{"gene":"IGBP1","run_date":"2026-06-10T01:55:22","timeline":{"discoveries":[{"year":2004,"finding":"Alpha4 (IGBP1), a noncatalytic subunit of PP2A, is required to repress apoptosis in murine cells. Alpha4 deletion leads to increased dephosphorylation of transcription factors c-Jun and p53, transcription of multiple proapoptotic genes, and cell death that is suppressible by blocking protein synthesis or overexpressing Bcl-xL.","method":"Conditional gene deletion (alpha4 knockout) in murine cells, epistasis with Bcl-xL overexpression and translation inhibitors, transcriptional profiling","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined cellular phenotype, multiple orthogonal approaches (genetic rescue, pharmacological rescue, transcriptional readout) in a single rigorous study","pmids":["15499020"],"is_preprint":false},{"year":2010,"finding":"Alpha4 (IGBP1) contains a novel ubiquitin-interacting motif (UIM, residues 46–60) that allows alpha4 to bind ubiquitin and act as an adaptor bridging PP2Ac and the E3 ubiquitin ligase Mid1. The UIM within alpha4 suppresses polyubiquitination of PP2Ac; deletion of the UIM enhances PP2Ac polyubiquitination.","method":"NMR analysis of alpha4–ubiquitin interaction; co-immunoprecipitation of alpha4, PP2Ac, and Mid1; UIM deletion mutants with ubiquitination assays","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structural validation of UIM-ubiquitin interaction plus mutagenesis and co-IP in mammalian cells, single lab but multiple orthogonal methods","pmids":["20092282"],"is_preprint":false},{"year":2011,"finding":"Both the C-terminal Mid1-binding domain and the N-terminal PP2Ac-binding domain of Alpha4 are required for Alpha4-mediated protection of PP2Ac from polyubiquitination and degradation. X-ray crystallography of the N-terminal domain showed a flexible TPR-like fold with a PP2Ac-binding helix in a more open conformation than yeast Tap42, and an embedded UIM.","method":"X-ray crystallography of Alpha4 N-terminal domain; double electron-electron resonance (DEER) spectroscopy; cycloheximide chase assays; tandem ubiquitin-binding entity precipitations; site-directed mutagenesis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with mutagenesis and functional ubiquitination assays in mammalian cells, multiple orthogonal methods in one study","pmids":["21454489"],"is_preprint":false},{"year":2007,"finding":"Alpha4 (IGBP1) promotes cell spreading and migration through activation of Rac1 GTPase. Fibroblasts lacking alpha4 show reduced Rac1-GTP levels and impaired spreading/migration; constitutively active Rac1 rescues the alpha4-null defects; inhibition of Rac1 blocks alpha4-promoted migration. T cell-specific alpha4 transgenic mice display increased lymphocyte motility and chemotaxis.","method":"Alpha4 conditional knockout fibroblasts; alpha4 overexpression; constitutively active Rac1 rescue; Rac1 GTPase pull-down assays; T cell-specific transgenic mice with chemotaxis assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal KO and OE with defined phenotypic readouts, epistasis with Rac1 mutants, replicated in two cell types","pmids":["17693407"],"is_preprint":false},{"year":2008,"finding":"Igbp1 (alpha4) mRNA is selectively recruited to polysomes downstream of SCF-induced PI3K activation in erythroblasts. Constitutive Igbp1 expression impairs erythroid differentiation, sustains 4EBP and p70S6k phosphorylation, and enhances polysome recruitment of multiple eIF4E-sensitive mRNAs, establishing a positive feedback loop on translation initiation that maintains PP2A/mTOR signaling.","method":"Polysome fractionation with microarray comparison; PI3K inhibitor treatments; eIF4E overexpression; retroviral constitutive Igbp1 expression with erythroid differentiation assays and phosphorylation analysis","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal approaches (polysome profiling, pharmacological inhibition, gain-of-function with defined signaling and differentiation readouts), single lab","pmids":["18625885"],"is_preprint":false},{"year":2009,"finding":"Alpha4 (IGBP1), together with PP2Ac, forms a macromolecular complex with mTOR and STAT1. Inactivation of mTOR enhances alpha4 association with the complex and increases STAT1 nuclear content in a PP2Ac-dependent manner. Depletion of alpha4 enhances STAT1-dependent gene expression (IRF-1, caspase-1, hiNOS, Fas), independently of p70 S6K and Akt.","method":"Co-immunoprecipitation of mTOR-STAT1-alpha4-PP2Ac complex; siRNA depletion of alpha4, PP2A, or mTOR; nuclear fractionation; gene expression analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP of complex plus siRNA knockdown with defined transcriptional readouts, single lab","pmids":["19553685"],"is_preprint":false},{"year":2010,"finding":"Alpha4 (IGBP1) interacts physically with EDD E3 ubiquitin ligase (at its C-terminal region, independent of the PP2Ac-binding site) and with poly(A)-binding protein (PABP) in multiple cell lines, suggesting involvement in translation initiation steps downstream of mTOR.","method":"Yeast two-hybrid screening; co-immunoprecipitation of alpha4 with EDD and PABP; alpha4 deletion mutant mapping of EDD-binding site","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — yeast two-hybrid and Co-IP in multiple cell lines, deletion mutant domain mapping, single lab","pmids":["20544796"],"is_preprint":false},{"year":2003,"finding":"T cell-specific deletion of alpha4 (IGBP1) severely arrests T cell development at the CD4/CD8 double-negative 3 stage due to decreased cell proliferation (not increased apoptosis). Alpha4-deficient thymocytes show impaired proliferative responses to anti-CD3 stimulation, IL-2, IL-1, and TNF, and severely reduced CD3-induced CD25 expression.","method":"Cre/loxP T cell-specific gene deletion (Lck-alpha4– mice); flow cytometry analysis of T cell subsets; proliferation assays; apoptosis assays","journal":"European journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean cell-type-specific KO with precise developmental-stage phenotyping and multiple functional readouts","pmids":["12811850"],"is_preprint":false},{"year":1997,"finding":"Human alpha4 (IGBP1) gene is located at Xq13.1–q13.3, is expressed ubiquitously as a 1.4-kb mRNA in immune and other tissues, and encodes a 45-kDa protein structurally related to yeast TAP42, a component of the rapamycin-sensitive signaling pathway.","method":"Genomic cloning; Northern blotting; anti-human alpha4 antibody detection of ~45-kDa protein; sequence alignment with TAP42","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct chromosomal mapping, protein detection by antibody, sequence homology establishing pathway membership; single lab","pmids":["9441740"],"is_preprint":false},{"year":2006,"finding":"Human alpha4 (IgBP1) and yeast Tap42 adopt elongated shapes in solution (Rg ~41–43 Å, Dmax ~142–147 Å) as determined by small-angle X-ray scattering. The N-terminal domain alone (deletion mutants alpha4Δ222 and alpha4Δ236) is globular, highly stable, and predominantly α-helical, while the C-terminal region is less structured and more susceptible to proteolysis.","method":"Small-angle X-ray scattering (SAXS); circular dichroism; thermal unfolding kinetics; recombinant