lab","pmids":["14604813"],"is_preprint":false},{"year":2003,"finding":"In murine T-cell lymphoma (LB) cells lacking IGF-1 receptors, insulin stimulates tyrosine phosphorylation of IRS-4 (160 kDa), which associates with and activates PI3-kinase and downstream p70(S6K), but not the Ras-MAPK pathway; PI3-kinase (not p70S6K or MEK) is required for insulin-stimulated DNA synthesis.","method":"Immunoprecipitation, kinase assays, PI3-kinase activity assay, selective inhibitor treatment, thymidine incorporation assay","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and selective inhibitor dissection in a defined cell model, single lab","pmids":["12618213"],"is_preprint":false},{"year":2006,"finding":"Insulin induces tyrosine phosphorylation of IRS-4 (pp160) in rat liver membranes; Angiotensin II pre-stimulation reduces this phosphorylation in a dose-dependent manner; PI3-kinase inhibitors increase IRS-4 phosphorylation, indicating a PI3K-dependent negative feedback on IRS-4 tyrosine phosphorylation.","method":"Tyrosine phosphorylation assay in rat liver membrane preparations, inhibitor studies (okadaic acid, genistein, wortmannin, LY294002), immunoblotting with anti-IRS-4 antibody","journal":"Molecular and cellular biochemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method (immunoblot/phosphorylation assay), no co-IP or kinase reconstitution","pmids":["16933034"],"is_preprint":false},{"year":2010,"finding":"In HepG2 cells, insulin induces tyrosine phosphorylation of IRS-4 and physical association between IRS-4 and PI3-kinase (co-immunoprecipitation); Angiotensin II via AT1 receptors potentiates IRS-4 tyrosine phosphorylation but does not alter IRS-4/PI3-K association or PI3-K activation.","method":"Co-immunoprecipitation, tyrosine phosphorylation assay, PI3-kinase activity measurement, PI3-K inhibitor treatment","journal":"Regulatory peptides","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, co-IP with limited mechanistic follow-up","pmids":["20079766"],"is_preprint":false},{"year":2011,"finding":"Asb-4 (ankyrin repeat and SOCS box containing protein 4) co-localizes with IRS4 in hypothalamic arcuate nucleus POMC and NPY neurons, physically interacts with IRS4 by co-immunoprecipitation (both in transfected HEK293 cells and in rat hypothalamic extracts), promotes IRS4 ubiquitination and proteasomal/lysosomal degradation via its SOCS box, and reduces insulin-stimulated AKT phosphorylation.","method":"In situ hybridization, co-immunoprecipitation (in HEK293 cells and rat hypothalamic extracts), ubiquitination assay, SOCS box deletion mutagenesis, AKT phosphorylation assay","journal":"BMC neuroscience","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP in both heterologous and endogenous settings, domain mutagenesis, ubiquitination assay, functional AKT readout; multiple orthogonal methods","pmids":["21955513"],"is_preprint":false},{"year":2013,"finding":"IRS4 expression in cancer cells with high IRS4 levels drives constitutively elevated PIP3, Akt, and p70 S6 kinase activities even in the absence of growth factors; PI3K signaling in these cells depends on IRS4 even though IRS1/2 are co-expressed. IRS4 knockdown inhibits cell proliferation in IRS4-high cells.","method":"RNAi knockdown, PIP3 measurement, Akt and S6K phosphorylation assay, cell proliferation assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — knockdown with multiple signaling readouts and proliferation assay, single lab","pmids":["24039912"],"is_preprint":false},{"year":2013,"finding":"Brain-specific deletion of Irs2 combined with whole-body Irs4 knockout (bIrs2−/− · Irs4−/y) causes severe obesity, decreased energy expenditure, hyperglycemia, and insulin resistance; these phenotypes are not observed with Irs4 knockout alone or with LepRb-specific Irs2 deletion plus Irs4 knockout, indicating that Irs2 and Irs4 synergize in non-LepRb hypothalamic neurons to control energy balance.","method":"Genetic epistasis using double-knockout mouse models (Cre-lox), metabolic phenotyping (body weight, energy expenditure, blood glucose, insulin tolerance)","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple defined KO combinations and quantitative metabolic phenotyping, clean mechanistic dissection of cell-type specificity","pmids":["24567904"],"is_preprint":false},{"year":2016,"finding":"IRS4 expression in mammary epithelial cells induces constitutive PI3K/AKT pathway hyperactivation, insulin/IGF1-independent cell proliferation, anchorage-independent growth, and in vivo tumorigenesis. The absence of a SHP2-binding domain in IRS4 (present in IRS1/2) is identified as the molecular basis for its constitutive, feedback-insensitive PI3K/AKT activation. IRS4 and ERBB2/HER2 synergistically induce tumorigenesis, and IRS4 expression confers resistance to HER2-targeted therapy.","method":"Insertional mutagenesis screen, retroviral overexpression in mammary epithelial cells, PI3K/AKT pathway phosphorylation assays, proliferation/anchorage-independent growth assays, in vivo tumorigenesis models, domain analysis/mutagenesis, HER2-targeted therapy resistance assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — insertional mutagenesis discovery, mechanistic domain analysis identifying SHP2-binding domain absence, multiple functional assays including in vivo, constitutive vs. stimulus-dependent PI3K activation compared across IRS family members","pmids":["27876799"],"is_preprint":false},{"year":2017,"finding":"IRS4 interacts with BMP receptor BMPRII and specifically targets Smad1 for proteasomal degradation, repressing BMP/Smad signaling while concomitantly activating the PI3K/Akt axis in C2C12 myoblasts. IRS4 promotes myogenesis and its knockdown inhibits myoblast differentiation.","method":"Co-immunoprecipitation, proteasome inhibitor assays, Smad1 phosphorylation/degradation measurements, PI3K/Akt activation assay, IRS4 knockdown in C2C12 cells, myogenic differentiation assay","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP identifying BMPRII interaction, proteasomal degradation assay, functional knockdown with differentiation readout; single lab with multiple methods","pmids":["28821740"],"is_preprint":false},{"year":2018,"finding":"IRS4 is phosphorylated at Ser859 by CK1γ2 in vitro and in vivo, which promotes polyubiquitination and degradation of IRS4 via the CHIP E3 ligase through the ubiquitin/lysosome pathway. A non-phosphorylatable IRS4 mutant (Ser859 mutant) shows higher p-Akt levels and faster tumor cell proliferation.","method":"In vitro kinase assay, mass spectrometry, co-immunoprecipitation, cycloheximide chase assay, ubiquitination assay, phospho-mutant overexpression, colony formation assay, xenograft mouse model","journal":"Theranostics","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — in vitro kinase assay establishing CK1γ2 as the kinase for Ser859, CHIP identified as E3 ligase by mass spectrometry and co-IP, phospho-mutant functional validation in vitro and in vivo; multiple orthogonal