{"gene":"IRS1","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":1992,"finding":"IRS-1 undergoes tyrosine phosphorylation at YXXM motifs upon insulin stimulation and activates PI3K by binding to the SH2 domains of the p85 regulatory subunit; phosphorylated YXXM-containing peptides block this interaction in vitro, and tyrosyl-phosphorylated IRS-1 activates PI3K in anti-p85 immunoprecipitates.","method":"In vitro kinase assay, SH2-domain fusion protein pulldown, synthetic phosphopeptide competition, co-immunoprecipitation, PI3K activity assay","journal":"The EMBO journal / PNAS","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal in vitro reconstitution experiments (peptide competition, SH2 pulldown, PI3K activity assay) replicated across two independent labs in the same year","pmids":["1380456","1332046"],"is_preprint":false},{"year":1992,"finding":"YMXM motifs in IRS-1 define substrate specificity of the insulin receptor kinase; the insulin receptor kinase preferentially phosphorylates peptides containing YMXM sequences (with methionine at Y+1 and Y+3), and when phosphorylated these motifs serve as recognition sites for SH2-domain-containing signaling proteins.","method":"In vitro peptide substrate kinase assay with synthetic peptides corresponding to IRS-1 tyrosine sites; structure-activity analysis with substituted YMXM peptides","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic assay with mutagenesis-equivalent substitution analysis, rigorous kinetic characterization (Km, kcat/Km)","pmids":["1312712"],"is_preprint":false},{"year":1992,"finding":"IRS-1 is a direct physiological substrate of the insulin receptor kinase: purified insulin receptor phosphorylates baculovirus-produced IRS-1 exclusively on tyrosine residues in vitro; IRS-1 associates with the insulin receptor during insulin stimulation; and co-expression of insulin receptor and IRS-1 strongly amplifies insulin-stimulated PI3K association and DNA synthesis.","method":"In vitro kinase assay with purified IR and recombinant IRS-1, co-immunoprecipitation, immunofluorescence localization, overexpression in CHO cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro phosphorylation plus multiple orthogonal cell-based assays; foundational paper","pmids":["1385403"],"is_preprint":false},{"year":1994,"finding":"Genetic disruption of IRS-1 in mice abolishes IRS-1 phosphorylation and IRS-1-associated PI3K activity; residual insulin/IGF-1 signaling is mediated by a distinct IRS-2 protein that binds PI3K, establishing IRS-1-dependent and IRS-1-independent pathways.","method":"Targeted gene knockout in mice, immunoprecipitation/PI3K activity assay, glucose uptake assays in vivo and in vitro","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic KO with defined biochemical readout (PI3K activity) and physiological phenotype, replicated across multiple tissue types","pmids":["7526222"],"is_preprint":false},{"year":1996,"finding":"The pleckstrin homology (PH) domain at the IRS-1 N-terminus is the principal link coupling IRS-1 to the insulin receptor; the PTB domain improves coupling but is not essential at high receptor levels, whereas the PH domain is essential at physiological low receptor levels for insulin-stimulated IRS-1 tyrosine phosphorylation, PI3K activity, and p70S6K phosphorylation.","method":"Domain deletion mutagenesis, peptide competition binding assays, reconstitution in 32D cells with insulin receptor and IRS-1 deletion mutants, PI3K activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct mutagenesis with functional reconstitution in cells; multiple orthogonal readouts (tyrosine phosphorylation, PI3K activity, p70S6K, DNA synthesis)","pmids":["8798677"],"is_preprint":false},{"year":1994,"finding":"IRS-1 and Shc compete for a limited cellular pool of Grb2; overexpression of IRS-1 sequesters Grb2 away from Shc, reducing insulin-stimulated MAP kinase activation and c-fos transcription, which proceed predominantly through the Shc-Grb2 pathway.","method":"Transfection overexpression, indirect co-immunoprecipitation, MAP kinase gel-shift assay, c-fos transcriptional reporter assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP experiments demonstrating competitive binding, supported by functional transcriptional and kinase readouts; single lab","pmids":["7983051"],"is_preprint":false},{"year":2001,"finding":"TNF-α and insulin/IGF-1 stimulate phosphorylation of IRS-1 at Ser307 via distinct kinase pathways: TNF-α acts through a PD98059-sensitive (ERK) pathway, while insulin acts through a PI3K-dependent (LY294002/wortmannin-sensitive) pathway; Ser307 phosphorylation inhibits insulin-stimulated IRS-1 tyrosine phosphorylation.","method":"Phosphospecific antibody (αpSer307) detection in cell lines and in vivo (muscle from insulin-injected rodents and human hyperinsulinemic clamp), kinase inhibitor dissection","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — phosphospecific antibody validated in multiple cell types and in vivo tissues including human; pharmacological pathway dissection with two inhibitors; recombinant JNK phosphorylation of IRS-1 at Ser307 demonstrated separately","pmids":["11160134"],"is_preprint":false},{"year":2002,"finding":"SOCS1 and SOCS3 target IRS-1 and IRS-2 for ubiquitin-mediated proteasomal degradation via the elongin BC ubiquitin-ligase complex; SOCS1 binds IRS-1/2 directly, and mutations in the SOCS box (which disrupt elongin BC binding) abrogate ubiquitination and degradation without affecting IRS binding.","method":"Co-immunoprecipitation (recombinant and endogenous proteins), ubiquitination assay, SOCS box mutant analysis, adenoviral expression in mouse liver with glucose tolerance testing","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — mechanistic dissection with domain mutants, in vitro ubiquitination assays, and in vivo adenoviral rescue experiment; multiple orthogonal approaches","pmids":["12228220"],"is_preprint":false},{"year":2004,"finding":"PKCθ phosphorylates IRS-1 at Ser1101, blocking IRS-1 tyrosine phosphorylation and downstream Akt activation; mutation of Ser1101 to alanine makes IRS-1 insensitive to PKCθ and restores insulin signaling.","method":"In vitro kinase assay (PKCθ phosphorylation of IRS-1), site-directed mutagenesis (S1101A), overexpression/inhibition in cultured cells, Western blot for tyrosine phosphorylation and Akt activation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis with functional rescue; direct identification of phosphorylation site and its functional consequence","pmids":["15364919"],"is_preprint":false},{"year":2006,"finding":"IRS-1 overexpression in the mammary gland causes constitutive IRS-1 phosphorylation, progressive mammary hyperplasia, tumorigenesis, and metastasis in transgenic mice; IRS-1 binds β-catenin in vitro and in vivo, implicating β-catenin signaling in IRS-1-driven tumorigenesis.","method":"Mammary-targeted transgenic mice, in vitro and in vivo co-immunoprecipitation for β-catenin binding, histological analysis of tumor phenotype","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transgenic in vivo model with defined phenotype plus co-IP for binding partner; β-catenin interaction established by reciprocal co-IP in vitro and in vivo","pmids":["17030631"],"is_preprint":false},{"year":2013,"finding":"MG53 is an E3 ubiquitin ligase that induces IRS-1 ubiquitination using UBE2H as the E2-conjugating enzyme; disruption of MG53's E3 ligase activity abolishes IRS-1 ubiquitination and enhances skeletal myogenesis and insulin signaling.","method":"E3 ligase activity assay, ubiquitination assay with UBE2H, MG53 E3-ligase-dead mutant, MG53 knockout mice (elevated IRS-1 levels), high-fat/high-sucrose diet challenge","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro ubiquitination reconstitution with E2/E3 components, mutagenesis of E3 function, KO mouse validation; multiple orthogonal methods","pmids":["23965929"],"is_preprint":false},{"year":2014,"finding":"PTEN acts as a protein tyrosine phosphatase that selectively dephosphorylates IRS-1; NEDD4, a PTEN ubiquitin ligase, antagonizes PTEN to support IGF/insulin signaling through IRS-1; ablation of PTEN rescues defective IRS-1 and AKT phosphorylation caused by NEDD4 deletion.","method":"Direct biochemical dephosphorylation assay (PTEN acting on IRS-1), cellular reconstitution, NEDD4 knockout cells, PTEN ablation rescue experiments","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical assay demonstrating PTEN protein phosphatase activity on IRS-1 substrate, confirmed by cellular reconstitution with multiple genetic controls","pmids":["24814346"],"is_preprint":false},{"year":2018,"finding":"IRS-1 interacts with the clathrin adaptor complex AP2 and delays AP2-mediated IGF-IR endocytosis after ligand stimulation by inhibiting recruitment of IGF-IR into clathrin-coated structures; this prolongs IGF-IR surface activity and shifts downstream signaling from transient to sustained Akt activation. An AP2-binding-deficient IRS-1 mutant fails to delay endocytosis.","method":"Co-immunoprecipitation (IRS-1/AP2), live-cell imaging, IRS-1 depletion/reconstitution with AP2-binding mutant, clathrin-coated structure tracking, Akt phosphorylation kinetics, FoxO transcriptional reporter","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal co-IP, functional mutant rescue, live imaging of endocytosis, and multiple downstream signaling readouts; novel mechanistic role established with orthogonal methods","pmids":["29661273"],"is_preprint":false},{"year":2020,"finding":"Rab5a directly interacts with IRS-1 in a GTP-dependent manner (enhanced by IGF-1 and myogenic differentiation); Rab5a modulates IRS-1 activation by coordinating the IRS-1/IGF receptor association and regulating intracellular membrane targeting of IRS-1, thereby controlling AKT-mTOR signaling and muscle regeneration.","method":"Co-immunoprecipitation (endogenous and overexpressed), GTP-dependent binding assay, site-directed mutagenesis (R207/R222 on IRS-1; Y82/Y89/Y90 on Rab5a), myogenic Rab5a-KO mice, AKT-mTOR signaling assays","journal":"Cell death and differentiation","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — direct binding