truncation mutants expressed in E. coli","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — SAXS low-resolution structure with complementary CD and stability assays; single lab, no mutagenesis-function link","pmids":["16517231"],"is_preprint":false},{"year":2011,"finding":"Alpha4 (IGBP1) is highly expressed in carcinogen-transformed human cells and primary human cancers. Elevated alpha4 increases cell proliferation, promotes survival, decreases PP2A-attributable phosphatase activity, and enables non-transformed cells to form tumors in immunodeficient mice. MiR-34b suppresses alpha4 expression by targeting its 3′-UTR.","method":"Alpha4 overexpression in HEK293/L02R cells with xenograft tumor formation; siRNA knockdown; PP2A activity assay; luciferase reporter for miR-34b target validation","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Strong — gain-of-function xenograft, loss-of-function knockdown, direct PP2A activity measurement, miRNA mechanistic validation; multiple orthogonal methods","pmids":["21339737"],"is_preprint":false},{"year":2011,"finding":"Binding of lactoferrin to IGBP1 reduces PP2A catalytic activity and triggers apoptosis in PC-14 lung adenocarcinoma cells. The lactoferrin-IGBP1 complex was confirmed by protein microarray screening, co-immunoprecipitation, and immunofluorescence.","method":"Protein microarray with lactoferrin as probe; co-immunoprecipitation; immunofluorescence co-localization; PP2A phosphatase activity assay; caspase-3/APAF-1 expression analysis","journal":"Anticancer research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and phosphatase activity assay confirming IGBP1-PP2Ac interaction and functional consequence, single lab with multiple complementary methods","pmids":["21378334"],"is_preprint":false},{"year":2017,"finding":"MiR-3941 (and miR-34b) suppress IGBP1 expression by directly targeting the 3′-UTR of IGBP1 mRNA. Transfection of either miRNA into lung adenocarcinoma cell lines suppresses IGBP1 protein expression, reduces cell proliferation, and induces apoptosis comparable to siIGBP1.","method":"MiRNA array; in silico TargetScan analysis; 3′-UTR luciferase reporter assay; miRNA transfection with IGBP1 protein/mRNA quantification; proliferation and apoptosis assays","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase reporter validation of direct 3′-UTR targeting plus functional rescue phenotype, single lab","pmids":["28012229"],"is_preprint":false},{"year":2018,"finding":"Alpha4 (IGBP1) controls intestinal epithelial homeostasis by stabilizing the RNA-binding protein HuR. Alpha4 silencing leads to IκB kinase α-mediated phosphorylation of HuR, triggering ubiquitin-mediated HuR proteolysis, which in turn reduces intercellular junction proteins and disrupts epithelial barrier function. Ectopic HuR expression in alpha4-deficient cells rescues junction proteins and barrier function.","method":"Intestinal epithelial cell-specific alpha4 conditional KO mice; siRNA knockdown in cultured IECs; HuR overexpression rescue; IκBKα phosphorylation assays; barrier function assays; immunofluorescence of junction proteins","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo KO phenotype plus in vitro mechanistic dissection with epistasis (HuR rescue and IκBKα pathway), multiple orthogonal methods","pmids":["29555726"],"is_preprint":false},{"year":2022,"finding":"IGBP1 mediates a 'PP2A switch' in GqPCR signaling: in resting cells, an IGBP1-PP2Ac dimer binds PI3K and dephosphorylates inhibitory pSer608-p85, maintaining high PI3K/AKT activity. Upon GqPCR activation, the IGBP1-PP2Ac dimer detaches from PI3K and instead associates with AKT together with PP2Aa, causing AKT dephosphorylation and inactivation that leads to JNK-dependent apoptosis.","method":"Co-immunoprecipitation of IGBP1-PP2Ac-PI3K and IGBP1-PP2Ac-AKT complexes; proximity ligation assay; kinase/phosphatase activity assays; TUNEL and PARP1 cleavage for apoptosis; phospho-specific antibodies for pSer608-p85 and pAKT","journal":"Cell communication and signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, proximity ligation assay, enzymatic activity measurements, and apoptosis readouts in a single study using multiple orthogonal methods","pmids":["34998390"],"is_preprint":false},{"year":2022,"finding":"Alpha4 (IGBP1) maintains insulin signaling in adipocytes by associating with Y-box protein 1 (YBX1), which suppresses PTP1B expression. Loss of alpha4 in adipocytes reduces α4-YBX1 association, elevates PTP1B, reduces insulin receptor tyrosine phosphorylation, and decreases PP2A levels, resulting in impaired Akt-mediated signaling, defective adipogenesis, altered mitochondrial oxidation, and systemic insulin resistance.","method":"Adipocyte-specific alpha4 knockout mice; co-immunoprecipitation of alpha4 with YBX1; PTP1B expression analysis; insulin receptor phosphorylation assays; metabolic phenotyping including thermogenesis and hepatosteatosis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean cell-type-specific KO with defined molecular mechanism (alpha4-YBX1-PTP1B axis), Co-IP, phosphorylation assays, and comprehensive metabolic phenotyping","pmids":["36241662"],"is_preprint":false}],"current_model":"IGBP1 (alpha4) is a multifunctional noncatalytic regulatory protein that binds the PP2A catalytic subunit (PP2Ac) via its N-terminal TPR-like domain and protects PP2Ac from polyubiquitination and degradation by acting as an adaptor between PP2Ac and the E3 ligase Mid1 through a C-terminal domain, while a ubiquitin-interacting motif in its N-terminal region further suppresses PP2Ac polyubiquitination; it participates in a stimulus-regulated 'PP2A switch' (e.g., downstream of GqPCRs) in which an IGBP1-PP2Ac dimer shifts association from PI3K to AKT, causing AKT dephosphorylation and apoptosis; it is required for cell viability by repressing transcription-initiated apoptosis via c-Jun and p53 dephosphorylation, promotes cell spreading and migration through Rac1 activation, sustains mTOR-dependent translation initiation in erythroblasts via a positive feedback loop, stabilizes HuR in intestinal epithelial cells to maintain barrier function, maintains insulin signaling in adipocytes through a YBX1-mediated suppression of PTP1B, and is required for early T cell development by supporting thymocyte proliferation."