methods","pmids":["30026872"],"is_preprint":false},{"year":2018,"finding":"Loss-of-function mutations in IRS4 (nonsense and frameshift) are associated with isolated congenital central hypothyroidism (CeH) in males; IRS4 mRNA is expressed in human hypothalamic nuclei (including paraventricular nucleus) and pituitary; female Irs4 knockout mice show decreased pituitary Tshb mRNA levels, linking IRS4 to TSH regulation in the hypothalamic-pituitary axis.","method":"Exome sequencing, Sanger sequencing, IRS4 expression analysis in human hypothalamus/pituitary, Irs4 knockout mouse model with pituitary Tshb mRNA measurement and serum thyroid hormone measurement, 24-hour TSH secretion profiling","journal":"Journal of medical genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human genetics combined with mouse KO model showing pituitary Tshb reduction; single lab but orthogonal approaches (human mutation + mouse model)","pmids":["30061370"],"is_preprint":false},{"year":2020,"finding":"IRS4-expressing neurons in the paraventricular, subparaventricular, and periventricular hypothalamus are sufficient and necessary for normal feeding and energy expenditure; activation of IRS4PVH neurons suppresses feeding and increases energy expenditure, and their silencing causes obesity; IRS4PVH neurons lie within hypothalamic circuitry innervating distinct hindbrain regions.","method":"Cre-dependent viral tools for chemogenetic activation and silencing of IRS4-expressing neurons, neuronal tracing, feeding and energy expenditure measurement in mice","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function using viral tools in defined neuronal populations with quantitative metabolic phenotyping; single lab","pmids":["32218485"],"is_preprint":false},{"year":2021,"finding":"IRS4 knockout suppresses proliferation, colony formation, migration, invasion, and tumor growth in A549 lung cancer cells; IRS4 activates both PI3K/Akt and Ras-MAPK pathways; IRS4 depletion significantly sensitizes EGFR-TKI-resistant cells to gefitinib.","method":"CRISPR/retroviral KO and stable overexpression, proliferation/colony/migration/invasion assays, PI3K/Akt and MAPK pathway phosphorylation assays, xenograft mouse model, gefitinib sensitivity assay","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional KO and overexpression with multiple functional readouts and pathway analysis, in vivo xenograft, single lab","pmids":["33894221"],"is_preprint":false},{"year":2022,"finding":"Non-receptor tyrosine kinase FER phosphorylates IRS4 at Tyr779 via its kinase domain interacting with the PH and PTB domains of IRS4; this phosphorylation enables IRS4 to recruit PIK3R2/p85β (regulatory subunit of PI3K), activating the PI3K-AKT pathway. Phosphorylation-defective IRS4 (Y779F) fails to rescue IRS4-null ovarian tumor cell proliferation in vitro and in vivo.","method":"Mass spectrometry substrate identification, co-immunoprecipitation, proximity-based tagging (BioID), in vitro kinase assay, phospho-mutant rescue experiments, in vitro and xenograft proliferation assays","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — mass spectrometry substrate identification confirmed by co-IP and proximity tagging, in vitro kinase assay, phospho-mutant functional rescue both in vitro and in vivo; multiple orthogonal methods in a rigorous study","pmids":["35550247"],"is_preprint":false},{"year":2014,"finding":"IRS-4 physically interacts with the copper transporter CTR1 (co-immunoprecipitation confirmed with FLAG-CTR1 and myc-CTR1); the interaction is enhanced when the CTR1 Y103A mutation is present.","method":"Proteomic analysis of CTR1-derived peptides, co-immunoprecipitation from HEK cells expressing FLAG-CTR1 or myc-CTR1","journal":"Biochemical pharmacology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single co-IP confirmation, mechanistic significance of the IRS4-CTR1 interaction not further characterized","pmids":["24967972"],"is_preprint":false},{"year":2026,"finding":"IRS4 drives cancer cell dependency through PI3K-Akt activation; domain analysis shows the PH and PTB domains are dispensable for IRS4's PI3K-activating oncogenic function, suggesting degradation-based therapeutic modalities; IRS4 expression in adult tumors is associated with enhancer hijacking rearrangements including GATA3-IRS4 and ANKRD30A-IRS4 in breast cancer.","method":"Pan-cancer dependency analysis, domain deletion analysis, PI3K-Akt pathway assays, genomic rearrangement analysis","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain deletion functional analysis with pathway readout, multiple cancer types analyzed; single study","pmids":["42054459"],"is_preprint":false},{"year":2021,"finding":"PD-L1 binds to eIF3I and promotes cutaneous diabetic wound healing by downregulating IRS4; the eIF3I-PD-L1-IRS4 axis contributes to wound healing defects. PD-L1 interacting proteins were identified by co-immunoprecipitation combined with mass spectrometry.","method":"Transcriptional profiling, co-immunoprecipitation combined with mass spectrometry, coimmunoprecipitation validation, in vivo and in vitro functional assays, immunohistochemistry","journal":"The Journal of investigative dermatology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — co-IP/MS identifies the interaction but the mechanistic basis of IRS4 downregulation by PD-L1/eIF3I is not deeply characterized; single lab","pmids":["34293353"],"is_preprint":false}],"current_model":"IRS4 is a cytoplasmic scaffold/adaptor protein that, upon tyrosine phosphorylation by receptor tyrosine kinases (and non-receptor kinases such as FER, which phosphorylates Tyr779), recruits PI3K regulatory subunits (p85α/β) to constitutively hyperactivate the PI3K/AKT pathway independently of upstream growth factor signals—a property mechanistically explained by its lack of a SHP2-binding domain that normally enables feedback inhibition; IRS4 also activates Ras-MAPK signaling through Grb-2 recruitment, acts as a negative regulator of IRS-1/IRS-2 signaling, mediates GLUT4 translocation, and is subject to post-translational regulation through CK1γ2-mediated phosphorylation at Ser859 that promotes CHIP-dependent ubiquitination and lysosomal degradation, and through Asb-4-mediated ubiquitination and proteasomal degradation; in the hypothalamus, IRS4-expressing neurons in the paraventricular nucleus are required for normal energy balance and TSH regulation, with Irs4 synergizing with Irs2 in non-LepRb neurons for metabolic homeostasis."