characterization with mutagenesis identifying interface residues, validated in KO mouse model with defined signaling readouts","pmids":["32051546"],"is_preprint":false},{"year":2024,"finding":"Serine phosphorylations within a region of IRS-1 directly C-terminal to the PTB domain (designated the PIR domain, encompassing Ser307, Ser312, Ser315, and Ser323) abrogate IRS-1 binding to the insulin receptor; the PTB-PIR module binds IR more strongly than PTB alone (by surface plasmon resonance), and PIR phosphomimetic mutations (S→E) decrease IR, IRS-1, and AKT phosphorylation in cells.","method":"Surface plasmon resonance (SPR) binding assays, hydrogen-deuterium exchange mass spectrometry (HDX-MS), phosphomimetic mutagenesis (S307E/S312E/S315E/S323E), Western blot of signaling in insulin-responsive cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — SPR quantitative binding assay, HDX-MS structural analysis, and mutagenesis with functional cell-based validation; multiple orthogonal methods in single rigorous study","pmids":["38625937"],"is_preprint":false},{"year":2003,"finding":"BCR-ABL binds to IRS-1 and constitutively phosphorylates it in K562 cells; this is associated with IRS-1/PI3K and IRS-1/Grb2 complex formation; imatinib treatment markedly attenuates BCR-ABL/IRS-1 association and IRS-1-associated PI3K activity.","method":"Co-immunoprecipitation, PI3K activity assay, imatinib treatment","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — co-IP and kinase activity assay in a single cell line; single lab, single paper","pmids":["12560071"],"is_preprint":false},{"year":2001,"finding":"IRS-1 and IRS-2 are tyrosine-phosphorylated substrates of both TrkA and the TRK-T1 oncogene; this phosphorylation recruits p85-PI3K, SHP-2, and Grb2 to IRS-1 and increases PI3K activity; TRK-T1 stimulates DNA synthesis in wild-type but not IRS-1−/− fibroblasts, and yeast two-hybrid analysis shows direct TRK–IRS interaction.","method":"Co-immunoprecipitation, PI3K activity assay, yeast two-hybrid, IRS-1 KO fibroblast reconstitution, DNA synthesis assay","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, genetic KO rescue, and yeast two-hybrid in the same study; single lab","pmids":["11147812"],"is_preprint":false},{"year":2011,"finding":"The Rheb-mTOR/raptor axis negatively regulates myogenic differentiation by suppressing IRS-1 protein levels and increasing Ser307 phosphorylation on IRS-1; IRS-1 knockdown eliminates the enhanced differentiation seen with raptor or Rheb knockdown, placing IRS-1 downstream of raptor/Rheb in myogenesis.","method":"siRNA knockdown of raptor, Rheb, and IRS-1 in C2C12 myoblasts, overexpression constructs, Akt phosphorylation and differentiation assays, Western blot for IRS-1 protein levels and Ser307 phosphorylation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis by double KD with defined phenotypic readout; multiple components tested; single lab","pmids":["21852229"],"is_preprint":false},{"year":2013,"finding":"Nexilin, an F-actin binding protein, preferentially binds IRS-1 (but not IRS-2) under basal conditions in L6 myotubes and the complex is disassembled by insulin; nexilin silencing has no effect on IRS-1 tyrosine phosphorylation but enhances p85 recruitment to IRS-1, PI(3,4,5)P3 formation, AKT activation, and glucose uptake; nexilin overexpression inhibits IRS-1→AKT signaling.","method":"Co-immunoprecipitation (nexilin/IRS-1/p85), siRNA knockdown, nexilin overexpression, PI(3,4,5)P3 assay, AKT phosphorylation, glucose uptake assay in L6 myotubes","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus gain- and loss-of-function with functional readouts; single lab, single cell model","pmids":["23383252"],"is_preprint":false},{"year":2013,"finding":"p38α MAPK activation during chronic insulin exposure reduces cardiac IRS-1 and IRS-2 protein levels, preventing subsequent insulin action; heart-specific IRS1/IRS2 double-KO mice develop dilated cardiomyopathy with impaired Akt→FoxO1 signaling and reduced ATP content.","method":"Heart-specific double-KO mice, neonatal rat ventricular cardiomyocyte chronic insulin treatment, p38 inhibitor experiments, echocardiography, Akt/FoxO1 signaling Western blot","journal":"Diabetes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — tissue-specific KO with defined cardiac phenotype plus mechanistic cell experiments linking p38 to IRS protein reduction; single lab","pmids":["24159000"],"is_preprint":false},{"year":2016,"finding":"IRS-1 acts as a molecular scaffold in osteoblasts: IGF-I stimulates IRS-1 phosphorylation and co-recruitment of PKCζ (via the p62 adaptor) and vimentin to phospho-IRS-1; activated PKCζ directly phosphorylates vimentin, enabling downstream RPTPβ inactivation, PTEN tyrosine phosphorylation, and AKT activation required for osteoblast differentiation.","method":"Immunoprecipitation of IRS-1 complexes containing PKCζ and vimentin, in vitro kinase assay (PKCζ phosphorylating vimentin from IRS-1 immunoprecipitates), disrupting peptides for p62/PKCζ and p62/IRS-1 interactions, primary mouse calvarial osteoblasts","journal":"Journal of bone and mineral research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP of multi-protein complex, in vitro kinase assay from immunoprecipitate, disrupting peptides with functional readouts; single lab","pmids":["26773517"],"is_preprint":false},{"year":2022,"finding":"Cathepsin K (CTSK) selectively cleaves IRS-1 in the region of amino acids 268–574, causing IRS-1 ubiquitination and degradation; CTSK knockout prevents IRS-1 degradation and preserves AKT-mTOR signaling in cachectic muscle; CTSK overexpression accelerates IRS-1 ubiquitination even without pro-cachectic stimulus.","method":"Co-immunoprecipitation, truncation mapping of IRS-1–CTSK interaction, ubiquitination assay, CTSK KO and overexpression in C2C12 cells and in vivo LLC tumor model, Western blot for IRS-1/Akt/mTOR","journal":"Journal of cachexia, sarcopenia and muscle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — domain mapping co-IP plus functional KO/OE with ubiquitination readout in vitro and in vivo; single lab","pmids":["35098692"],"is_preprint":false},{"year":2019,"finding":"TAZ transcriptionally upregulates IRS1 expression by physically interacting with c-Jun and Tead4 to induce IRS1 transcription; muscle-specific TAZ-KO mice show decreased IRS1 expression and insulin sensitivity; Wnt/APC signaling requires TAZ for IRS1-dependent insulin signaling in muscle.","method":"Muscle-specific TAZ-KO mice, APC/TAZ double-KO mice, ChIP/co-immunoprecipitation (TAZ with c-Jun and Tead4), IRS1 promoter reporter assay, glucose uptake assay","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse model with defined IRS1/insulin sensitivity phenotype, plus co-IP and promoter assays; single lab, multiple orthogonal methods","pmids":["30679431"],"is_preprint":false},{"year":2007,"finding":"IRS-1 (but not IRS-2) is required for normal epidermal differentiation: IRS-1-null mouse skin is thinner due to reduced spinous layer, with impaired keratinocyte differentiation marker K1 induction; IRS-2-null skin appears normal, establishing distinct roles for the two paralogs in epidermis.","method":"IRS-1 and IRS-2 KO mice, histological analysis, primary skin cell differentiation assays, K1 marker expression","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined tissue phenotype and molecular marker readout; IRS-1 vs IRS-2 specificity established; single lab","pmids":["17508357"],"is_preprint":false},{"year":2016,"finding":"IRS-1 deficiency in β-cells protects against ER stress-induced apoptosis by reducing nuclear accumulation of spliced XBP-1 (via proteasomal degradation), attenuating general translation (increased eEF2 phosphorylation), and maintaining elevated ER calcium levels.","method":"IRS1-KO and IRS2-KO β-cells, ER stress induction, nuclear fractionation for XBP-1, polyribosomal profiling, eEF2 phosphorylation assay, ER calcium measurement","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple orthogonal mechanistic readouts (XBP-1 stability, polysome profiling, calcium); single lab","pmids":["27378176"],"is_preprint":false},{"year":2024,"finding":"PYCR1 promotes IRS1 transcription in liver cancer by increasing H3K18 lactylation at the IRS1 promoter; knockout or inhibition of PYCR1 reduces glycolysis, lowers H3K18 lactylation at the IRS1 promoter, and decreases IRS1 expression and downstream PI3K/AKT/mTOR signaling.","method":"ChIP assay (H3K18 lactylation at IRS1 promoter), PYCR1 KO, metabolomics, transcriptome sequencing, Western blot for IRS1 and pathway components","journal":"Clinical and translational medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP demonstrating epigenetic mark at IRS1 promoter linked to PYCR1 activity; genetic KO with functional readouts; single lab","pmids":["39422696"],"is_preprint":false},{"year":2009,"finding":"PTP1B dephosphorylates the insulin receptor and thereby determines IRS-1-mediated PI3K/Akt/FoxO1 signaling in liver; in IRS2-deficient mice (which develop hyperglycemia), elevated PTP1B impairs IRS1 signaling, and deletion or pharmacological inhibition of PTP1B restores IRS1-dependent hepatic insulin signaling.","method":"IRS2-KO / PTP1B-KO double-KO mice, resveratrol pharmacological PTP1B inhibition, hepatic insulin signaling Western blots, isolated hepatocytes","journal":"Diabetes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis (double KO) plus pharmacological validation; single lab","pmids":["20028942"],"is_preprint":false}],"current_model":"IRS-1 is a cytoplasmic scaffold protein that is directly phosphorylated on multiple YMXM tyrosine motifs by the insulin and IGF-1 receptor kinases (requiring the N-terminal PH and PTB domains for receptor coupling), whereupon it recruits and activates PI3K (via SH2-domain binding of p85), Grb2-Sos, SHP-2, and other effectors to propagate metabolic and mitogenic signals; its activity is precisely regulated by a complex network of inhibitory serine/threonine phosphorylations (by JNK at Ser307, PKCθ at Ser1101, and mTOR/S6K1 among others, which disrupt IR-IRS-1 interaction via the PIR domain), ubiquitin-mediated proteasomal degradation (facilitated by SOCS1/3 via elongin BC, MG53/UBE2H, and CTSK), and dephosphorylation by PTEN (which acts as an IRS-1 protein tyrosine phosphatase antagonized by NEDD4); additionally, IRS-1 modulates IGF-IR endocytosis via AP2 to sustain surface receptor signaling, and its transcription is regulated by TAZ/c-Jun/Tead4 and epigenetic mechanisms including H3K18 lactylation."