},"narrative":{"mechanistic_narrative":"IGBP1 (alpha4) is a noncatalytic regulatory partner of the PP2A catalytic subunit (PP2Ac) that governs PP2Ac stability and directs its phosphatase activity toward distinct substrates to control cell survival, proliferation, signaling, and tissue homeostasis [PMID:15499020, PMID:34998390]. Structurally it is an elongated protein whose stable, predominantly α-helical N-terminal TPR-like domain binds PP2Ac and contains an embedded ubiquitin-interacting motif (residues 46–60), while its less-structured C-terminal region engages E3 ligases [PMID:21454489, PMID:16517231]. Through the UIM and a C-terminal Mid1-binding domain, IGBP1 acts as an adaptor that bridges PP2Ac to the E3 ligase Mid1 and suppresses PP2Ac polyubiquitination, protecting it from degradation; both the N- and C-terminal domains are required for this protection [PMID:20092282, PMID:21454489]. By repressing PP2A-mediated dephosphorylation of c-Jun and p53, IGBP1 prevents transcription-initiated apoptosis and is required for cell viability [PMID:15499020]. It directs PP2A-dependent signaling outputs in multiple contexts: it activates Rac1 to promote cell spreading and migration [PMID:17693407], operates a GqPCR-triggered 'PP2A switch' in which an IGBP1–PP2Ac dimer shifts from PI3K to AKT to drive AKT dephosphorylation and JNK-dependent apoptosis [PMID:34998390], sustains mTOR-dependent translation initiation through a positive feedback loop in erythroblasts [PMID:18625885], maintains insulin signaling in adipocytes via a YBX1–PTP1B axis [PMID:36241662], and stabilizes the RNA-binding protein HuR to preserve intestinal epithelial barrier function [PMID:29555726]. IGBP1 is required for early T cell development by supporting thymocyte proliferation [PMID:12811850], and is elevated in human cancers where it promotes proliferation and transformation and is suppressed by miR-34b and miR-3941 [PMID:21339737, PMID:28012229].","teleology":[{"year":1997,"claim":"Establishing the gene's identity and pathway context: human alpha4/IGBP1 was cloned and recognized as a TAP42-related protein, placing it in a rapamycin-sensitive signaling pathway before its mechanism was known.","evidence":"Genomic cloning, Northern blot, antibody detection, and TAP42 sequence alignment","pmids":["9441740"],"confidence":"Medium","gaps":["Homology to TAP42 inferred function but provided no direct biochemical activity","No PP2Ac interaction demonstrated in this study"]},{"year":2003,"claim":"Defined the first in vivo requirement: T cell-specific deletion showed IGBP1 is needed for thymocyte proliferation and developmental progression, not for suppressing apoptosis in this lineage.","evidence":"Cre/loxP T cell-specific knockout mice with developmental-stage flow cytometry and proliferation/apoptosis assays","pmids":["12811850"],"confidence":"High","gaps":["Molecular link between IGBP1 and proliferative signaling in thymocytes not resolved","PP2A involvement in this phenotype not directly tested"]},{"year":2004,"claim":"Identified a core function in cell survival: IGBP1 loss unleashes PP2A-mediated dephosphorylation of c-Jun and p53, driving proapoptotic transcription and death, establishing IGBP1 as a repressor of transcription-initiated apoptosis.","evidence":"Conditional knockout in murine cells with Bcl-xL and translation-inhibitor rescue plus transcriptional profiling","pmids":["15499020"],"confidence":"High","gaps":["How IGBP1 restrains PP2Ac substrate access to c-Jun/p53 not structurally defined","Direct dephosphorylation events not biochemically reconstituted"]},{"year":2006,"claim":"Provided the first solution architecture: IGBP1 is elongated with a stable α-helical N-terminal domain and a less-structured, proteolysis-prone C-terminus, predicting a modular domain organization.","evidence":"SAXS, circular dichroism, and thermal unfolding of recombinant truncation mutants","pmids":["16517231"],"confidence":"Medium","gaps":["No mutagenesis linking domain features to function","Low-resolution envelope only, no atomic model"]},{"year":2007,"claim":"Connected IGBP1 to cytoskeletal dynamics: it promotes cell spreading and migration through Rac1 activation, broadening its role beyond survival.","evidence":"Knockout fibroblasts, overexpression, constitutively active Rac1 rescue, GTPase pull-down, and T cell transgenic chemotaxis","pmids":["17693407"],"confidence":"High","gaps":["Mechanism linking IGBP1/PP2A to Rac1 GTP loading not defined","GEF/GAP intermediary not identified"]},{"year":2008,"claim":"Embedded IGBP1 in a translation-regulatory feedback loop: its mRNA is selectively polysome-recruited downstream of PI3K, and constitutive expression sustains 4EBP/p70S6K phosphorylation, linking IGBP1 to mTOR-dependent translation initiation in erythroblasts.","evidence":"Polysome profiling with microarray, PI3K inhibition, eIF4E overexpression, and constitutive Igbp1 expression in erythroid differentiation","pmids":["18625885"],"confidence":"High","gaps":["Direct biochemical role of IGBP1 in initiation-complex assembly not shown","Feedback wiring inferred from gain-of-function"]},{"year":2009,"claim":"Placed IGBP1 in a regulatory complex with mTOR and STAT1: mTOR inactivation increases IGBP1 association and PP2Ac-dependent STAT1 nuclear accumulation, controlling STAT1-driven gene expression.","evidence":"Reciprocal Co-IP of mTOR-STAT1-IGBP1-PP2Ac complex, siRNA depletion, nuclear fractionation, and gene expression analysis","pmids":["19553685"],"confidence":"Medium","gaps":["Direct STAT1 dephosphorylation by the complex not demonstrated","Single lab, mechanism of mTOR-dependent recruitment unclear"]},{"year":2010,"claim":"Defined the ubiquitin-adaptor mechanism: a novel UIM (residues 46–60) lets IGBP1 bind ubiquitin and bridge PP2Ac to the E3 ligase Mid1, with the UIM suppressing PP2Ac polyubiquitination.","evidence":"NMR of IGBP1-ubiquitin interaction, Co-IP of IGBP1/PP2Ac/Mid1, and UIM-deletion ubiquitination assays","pmids":["20092282"],"confidence":"High","gaps":["How UIM occupancy blocks ubiquitin chain extension mechanistically unresolved","In vivo physiological consequence of UIM loss not tested in animals"]},{"year":2010,"claim":"Expanded the C-terminal interactome: IGBP1 binds EDD E3 ligase (independent of the PP2Ac site) and PABP, implicating it in translation-initiation steps downstream of mTOR.","evidence":"Yeast two-hybrid screen, Co-IP in multiple cell lines, and deletion-mutant domain mapping","pmids":["20544796"],"confidence":"Medium","gaps":["Functional consequence of EDD and PABP binding not established","No demonstration that these interactions affect specific mRNA translation"]},{"year":2011,"claim":"Resolved the structural basis of PP2Ac protection: a crystallized TPR-like N-terminal domain with an open PP2Ac-binding helix and embedded UIM, plus the C-terminal Mid1-binding domain, are both required to shield PP2Ac from degradation.","evidence":"X-ray crystallography, DEER spectroscopy, cycloheximide chase, tandem ubiquitin-binding precipitation, and mutagenesis","pmids":["21454489"],"confidence":"High","gaps":["Full-length IGBP1-PP2Ac-Mid1 complex structure not determined","Conformational switching between protection and degradation not captured"]},{"year":2011,"claim":"Linked IGBP1 to oncogenic transformation and its regulation: elevated IGBP1 lowers PP2A activity, promotes proliferation/survival and tumor formation, and is repressed by miR-34b targeting its 3'-UTR.","evidence":"Overexpression xenografts, siRNA knockdown, PP2A activity assays, and miR-34b luciferase reporter validation","pmids":["21339737"],"confidence":"High","gaps":["How elevated IGBP1 selectively reduces PP2A activity not mechanistically dissected","Driver vs passenger status in primary tumors not established"]},{"year":2011,"claim":"Identified a ligand that converts IGBP1 to a proapoptotic node: lactoferrin binding to IGBP1 reduces PP2A activity and triggers apoptosis in lung adenocarcinoma cells.","evidence":"Protein microarray, Co-IP, immunofluorescence, PP2A activity assay, and caspase-3/APAF-1 analysis","pmids":["21378334"],"confidence":"Medium","gaps":["Single