},"narrative":{"mechanistic_narrative":"IRS4 is a cytoplasmic insulin-receptor-substrate adaptor that couples receptor tyrosine kinase signaling to the PI3K/AKT axis, mediating metabolic and mitogenic outputs while functioning distinctly from IRS-1 and IRS-2 [PMID:10594015, PMID:10077007]. Upon tyrosine phosphorylation, IRS4 recruits PI3K regulatory subunits to drive AKT activation, BAD phosphorylation, and—via Grb-2—MAPK signaling, and it suffices to stimulate PI3K-dependent GLUT4 translocation independently of insulin [PMID:10594015, PMID:10077007]. The non-receptor kinase FER phosphorylates IRS4 at Tyr779 through interaction with its PH and PTB domains, enabling recruitment of PIK3R2/p85β to activate PI3K-AKT [PMID:35550247]. A defining feature of IRS4 is constitutive, growth-factor-independent and feedback-insensitive PI3K/AKT activation, attributed to its lack of a SHP2-binding domain present in IRS1/2; this drives insulin/IGF1-independent proliferation, anchorage-independent growth, and tumorigenesis, synergy with ERBB2/HER2, and resistance to HER2- and EGFR-targeted therapies [PMID:27876799, PMID:33894221, PMID:42054459]. IRS4 also acts as a negative regulator of IRS-1/IRS-2 signaling by reducing IRS-2 levels and impairing IGF-1-stimulated IRS-1/2 phosphorylation [PMID:11113178]. IRS4 abundance is controlled by ubiquitin-dependent degradation: Asb-4 promotes IRS4 ubiquitination and degradation via its SOCS box [PMID:21955513], and CK1γ2-mediated phosphorylation at Ser859 promotes CHIP-dependent polyubiquitination and lysosomal degradation, with degradation-resistant IRS4 elevating p-AKT and proliferation [PMID:30026872]. In the brain, IRS4-expressing paraventricular hypothalamic neurons are required for normal feeding and energy expenditure, IRS4 synergizes with IRS2 in non-LepRb neurons for energy balance, and loss-of-function IRS4 mutations cause isolated congenital central hypothyroidism in males via the hypothalamic-pituitary TSH axis [PMID:24567904, PMID:30061370, PMID:32218485].","teleology":[{"year":2000,"claim":"Established that IRS4 transduces insulin signals to AKT/BAD and MAPK but is functionally distinct from IRS-1/2, defining it as a non-redundant adaptor.","evidence":"Retroviral expression in 32D(IR) myeloid cells with co-IP, kinase, phosphorylation, and apoptosis assays comparing IRS-1/2/4","pmids":["10594015"],"confidence":"High","gaps":["Did not identify the receptor kinases or sites driving IRS4 phosphorylation","Weak p85/PI3K coupling left the basis of pathway selectivity unresolved"]},{"year":1999,"claim":"Showed IRS4 can drive a core metabolic insulin output—GLUT4 translocation—in a PI3K- and YXXM-motif-dependent manner, even without insulin.","evidence":"Cotransfection of HA-GLUT4 and IRS-4 in rat adipose cells with surface GLUT4 measurement, PI3K inhibitors, and YXXM mutagenesis","pmids":["10077007"],"confidence":"High","gaps":["Overexpression context may not reflect endogenous stoichiometry","Mechanism of insulin-independent activation not defined"]},{"year":2001,"claim":"Revealed a paradoxical negative-regulatory role: IRS4 suppresses IRS-2 levels and IRS-1/2 phosphorylation while raising basal PI3K/AKT, separating its mitogenic from metabolic functions.","evidence":"Retroviral transduction into WT and IRS-1 KO 3T3 fibroblasts with immunoblot, PI3K, and MAPK assays","pmids":["11113178"],"confidence":"High","gaps":["Mechanism by which IRS4 reduces IRS-2 not defined","Failure to rescue mitogenesis in IRS-1 KO left signaling output incomplete"]},{"year":2003,"claim":"Demonstrated cell-context-dependent PI3K coupling: in beta-cells IRS4 compensates for IRS-2 to support survival/mitogenesis, while in IGF1R-null T-lymphoma cells insulin-driven IRS4 activates PI3K/p70S6K but not Ras-MAPK.","evidence":"Adenoviral gain/loss in INS-1 cells and IP/kinase/inhibitor dissection in LB T-cell lymphoma cells","pmids":["14604813","12618213"],"confidence":"Medium","gaps":["Context-dependence of MAPK coupling not mechanistically explained","Single-lab cell-line studies"]},{"year":2010,"claim":"Confirmed insulin-induced IRS4 tyrosine phosphorylation and physical IRS4/PI3K association in hepatic cells, with crosstalk modulation by Angiotensin II.","evidence":"Co-IP, tyrosine phosphorylation and PI3K activity assays in HepG2 cells and rat liver membranes with AT1 receptor manipulation","pmids":["20079766","16933034"],"confidence":"Low","gaps":["Single-method phosphorylation readouts without kinase reconstitution","Physiological relevance of AngII crosstalk unclear"]},{"year":2011,"claim":"Identified Asb-4 as a hypothalamic regulator that ubiquitinates and degrades IRS4 via its SOCS box, establishing post-translational control of IRS4-dependent AKT signaling in feeding-relevant neurons.","evidence":"Reciprocal co-IP in HEK293 and rat hypothalamic extracts, SOCS box deletion, ubiquitination and AKT assays, in situ hybridization","pmids":["21955513"],"confidence":"High","gaps":["Did not establish whether Asb-4-mediated degradation is proteasomal vs lysosomal definitively","In vivo consequence of Asb-4 loss on IRS4 not tested"]},{"year":2013,"claim":"Showed IRS4 drives constitutive, IRS1/2-independent PI3K/AKT/S6K activity in cancer cells and is required for their proliferation, framing IRS4 as an oncogenic driver.","evidence":"RNAi knockdown with PIP3, AKT/S6K phosphorylation, and proliferation assays in IRS4-high cancer cells","pmids":["24039912"],"confidence":"Medium","gaps":["Did not explain why IRS4 dominates over co-expressed IRS1/2","No in vivo validation"]},{"year":2013,"claim":"Defined a brain-specific, cell-type-resolved role: Irs2/Irs4 synergize in non-LepRb hypothalamic neurons to control energy balance.","evidence":"Genetic epistasis across bIrs2/Irs4 double-knockout combinations with metabolic phenotyping in mice","pmids":["24567904"],"confidence":"High","gaps":["Molecular signaling underlying Irs2/Irs4 synergy not resolved","Specific neuronal subtypes not fully defined"]},{"year":2016,"claim":"Provided the molecular basis for constitutive PI3K/AKT activation—absence of a SHP2-binding domain renders IRS4 feedback-insensitive—and demonstrated tumorigenicity and HER2-therapy resistance.","evidence":"Insertional mutagenesis screen, retroviral overexpression in mammary cells, domain mutagenesis, in vivo tumorigenesis and HER2-resistance assays","pmids":["27876799"],"confidence":"High","gaps":["Did not identify the upstream kinase normally phosphorylating IRS4 in tumors","Did not address regulation of IRS4 abundance in this setting"]},{"year":2017,"claim":"Extended IRS4's role to BMP signaling, where it binds BMPRII, targets Smad1 for degradation, and promotes myogenesis while activating PI3K/Akt.","evidence":"Co-IP, proteasome inhibitor and Smad1 degradation assays, knockdown and differentiation assays in C2C12 myoblasts","pmids":["28821740"],"confidence":"Medium","gaps":["Mechanism linking IRS4 to Smad1 degradation not defined","Single cell-type model"]},{"year":2018,"claim":"Identified the CK1γ2–Ser859–CHIP axis controlling IRS4 stability, linking phospho-dependent degradation to suppression of AKT signaling and tumor proliferation.","evidence":"In vitro kinase assay, mass spectrometry, cycloheximide chase, ubiquitination assays, phospho-mutant validation in vitro and xenograft","pmids":["30026872"],"confidence":"High","gaps":["Upstream signals controlling CK1γ2 activity on IRS4 unknown","Relationship between CHIP and Asb-4 degradation routes not reconciled"]},{"year":2018,"claim":"Connected IRS4 loss-of-function to human disease, identifying it as a cause of isolated congenital central hypothyroidism