},"narrative":{"mechanistic_narrative":"IRS-1 is a cytoplasmic scaffold/adaptor protein that serves as the principal proximal substrate of the insulin and IGF-1 receptor tyrosine kinases, coupling receptor activation to PI3K-driven metabolic and mitogenic signaling [PMID:1385403, PMID:1380456, PMID:1332046]. Following receptor engagement, IRS-1 is phosphorylated exclusively on tyrosines within YMXM motifs that define insulin-receptor substrate specificity; these phosphotyrosines then dock the SH2 domains of the p85 regulatory subunit to recruit and activate PI3K, and also engage Grb2 and SHP-2 to relay downstream signals [PMID:1380456, PMID:1332046, PMID:1312712, PMID:11147812]. Receptor coupling depends on the N-terminal PH domain (essential at physiological receptor levels, with the PTB domain enhancing binding) and on a serine-rich PIR region C-terminal to the PTB domain that, together with PTB, mediates high-affinity insulin-receptor binding [PMID:8798677, PMID:38625937]. Because IRS-1 sequesters a limited pool of Grb2 from Shc, its abundance helps partition signaling between metabolic and MAP-kinase outputs [PMID:7983051]. IRS-1 signaling output is constrained by a dense regulatory network: inhibitory serine/threonine phosphorylation — at Ser307 by ERK- and PI3K-dependent kinases and JNK, at Ser1101 by PKCθ, and within the PIR domain — disrupts receptor coupling and blocks downstream Akt activation [PMID:11160134, PMID:15364919, PMID:38625937]; tyrosine dephosphorylation by PTEN (antagonized by NEDD4) and receptor dephosphorylation by PTP1B reverse activating marks [PMID:24814346, PMID:20028942]; and IRS-1 protein levels are set by ubiquitin-mediated proteasomal degradation through SOCS1/3–elongin BC, the MG53–UBE2H E3/E2 pair, and cathepsin K–triggered cleavage and degradation [PMID:12228220, PMID:23965929, PMID:35098692]. IRS-1 also functions beyond signal transmission: it binds the AP2 clathrin adaptor to delay IGF-IR endocytosis and sustain surface receptor signaling, and interacts with GTP-bound Rab5a to control its membrane targeting and IGF-receptor association [PMID:29661273, PMID:32051546]. Genetically, IRS-1 defines an IRS-1-dependent branch of insulin/IGF-1 signaling distinct from IRS-2, with tissue-specific roles in skeletal muscle regeneration, myogenic differentiation, epidermal differentiation, and β-cell ER-stress responses [PMID:7526222, PMID:32051546, PMID:21852229, PMID:17508357, PMID:27378176]. IRS1 transcription is controlled by a TAZ/c-Jun/Tead4 complex and by PYCR1-driven H3K18 lactylation at its promoter [PMID:30679431, PMID:39422696].","teleology":[{"year":1992,"claim":"Established that IRS-1 is a direct insulin-receptor kinase substrate whose tyrosine-phosphorylated YMXM motifs recruit and activate PI3K via p85 SH2 domains, defining the core insulin-signaling relay.","evidence":"In vitro kinase assays with purified IR and recombinant IRS-1, synthetic phosphopeptide competition, SH2 pulldown, PI3K activity assay, and overexpression in CHO cells across independent labs","pmids":["1380456","1332046","1312712","1385403"],"confidence":"High","gaps":["Did not enumerate which of the multiple IRS-1 tyrosines are physiologically engaged in vivo","Did not resolve stoichiometry of PI3K versus other SH2 effectors on a single IRS-1 molecule"]},{"year":1994,"claim":"Genetic knockout separated IRS-1-dependent from IRS-1-independent signaling, showing a paralog (IRS-2) sustains residual PI3K coupling.","evidence":"Targeted IRS-1 knockout mice with PI3K activity assays and glucose uptake measurements","pmids":["7526222"],"confidence":"High","gaps":["Did not define which tissues rely preferentially on IRS-1 versus IRS-2","Mechanism of functional redundancy at the molecular level unresolved"]},{"year":1994,"claim":"Demonstrated that IRS-1 competes with Shc for a limited Grb2 pool, providing a mechanism for partitioning insulin signaling between metabolic and MAP-kinase/mitogenic outputs.","evidence":"Transfection overexpression, reciprocal co-IP, MAP kinase gel-shift, and c-fos reporter assays in a single lab","pmids":["7983051"],"confidence":"Medium","gaps":["Based on overexpression which may exaggerate competition","In vivo relevance of Grb2 sequestration not established"]},{"year":1996,"claim":"Mapped the receptor-coupling determinants to the N-terminal PH and PTB domains, with the PH domain essential at physiological receptor levels.","evidence":"Domain deletion mutagenesis and functional reconstitution in 32D cells with PI3K and p70S6K readouts","pmids":["8798677"],"confidence":"High","gaps":["Structural basis of PH-domain receptor coupling not resolved","Identity of any PH-domain lipid/protein ligand not defined"]},{"year":2001,"claim":"Identified Ser307 as an inhibitory phosphosite engaged by distinct ERK- and PI3K-dependent pathways (and JNK), establishing feedback/cross-talk suppression of IRS-1.","evidence":"Phosphospecific antibody detection in cells, rodent muscle, and human hyperinsulinemic clamp with kinase-inhibitor dissection","pmids":["11160134"],"confidence":"High","gaps":["Precise kinase responsible in each context not fully isolated","Quantitative contribution of Ser307 to whole-cell insulin resistance not defined"]},{"year":2002,"claim":"Showed IRS-1 abundance is controlled by SOCS1/3-directed ubiquitin-proteasome degradation via the elongin BC ligase, linking cytokine signaling to IRS-1 turnover.","evidence":"Co-IP, ubiquitination assays, SOCS box mutants, and adenoviral expression in mouse liver with glucose tolerance testing","pmids":["12228220"],"confidence":"High","gaps":["Identity of the catalytic E3/E2 components beyond elongin BC scaffolding not fully defined here","Lysine acceptor sites on IRS-1 not mapped"]},{"year":2004,"claim":"Defined Ser1101 as a PKCθ inhibitory site, providing a lipid/diacylglycerol-responsive route to IRS-1 inactivation.","evidence":"In vitro PKCθ kinase assay, S1101A mutagenesis with functional rescue of insulin signaling in cells","pmids":["15364919"],"confidence":"High","gaps":["Upstream signals activating PKCθ toward IRS-1 in vivo not delineated","Interplay with other inhibitory serines not addressed"]},{"year":2003,"claim":"Connected oncogenic tyrosine kinases to IRS-1, showing BCR-ABL binds and constitutively phosphorylates IRS-1 to drive PI3K and Grb2 complexes.","evidence":"Co-IP, PI3K activity assay, and imatinib treatment in K562 cells","pmids":["12560071"],"confidence":"Medium","gaps":["Single cell line, single lab","Direct versus indirect BCR-ABL–IRS-1 interaction not distinguished"]},{"year":2001,"claim":"Extended IRS-1 effector coupling to neurotrophin/oncogenic TRK kinases, with IRS-1 required for TRK-T1-driven DNA synthesis.","evidence":"Co-IP, PI3K assay, yeast two-hybrid, and IRS-1-null fibroblast reconstitution","pmids":["11147812"],"confidence":"Medium","gaps":["Physiological relevance in neuronal contexts not tested","Single lab"]},{"year":2006,"claim":"Linked IRS-1 hyperactivity to tumorigenesis and identified β-catenin as a binding partner in the mammary gland.","evidence":"Mammary-targeted transgenic mice with in vitro and in vivo co-IP for β-catenin","pmids":["17030631"],"confidence":"Medium","gaps":["Mechanism by which IRS-1–β-catenin binding drives transformation unresolved","Overexpression model may not reflect endogenous biology"]},{"year":2007,"claim":"Distinguished IRS-1 from IRS-2 in epidermal differentiation, showing IRS-1 is specifically required for keratinocyte differentiation.","evidence":"IRS-1 and IRS-2 KO mice with histology and K1 marker analysis","pmids":["17508357"],"confidence":"Medium","gaps":["Molecular basis of paralog specificity in skin not defined","Single lab"]},{"year":2009,"claim":"Showed PTP1B sets IRS-1 signaling indirectly by dephosphorylating the insulin receptor, with deletion/inhibition restoring hepatic IRS-1 signaling.","evidence":"IRS2-KO/PTP1B-KO double-KO mice, resveratrol inhibition, and hepatic signaling Westerns","pmids":["20028942"],"confidence":"Medium","gaps":["Action is on the receptor, not IRS-1 directly","Single lab"]},{"year":2011,"claim":"Placed IRS-1 downstream of the Rheb-mTOR/raptor axis in myogenesis via suppression of IRS-1 protein and Ser307 phosphorylation.","evidence":"siRNA epistasis (raptor/Rheb/IRS-1) in C2C12 myoblasts with differentiation and Akt readouts","pmids":["21852229"],"confidence":"Medium","gaps":["Direct kinase mediating Ser307 in this axis not identified","Single cell model"]},{"year":2013,"claim":"Identified MG53 as an E3 ligase using UBE2H to ubiquitinate IRS-1, controlling IRS-1 levels in skeletal muscle and insulin signaling.","evidence":"In vitro ubiquitination reconstitution with E2/E3, E3-dead mutant, and MG53-KO mice on metabolic challenge","pmids":["23965929"],"confidence":"High","gaps":["IRS-1 ubiquitin acceptor sites not mapped","Tissue selectivity of MG53 action not fully defined"]},{"year":2013,"claim":"Revealed nexilin as a basal IRS-1 (not IRS-2) binding partner that restrains p85 recruitment, disassembled by insulin.","evidence":"Reciprocal co-IP plus gain/loss of function with PIP3, AKT, and glucose uptake readouts in L6 myotubes","pmids":["23383252"],"confidence":"Medium","gaps":["Structural basis of nexilin–IRS-1 selectivity unknown","Single lab, single cell model"]},{"year":2013,"claim":"Demonstrated p38α MAPK reduces cardiac IRS-1/IRS-2 protein during chronic insulin exposure, with combined loss causing dilated cardiomyopathy.","evidence":"Heart-specific IRS1/IRS2 double-KO mice, cardiomyocyte chronic insulin treatment, p38 inhibition, echocardiography","pmids":["24159000"],"confidence":"Medium","gaps":["Mechanism of p38-driven IRS protein loss not detailed","Single lab"]},{"year":2014,"claim":"Established PTEN as a direct IRS-1 protein-tyrosine phosphatase antagonized by NEDD4, adding a phosphatase