cell line and single lab","Structural basis of lactoferrin-IGBP1 binding and its effect on PP2Ac not defined"]},{"year":2017,"claim":"Extended miRNA control: miR-3941 and miR-34b directly target the IGBP1 3'-UTR to suppress its expression and induce apoptosis, reinforcing IGBP1 as a survival factor in lung adenocarcinoma.","evidence":"miRNA array, TargetScan prediction, 3'-UTR luciferase reporter, and miRNA transfection with proliferation/apoptosis readouts","pmids":["28012229"],"confidence":"Medium","gaps":["In vivo relevance of these miRNA-IGBP1 axes not tested","Downstream survival effectors not identified in this study"]},{"year":2018,"claim":"Revealed a non-PP2A-centric output in epithelium: IGBP1 stabilizes the RNA-binding protein HuR by preventing IKKα-mediated phosphorylation and degradation, maintaining junction proteins and intestinal barrier function.","evidence":"Intestinal epithelial cell-specific knockout mice, siRNA, HuR overexpression rescue, IKKα phosphorylation and barrier assays","pmids":["29555726"],"confidence":"High","gaps":["How IGBP1 restrains IKKα-mediated HuR phosphorylation mechanistically unclear","Whether PP2A activity is involved in HuR stabilization not resolved"]},{"year":2022,"claim":"Defined a stimulus-regulated 'PP2A switch': an IGBP1-PP2Ac dimer dephosphorylates inhibitory pSer608-p85 to sustain PI3K/AKT activity in resting cells, then upon GqPCR activation shifts to AKT to drive its dephosphorylation and JNK-dependent apoptosis.","evidence":"Reciprocal Co-IP, proximity ligation, kinase/phosphatase activity assays, and TUNEL/PARP1 apoptosis readouts","pmids":["34998390"],"confidence":"High","gaps":["Signal that triggers the IGBP1-PP2Ac relocation from PI3K to AKT not identified","Generality across receptor types not established"]},{"year":2022,"claim":"Established a metabolic role: IGBP1 maintains adipocyte insulin signaling by associating with YBX1 to suppress PTP1B, sustaining insulin receptor phosphorylation, adipogenesis, and systemic insulin sensitivity.","evidence":"Adipocyte-specific knockout mice, Co-IP of IGBP1-YBX1, PTP1B and insulin receptor phosphorylation analysis, and metabolic phenotyping","pmids":["36241662"],"confidence":"High","gaps":["Mechanism by which IGBP1-YBX1 represses PTP1B expression not defined","Relative contributions of PP2A stabilization vs YBX1 axis not separated"]},{"year":null,"claim":"How IGBP1 dictates PP2Ac substrate selectivity and orchestrates its switching between distinct effector complexes (PI3K, AKT, mTOR-STAT1, c-Jun/p53) across tissues remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No unified model of how one IGBP1-PP2Ac dimer selects context-specific substrates","Upstream signals controlling complex reassignment largely undefined","No full-length structural model of IGBP1 in any effector complex"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,2]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,14]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[1,2,13]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[14]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[14,15]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[0,14]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[1,2]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[4,13]}],"complexes":["IGBP1-PP2Ac dimer","mTOR-STAT1-IGBP1-PP2Ac complex"],"partners":["PP2AC","MID1","AKT","PIK3R1","STAT1","EDD","PABP","YBX1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P78318","full_name":"Immunoglobulin-binding protein 1","aliases":["B-cell signal transduction molecule alpha 4","Protein alpha-4","CD79a-binding protein 1","Protein phosphatase 2/4/6 regulatory subunit","Renal carcinoma antigen NY-REN-16"],"length_aa":339,"mass_kda":39.2,"function":"Associated to surface IgM-receptor; may be involved in signal transduction. Involved in regulation of the catalytic activity of the phosphatases PP2A, PP4 and PP6 by protecting their partially folded catalytic subunits from degradative polyubiquitination until they associate with regulatory subunits","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/P78318/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/IGBP1","classification":"Common Essential","n_dependent_lines":1183,"n_total_lines":1208,"dependency_fraction":0.9793046357615894},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CCT2","stoichiometry":0.2},{"gene":"CCT4","stoichiometry":0.2},{"gene":"CCT6A","stoichiometry":0.2},{"gene":"PPP2CA","stoichiometry":0.2},{"gene":"PPP2CB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/IGBP1","total_profiled":1310},"omim":[{"mim_id":"611807","title":"TIP41-LIKE PROTEIN; TIPRL","url":"https://www.omim.org/entry/611807"},{"mim_id":"300552","title":"MIDLINE 1; MID1","url":"https://www.omim.org/entry/300552"},{"mim_id":"300472","title":"CORPUS CALLOSUM, AGENESIS OF, WITH IMPAIRED INTELLECTUAL DEVELOPMENT, OCULAR COLOBOMA, AND MICROGNATHIA","url":"https://www.omim.org/entry/300472"},{"mim_id":"300139","title":"IMMUNOGLOBULIN-BINDING PROTEIN 1; IGBP1","url":"https://www.omim.org/entry/300139"},{"mim_id":"300000","title":"OPITZ GBBB SYNDROME; GBBB","url":"https://www.omim.org/entry/300000"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Microtubules","reliability":"Approved"},{"location":"Primary cilium","reliability":"Approved"},{"location":"Cytokinetic bridge","reliability":"Additional"},{"location":"Basal body","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/IGBP1"},"hgnc":{"alias_symbol":["α4"],"prev_symbol":["IBP1"]},"alphafold":{"accession":"P78318","domains":[{"cath_id":"1.25.40.540","chopping":"13-129_160-226","consensus_level":"high","plddt":93.829,"start":13,"end":226}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P78318","model_url":"https://alphafold.ebi.ac.uk/files/AF-P78318-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P78318-F1-predicted_aligned_error_v6.png","plddt_mean":81.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=IGBP1","jax_strain_url":"https://www.jax.org/strain/search?query=IGBP1"},"sequence":{"accession":"P78318","fasta_url":"https://rest.uniprot.org/uniprotkb/P78318.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P78318/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P78318"}},"corpus_meta":[{"pmid":"9582073","id":"PMC_9582073","title":"GABA(A) receptor alpha4 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receptors.","date":"2011","source":"Neuropharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/21640733","citation_count":17,"is_preprint":false},{"pmid":"16819276","id":"PMC_16819276","title":"The role of the alpha4 integrin-paxillin interaction in regulating leukocyte trafficking.","date":"2006","source":"Experimental & molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/16819276","citation_count":17,"is_preprint":false},{"pmid":"21880631","id":"PMC_21880631","title":"SWAP-70 regulates erythropoiesis by controlling α4 integrin.","date":"2011","source":"Haematologica","url":"https://pubmed.ncbi.nlm.nih.gov/21880631","citation_count":16,"is_preprint":false},{"pmid":"19655168","id":"PMC_19655168","title":"Aberrant DNA methylation of integrin alpha4: a potential novel role for metastasis of cholangiocarcinoma.","date":"2009","source":"Journal