via the hypothalamic-pituitary TSH axis.","evidence":"Exome/Sanger sequencing of CeH patients, human hypothalamus/pituitary expression, and Irs4 KO mouse pituitary Tshb/TSH profiling","pmids":["30061370"],"confidence":"Medium","gaps":["Signaling pathway linking IRS4 to TSH regulation not defined","Male-restricted phenotype mechanism unexplained"]},{"year":2020,"claim":"Resolved the neuronal circuit: IRS4-expressing PVH/periventricular neurons are necessary and sufficient for feeding and energy expenditure control.","evidence":"Cre-dependent chemogenetic activation/silencing, neuronal tracing, and metabolic measurement in mice","pmids":["32218485"],"confidence":"Medium","gaps":["Role of cell-intrinsic IRS4 signaling vs neuron identity not separated","Downstream hindbrain effectors not mechanistically mapped"]},{"year":2022,"claim":"Identified FER as the kinase phosphorylating IRS4 at Tyr779 through PH/PTB domain interaction to recruit p85β and activate PI3K-AKT, supplying an upstream activator of oncogenic IRS4.","evidence":"Mass spectrometry substrate ID, co-IP, BioID, in vitro kinase assay, and Y779F phospho-mutant rescue in vitro and in xenografts","pmids":["35550247"],"confidence":"High","gaps":["Generality of FER as the activating kinase across tissues unknown","Other phosphosites contributing to PI3K recruitment not enumerated"]},{"year":2026,"claim":"Mapped IRS4 as a pan-cancer dependency whose PH/PTB domains are dispensable for PI3K-activating oncogenic function and whose tumor expression arises through enhancer-hijacking rearrangements, motivating degradation-based therapy.","evidence":"Pan-cancer dependency analysis, domain deletion with PI3K-Akt readouts, and genomic rearrangement analysis (GATA3-IRS4, ANKRD30A-IRS4)","pmids":["42054459"],"confidence":"Medium","gaps":["Reconciling dispensable PH/PTB here with FER-domain dependence elsewhere unresolved","Degradation-based therapeutic feasibility not demonstrated"]},{"year":null,"claim":"How IRS4's constitutive, feedback-insensitive PI3K activation is integrated with its phospho-dependent degradation, its receptor/kinase inputs across tissues, and its disease-relevant hypothalamic signaling remains incompletely unified.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of IRS4–p85 or IRS4–FER complexes","Tissue-specific upstream activators beyond FER not defined","Mechanism of IRS4-mediated IRS-2 suppression unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,16]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,10,16]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[10,13,15]},{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[2,9]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[7,12]}],"complexes":[],"partners":["PIK3R2","FER","ASB4","STUB1","CSNK1G2","BMPR2","GRB2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O14654","full_name":"Insulin receptor substrate 4","aliases":["160 kDa phosphotyrosine protein","py160","Phosphoprotein of 160 kDa","pp160"],"length_aa":1257,"mass_kda":133.8,"function":"Acts as an interface between multiple growth factor receptors possessing tyrosine kinase activity, such as insulin receptor, IGF1R and FGFR1, and a complex network of intracellular signaling molecules containing SH2 domains. Involved in the IGF1R mitogenic signaling pathway. Promotes the AKT1 signaling pathway and BAD phosphorylation during insulin stimulation without activation of RPS6KB1 or the inhibition of apoptosis. Interaction with GRB2 enhances insulin-stimulated mitogen-activated protein kinase activity. May be involved in nonreceptor tyrosine kinase signaling in myoblasts. Plays a pivotal role in the proliferation/differentiation of hepatoblastoma cell through EPHB2 activation upon IGF1 stimulation. May play a role in the signal transduction in response to insulin and to a lesser extent in response to IL4 and GH on mitogenesis. Plays a role in growth, reproduction and glucose homeostasis. May act as negative regulators of the IGF1 signaling pathway by suppressing the function of IRS1 and IRS2","subcellular_location":"Cell membrane","url":"https://www.uniprot.org/uniprotkb/O14654/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IRS4","classification":"Not Classified","n_dependent_lines":14,"n_total_lines":1208,"dependency_fraction":0.011589403973509934},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"PIK3R1","stoichiometry":4.0},{"gene":"PIK3R2","stoichiometry":4.0},{"gene":"CAPZB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/IRS4","total_profiled":1310},"omim":[{"mim_id":"605761","title":"ANKYRIN REPEAT- AND SOCS BOX-CONTAINING PROTEIN 4; ASB4","url":"https://www.omim.org/entry/605761"},{"mim_id":"301035","title":"HYPOTHYROIDISM, CONGENITAL, NONGOITROUS, 9; CHNG9","url":"https://www.omim.org/entry/301035"},{"mim_id":"300904","title":"INSULIN RECEPTOR SUBSTRATE 4; IRS4","url":"https://www.omim.org/entry/300904"},{"mim_id":"275200","title":"HYPOTHYROIDISM, CONGENITAL, NONGOITROUS, 1; CHNG1","url":"https://www.omim.org/entry/275200"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Group enriched","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"brain","ntpm":6.0},{"tissue":"pituitary gland","ntpm":23.6}],"url":"https://www.proteinatlas.org/search/IRS4"},"hgnc":{"alias_symbol":["PY160","IRS-4"],"prev_symbol":[]},"alphafold":{"accession":"O14654","domains":[{"cath_id":"2.30.29.30","chopping":"76-207","consensus_level":"medium","plddt":87.6178,"start":76,"end":207},{"cath_id":"2.30.29.30","chopping":"232-345","consensus_level":"medium","plddt":87.5379,"start":232,"end":345}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O14654","model_url":"https://alphafold.ebi.ac.uk/files/AF-O14654-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O14654-F1-predicted_aligned_error_v6.png","plddt_mean":48.22},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IRS4","jax_strain_url":"https://www.jax.org/strain/search?query=IRS4"},"sequence":{"accession":"O14654","fasta_url":"https://rest.uniprot.org/uniprotkb/O14654.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O14654/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O14654"}},"corpus_meta":[{"pmid":"27869826","id":"PMC_27869826","title":"Pan-cancer analysis of somatic copy-number alterations implicates IRS4 and IGF2 in enhancer hijacking.","date":"2016","source":"Nature genetics","url":"https://pubmed.ncbi.nlm.nih.gov/27869826","citation_count":318,"is_preprint":false},{"pmid":"11113178","id":"PMC_11113178","title":"Insulin receptor substrate 3 (IRS-3) and IRS-4 impair IRS-1- and IRS-2-mediated signaling.","date":"2001","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/11113178","citation_count":78,"is_preprint":false},{"pmid":"14604813","id":"PMC_14604813","title":"Decreasing IRS-2 expression in pancreatic beta-cells (INS-1) promotes apoptosis, which can be compensated for by introduction of IRS-4 expression.","date":"2003","source":"Molecular and cellular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/14604813","citation_count":65,"is_preprint":false},{"pmid":"27876799","id":"PMC_27876799","title":"IRS4 induces mammary tumorigenesis and confers resistance to HER2-targeted therapy through 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IRS-4 also promotes Grb-2 association and MAPK activation similarly to IRS-1.