arm to IRS-1 regulation.","evidence":"Direct dephosphorylation assay, cellular reconstitution, NEDD4-KO cells, and PTEN-ablation rescue","pmids":["24814346"],"confidence":"High","gaps":["Which IRS-1 phosphotyrosines PTEN targets not mapped","Balance between PTEN lipid- and protein-phosphatase activities in vivo unresolved"]},{"year":2016,"claim":"Detailed an IRS-1 scaffolding role in osteoblasts assembling PKCζ (via p62) and vimentin to drive PTEN tyrosine phosphorylation and AKT-dependent differentiation.","evidence":"Multi-protein co-IP, in vitro kinase assay from immunoprecipitates, and disrupting peptides in primary calvarial osteoblasts","pmids":["26773517"],"confidence":"Medium","gaps":["Generality beyond osteoblasts not tested","Single lab"]},{"year":2016,"claim":"Showed IRS-1 loss protects β-cells from ER stress apoptosis by reducing spliced XBP-1, attenuating translation, and preserving ER calcium.","evidence":"IRS1-KO and IRS2-KO β-cells with XBP-1 fractionation, polysome profiling, eEF2 phosphorylation, and ER calcium measurements","pmids":["27378176"],"confidence":"Medium","gaps":["Direct molecular link between IRS-1 and XBP-1 stability not defined","Single lab"]},{"year":2018,"claim":"Uncovered a non-canonical role: IRS-1 binds AP2 to delay IGF-IR clathrin-mediated endocytosis, converting transient into sustained Akt signaling.","evidence":"Reciprocal co-IP, live-cell imaging of clathrin structures, AP2-binding mutant rescue, and Akt/FoxO readouts","pmids":["29661273"],"confidence":"High","gaps":["AP2-binding motif on IRS-1 not precisely mapped","Generality to insulin receptor versus IGF-IR not addressed"]},{"year":2019,"claim":"Identified transcriptional control of IRS1 by a TAZ/c-Jun/Tead4 complex governing muscle insulin sensitivity downstream of Wnt/APC.","evidence":"Muscle-specific TAZ-KO and APC/TAZ double-KO mice, ChIP/co-IP, promoter reporter, and glucose uptake","pmids":["30679431"],"confidence":"Medium","gaps":["Direct TAZ binding element on IRS1 promoter not finely mapped","Single lab"]},{"year":2020,"claim":"Showed GTP-bound Rab5a directly binds IRS-1 to coordinate its membrane targeting and IGF-receptor association, controlling AKT-mTOR signaling in muscle regeneration.","evidence":"Co-IP, GTP-dependent binding, interface-residue mutagenesis, and myogenic Rab5a-KO mice","pmids":["32051546"],"confidence":"High","gaps":["Spatial dynamics of IRS-1 membrane targeting not directly visualized","Relationship to AP2-mediated trafficking unresolved"]},{"year":2022,"claim":"Defined cathepsin K as a protease that cleaves IRS-1 (aa 268–574) to trigger its ubiquitination and degradation, driving muscle cachexia.","evidence":"Co-IP, truncation mapping, ubiquitination assay, and CTSK KO/overexpression in C2C12 and an in vivo tumor model","pmids":["35098692"],"confidence":"Medium","gaps":["Coupling between cleavage and ubiquitination machinery not detailed","Single lab"]},{"year":2024,"claim":"Defined the PTB-adjacent PIR domain (Ser307/312/315/323) as a high-affinity receptor-binding module whose serine phosphorylation disrupts IR coupling, unifying inhibitory phosphorylation into a structural mechanism.","evidence":"SPR binding, HDX-MS, and phosphomimetic mutagenesis with signaling readouts in insulin-responsive cells","pmids":["38625937"],"confidence":"High","gaps":["Endogenous kinases acting on individual PIR serines in vivo not fully assigned","Structure of the full PTB-PIR–receptor complex not solved"]},{"year":2024,"claim":"Linked metabolic enzyme PYCR1 to epigenetic activation of IRS1 transcription via H3K18 lactylation in liver cancer.","evidence":"ChIP for H3K18la at the IRS1 promoter, PYCR1 KO, metabolomics, and pathway Westerns","pmids":["39422696"],"confidence":"Medium","gaps":["Direct enzymology connecting PYCR1 to promoter lactylation not established","Single lab"]},{"year":null,"claim":"How the full set of activating tyrosine and inhibitory serine modifications, phosphatases, ubiquitin ligases, and trafficking partners are integrated on a single IRS-1 molecule in real time remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated structural model of IRS-1 with bound receptor and effectors","Quantitative hierarchy among competing regulatory inputs undefined","Tissue-specific determinants of IRS-1 versus IRS-2 usage incompletely 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Plays therefore an important role in development, growth, glucose homeostasis as well as lipid metabolism (PubMed:19639489). Upon phosphorylation by the insulin receptor, functions as a signaling scaffold that propagates insulin action through binding to SH2 domain-containing proteins including the p85 regulatory subunit of PI3K, NCK1, NCK2, GRB2 or SHP2 (PubMed:11171109, PubMed:8265614). Recruitment of GRB2 leads to the activation of the guanine nucleotide exchange factor SOS1 which in turn triggers the Ras/Raf/MEK/MAPK signaling cascade (By similarity). Activation of the PI3K/AKT pathway is responsible for most of insulin metabolic effects in the cell, and the Ras/Raf/MEK/MAPK is involved in the regulation of gene expression and in cooperation with the PI3K pathway regulates cell growth and differentiation. Acts a positive regulator of the Wnt/beta-catenin signaling pathway through suppression of DVL2 autophagy-mediated degradation leading to cell proliferation (PubMed:24616100)","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/P35568/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/IRS1","classification":"Not Classified","n_dependent_lines":59,"n_total_lines":1208,"dependency_fraction":0.048841059602649006},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/IRS1","total_profiled":1310},"omim":[{"mim_id":"619393","title":"KELCH REPEAT- AND BTB DOMAIN-CONTAINING PROTEIN 2; KBTBD2","url":"https://www.omim.org/entry/619393"},{"mim_id":"617535","title":"FAS APOPTOTIC INHIBITORY MOLECULE; 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phosphorylations in the IRS-1 PIR domain abrogate IRS-1 and IR interaction.","date":"2024","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/38625937","citation_count":27,"is_preprint":false},{"pmid":"37778516","id":"PMC_37778516","title":"Esculin ameliorates obesity-induced insulin resistance by improving adipose tissue remodeling and activating the IRS1/PI3K/AKT/GLUT4 pathway.","date":"2023","source":"Journal of ethnopharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/37778516","citation_count":27,"is_preprint":false},{"pmid":"32026479","id":"PMC_32026479","title":"MiRNA-7 enhances erlotinib sensitivity of glioblastoma cells by blocking the IRS-1 and IRS-2 expression.","date":"2020","source":"The Journal of pharmacy and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/32026479","citation_count":27,"is_preprint":false},{"pmid":"26352220","id":"PMC_26352220","title":"MicroRNA-128 suppresses cell growth and metastasis in colorectal carcinoma by targeting IRS1.","date":"2015","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/26352220","citation_count":26,"is_preprint":false},{"pmid":"35579013","id":"PMC_35579013","title":"Estrogen Protects Cardiac Function and Energy Metabolism in Dilated Cardiomyopathy Induced by Loss of Cardiac IRS1 and IRS2.","date":"2022","source":"Circulation. Heart failure","url":"https://pubmed.ncbi.nlm.nih.gov/35579013","citation_count":26,"is_preprint":false},{"pmid":"26773517","id":"PMC_26773517","title":"IRS-1 Functions as a Molecular Scaffold to Coordinate IGF-I/IGFBP-2 Signaling During Osteoblast Differentiation.","date":"2016","source":"Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research","url":"https://pubmed.ncbi.nlm.nih.gov/26773517","citation_count":26,"is_preprint":false},{"pmid":"33109107","id":"PMC_33109107","title":"miR-203 inhibits cell proliferation and ERK pathway in prostate cancer by targeting IRS-1.","date":"2020","source":"BMC cancer","url":"https://pubmed.ncbi.nlm.nih.gov/33109107","citation_count":25,"is_preprint":false},{"pmid":"33723215","id":"PMC_33723215","title":"FoxP3-miR-150-5p/3p suppresses ovarian tumorigenesis via an IGF1R/IRS1 pathway feedback loop.","date":"2021","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/33723215","citation_count":24,"is_preprint":false},{"pmid":"22523112","id":"PMC_22523112","title":"Association of IRS-1 and IRS-2 genes polymorphisms with polycystic ovary syndrome: a meta-analysis.","date":"2012","source":"Endocrine journal","url":"https://pubmed.ncbi.nlm.nih.gov/22523112","citation_count":24,"is_preprint":false},{"pmid":"29749571","id":"PMC_29749571","title":"Hepatic IRS1 and ß-catenin expression is associated with histological progression and overt diabetes emergence in NAFLD patients.","date":"2018","source":"Journal of gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/29749571","citation_count":24,"is_preprint":false},{"pmid":"32296029","id":"PMC_32296029","title":"NT157 has antineoplastic effects and inhibits IRS1/2 and STAT3/5 in JAK2V617F-positive myeloproliferative neoplasm cells.","date":"2020","source":"Signal transduction and targeted therapy","url":"https://pubmed.ncbi.nlm.nih.gov/32296029","citation_count":23,"is_preprint":false},{"pmid":"20837540","id":"PMC_20837540","title":"Spontaneous Irs1 passenger mutation linked to a gene-targeted SerpinB2 allele.","date":"2010","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/20837540","citation_count":23,"is_preprint":false},{"pmid":"35098692","id":"PMC_35098692","title":"Cathepsin K activity controls cachexia-induced muscle atrophy via the modulation of IRS1 ubiquitination.","date":"2022","source":"Journal of cachexia, sarcopenia and muscle","url":"https://pubmed.ncbi.nlm.nih.gov/35098692","citation_count":23,"is_preprint":false},{"pmid":"23383252","id":"PMC_23383252","title":"Nexilin, a cardiomyopathy-associated F-actin binding protein, binds and regulates IRS1 signaling in skeletal muscle cells.","date":"2013","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/23383252","citation_count":23,"is_preprint":false},{"pmid":"32560812","id":"PMC_32560812","title":"Regulation of IRS-1, insulin signaling and glucose uptake by miR-143/145 in vascular smooth muscle cells.","date":"2020","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/32560812","citation_count":22,"is_preprint":false},{"pmid":"22859932","id":"PMC_22859932","title":"The transcriptional coactivators p/CIP and SRC-1 control insulin resistance through IRS1 in obesity models.