of cancer research and clinical oncology","url":"https://pubmed.ncbi.nlm.nih.gov/19655168","citation_count":16,"is_preprint":false},{"pmid":"26857960","id":"PMC_26857960","title":"Ethanol Regulation of Synaptic GABAA α4 Receptors Is Prevented by Protein Kinase A Activation.","date":"2016","source":"The Journal of pharmacology and experimental therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/26857960","citation_count":16,"is_preprint":false},{"pmid":"34998390","id":"PMC_34998390","title":"GqPCR-stimulated dephosphorylation of AKT is induced by an IGBP1-mediated PP2A switch.","date":"2022","source":"Cell communication and signaling : CCS","url":"https://pubmed.ncbi.nlm.nih.gov/34998390","citation_count":15,"is_preprint":false},{"pmid":"32934887","id":"PMC_32934887","title":"SOD3 boosts T cell infiltration by normalizing the tumor endothelium and inducing laminin-α4.","date":"2020","source":"Oncoimmunology","url":"https://pubmed.ncbi.nlm.nih.gov/32934887","citation_count":15,"is_preprint":false},{"pmid":"16517231","id":"PMC_16517231","title":"Low resolution structure of the human alpha4 protein (IgBP1) and studies on the stability of alpha4 and of its yeast ortholog Tap42.","date":"2006","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/16517231","citation_count":15,"is_preprint":false},{"pmid":"12811850","id":"PMC_12811850","title":"T cell-specific gene targeting reveals that alpha4 is required for early T cell development.","date":"2003","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/12811850","citation_count":15,"is_preprint":false},{"pmid":"36241662","id":"PMC_36241662","title":"Phosphatase protector alpha4 (α4) is involved in adipocyte maintenance and mitochondrial homeostasis through regulation of insulin signaling.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/36241662","citation_count":15,"is_preprint":false},{"pmid":"15864437","id":"PMC_15864437","title":"Biochemical characterization of Silene alba alpha4-fucosyltransferase and Lewis a products.","date":"2005","source":"Glycoconjugate journal","url":"https://pubmed.ncbi.nlm.nih.gov/15864437","citation_count":15,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":50925,"output_tokens":4680,"usd":0.111488,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12855,"output_tokens":5453,"usd":0.1003,"stage2_stop_reason":"end_turn"},"total_usd":0.211788,"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\": 2004,\n      \"finding\": \"Alpha4 (IGBP1), a noncatalytic subunit of PP2A, is required to repress apoptosis in murine cells. Alpha4 deletion leads to increased dephosphorylation of transcription factors c-Jun and p53, transcription of multiple proapoptotic genes, and cell death that is suppressible by blocking protein synthesis or overexpressing Bcl-xL.\",\n      \"method\": \"Conditional gene deletion (alpha4 knockout) in murine cells, epistasis with Bcl-xL overexpression and translation inhibitors, transcriptional profiling\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined cellular phenotype, multiple orthogonal approaches (genetic rescue, pharmacological rescue, transcriptional readout) in a single rigorous study\",\n      \"pmids\": [\"15499020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Alpha4 (IGBP1) contains a novel ubiquitin-interacting motif (UIM, residues 46–60) that allows alpha4 to bind ubiquitin and act as an adaptor bridging PP2Ac and the E3 ubiquitin ligase Mid1. The UIM within alpha4 suppresses polyubiquitination of PP2Ac; deletion of the UIM enhances PP2Ac polyubiquitination.\",\n      \"method\": \"NMR analysis of alpha4–ubiquitin interaction; co-immunoprecipitation of alpha4, PP2Ac, and Mid1; UIM deletion mutants with ubiquitination assays\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structural validation of UIM-ubiquitin interaction plus mutagenesis and co-IP in mammalian cells, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"20092282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Both the C-terminal Mid1-binding domain and the N-terminal PP2Ac-binding domain of Alpha4 are required for Alpha4-mediated protection of PP2Ac from polyubiquitination and degradation. X-ray crystallography of the N-terminal domain showed a flexible TPR-like fold with a PP2Ac-binding helix in a more open conformation than yeast Tap42, and an embedded UIM.\",\n      \"method\": \"X-ray crystallography of Alpha4 N-terminal domain; double electron-electron resonance (DEER) spectroscopy; cycloheximide chase assays; tandem ubiquitin-binding entity precipitations; site-directed mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with mutagenesis and functional ubiquitination assays in mammalian cells, multiple orthogonal methods in one study\",\n      \"pmids\": [\"21454489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Alpha4 (IGBP1) promotes cell spreading and migration through activation of Rac1 GTPase. Fibroblasts lacking alpha4 show reduced Rac1-GTP levels and impaired spreading/migration; constitutively active Rac1 rescues the alpha4-null defects; inhibition of Rac1 blocks alpha4-promoted migration. T cell-specific alpha4 transgenic mice display increased lymphocyte motility and chemotaxis.\",\n      \"method\": \"Alpha4 conditional knockout fibroblasts; alpha4 overexpression; constitutively active Rac1 rescue; Rac1 GTPase pull-down assays; T cell-specific transgenic mice with chemotaxis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal KO and OE with defined phenotypic readouts, epistasis with Rac1 mutants, replicated in two cell types\",\n      \"pmids\": [\"17693407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Igbp1 (alpha4) mRNA is selectively recruited to polysomes downstream of SCF-induced PI3K activation in erythroblasts. Constitutive Igbp1 expression impairs erythroid differentiation, sustains 4EBP and p70S6k phosphorylation, and enhances polysome recruitment of multiple eIF4E-sensitive mRNAs, establishing a positive feedback loop on translation initiation that maintains PP2A/mTOR signaling.\",\n      \"method\": \"Polysome fractionation with microarray comparison; PI3K inhibitor treatments; eIF4E overexpression; retroviral constitutive Igbp1 expression with erythroid differentiation assays and phosphorylation analysis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal approaches (polysome profiling, pharmacological inhibition, gain-of-function with defined signaling and differentiation readouts), single lab\",\n      \"pmids\": [\"18625885\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Alpha4 (IGBP1), together with PP2Ac, forms a macromolecular complex with mTOR and STAT1. Inactivation of mTOR enhances alpha4 association with the complex and increases STAT1 nuclear content in a PP2Ac-dependent manner. Depletion of alpha4 enhances STAT1-dependent gene expression (IRF-1, caspase-1, hiNOS, Fas), independently of p70 S6K and Akt.\",\n      \"method\": \"Co-immunoprecipitation of mTOR-STAT1-alpha4-PP2Ac complex; siRNA depletion of alpha4, PP2A, or mTOR; nuclear fractionation; gene expression analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP of complex plus siRNA knockdown with defined transcriptional readouts, single lab\",\n      \"pmids\": [\"19553685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Alpha4 (IGBP1) interacts physically with EDD E3 ubiquitin ligase (at its C-terminal region, independent of the PP2Ac-binding site) and with poly(A)-binding protein (PABP) in multiple cell lines, suggesting involvement in translation initiation steps downstream of mTOR.