\",\n      \"method\": \"Retroviral expression in 32D(IR) cells, co-immunoprecipitation, kinase assays, apoptosis assays, phosphorylation measurements\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (co-IP, kinase assay, apoptosis assay, phosphorylation measurements) with clear functional readouts; functionally compared IRS-1, IRS-2, and IRS-4 side-by-side\",\n      \"pmids\": [\"10594015\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"IRS-4 overexpression decreases IRS-2 mRNA and protein levels and impairs IGF-1-stimulated tyrosine phosphorylation of IRS-1 and IRS-2, increases basal PI 3-kinase activity and Akt phosphorylation, but fails to reconstitute the mitogenic response to IGF-1 in IRS-1 KO cells, acting as a negative regulator of IGF-1 signaling.\",\n      \"method\": \"Retroviral transduction into 3T3 fibroblasts from WT and IRS-1 KO mice, immunoblotting, PI 3-kinase activity assay, MAPK phosphorylation assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods across WT and KO cell backgrounds, replicated signaling pathway analysis\",\n      \"pmids\": [\"11113178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"IRS-4 overexpression in rat adipose cells stimulates GLUT4 translocation to the cell surface in a PI 3-kinase-dependent manner, even in the absence of insulin, demonstrating that IRS-4 can mediate insulin metabolic actions.\",\n      \"method\": \"Cotransfection of HA-tagged GLUT4 and IRS-4 in rat adipose cells, cell surface GLUT4 measurement, PI 3-kinase inhibitor studies, YXXM motif mutagenesis\",\n      \"journal\": \"Molecular endocrinology (Baltimore, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — direct functional assay with mutagenesis (IRS-3-F4 YXXM mutant confirmed PI3K-dependence), multiple conditions tested in a single study\",\n      \"pmids\": [\"10077007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"IRS-4 expression in INS-1 pancreatic beta-cells compensates for IRS-2 depletion by enhancing glucose/IGF-1-induced mitogenesis and protecting against fatty acid-induced apoptosis via PKB activation and decreased caspase-9 activation.\",\n      \"method\": \"Adenoviral-mediated overexpression and antisense knockdown in INS-1 cells, PKB phosphorylation assay, caspase-9 activation assay, apoptosis assay\",\n      \"journal\": \"Molecular and cellular endocrinology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — adenoviral gain/loss of function with multiple signaling readouts in a single lab\",\n      \"pmids\": [\"14604813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In murine T-cell lymphoma (LB) cells lacking IGF-1 receptors, insulin stimulates tyrosine phosphorylation of IRS-4 (160 kDa), which associates with and activates PI3-kinase and downstream p70(S6K), but not the Ras-MAPK pathway; PI3-kinase (not p70S6K or MEK) is required for insulin-stimulated DNA synthesis.\",\n      \"method\": \"Immunoprecipitation, kinase assays, PI3-kinase activity assay, selective inhibitor treatment, thymidine incorporation assay\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and selective inhibitor dissection in a defined cell model, single lab\",\n      \"pmids\": [\"12618213\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Insulin induces tyrosine phosphorylation of IRS-4 (pp160) in rat liver membranes; Angiotensin II pre-stimulation reduces this phosphorylation in a dose-dependent manner; PI3-kinase inhibitors increase IRS-4 phosphorylation, indicating a PI3K-dependent negative feedback on IRS-4 tyrosine phosphorylation.\",\n      \"method\": \"Tyrosine phosphorylation assay in rat liver membrane preparations, inhibitor studies (okadaic acid, genistein, wortmannin, LY294002), immunoblotting with anti-IRS-4 antibody\",\n      \"journal\": \"Molecular and cellular biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method (immunoblot/phosphorylation assay), no co-IP or kinase reconstitution\",\n      \"pmids\": [\"16933034\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In HepG2 cells, insulin induces tyrosine phosphorylation of IRS-4 and physical association between IRS-4 and PI3-kinase (co-immunoprecipitation); Angiotensin II via AT1 receptors potentiates IRS-4 tyrosine phosphorylation but does not alter IRS-4/PI3-K association or PI3-K activation.\",\n      \"method\": \"Co-immunoprecipitation, tyrosine phosphorylation assay, PI3-kinase activity measurement, PI3-K inhibitor treatment\",\n      \"journal\": \"Regulatory peptides\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, co-IP with limited mechanistic follow-up\",\n      \"pmids\": [\"20079766\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Asb-4 (ankyrin repeat and SOCS box containing protein 4) co-localizes with IRS4 in hypothalamic arcuate nucleus POMC and NPY neurons, physically interacts with IRS4 by co-immunoprecipitation (both in transfected HEK293 cells and in rat hypothalamic extracts), promotes IRS4 ubiquitination and proteasomal/lysosomal degradation via its SOCS box, and reduces insulin-stimulated AKT phosphorylation.\",\n      \"method\": \"In situ hybridization, co-immunoprecipitation (in HEK293 cells and rat hypothalamic extracts), ubiquitination assay, SOCS box deletion mutagenesis, AKT phosphorylation assay\",\n      \"journal\": \"BMC neuroscience\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP in both heterologous and endogenous settings, domain mutagenesis, ubiquitination assay, functional AKT readout; multiple orthogonal methods\",\n      \"pmids\": [\"21955513\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"IRS4 expression in cancer cells with high IRS4 levels drives constitutively elevated PIP3, Akt, and p70 S6 kinase activities even in the absence of growth factors; PI3K signaling in these cells depends on IRS4 even though IRS1/2 are co-expressed. IRS4 knockdown inhibits cell proliferation in IRS4-high cells.\",\n      \"method\": \"RNAi knockdown, PIP3 measurement, Akt and S6K phosphorylation assay, cell proliferation assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — knockdown with multiple signaling readouts and proliferation assay, single lab\",\n      \"pmids\": [\"24039912\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Brain-specific deletion of Irs2 combined with whole-body Irs4 knockout (bIrs2−/− · Irs4−/y) causes severe obesity, decreased energy expenditure, hyperglycemia, and insulin resistance; these phenotypes are not observed with Irs4 knockout alone or with LepRb-specific Irs2 deletion plus Irs4 knockout, indicating that Irs2 and Irs4 synergize in non-LepRb hypothalamic neurons to control energy balance.