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22859932","citation_count":22,"is_preprint":false},{"pmid":"21991327","id":"PMC_21991327","title":"Constitutive expression of insulin receptor substrate (IRS)-1 inhibits myogenic differentiation through nuclear exclusion of Foxo1 in L6 myoblasts.","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21991327","citation_count":22,"is_preprint":false},{"pmid":"30530508","id":"PMC_30530508","title":"IRS-1 increases TAZ expression and promotes osteogenic differentiation in rat bone marrow mesenchymal stem cells.","date":"2018","source":"Biology open","url":"https://pubmed.ncbi.nlm.nih.gov/30530508","citation_count":22,"is_preprint":false},{"pmid":"28055425","id":"PMC_28055425","title":"IGF1 regulates RUNX1 expression via IRS1/2: Implications for antler chondrocyte differentiation.","date":"2017","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/28055425","citation_count":21,"is_preprint":false},{"pmid":"27378176","id":"PMC_27378176","title":"IRS1 deficiency protects β-cells against ER stress-induced apoptosis by modulating sXBP-1 stability and protein translation.","date":"2016","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/27378176","citation_count":21,"is_preprint":false},{"pmid":"33007330","id":"PMC_33007330","title":"FGFR1 overexpression renders breast cancer cells resistant to metformin through activation of IRS1/ERK signaling.","date":"2020","source":"Biochimica et biophysica acta. Molecular cell research","url":"https://pubmed.ncbi.nlm.nih.gov/33007330","citation_count":21,"is_preprint":false},{"pmid":"17508357","id":"PMC_17508357","title":"Insulin receptor substrate 1 (IRS-1) plays a unique role in normal epidermal physiology.","date":"2007","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/17508357","citation_count":20,"is_preprint":false},{"pmid":"35842608","id":"PMC_35842608","title":"H19 inhibition increases HDAC6 and regulates IRS1 levels and insulin signaling in the skeletal muscle during diabetes.","date":"2022","source":"Molecular medicine (Cambridge, Mass.)","url":"https://pubmed.ncbi.nlm.nih.gov/35842608","citation_count":19,"is_preprint":false},{"pmid":"35008541","id":"PMC_35008541","title":"chi-miR-487b-3p Inhibits Goat Myoblast Proliferation and Differentiation by Targeting IRS1 through the IRS1/PI3K/Akt Signaling Pathway.","date":"2021","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/35008541","citation_count":19,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":51681,"output_tokens":7467,"usd":0.133524,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":16852,"output_tokens":7175,"usd":0.131818,"stage2_stop_reason":"end_turn"},"total_usd":0.265342,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"IRS-1 undergoes tyrosine phosphorylation at YXXM motifs upon insulin stimulation and activates PI3K by binding to the SH2 domains of the p85 regulatory subunit; phosphorylated YXXM-containing peptides block this interaction in vitro, and tyrosyl-phosphorylated IRS-1 activates PI3K in anti-p85 immunoprecipitates.\",\n      \"method\": \"In vitro kinase assay, SH2-domain fusion protein pulldown, synthetic phosphopeptide competition, co-immunoprecipitation, PI3K activity assay\",\n      \"journal\": \"The EMBO journal / PNAS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal in vitro reconstitution experiments (peptide competition, SH2 pulldown, PI3K activity assay) replicated across two independent labs in the same year\",\n      \"pmids\": [\"1380456\", \"1332046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"YMXM motifs in IRS-1 define substrate specificity of the insulin receptor kinase; the insulin receptor kinase preferentially phosphorylates peptides containing YMXM sequences (with methionine at Y+1 and Y+3), and when phosphorylated these motifs serve as recognition sites for SH2-domain-containing signaling proteins.\",\n      \"method\": \"In vitro peptide substrate kinase assay with synthetic peptides corresponding to IRS-1 tyrosine sites; structure-activity analysis with substituted YMXM peptides\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic assay with mutagenesis-equivalent substitution analysis, rigorous kinetic characterization (Km, kcat/Km)\",\n      \"pmids\": [\"1312712\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"IRS-1 is a direct physiological substrate of the insulin receptor kinase: purified insulin receptor phosphorylates baculovirus-produced IRS-1 exclusively on tyrosine residues in vitro; IRS-1 associates with the insulin receptor during insulin stimulation; and co-expression of insulin receptor and IRS-1 strongly amplifies insulin-stimulated PI3K association and DNA synthesis.\",\n      \"method\": \"In vitro kinase assay with purified IR and recombinant IRS-1, co-immunoprecipitation, immunofluorescence localization, overexpression in CHO cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro phosphorylation plus multiple orthogonal cell-based assays; foundational paper\",\n      \"pmids\": [\"1385403\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Genetic disruption of IRS-1 in mice abolishes IRS-1 phosphorylation and IRS-1-associated PI3K activity; residual insulin/IGF-1 signaling is mediated by a distinct IRS-2 protein that binds PI3K, establishing IRS-1-dependent and IRS-1-independent pathways.\",\n      \"method\": \"Targeted gene knockout in mice, immunoprecipitation/PI3K activity assay, glucose uptake assays in vivo and in vitro\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic KO with defined biochemical readout (PI3K activity) and physiological phenotype, replicated across multiple tissue types\",\n      \"pmids\": [\"7526222\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"The pleckstrin homology (PH) domain at the IRS-1 N-terminus is the principal link coupling IRS-1 to the insulin receptor; the PTB domain improves coupling but is not essential at high receptor levels, whereas the PH domain is essential at physiological low receptor levels for insulin-stimulated IRS-1 tyrosine phosphorylation, PI3K activity, and p70S6K phosphorylation.\",\n      \"method\": \"Domain deletion mutagenesis, peptide competition binding assays, reconstitution in 32D cells with insulin receptor and IRS-1 deletion mutants, PI3K activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct mutagenesis with functional reconstitution in cells; multiple orthogonal readouts (tyrosine phosphorylation, PI3K activity, p70S6K, DNA synthesis)\",\n      \"pmids\": [\"8798677\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"IRS-1 and Shc compete for a limited cellular pool of Grb2; overexpression of IRS-1 sequesters Grb2 away from Shc, reducing insulin-stimulated MAP kinase activation and c-fos transcription, which proceed predominantly through the Shc-Grb2 pathway.\",\n      \"method\": \"Transfection overexpression, indirect co-immunoprecipitation, MAP kinase gel-shift assay, c-fos transcriptional reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP experiments demonstrating competitive binding, supported by functional transcriptional and kinase readouts; single lab\",\n      \"pmids\": [\"7983051\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"TNF-α and insulin/IGF-1 stimulate phosphorylation of IRS-1 at Ser307 via distinct kinase pathways: TNF-α acts through a PD98059-sensitive (ERK) pathway, while insulin acts through a PI3K-dependent (LY294002/wortmannin-sensitive) pathway; Ser307 phosphorylation inhibits insulin-stimulated IRS-1 tyrosine phosphorylation.\",\n      \"method\": \"Phosphospecific antibody (αpSer307) detection in cell lines and in vivo (muscle from insulin-injected rodents and human hyperinsulinemic clamp), kinase inhibitor dissection\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — phosphospecific antibody validated in multiple cell types and in vivo tissues including human; pharmacological pathway dissection with two inhibitors; recombinant JNK phosphorylation of IRS-1 at Ser307 demonstrated separately\",\n      \"pmids\": [\"11160134\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SOCS1 and SOCS3 target IRS-1 and IRS-2 for ubiquitin-mediated proteasomal degradation via the elongin BC ubiquitin-ligase complex; SOCS1 binds IRS-1/2 directly, and mutations in the SOCS box (which disrupt elongin BC binding) abrogate ubiquitination and degradation without affecting IRS binding.\",\n      \"method\": \"Co-immunoprecipitation (recombinant and endogenous proteins), ubiquitination assay, SOCS box mutant analysis, adenoviral expression in mouse liver with glucose tolerance testing\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — mechanistic dissection with domain mutants, in vitro ubiquitination assays, and in vivo adenoviral rescue experiment; multiple orthogonal approaches\",\n      \"pmids\": [\"12228220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"PKCθ phosphorylates IRS-1 at Ser1101, blocking IRS-1 tyrosine phosphorylation and downstream Akt activation; mutation of Ser1101 to alanine makes IRS-1 insensitive to PKCθ and restores insulin signaling.\",\n      \"method\": \"In vitro kinase assay (PKCθ phosphorylation of IRS-1), site-directed mutagenesis (S1101A), overexpression/inhibition in cultured cells, Western blot for tyrosine phosphorylation and Akt activation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis with functional rescue; direct identification of phosphorylation site and its functional consequence\",\n      \"pmids\": [\"15364919\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"IRS-1 overexpression in the mammary gland causes constitutive IRS-1 phosphorylation, progressive mammary hyperplasia, tumorigenesis, and metastasis in transgenic mice; IRS-1 binds β-catenin in vitro and in vivo, implicating β-catenin signaling in IRS-1-driven tumorigenesis.