\",\n      \"method\": \"Yeast two-hybrid screening; co-immunoprecipitation of alpha4 with EDD and PABP; alpha4 deletion mutant mapping of EDD-binding site\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — yeast two-hybrid and Co-IP in multiple cell lines, deletion mutant domain mapping, single lab\",\n      \"pmids\": [\"20544796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"T cell-specific deletion of alpha4 (IGBP1) severely arrests T cell development at the CD4/CD8 double-negative 3 stage due to decreased cell proliferation (not increased apoptosis). Alpha4-deficient thymocytes show impaired proliferative responses to anti-CD3 stimulation, IL-2, IL-1, and TNF, and severely reduced CD3-induced CD25 expression.\",\n      \"method\": \"Cre/loxP T cell-specific gene deletion (Lck-alpha4– mice); flow cytometry analysis of T cell subsets; proliferation assays; apoptosis assays\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean cell-type-specific KO with precise developmental-stage phenotyping and multiple functional readouts\",\n      \"pmids\": [\"12811850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Human alpha4 (IGBP1) gene is located at Xq13.1–q13.3, is expressed ubiquitously as a 1.4-kb mRNA in immune and other tissues, and encodes a 45-kDa protein structurally related to yeast TAP42, a component of the rapamycin-sensitive signaling pathway.\",\n      \"method\": \"Genomic cloning; Northern blotting; anti-human alpha4 antibody detection of ~45-kDa protein; sequence alignment with TAP42\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct chromosomal mapping, protein detection by antibody, sequence homology establishing pathway membership; single lab\",\n      \"pmids\": [\"9441740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Human alpha4 (IgBP1) and yeast Tap42 adopt elongated shapes in solution (Rg ~41–43 Å, Dmax ~142–147 Å) as determined by small-angle X-ray scattering. The N-terminal domain alone (deletion mutants alpha4Δ222 and alpha4Δ236) is globular, highly stable, and predominantly α-helical, while the C-terminal region is less structured and more susceptible to proteolysis.\",\n      \"method\": \"Small-angle X-ray scattering (SAXS); circular dichroism; thermal unfolding kinetics; recombinant truncation mutants expressed in E. coli\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — SAXS low-resolution structure with complementary CD and stability assays; single lab, no mutagenesis-function link\",\n      \"pmids\": [\"16517231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Alpha4 (IGBP1) is highly expressed in carcinogen-transformed human cells and primary human cancers. Elevated alpha4 increases cell proliferation, promotes survival, decreases PP2A-attributable phosphatase activity, and enables non-transformed cells to form tumors in immunodeficient mice. MiR-34b suppresses alpha4 expression by targeting its 3′-UTR.\",\n      \"method\": \"Alpha4 overexpression in HEK293/L02R cells with xenograft tumor formation; siRNA knockdown; PP2A activity assay; luciferase reporter for miR-34b target validation\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gain-of-function xenograft, loss-of-function knockdown, direct PP2A activity measurement, miRNA mechanistic validation; multiple orthogonal methods\",\n      \"pmids\": [\"21339737\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Binding of lactoferrin to IGBP1 reduces PP2A catalytic activity and triggers apoptosis in PC-14 lung adenocarcinoma cells. The lactoferrin-IGBP1 complex was confirmed by protein microarray screening, co-immunoprecipitation, and immunofluorescence.\",\n      \"method\": \"Protein microarray with lactoferrin as probe; co-immunoprecipitation; immunofluorescence co-localization; PP2A phosphatase activity assay; caspase-3/APAF-1 expression analysis\",\n      \"journal\": \"Anticancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and phosphatase activity assay confirming IGBP1-PP2Ac interaction and functional consequence, single lab with multiple complementary methods\",\n      \"pmids\": [\"21378334\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"MiR-3941 (and miR-34b) suppress IGBP1 expression by directly targeting the 3′-UTR of IGBP1 mRNA. Transfection of either miRNA into lung adenocarcinoma cell lines suppresses IGBP1 protein expression, reduces cell proliferation, and induces apoptosis comparable to siIGBP1.\",\n      \"method\": \"MiRNA array; in silico TargetScan analysis; 3′-UTR luciferase reporter assay; miRNA transfection with IGBP1 protein/mRNA quantification; proliferation and apoptosis assays\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase reporter validation of direct 3′-UTR targeting plus functional rescue phenotype, single lab\",\n      \"pmids\": [\"28012229\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Alpha4 (IGBP1) controls intestinal epithelial homeostasis by stabilizing the RNA-binding protein HuR. Alpha4 silencing leads to IκB kinase α-mediated phosphorylation of HuR, triggering ubiquitin-mediated HuR proteolysis, which in turn reduces intercellular junction proteins and disrupts epithelial barrier function. Ectopic HuR expression in alpha4-deficient cells rescues junction proteins and barrier function.\",\n      \"method\": \"Intestinal epithelial cell-specific alpha4 conditional KO mice; siRNA knockdown in cultured IECs; HuR overexpression rescue; IκBKα phosphorylation assays; barrier function assays; immunofluorescence of junction proteins\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo KO phenotype plus in vitro mechanistic dissection with epistasis (HuR rescue and IκBKα pathway), multiple orthogonal methods\",\n      \"pmids\": [\"29555726\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"IGBP1 mediates a 'PP2A switch' in GqPCR signaling: in resting cells, an IGBP1-PP2Ac dimer binds PI3K and dephosphorylates inhibitory pSer608-p85, maintaining high PI3K/AKT activity. Upon GqPCR activation, the IGBP1-PP2Ac dimer detaches from PI3K and instead associates with AKT together with PP2Aa, causing AKT dephosphorylation and inactivation that leads to JNK-dependent apoptosis.\",\n      \"method\": \"Co-immunoprecipitation of IGBP1-PP2Ac-PI3K and IGBP1-PP2Ac-AKT complexes; proximity ligation assay; kinase/phosphatase activity assays; TUNEL and PARP1 cleavage for apoptosis; phospho-specific antibodies for pSer608-p85 and pAKT\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, proximity ligation assay, enzymatic activity measurements, and apoptosis readouts in a single study using multiple orthogonal methods\",\n      \"pmids\": [\"34998390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Alpha4 (IGBP1) maintains insulin signaling in adipocytes by associating with Y-box protein 1 (YBX1), which suppresses PTP1B expression. Loss of alpha4 in adipocytes reduces α4-YBX1 association, elevates PTP1B, reduces insulin receptor tyrosine phosphorylation, and decreases PP2A levels, resulting in impaired Akt-mediated signaling, defective adipogenesis, altered mitochondrial oxidation, and systemic insulin resistance.