\",\n      \"method\": \"Genetic epistasis using double-knockout mouse models (Cre-lox), metabolic phenotyping (body weight, energy expenditure, blood glucose, insulin tolerance)\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple defined KO combinations and quantitative metabolic phenotyping, clean mechanistic dissection of cell-type specificity\",\n      \"pmids\": [\"24567904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IRS4 expression in mammary epithelial cells induces constitutive PI3K/AKT pathway hyperactivation, insulin/IGF1-independent cell proliferation, anchorage-independent growth, and in vivo tumorigenesis. The absence of a SHP2-binding domain in IRS4 (present in IRS1/2) is identified as the molecular basis for its constitutive, feedback-insensitive PI3K/AKT activation. IRS4 and ERBB2/HER2 synergistically induce tumorigenesis, and IRS4 expression confers resistance to HER2-targeted therapy.\",\n      \"method\": \"Insertional mutagenesis screen, retroviral overexpression in mammary epithelial cells, PI3K/AKT pathway phosphorylation assays, proliferation/anchorage-independent growth assays, in vivo tumorigenesis models, domain analysis/mutagenesis, HER2-targeted therapy resistance assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — insertional mutagenesis discovery, mechanistic domain analysis identifying SHP2-binding domain absence, multiple functional assays including in vivo, constitutive vs. stimulus-dependent PI3K activation compared across IRS family members\",\n      \"pmids\": [\"27876799\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"IRS4 interacts with BMP receptor BMPRII and specifically targets Smad1 for proteasomal degradation, repressing BMP/Smad signaling while concomitantly activating the PI3K/Akt axis in C2C12 myoblasts. IRS4 promotes myogenesis and its knockdown inhibits myoblast differentiation.\",\n      \"method\": \"Co-immunoprecipitation, proteasome inhibitor assays, Smad1 phosphorylation/degradation measurements, PI3K/Akt activation assay, IRS4 knockdown in C2C12 cells, myogenic differentiation assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP identifying BMPRII interaction, proteasomal degradation assay, functional knockdown with differentiation readout; single lab with multiple methods\",\n      \"pmids\": [\"28821740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IRS4 is phosphorylated at Ser859 by CK1γ2 in vitro and in vivo, which promotes polyubiquitination and degradation of IRS4 via the CHIP E3 ligase through the ubiquitin/lysosome pathway. A non-phosphorylatable IRS4 mutant (Ser859 mutant) shows higher p-Akt levels and faster tumor cell proliferation.\",\n      \"method\": \"In vitro kinase assay, mass spectrometry, co-immunoprecipitation, cycloheximide chase assay, ubiquitination assay, phospho-mutant overexpression, colony formation assay, xenograft mouse model\",\n      \"journal\": \"Theranostics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — in vitro kinase assay establishing CK1γ2 as the kinase for Ser859, CHIP identified as E3 ligase by mass spectrometry and co-IP, phospho-mutant functional validation in vitro and in vivo; multiple orthogonal methods\",\n      \"pmids\": [\"30026872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Loss-of-function mutations in IRS4 (nonsense and frameshift) are associated with isolated congenital central hypothyroidism (CeH) in males; IRS4 mRNA is expressed in human hypothalamic nuclei (including paraventricular nucleus) and pituitary; female Irs4 knockout mice show decreased pituitary Tshb mRNA levels, linking IRS4 to TSH regulation in the hypothalamic-pituitary axis.\",\n      \"method\": \"Exome sequencing, Sanger sequencing, IRS4 expression analysis in human hypothalamus/pituitary, Irs4 knockout mouse model with pituitary Tshb mRNA measurement and serum thyroid hormone measurement, 24-hour TSH secretion profiling\",\n      \"journal\": \"Journal of medical genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human genetics combined with mouse KO model showing pituitary Tshb reduction; single lab but orthogonal approaches (human mutation + mouse model)\",\n      \"pmids\": [\"30061370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"IRS4-expressing neurons in the paraventricular, subparaventricular, and periventricular hypothalamus are sufficient and necessary for normal feeding and energy expenditure; activation of IRS4PVH neurons suppresses feeding and increases energy expenditure, and their silencing causes obesity; IRS4PVH neurons lie within hypothalamic circuitry innervating distinct hindbrain regions.\",\n      \"method\": \"Cre-dependent viral tools for chemogenetic activation and silencing of IRS4-expressing neurons, neuronal tracing, feeding and energy expenditure measurement in mice\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function using viral tools in defined neuronal populations with quantitative metabolic phenotyping; single lab\",\n      \"pmids\": [\"32218485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"IRS4 knockout suppresses proliferation, colony formation, migration, invasion, and tumor growth in A549 lung cancer cells; IRS4 activates both PI3K/Akt and Ras-MAPK pathways; IRS4 depletion significantly sensitizes EGFR-TKI-resistant cells to gefitinib.\",\n      \"method\": \"CRISPR/retroviral KO and stable overexpression, proliferation/colony/migration/invasion assays, PI3K/Akt and MAPK pathway phosphorylation assays, xenograft mouse model, gefitinib sensitivity assay\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional KO and overexpression with multiple functional readouts and pathway analysis, in vivo xenograft, single lab\",\n      \"pmids\": [\"33894221\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Non-receptor tyrosine kinase FER phosphorylates IRS4 at Tyr779 via its kinase domain interacting with the PH and PTB domains of IRS4; this phosphorylation enables IRS4 to recruit PIK3R2/p85β (regulatory subunit of PI3K), activating the PI3K-AKT pathway. Phosphorylation-defective IRS4 (Y779F) fails to rescue IRS4-null ovarian tumor cell proliferation in vitro and in vivo.\",\n      \"method\": \"Mass spectrometry substrate identification, co-immunoprecipitation, proximity-based tagging (BioID), in vitro kinase assay, phospho-mutant rescue experiments, in vitro and xenograft proliferation assays\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — mass spectrometry substrate identification confirmed by co-IP and proximity tagging, in vitro kinase assay, phospho-mutant functional rescue both in vitro and in vivo; multiple orthogonal methods in a rigorous study\",\n      \"pmids\": [\"35550247\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"IRS-4 physically interacts with the copper transporter CTR1 (co-immunoprecipitation confirmed with FLAG-CTR1 and myc-CTR1); the interaction is enhanced when the CTR1 Y103A mutation is present.