\",\n      \"method\": \"Mammary-targeted transgenic mice, in vitro and in vivo co-immunoprecipitation for β-catenin binding, histological analysis of tumor phenotype\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transgenic in vivo model with defined phenotype plus co-IP for binding partner; β-catenin interaction established by reciprocal co-IP in vitro and in vivo\",\n      \"pmids\": [\"17030631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"MG53 is an E3 ubiquitin ligase that induces IRS-1 ubiquitination using UBE2H as the E2-conjugating enzyme; disruption of MG53's E3 ligase activity abolishes IRS-1 ubiquitination and enhances skeletal myogenesis and insulin signaling.\",\n      \"method\": \"E3 ligase activity assay, ubiquitination assay with UBE2H, MG53 E3-ligase-dead mutant, MG53 knockout mice (elevated IRS-1 levels), high-fat/high-sucrose diet challenge\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro ubiquitination reconstitution with E2/E3 components, mutagenesis of E3 function, KO mouse validation; multiple orthogonal methods\",\n      \"pmids\": [\"23965929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PTEN acts as a protein tyrosine phosphatase that selectively dephosphorylates IRS-1; NEDD4, a PTEN ubiquitin ligase, antagonizes PTEN to support IGF/insulin signaling through IRS-1; ablation of PTEN rescues defective IRS-1 and AKT phosphorylation caused by NEDD4 deletion.\",\n      \"method\": \"Direct biochemical dephosphorylation assay (PTEN acting on IRS-1), cellular reconstitution, NEDD4 knockout cells, PTEN ablation rescue experiments\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical assay demonstrating PTEN protein phosphatase activity on IRS-1 substrate, confirmed by cellular reconstitution with multiple genetic controls\",\n      \"pmids\": [\"24814346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"IRS-1 interacts with the clathrin adaptor complex AP2 and delays AP2-mediated IGF-IR endocytosis after ligand stimulation by inhibiting recruitment of IGF-IR into clathrin-coated structures; this prolongs IGF-IR surface activity and shifts downstream signaling from transient to sustained Akt activation. An AP2-binding-deficient IRS-1 mutant fails to delay endocytosis.\",\n      \"method\": \"Co-immunoprecipitation (IRS-1/AP2), live-cell imaging, IRS-1 depletion/reconstitution with AP2-binding mutant, clathrin-coated structure tracking, Akt phosphorylation kinetics, FoxO transcriptional reporter\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal co-IP, functional mutant rescue, live imaging of endocytosis, and multiple downstream signaling readouts; novel mechanistic role established with orthogonal methods\",\n      \"pmids\": [\"29661273\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Rab5a directly interacts with IRS-1 in a GTP-dependent manner (enhanced by IGF-1 and myogenic differentiation); Rab5a modulates IRS-1 activation by coordinating the IRS-1/IGF receptor association and regulating intracellular membrane targeting of IRS-1, thereby controlling AKT-mTOR signaling and muscle regeneration.\",\n      \"method\": \"Co-immunoprecipitation (endogenous and overexpressed), GTP-dependent binding assay, site-directed mutagenesis (R207/R222 on IRS-1; Y82/Y89/Y90 on Rab5a), myogenic Rab5a-KO mice, AKT-mTOR signaling assays\",\n      \"journal\": \"Cell death and differentiation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — direct binding characterization with mutagenesis identifying interface residues, validated in KO mouse model with defined signaling readouts\",\n      \"pmids\": [\"32051546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Serine phosphorylations within a region of IRS-1 directly C-terminal to the PTB domain (designated the PIR domain, encompassing Ser307, Ser312, Ser315, and Ser323) abrogate IRS-1 binding to the insulin receptor; the PTB-PIR module binds IR more strongly than PTB alone (by surface plasmon resonance), and PIR phosphomimetic mutations (S→E) decrease IR, IRS-1, and AKT phosphorylation in cells.\",\n      \"method\": \"Surface plasmon resonance (SPR) binding assays, hydrogen-deuterium exchange mass spectrometry (HDX-MS), phosphomimetic mutagenesis (S307E/S312E/S315E/S323E), Western blot of signaling in insulin-responsive cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — SPR quantitative binding assay, HDX-MS structural analysis, and mutagenesis with functional cell-based validation; multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"38625937\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"BCR-ABL binds to IRS-1 and constitutively phosphorylates it in K562 cells; this is associated with IRS-1/PI3K and IRS-1/Grb2 complex formation; imatinib treatment markedly attenuates BCR-ABL/IRS-1 association and IRS-1-associated PI3K activity.\",\n      \"method\": \"Co-immunoprecipitation, PI3K activity assay, imatinib treatment\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — co-IP and kinase activity assay in a single cell line; single lab, single paper\",\n      \"pmids\": [\"12560071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"IRS-1 and IRS-2 are tyrosine-phosphorylated substrates of both TrkA and the TRK-T1 oncogene; this phosphorylation recruits p85-PI3K, SHP-2, and Grb2 to IRS-1 and increases PI3K activity; TRK-T1 stimulates DNA synthesis in wild-type but not IRS-1−/− fibroblasts, and yeast two-hybrid analysis shows direct TRK–IRS interaction.\",\n      \"method\": \"Co-immunoprecipitation, PI3K activity assay, yeast two-hybrid, IRS-1 KO fibroblast reconstitution, DNA synthesis assay\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, genetic KO rescue, and yeast two-hybrid in the same study; single lab\",\n      \"pmids\": [\"11147812\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The Rheb-mTOR/raptor axis negatively regulates myogenic differentiation by suppressing IRS-1 protein levels and increasing Ser307 phosphorylation on IRS-1; IRS-1 knockdown eliminates the enhanced differentiation seen with raptor or Rheb knockdown, placing IRS-1 downstream of raptor/Rheb in myogenesis.\",\n      \"method\": \"siRNA knockdown of raptor, Rheb, and IRS-1 in C2C12 myoblasts, overexpression constructs, Akt phosphorylation and differentiation assays, Western blot for IRS-1 protein levels and Ser307 phosphorylation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis by double KD with defined phenotypic readout; multiple components tested; single lab\",\n      \"pmids\": [\"21852229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Nexilin, an F-actin binding protein, preferentially binds IRS-1 (but not IRS-2) under basal conditions in L6 myotubes and the complex is disassembled by insulin; nexilin silencing has no effect on IRS-1 tyrosine phosphorylation but enhances p85 recruitment to IRS-1, PI(3,4,5)P3 formation, AKT activation, and glucose uptake; nexilin overexpression inhibits IRS-1→AKT signaling.\",\n      \"method\": \"Co-immunoprecipitation (nexilin/IRS-1/p85), siRNA knockdown, nexilin overexpression, PI(3,4,5)P3 assay, AKT phosphorylation, glucose uptake assay in L6 myotubes\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus gain- and loss-of-function with functional readouts; single lab, single cell model\",\n      \"pmids\": [\"23383252\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"p38α MAPK activation during chronic insulin exposure reduces cardiac IRS-1 and IRS-2 protein levels, preventing subsequent insulin action; heart-specific IRS1/IRS2 double-KO mice develop dilated cardiomyopathy with impaired Akt→FoxO1 signaling and reduced ATP content.\",\n      \"method\": \"Heart-specific double-KO mice, neonatal rat ventricular cardiomyocyte chronic insulin treatment, p38 inhibitor experiments, echocardiography, Akt/FoxO1 signaling Western blot\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — tissue-specific KO with defined cardiac phenotype plus mechanistic cell experiments linking p38 to IRS protein reduction; single lab\",\n      \"pmids\": [\"24159000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IRS-1 acts as a molecular scaffold in osteoblasts: IGF-I stimulates IRS-1 phosphorylation and co-recruitment of PKCζ (via the p62 adaptor) and vimentin to phospho-IRS-1; activated PKCζ directly phosphorylates vimentin, enabling downstream RPTPβ inactivation, PTEN tyrosine phosphorylation, and AKT activation required for osteoblast differentiation.\",\n      \"method\": \"Immunoprecipitation of IRS-1 complexes containing PKCζ and vimentin, in vitro kinase assay (PKCζ phosphorylating vimentin from IRS-1 immunoprecipitates), disrupting peptides for p62/PKCζ and p62/IRS-1 interactions, primary mouse calvarial osteoblasts\",\n      \"journal\": \"Journal of bone and mineral research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP of multi-protein complex, in vitro kinase assay from immunoprecipitate, disrupting peptides with functional readouts; single lab\",\n      \"pmids\": [\"26773517\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Cathepsin K (CTSK) selectively cleaves IRS-1 in the region of amino acids 268–574, causing IRS-1 ubiquitination and degradation; CTSK knockout prevents IRS-1 degradation and preserves AKT-mTOR signaling in cachectic muscle; CTSK overexpression accelerates IRS-1 ubiquitination even without pro-cachectic stimulus.\",\n      \"method\": \"Co-immunoprecipitation, truncation mapping of IRS-1–CTSK interaction, ubiquitination assay, CTSK KO and overexpression in C2C12 cells and in vivo LLC tumor model, Western blot for IRS-1/Akt/mTOR\",\n      \"journal\": \"Journal of cachexia, sarcopenia and muscle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — domain mapping co-IP plus functional KO/OE with ubiquitination readout in vitro and in vivo; single lab\",\n      \"pmids\": [\"35098692\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"TAZ transcriptionally upregulates IRS1 expression by physically interacting with c-Jun and Tead4 to induce IRS1 transcription; muscle-specific TAZ-KO mice show decreased IRS1 expression and insulin sensitivity; Wnt/APC signaling requires TAZ for IRS1-dependent insulin signaling in muscle.