\",\n      \"method\": \"Adipocyte-specific alpha4 knockout mice; co-immunoprecipitation of alpha4 with YBX1; PTP1B expression analysis; insulin receptor phosphorylation assays; metabolic phenotyping including thermogenesis and hepatosteatosis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean cell-type-specific KO with defined molecular mechanism (alpha4-YBX1-PTP1B axis), Co-IP, phosphorylation assays, and comprehensive metabolic phenotyping\",\n      \"pmids\": [\"36241662\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"IGBP1 (alpha4) is a multifunctional noncatalytic regulatory protein that binds the PP2A catalytic subunit (PP2Ac) via its N-terminal TPR-like domain and protects PP2Ac from polyubiquitination and degradation by acting as an adaptor between PP2Ac and the E3 ligase Mid1 through a C-terminal domain, while a ubiquitin-interacting motif in its N-terminal region further suppresses PP2Ac polyubiquitination; it participates in a stimulus-regulated 'PP2A switch' (e.g., downstream of GqPCRs) in which an IGBP1-PP2Ac dimer shifts association from PI3K to AKT, causing AKT dephosphorylation and apoptosis; it is required for cell viability by repressing transcription-initiated apoptosis via c-Jun and p53 dephosphorylation, promotes cell spreading and migration through Rac1 activation, sustains mTOR-dependent translation initiation in erythroblasts via a positive feedback loop, stabilizes HuR in intestinal epithelial cells to maintain barrier function, maintains insulin signaling in adipocytes through a YBX1-mediated suppression of PTP1B, and is required for early T cell development by supporting thymocyte proliferation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"IGBP1 (alpha4) is a noncatalytic regulatory partner of the PP2A catalytic subunit (PP2Ac) that governs PP2Ac stability and directs its phosphatase activity toward distinct substrates to control cell survival, proliferation, signaling, and tissue homeostasis [#0, #14]. Structurally it is an elongated protein whose stable, predominantly α-helical N-terminal TPR-like domain binds PP2Ac and contains an embedded ubiquitin-interacting motif (residues 46–60), while its less-structured C-terminal region engages E3 ligases [#2, #9]. Through the UIM and a C-terminal Mid1-binding domain, IGBP1 acts as an adaptor that bridges PP2Ac to the E3 ligase Mid1 and suppresses PP2Ac polyubiquitination, protecting it from degradation; both the N- and C-terminal domains are required for this protection [#1, #2]. By repressing PP2A-mediated dephosphorylation of c-Jun and p53, IGBP1 prevents transcription-initiated apoptosis and is required for cell viability [#0]. It directs PP2A-dependent signaling outputs in multiple contexts: it activates Rac1 to promote cell spreading and migration [#3], operates a GqPCR-triggered 'PP2A switch' in which an IGBP1–PP2Ac dimer shifts from PI3K to AKT to drive AKT dephosphorylation and JNK-dependent apoptosis [#14], sustains mTOR-dependent translation initiation through a positive feedback loop in erythroblasts [#4], maintains insulin signaling in adipocytes via a YBX1–PTP1B axis [#15], and stabilizes the RNA-binding protein HuR to preserve intestinal epithelial barrier function [#13]. IGBP1 is required for early T cell development by supporting thymocyte proliferation [#7], and is elevated in human cancers where it promotes proliferation and transformation and is suppressed by miR-34b and miR-3941 [#10, #12].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Establishing the gene's identity and pathway context: human alpha4/IGBP1 was cloned and recognized as a TAP42-related protein, placing it in a rapamycin-sensitive signaling pathway before its mechanism was known.\",\n      \"evidence\": \"Genomic cloning, Northern blot, antibody detection, and TAP42 sequence alignment\",\n      \"pmids\": [\"9441740\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Homology to TAP42 inferred function but provided no direct biochemical activity\", \"No PP2Ac interaction demonstrated in this study\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined the first in vivo requirement: T cell-specific deletion showed IGBP1 is needed for thymocyte proliferation and developmental progression, not for suppressing apoptosis in this lineage.\",\n      \"evidence\": \"Cre/loxP T cell-specific knockout mice with developmental-stage flow cytometry and proliferation/apoptosis assays\",\n      \"pmids\": [\"12811850\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link between IGBP1 and proliferative signaling in thymocytes not resolved\", \"PP2A involvement in this phenotype not directly tested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Identified a core function in cell survival: IGBP1 loss unleashes PP2A-mediated dephosphorylation of c-Jun and p53, driving proapoptotic transcription and death, establishing IGBP1 as a repressor of transcription-initiated apoptosis.\",\n      \"evidence\": \"Conditional knockout in murine cells with Bcl-xL and translation-inhibitor rescue plus transcriptional profiling\",\n      \"pmids\": [\"15499020\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How IGBP1 restrains PP2Ac substrate access to c-Jun/p53 not structurally defined\", \"Direct dephosphorylation events not biochemically reconstituted\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Provided the first solution architecture: IGBP1 is elongated with a stable α-helical N-terminal domain and a less-structured, proteolysis-prone C-terminus, predicting a modular domain organization.\",\n      \"evidence\": \"SAXS, circular dichroism, and thermal unfolding of recombinant truncation mutants\",\n      \"pmids\": [\"16517231\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mutagenesis linking domain features to function\", \"Low-resolution envelope only, no atomic model\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Connected IGBP1 to cytoskeletal dynamics: it promotes cell spreading and migration through Rac1 activation, broadening its role beyond survival.\",\n      \"evidence\": \"Knockout fibroblasts, overexpression, constitutively active Rac1 rescue, GTPase pull-down, and T cell transgenic chemotaxis\",\n      \"pmids\": [\"17693407\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking IGBP1/PP2A to Rac1 GTP loading not defined\", \"GEF/GAP intermediary not identified\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Embedded IGBP1 in a translation-regulatory feedback loop: its mRNA is selectively polysome-recruited downstream of PI3K, and constitutive expression sustains 4EBP/p70S6K phosphorylation, linking IGBP1 to mTOR-dependent translation initiation in erythroblasts.\",\n      \"evidence\": \"Polysome profiling with microarray, PI3K inhibition, eIF4E overexpression, and constitutive Igbp1 expression in erythroid differentiation\",\n      \"pmids\": [\"18625885\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct biochemical role of IGBP1 in initiation-complex assembly not shown\", \"Feedback wiring inferred from gain-of-function\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Placed IGBP1 in a regulatory complex with mTOR and STAT1: mTOR inactivation increases IGBP1 association and PP2Ac-dependent STAT1 nuclear accumulation, controlling STAT1-driven gene expression.