\",\n      \"method\": \"Proteomic analysis of CTR1-derived peptides, co-immunoprecipitation from HEK cells expressing FLAG-CTR1 or myc-CTR1\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single co-IP confirmation, mechanistic significance of the IRS4-CTR1 interaction not further characterized\",\n      \"pmids\": [\"24967972\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"IRS4 drives cancer cell dependency through PI3K-Akt activation; domain analysis shows the PH and PTB domains are dispensable for IRS4's PI3K-activating oncogenic function, suggesting degradation-based therapeutic modalities; IRS4 expression in adult tumors is associated with enhancer hijacking rearrangements including GATA3-IRS4 and ANKRD30A-IRS4 in breast cancer.\",\n      \"method\": \"Pan-cancer dependency analysis, domain deletion analysis, PI3K-Akt pathway assays, genomic rearrangement analysis\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain deletion functional analysis with pathway readout, multiple cancer types analyzed; single study\",\n      \"pmids\": [\"42054459\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PD-L1 binds to eIF3I and promotes cutaneous diabetic wound healing by downregulating IRS4; the eIF3I-PD-L1-IRS4 axis contributes to wound healing defects. PD-L1 interacting proteins were identified by co-immunoprecipitation combined with mass spectrometry.\",\n      \"method\": \"Transcriptional profiling, co-immunoprecipitation combined with mass spectrometry, coimmunoprecipitation validation, in vivo and in vitro functional assays, immunohistochemistry\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — co-IP/MS identifies the interaction but the mechanistic basis of IRS4 downregulation by PD-L1/eIF3I is not deeply characterized; single lab\",\n      \"pmids\": [\"34293353\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IRS4 is a cytoplasmic scaffold/adaptor protein that, upon tyrosine phosphorylation by receptor tyrosine kinases (and non-receptor kinases such as FER, which phosphorylates Tyr779), recruits PI3K regulatory subunits (p85α/β) to constitutively hyperactivate the PI3K/AKT pathway independently of upstream growth factor signals—a property mechanistically explained by its lack of a SHP2-binding domain that normally enables feedback inhibition; IRS4 also activates Ras-MAPK signaling through Grb-2 recruitment, acts as a negative regulator of IRS-1/IRS-2 signaling, mediates GLUT4 translocation, and is subject to post-translational regulation through CK1γ2-mediated phosphorylation at Ser859 that promotes CHIP-dependent ubiquitination and lysosomal degradation, and through Asb-4-mediated ubiquitination and proteasomal degradation; in the hypothalamus, IRS4-expressing neurons in the paraventricular nucleus are required for normal energy balance and TSH regulation, with Irs4 synergizing with Irs2 in non-LepRb neurons for metabolic homeostasis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IRS4 is a cytoplasmic insulin-receptor-substrate adaptor that couples receptor tyrosine kinase signaling to the PI3K/AKT axis, mediating metabolic and mitogenic outputs while functioning distinctly from IRS-1 and IRS-2 [#0, #2]. Upon tyrosine phosphorylation, IRS4 recruits PI3K regulatory subunits to drive AKT activation, BAD phosphorylation, and—via Grb-2—MAPK signaling, and it suffices to stimulate PI3K-dependent GLUT4 translocation independently of insulin [#0, #2]. The non-receptor kinase FER phosphorylates IRS4 at Tyr779 through interaction with its PH and PTB domains, enabling recruitment of PIK3R2/p85β to activate PI3K-AKT [#16]. A defining feature of IRS4 is constitutive, growth-factor-independent and feedback-insensitive PI3K/AKT activation, attributed to its lack of a SHP2-binding domain present in IRS1/2; this drives insulin/IGF1-independent proliferation, anchorage-independent growth, and tumorigenesis, synergy with ERBB2/HER2, and resistance to HER2- and EGFR-targeted therapies [#10, #15, #18]. IRS4 also acts as a negative regulator of IRS-1/IRS-2 signaling by reducing IRS-2 levels and impairing IGF-1-stimulated IRS-1/2 phosphorylation [#1]. IRS4 abundance is controlled by ubiquitin-dependent degradation: Asb-4 promotes IRS4 ubiquitination and degradation via its SOCS box [#7], and CK1γ2-mediated phosphorylation at Ser859 promotes CHIP-dependent polyubiquitination and lysosomal degradation, with degradation-resistant IRS4 elevating p-AKT and proliferation [#12]. In the brain, IRS4-expressing paraventricular hypothalamic neurons are required for normal feeding and energy expenditure, IRS4 synergizes with IRS2 in non-LepRb neurons for energy balance, and loss-of-function IRS4 mutations cause isolated congenital central hypothyroidism in males via the hypothalamic-pituitary TSH axis [#9, #13, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that IRS4 transduces insulin signals to AKT/BAD and MAPK but is functionally distinct from IRS-1/2, defining it as a non-redundant adaptor.\",\n      \"evidence\": \"Retroviral expression in 32D(IR) myeloid cells with co-IP, kinase, phosphorylation, and apoptosis assays comparing IRS-1/2/4\",\n      \"pmids\": [\"10594015\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the receptor kinases or sites driving IRS4 phosphorylation\", \"Weak p85/PI3K coupling left the basis of pathway selectivity unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Showed IRS4 can drive a core metabolic insulin output—GLUT4 translocation—in a PI3K- and YXXM-motif-dependent manner, even without insulin.\",\n      \"evidence\": \"Cotransfection of HA-GLUT4 and IRS-4 in rat adipose cells with surface GLUT4 measurement, PI3K inhibitors, and YXXM mutagenesis\",\n      \"pmids\": [\"10077007\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Overexpression context may not reflect endogenous stoichiometry\", \"Mechanism of insulin-independent activation not defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Revealed a paradoxical negative-regulatory role: IRS4 suppresses IRS-2 levels and IRS-1/2 phosphorylation while raising basal PI3K/AKT, separating its mitogenic from metabolic functions.\",\n      \"evidence\": \"Retroviral transduction into WT and IRS-1 KO 3T3 fibroblasts with immunoblot, PI3K, and MAPK assays\",\n      \"pmids\": [\"11113178\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which IRS4 reduces IRS-2 not defined\", \"Failure to rescue mitogenesis in IRS-1 KO left signaling output incomplete\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Demonstrated cell-context-dependent PI3K coupling: in beta-cells IRS4 compensates for IRS-2 to support survival/mitogenesis, while in IGF1R-null T-lymphoma cells insulin-driven IRS4 activates PI3K/p70S6K but not Ras-MAPK.\",\n      \"evidence\": \"Adenoviral gain/loss in INS-1 cells and IP/kinase/inhibitor dissection in LB T-cell lymphoma cells\",\n      \"pmids\": [\"14604813\", \"12618213\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Context-dependence of MAPK coupling not mechanistically explained\", \"Single-lab cell-line studies\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Confirmed insulin-induced IRS4 tyrosine phosphorylation and physical IRS4/PI3K association in hepatic cells, with crosstalk modulation by Angiotensin II.