\",\n      \"method\": \"Muscle-specific TAZ-KO mice, APC/TAZ double-KO mice, ChIP/co-immunoprecipitation (TAZ with c-Jun and Tead4), IRS1 promoter reporter assay, glucose uptake assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse model with defined IRS1/insulin sensitivity phenotype, plus co-IP and promoter assays; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"30679431\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"IRS-1 (but not IRS-2) is required for normal epidermal differentiation: IRS-1-null mouse skin is thinner due to reduced spinous layer, with impaired keratinocyte differentiation marker K1 induction; IRS-2-null skin appears normal, establishing distinct roles for the two paralogs in epidermis.\",\n      \"method\": \"IRS-1 and IRS-2 KO mice, histological analysis, primary skin cell differentiation assays, K1 marker expression\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined tissue phenotype and molecular marker readout; IRS-1 vs IRS-2 specificity established; single lab\",\n      \"pmids\": [\"17508357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"IRS-1 deficiency in β-cells protects against ER stress-induced apoptosis by reducing nuclear accumulation of spliced XBP-1 (via proteasomal degradation), attenuating general translation (increased eEF2 phosphorylation), and maintaining elevated ER calcium levels.\",\n      \"method\": \"IRS1-KO and IRS2-KO β-cells, ER stress induction, nuclear fractionation for XBP-1, polyribosomal profiling, eEF2 phosphorylation assay, ER calcium measurement\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple orthogonal mechanistic readouts (XBP-1 stability, polysome profiling, calcium); single lab\",\n      \"pmids\": [\"27378176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PYCR1 promotes IRS1 transcription in liver cancer by increasing H3K18 lactylation at the IRS1 promoter; knockout or inhibition of PYCR1 reduces glycolysis, lowers H3K18 lactylation at the IRS1 promoter, and decreases IRS1 expression and downstream PI3K/AKT/mTOR signaling.\",\n      \"method\": \"ChIP assay (H3K18 lactylation at IRS1 promoter), PYCR1 KO, metabolomics, transcriptome sequencing, Western blot for IRS1 and pathway components\",\n      \"journal\": \"Clinical and translational medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP demonstrating epigenetic mark at IRS1 promoter linked to PYCR1 activity; genetic KO with functional readouts; single lab\",\n      \"pmids\": [\"39422696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PTP1B dephosphorylates the insulin receptor and thereby determines IRS-1-mediated PI3K/Akt/FoxO1 signaling in liver; in IRS2-deficient mice (which develop hyperglycemia), elevated PTP1B impairs IRS1 signaling, and deletion or pharmacological inhibition of PTP1B restores IRS1-dependent hepatic insulin signaling.\",\n      \"method\": \"IRS2-KO / PTP1B-KO double-KO mice, resveratrol pharmacological PTP1B inhibition, hepatic insulin signaling Western blots, isolated hepatocytes\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis (double KO) plus pharmacological validation; single lab\",\n      \"pmids\": [\"20028942\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IRS-1 is a cytoplasmic scaffold protein that is directly phosphorylated on multiple YMXM tyrosine motifs by the insulin and IGF-1 receptor kinases (requiring the N-terminal PH and PTB domains for receptor coupling), whereupon it recruits and activates PI3K (via SH2-domain binding of p85), Grb2-Sos, SHP-2, and other effectors to propagate metabolic and mitogenic signals; its activity is precisely regulated by a complex network of inhibitory serine/threonine phosphorylations (by JNK at Ser307, PKCθ at Ser1101, and mTOR/S6K1 among others, which disrupt IR-IRS-1 interaction via the PIR domain), ubiquitin-mediated proteasomal degradation (facilitated by SOCS1/3 via elongin BC, MG53/UBE2H, and CTSK), and dephosphorylation by PTEN (which acts as an IRS-1 protein tyrosine phosphatase antagonized by NEDD4); additionally, IRS-1 modulates IGF-IR endocytosis via AP2 to sustain surface receptor signaling, and its transcription is regulated by TAZ/c-Jun/Tead4 and epigenetic mechanisms including H3K18 lactylation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IRS-1 is a cytoplasmic scaffold/adaptor protein that serves as the principal proximal substrate of the insulin and IGF-1 receptor tyrosine kinases, coupling receptor activation to PI3K-driven metabolic and mitogenic signaling [#2, #0]. Following receptor engagement, IRS-1 is phosphorylated exclusively on tyrosines within YMXM motifs that define insulin-receptor substrate specificity; these phosphotyrosines then dock the SH2 domains of the p85 regulatory subunit to recruit and activate PI3K, and also engage Grb2 and SHP-2 to relay downstream signals [#0, #1, #16]. Receptor coupling depends on the N-terminal PH domain (essential at physiological receptor levels, with the PTB domain enhancing binding) and on a serine-rich PIR region C-terminal to the PTB domain that, together with PTB, mediates high-affinity insulin-receptor binding [#4, #14]. Because IRS-1 sequesters a limited pool of Grb2 from Shc, its abundance helps partition signaling between metabolic and MAP-kinase outputs [#5]. IRS-1 signaling output is constrained by a dense regulatory network: inhibitory serine/threonine phosphorylation — at Ser307 by ERK- and PI3K-dependent kinases and JNK, at Ser1101 by PKC\\u03b8, and within the PIR domain — disrupts receptor coupling and blocks downstream Akt activation [#6, #8, #14]; tyrosine dephosphorylation by PTEN (antagonized by NEDD4) and receptor dephosphorylation by PTP1B reverse activating marks [#11, #26]; and IRS-1 protein levels are set by ubiquitin-mediated proteasomal degradation through SOCS1/3\\u2013elongin BC, the MG53\\u2013UBE2H E3/E2 pair, and cathepsin K\\u2013triggered cleavage and degradation [#7, #10, #21]. IRS-1 also functions beyond signal transmission: it binds the AP2 clathrin adaptor to delay IGF-IR endocytosis and sustain surface receptor signaling, and interacts with GTP-bound Rab5a to control its membrane targeting and IGF-receptor association [#12, #13]. Genetically, IRS-1 defines an IRS-1-dependent branch of insulin/IGF-1 signaling distinct from IRS-2, with tissue-specific roles in skeletal muscle regeneration, myogenic differentiation, epidermal differentiation, and \\u03b2-cell ER-stress responses [#3, #13, #17, #23, #24]. IRS1 transcription is controlled by a TAZ/c-Jun/Tead4 complex and by PYCR1-driven H3K18 lactylation at its promoter [#22, #25].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Established that IRS-1 is a direct insulin-receptor kinase substrate whose tyrosine-phosphorylated YMXM motifs recruit and activate PI3K via p85 SH2 domains, defining the core insulin-signaling relay.\",\n      \"evidence\": \"In vitro kinase assays with purified IR and recombinant IRS-1, synthetic phosphopeptide competition, SH2 pulldown, PI3K activity assay, and overexpression in CHO cells across independent labs\",\n      \"pmids\": [\"1380456\", \"1332046\", \"1312712\", \"1385403\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not enumerate which of the multiple IRS-1 tyrosines are physiologically engaged in vivo\", \"Did not resolve stoichiometry of PI3K versus other SH2 effectors on a single IRS-1 molecule\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Genetic knockout separated IRS-1-dependent from IRS-1-independent signaling, showing a paralog (IRS-2) sustains residual PI3K coupling.\",\n      \"evidence\": \"Targeted IRS-1 knockout mice with PI3K activity assays and glucose uptake measurements\",\n      \"pmids\": [\"7526222\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which tissues rely preferentially on IRS-1 versus IRS-2\", \"Mechanism of functional redundancy at the molecular level unresolved\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Demonstrated that IRS-1 competes with Shc for a limited Grb2 pool, providing a mechanism for partitioning insulin signaling between metabolic and MAP-kinase/mitogenic outputs.\",\n      \"evidence\": \"Transfection overexpression, reciprocal co-IP, MAP kinase gel-shift, and c-fos reporter assays in a single lab\",\n      \"pmids\": [\"7983051\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Based on overexpression which may exaggerate competition\", \"In vivo relevance of Grb2 sequestration not established\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Mapped the receptor-coupling determinants to the N-terminal PH and PTB domains, with the PH domain essential at physiological receptor levels.\",\n      \"evidence\": \"Domain deletion mutagenesis and functional reconstitution in 32D cells with PI3K and p70S6K readouts\",\n      \"pmids\": [\"8798677\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of PH-domain receptor coupling not resolved\", \"Identity of any PH-domain lipid/protein ligand not defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identified Ser307 as an inhibitory phosphosite engaged by distinct ERK- and PI3K-dependent pathways (and JNK), establishing feedback/cross-talk suppression of IRS-1.\",\n      \"evidence\": \"Phosphospecific antibody detection in cells, rodent muscle, and human hyperinsulinemic clamp with kinase-inhibitor dissection\",\n      \"pmids\": [\"11160134\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise kinase responsible in each context not fully isolated\", \"Quantitative contribution of Ser307 to whole-cell insulin resistance not defined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Showed IRS-1 abundance is controlled by SOCS1/3-directed ubiquitin-proteasome degradation via the elongin BC ligase, linking cytokine signaling to IRS-1 turnover.\",\n      \"evidence\": \"Co-IP, ubiquitination assays, SOCS box mutants, and adenoviral expression in mouse liver with glucose tolerance testing\",\n      \"pmids\": [\"12228220\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the catalytic E3/E2 components beyond elongin BC scaffolding not fully defined here\", \"Lysine acceptor sites on IRS-1 not mapped\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined Ser1101 as a PKC\\u03b8 inhibitory site, providing a lipid/diacylglycerol-responsive route to IRS-1 inactivation.