\",\n      \"evidence\": \"Reciprocal Co-IP of mTOR-STAT1-IGBP1-PP2Ac complex, siRNA depletion, nuclear fractionation, and gene expression analysis\",\n      \"pmids\": [\"19553685\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct STAT1 dephosphorylation by the complex not demonstrated\", \"Single lab, mechanism of mTOR-dependent recruitment unclear\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the ubiquitin-adaptor mechanism: a novel UIM (residues 46–60) lets IGBP1 bind ubiquitin and bridge PP2Ac to the E3 ligase Mid1, with the UIM suppressing PP2Ac polyubiquitination.\",\n      \"evidence\": \"NMR of IGBP1-ubiquitin interaction, Co-IP of IGBP1/PP2Ac/Mid1, and UIM-deletion ubiquitination assays\",\n      \"pmids\": [\"20092282\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How UIM occupancy blocks ubiquitin chain extension mechanistically unresolved\", \"In vivo physiological consequence of UIM loss not tested in animals\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Expanded the C-terminal interactome: IGBP1 binds EDD E3 ligase (independent of the PP2Ac site) and PABP, implicating it in translation-initiation steps downstream of mTOR.\",\n      \"evidence\": \"Yeast two-hybrid screen, Co-IP in multiple cell lines, and deletion-mutant domain mapping\",\n      \"pmids\": [\"20544796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of EDD and PABP binding not established\", \"No demonstration that these interactions affect specific mRNA translation\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Resolved the structural basis of PP2Ac protection: a crystallized TPR-like N-terminal domain with an open PP2Ac-binding helix and embedded UIM, plus the C-terminal Mid1-binding domain, are both required to shield PP2Ac from degradation.\",\n      \"evidence\": \"X-ray crystallography, DEER spectroscopy, cycloheximide chase, tandem ubiquitin-binding precipitation, and mutagenesis\",\n      \"pmids\": [\"21454489\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length IGBP1-PP2Ac-Mid1 complex structure not determined\", \"Conformational switching between protection and degradation not captured\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Linked IGBP1 to oncogenic transformation and its regulation: elevated IGBP1 lowers PP2A activity, promotes proliferation/survival and tumor formation, and is repressed by miR-34b targeting its 3'-UTR.\",\n      \"evidence\": \"Overexpression xenografts, siRNA knockdown, PP2A activity assays, and miR-34b luciferase reporter validation\",\n      \"pmids\": [\"21339737\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How elevated IGBP1 selectively reduces PP2A activity not mechanistically dissected\", \"Driver vs passenger status in primary tumors not established\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified a ligand that converts IGBP1 to a proapoptotic node: lactoferrin binding to IGBP1 reduces PP2A activity and triggers apoptosis in lung adenocarcinoma cells.\",\n      \"evidence\": \"Protein microarray, Co-IP, immunofluorescence, PP2A activity assay, and caspase-3/APAF-1 analysis\",\n      \"pmids\": [\"21378334\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell line and single lab\", \"Structural basis of lactoferrin-IGBP1 binding and its effect on PP2Ac not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended miRNA control: miR-3941 and miR-34b directly target the IGBP1 3'-UTR to suppress its expression and induce apoptosis, reinforcing IGBP1 as a survival factor in lung adenocarcinoma.\",\n      \"evidence\": \"miRNA array, TargetScan prediction, 3'-UTR luciferase reporter, and miRNA transfection with proliferation/apoptosis readouts\",\n      \"pmids\": [\"28012229\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of these miRNA-IGBP1 axes not tested\", \"Downstream survival effectors not identified in this study\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Revealed a non-PP2A-centric output in epithelium: IGBP1 stabilizes the RNA-binding protein HuR by preventing IKKα-mediated phosphorylation and degradation, maintaining junction proteins and intestinal barrier function.\",\n      \"evidence\": \"Intestinal epithelial cell-specific knockout mice, siRNA, HuR overexpression rescue, IKKα phosphorylation and barrier assays\",\n      \"pmids\": [\"29555726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How IGBP1 restrains IKKα-mediated HuR phosphorylation mechanistically unclear\", \"Whether PP2A activity is involved in HuR stabilization not resolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a stimulus-regulated 'PP2A switch': an IGBP1-PP2Ac dimer dephosphorylates inhibitory pSer608-p85 to sustain PI3K/AKT activity in resting cells, then upon GqPCR activation shifts to AKT to drive its dephosphorylation and JNK-dependent apoptosis.\",\n      \"evidence\": \"Reciprocal Co-IP, proximity ligation, kinase/phosphatase activity assays, and TUNEL/PARP1 apoptosis readouts\",\n      \"pmids\": [\"34998390\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signal that triggers the IGBP1-PP2Ac relocation from PI3K to AKT not identified\", \"Generality across receptor types not established\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Established a metabolic role: IGBP1 maintains adipocyte insulin signaling by associating with YBX1 to suppress PTP1B, sustaining insulin receptor phosphorylation, adipogenesis, and systemic insulin sensitivity.\",\n      \"evidence\": \"Adipocyte-specific knockout mice, Co-IP of IGBP1-YBX1, PTP1B and insulin receptor phosphorylation analysis, and metabolic phenotyping\",\n      \"pmids\": [\"36241662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which IGBP1-YBX1 represses PTP1B expression not defined\", \"Relative contributions of PP2A stabilization vs YBX1 axis not separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How IGBP1 dictates PP2Ac substrate selectivity and orchestrates its switching between distinct effector complexes (PI3K, AKT, mTOR-STAT1, c-Jun/p53) across tissues remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No unified model of how one IGBP1-PP2Ac dimer selects context-specific substrates\", \"Upstream signals controlling complex reassignment largely undefined\", \"No full-length structural model of IGBP1 in any effector complex\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 14]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [1, 2, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [14]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [14, 15]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [0, 14]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [4, 13]}\n    ],\n    \"complexes\": [\n      \"IGBP1-PP2Ac dimer\",\n      \"mTOR-STAT1-IGBP1-PP2Ac complex\"\n    ],\n    \"partners\": [\n      \"PP2Ac\",\n      \"MID1\",\n      \"AKT\",\n      \"PIK3R1\",\n      \"STAT1\",\n      \"EDD\",\n      \"PABP\",\n      \"YBX1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}