\",\n      \"evidence\": \"Co-IP, tyrosine phosphorylation and PI3K activity assays in HepG2 cells and rat liver membranes with AT1 receptor manipulation\",\n      \"pmids\": [\"20079766\", \"16933034\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single-method phosphorylation readouts without kinase reconstitution\", \"Physiological relevance of AngII crosstalk unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified Asb-4 as a hypothalamic regulator that ubiquitinates and degrades IRS4 via its SOCS box, establishing post-translational control of IRS4-dependent AKT signaling in feeding-relevant neurons.\",\n      \"evidence\": \"Reciprocal co-IP in HEK293 and rat hypothalamic extracts, SOCS box deletion, ubiquitination and AKT assays, in situ hybridization\",\n      \"pmids\": [\"21955513\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish whether Asb-4-mediated degradation is proteasomal vs lysosomal definitively\", \"In vivo consequence of Asb-4 loss on IRS4 not tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed IRS4 drives constitutive, IRS1/2-independent PI3K/AKT/S6K activity in cancer cells and is required for their proliferation, framing IRS4 as an oncogenic driver.\",\n      \"evidence\": \"RNAi knockdown with PIP3, AKT/S6K phosphorylation, and proliferation assays in IRS4-high cancer cells\",\n      \"pmids\": [\"24039912\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not explain why IRS4 dominates over co-expressed IRS1/2\", \"No in vivo validation\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined a brain-specific, cell-type-resolved role: Irs2/Irs4 synergize in non-LepRb hypothalamic neurons to control energy balance.\",\n      \"evidence\": \"Genetic epistasis across bIrs2/Irs4 double-knockout combinations with metabolic phenotyping in mice\",\n      \"pmids\": [\"24567904\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular signaling underlying Irs2/Irs4 synergy not resolved\", \"Specific neuronal subtypes not fully defined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Provided the molecular basis for constitutive PI3K/AKT activation—absence of a SHP2-binding domain renders IRS4 feedback-insensitive—and demonstrated tumorigenicity and HER2-therapy resistance.\",\n      \"evidence\": \"Insertional mutagenesis screen, retroviral overexpression in mammary cells, domain mutagenesis, in vivo tumorigenesis and HER2-resistance assays\",\n      \"pmids\": [\"27876799\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the upstream kinase normally phosphorylating IRS4 in tumors\", \"Did not address regulation of IRS4 abundance in this setting\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended IRS4's role to BMP signaling, where it binds BMPRII, targets Smad1 for degradation, and promotes myogenesis while activating PI3K/Akt.\",\n      \"evidence\": \"Co-IP, proteasome inhibitor and Smad1 degradation assays, knockdown and differentiation assays in C2C12 myoblasts\",\n      \"pmids\": [\"28821740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking IRS4 to Smad1 degradation not defined\", \"Single cell-type model\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified the CK1γ2–Ser859–CHIP axis controlling IRS4 stability, linking phospho-dependent degradation to suppression of AKT signaling and tumor proliferation.\",\n      \"evidence\": \"In vitro kinase assay, mass spectrometry, cycloheximide chase, ubiquitination assays, phospho-mutant validation in vitro and xenograft\",\n      \"pmids\": [\"30026872\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream signals controlling CK1γ2 activity on IRS4 unknown\", \"Relationship between CHIP and Asb-4 degradation routes not reconciled\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Connected IRS4 loss-of-function to human disease, identifying it as a cause of isolated congenital central hypothyroidism via the hypothalamic-pituitary TSH axis.\",\n      \"evidence\": \"Exome/Sanger sequencing of CeH patients, human hypothalamus/pituitary expression, and Irs4 KO mouse pituitary Tshb/TSH profiling\",\n      \"pmids\": [\"30061370\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signaling pathway linking IRS4 to TSH regulation not defined\", \"Male-restricted phenotype mechanism unexplained\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the neuronal circuit: IRS4-expressing PVH/periventricular neurons are necessary and sufficient for feeding and energy expenditure control.\",\n      \"evidence\": \"Cre-dependent chemogenetic activation/silencing, neuronal tracing, and metabolic measurement in mice\",\n      \"pmids\": [\"32218485\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Role of cell-intrinsic IRS4 signaling vs neuron identity not separated\", \"Downstream hindbrain effectors not mechanistically mapped\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified FER as the kinase phosphorylating IRS4 at Tyr779 through PH/PTB domain interaction to recruit p85β and activate PI3K-AKT, supplying an upstream activator of oncogenic IRS4.\",\n      \"evidence\": \"Mass spectrometry substrate ID, co-IP, BioID, in vitro kinase assay, and Y779F phospho-mutant rescue in vitro and in xenografts\",\n      \"pmids\": [\"35550247\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality of FER as the activating kinase across tissues unknown\", \"Other phosphosites contributing to PI3K recruitment not enumerated\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Mapped IRS4 as a pan-cancer dependency whose PH/PTB domains are dispensable for PI3K-activating oncogenic function and whose tumor expression arises through enhancer-hijacking rearrangements, motivating degradation-based therapy.\",\n      \"evidence\": \"Pan-cancer dependency analysis, domain deletion with PI3K-Akt readouts, and genomic rearrangement analysis (GATA3-IRS4, ANKRD30A-IRS4)\",\n      \"pmids\": [\"42054459\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciling dispensable PH/PTB here with FER-domain dependence elsewhere unresolved\", \"Degradation-based therapeutic feasibility not demonstrated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How IRS4's constitutive, feedback-insensitive PI3K activation is integrated with its phospho-dependent degradation, its receptor/kinase inputs across tissues, and its disease-relevant hypothalamic signaling remains incompletely unified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of IRS4–p85 or IRS4–FER complexes\", \"Tissue-specific upstream activators beyond FER not defined\", \"Mechanism of IRS4-mediated IRS-2 suppression unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 16]},\n      {\"term_id\": \"GO:0005159\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 10, 16]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [10, 13, 15]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [2, 9]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [7, 12]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"PIK3R2\", \"FER\", \"ASB4\", \"STUB1\", \"CSNK1G2\", \"BMPR2\", \"GRB2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}