\",\n      \"evidence\": \"In vitro PKC\\u03b8 kinase assay, S1101A mutagenesis with functional rescue of insulin signaling in cells\",\n      \"pmids\": [\"15364919\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream signals activating PKC\\u03b8 toward IRS-1 in vivo not delineated\", \"Interplay with other inhibitory serines not addressed\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Connected oncogenic tyrosine kinases to IRS-1, showing BCR-ABL binds and constitutively phosphorylates IRS-1 to drive PI3K and Grb2 complexes.\",\n      \"evidence\": \"Co-IP, PI3K activity assay, and imatinib treatment in K562 cells\",\n      \"pmids\": [\"12560071\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell line, single lab\", \"Direct versus indirect BCR-ABL\\u2013IRS-1 interaction not distinguished\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Extended IRS-1 effector coupling to neurotrophin/oncogenic TRK kinases, with IRS-1 required for TRK-T1-driven DNA synthesis.\",\n      \"evidence\": \"Co-IP, PI3K assay, yeast two-hybrid, and IRS-1-null fibroblast reconstitution\",\n      \"pmids\": [\"11147812\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological relevance in neuronal contexts not tested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Linked IRS-1 hyperactivity to tumorigenesis and identified \\u03b2-catenin as a binding partner in the mammary gland.\",\n      \"evidence\": \"Mammary-targeted transgenic mice with in vitro and in vivo co-IP for \\u03b2-catenin\",\n      \"pmids\": [\"17030631\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which IRS-1\\u2013\\u03b2-catenin binding drives transformation unresolved\", \"Overexpression model may not reflect endogenous biology\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Distinguished IRS-1 from IRS-2 in epidermal differentiation, showing IRS-1 is specifically required for keratinocyte differentiation.\",\n      \"evidence\": \"IRS-1 and IRS-2 KO mice with histology and K1 marker analysis\",\n      \"pmids\": [\"17508357\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of paralog specificity in skin not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed PTP1B sets IRS-1 signaling indirectly by dephosphorylating the insulin receptor, with deletion/inhibition restoring hepatic IRS-1 signaling.\",\n      \"evidence\": \"IRS2-KO/PTP1B-KO double-KO mice, resveratrol inhibition, and hepatic signaling Westerns\",\n      \"pmids\": [\"20028942\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Action is on the receptor, not IRS-1 directly\", \"Single lab\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Placed IRS-1 downstream of the Rheb-mTOR/raptor axis in myogenesis via suppression of IRS-1 protein and Ser307 phosphorylation.\",\n      \"evidence\": \"siRNA epistasis (raptor/Rheb/IRS-1) in C2C12 myoblasts with differentiation and Akt readouts\",\n      \"pmids\": [\"21852229\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct kinase mediating Ser307 in this axis not identified\", \"Single cell model\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Identified MG53 as an E3 ligase using UBE2H to ubiquitinate IRS-1, controlling IRS-1 levels in skeletal muscle and insulin signaling.\",\n      \"evidence\": \"In vitro ubiquitination reconstitution with E2/E3, E3-dead mutant, and MG53-KO mice on metabolic challenge\",\n      \"pmids\": [\"23965929\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"IRS-1 ubiquitin acceptor sites not mapped\", \"Tissue selectivity of MG53 action not fully defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed nexilin as a basal IRS-1 (not IRS-2) binding partner that restrains p85 recruitment, disassembled by insulin.\",\n      \"evidence\": \"Reciprocal co-IP plus gain/loss of function with PIP3, AKT, and glucose uptake readouts in L6 myotubes\",\n      \"pmids\": [\"23383252\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of nexilin\\u2013IRS-1 selectivity unknown\", \"Single lab, single cell model\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated p38\\u03b1 MAPK reduces cardiac IRS-1/IRS-2 protein during chronic insulin exposure, with combined loss causing dilated cardiomyopathy.\",\n      \"evidence\": \"Heart-specific IRS1/IRS2 double-KO mice, cardiomyocyte chronic insulin treatment, p38 inhibition, echocardiography\",\n      \"pmids\": [\"24159000\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of p38-driven IRS protein loss not detailed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Established PTEN as a direct IRS-1 protein-tyrosine phosphatase antagonized by NEDD4, adding a phosphatase arm to IRS-1 regulation.\",\n      \"evidence\": \"Direct dephosphorylation assay, cellular reconstitution, NEDD4-KO cells, and PTEN-ablation rescue\",\n      \"pmids\": [\"24814346\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which IRS-1 phosphotyrosines PTEN targets not mapped\", \"Balance between PTEN lipid- and protein-phosphatase activities in vivo unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Detailed an IRS-1 scaffolding role in osteoblasts assembling PKC\\u03b6 (via p62) and vimentin to drive PTEN tyrosine phosphorylation and AKT-dependent differentiation.\",\n      \"evidence\": \"Multi-protein co-IP, in vitro kinase assay from immunoprecipitates, and disrupting peptides in primary calvarial osteoblasts\",\n      \"pmids\": [\"26773517\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generality beyond osteoblasts not tested\", \"Single lab\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Showed IRS-1 loss protects \\u03b2-cells from ER stress apoptosis by reducing spliced XBP-1, attenuating translation, and preserving ER calcium.\",\n      \"evidence\": \"IRS1-KO and IRS2-KO \\u03b2-cells with XBP-1 fractionation, polysome profiling, eEF2 phosphorylation, and ER calcium measurements\",\n      \"pmids\": [\"27378176\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct molecular link between IRS-1 and XBP-1 stability not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Uncovered a non-canonical role: IRS-1 binds AP2 to delay IGF-IR clathrin-mediated endocytosis, converting transient into sustained Akt signaling.\",\n      \"evidence\": \"Reciprocal co-IP, live-cell imaging of clathrin structures, AP2-binding mutant rescue, and Akt/FoxO readouts\",\n      \"pmids\": [\"29661273\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"AP2-binding motif on IRS-1 not precisely mapped\", \"Generality to insulin receptor versus IGF-IR not addressed\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified transcriptional control of IRS1 by a TAZ/c-Jun/Tead4 complex governing muscle insulin sensitivity downstream of Wnt/APC.\",\n      \"evidence\": \"Muscle-specific TAZ-KO and APC/TAZ double-KO mice, ChIP/co-IP, promoter reporter, and glucose uptake\",\n      \"pmids\": [\"30679431\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct TAZ binding element on IRS1 promoter not finely mapped\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Showed GTP-bound Rab5a directly binds IRS-1 to coordinate its membrane targeting and IGF-receptor association, controlling AKT-mTOR signaling in muscle regeneration.\",\n      \"evidence\": \"Co-IP, GTP-dependent binding, interface-residue mutagenesis, and myogenic Rab5a-KO mice\",\n      \"pmids\": [\"32051546\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatial dynamics of IRS-1 membrane targeting not directly visualized\", \"Relationship to AP2-mediated trafficking unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined cathepsin K as a protease that cleaves IRS-1 (aa 268\\u2013574) to trigger its ubiquitination and degradation, driving muscle cachexia.\",\n      \"evidence\": \"Co-IP, truncation mapping, ubiquitination assay, and CTSK KO/overexpression in C2C12 and an in vivo tumor model\",\n      \"pmids\": [\"35098692\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Coupling between cleavage and ubiquitination machinery not detailed\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined the PTB-adjacent PIR domain (Ser307/312/315/323) as a high-affinity receptor-binding module whose serine phosphorylation disrupts IR coupling, unifying inhibitory phosphorylation into a structural mechanism.\",\n      \"evidence\": \"SPR binding, HDX-MS, and phosphomimetic mutagenesis with signaling readouts in insulin-responsive cells\",\n      \"pmids\": [\"38625937\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous kinases acting on individual PIR serines in vivo not fully assigned\", \"Structure of the full PTB-PIR\\u2013receptor complex not solved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Linked metabolic enzyme PYCR1 to epigenetic activation of IRS1 transcription via H3K18 lactylation in liver cancer.\",\n      \"evidence\": \"ChIP for H3K18la at the IRS1 promoter, PYCR1 KO, metabolomics, and pathway Westerns\",\n      \"pmids\": [\"39422696\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct enzymology connecting PYCR1 to promoter lactylation not established\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the full set of activating tyrosine and inhibitory serine modifications, phosphatases, ubiquitin ligases, and trafficking partners are integrated on a single IRS-1 molecule in real time remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No integrated structural model of IRS-1 with bound receptor and effectors\", \"Quantitative hierarchy among competing regulatory inputs undefined\", \"Tissue-specific determinants of IRS-1 versus IRS-2 usage incompletely mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 12, 16, 18, 20]},\n      {\"term_id\": \"GO:0005515\", \"supporting_discovery_ids\": [0, 12, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [12, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 4]},\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [3, 26, 22]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [7, 10, 21]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [12, 13]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"INSR\", \"IGF1R\", \"PIK3R1\", \"GRB2\", \"PTEN\", \"AP2\", \"RAB5A\", \"SOCS1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":8,"faith_pct":87.5}}