{"gene":"ITFG2","run_date":"2026-04-28T18:06:54","timeline":{"discoveries":[{"year":2017,"finding":"ITFG2 is a component of the KICSTOR complex (together with KPTN, C12orf66, and SZT2) that localizes to lysosomes, recruits GATOR1 (but not GATOR2) to the lysosomal surface, and is required for amino acid or glucose deprivation to inhibit mTORC1; KICSTOR is necessary for GATOR1 to interact with its substrates the Rag GTPases and with GATOR2.","method":"Co-immunoprecipitation, lysosomal fractionation/localization, genetic knockout in cultured human cells and mouse tissues, epistasis with GATOR1/GATOR2/Rag GTPase components","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, fractionation, KO phenotype, pathway epistasis; replicated across multiple orthogonal methods in a highly-cited foundational study","pmids":["28199306"],"is_preprint":false},{"year":2022,"finding":"The KICSTOR complex (including ITFG2) serves as the docking platform through which SAMTOR (an S-adenosylmethionine sensor) communicates with GATOR1 to regulate mTORC1; SAM-induced conformational change in SAMTOR's helical domain modulates its interaction with the GATOR1-KICSTOR complex.","method":"Crystal structure of SAMTOR in apo and SAM-bound forms, in vitro binding/functional assays, mutagenesis","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with functional validation and mutagenesis; KICSTOR/ITFG2 role confirmed biochemically","pmids":["35776786"],"is_preprint":false},{"year":2013,"finding":"ITFG2 (Itfg2) is an intracellular protein (not surface-expressed) that plays a critical role in B cell differentiation: Itfg2-deficient mice retain B cells in the spleen, show reduced serum IgG, defective B cell migration in vitro, a shift from germinal center to extrafollicular B cell maturation, and failure of antigen-specific plasma cell homing to bone marrow; bone marrow transplantation confirmed hematopoietic cell-intrinsic activity.","method":"Itfg2 knockout mouse model, bone marrow transplantation, immunization with thymus-dependent antigen, in vitro migration assays, flow cytometry","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — clean KO with multiple defined cellular phenotypes, bone marrow transplant epistasis, replicated across multiple readouts","pmids":["23997217"],"is_preprint":false},{"year":2024,"finding":"ITFG2 forms a complex with NEDD4-2 and ATP5b (mitochondrial ATP synthase β-subunit), inhibiting the binding of NEDD4-2 to ATP5b and thereby reducing ubiquitination and degradation of ATP5b; this protects mitochondrial function (ATP production, ROS, membrane potential) in cardiomyocytes under hypoxia/ischemia.","method":"Co-immunoprecipitation, AAV9-mediated overexpression and shRNA knockdown in vivo (MI mouse model), primary cardiomyocyte hypoxia assays, ubiquitination assays","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and ubiquitination assays with in vivo validation; single lab, moderate orthogonal support","pmids":["38848780"],"is_preprint":false},{"year":2024,"finding":"ITFG2 binds NEDD4-2 and reduces its interaction with SERCA2a, preventing NEDD4-2-mediated ubiquitination and degradation of SERCA2a, thereby stabilizing calcium homeostasis in cardiomyocytes under ischemic conditions.","method":"Co-immunoprecipitation, AAV9 overexpression and knockdown in MI mouse model, primary cardiomyocyte hypoxia model, ubiquitination assay, echocardiography","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP, ubiquitination assay, in vivo functional readout; single lab","pmids":["39477020"],"is_preprint":false},{"year":2025,"finding":"ITFG2 inhibits NEDD4-2-mediated ubiquitination of Nav1.5 by reducing the binding affinity between NEDD4-2 and Nav1.5, thereby upregulating Nav1.5 protein levels and sodium current in ventricular cardiomyocytes after myocardial infarction, reducing susceptibility to ischemic ventricular arrhythmias.","method":"Co-immunoprecipitation, AAV9 overexpression and shRNA knockdown in MI mouse model, patch-clamp electrophysiology, ubiquitination assay in neonatal cardiomyocytes under hypoxia","journal":"European journal of pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP, patch-clamp, ubiquitination assay, in vivo phenotype; single lab","pmids":["39864577"],"is_preprint":false},{"year":2025,"finding":"Cryo-EM structural analysis revealed that within the KICSTOR complex, SZT2 forms a crescent-shaped scaffold that binds the ITFG2-KPTN heterodimer at its C terminus; FBXO2-mediated ubiquitination of KPTN (at K49, K67, K262, K265) disrupts the KPTN-ITFG2 and KPTN-SZT2 interactions, impairing KICSTOR's ability to recruit GATOR1 to the lysosomal surface.","method":"Cryo-electron microscopy, computational modeling, biochemical binding assays, co-immunoprecipitation, ubiquitination assay, mTORC1 signaling readouts","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structure plus biochemical validation and mutagenesis in a single rigorous study","pmids":["41198956","41401028"],"is_preprint":false},{"year":2021,"finding":"Loss of ITFG2 (identified in a genome-wide CRISPR/Cas9 knockout screen) results in sustained mTOR signaling under pharmacologic inhibition of PI3K-AKT, confirming ITFG2 as a negative regulator of mTORC1 in cancer cells; resistance could be reversed by mTOR inhibition.","method":"Whole genome CRISPR/Cas9 knockout screen, validated by individual gene knockout with mTOR signaling readouts","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — genome-wide CRISPR screen with individual validation; confirms mTORC1-negative regulator role in cancer context","pmids":["33685991"],"is_preprint":false}],"current_model":"ITFG2 is a core subunit of the KICSTOR complex (with KPTN, C12orf66, and SZT2) that localizes to lysosomes where it recruits GATOR1 to enable nutrient-sensing inhibition of mTORC1; outside of mTORC1 regulation, ITFG2 acts as an inhibitor of the E3 ubiquitin ligase NEDD4-2, protecting multiple substrates (ATP5b, SERCA2a, Nav1.5) from ubiquitin-mediated degradation in cardiomyocytes, and plays a cell-intrinsic role in B cell differentiation and migration."},"narrative":{"teleology":[{"year":2013,"claim":"The first in vivo function of ITFG2 was established: it is required cell-intrinsically for B cell differentiation, germinal center maturation, and plasma cell migration to bone marrow, resolving whether it acts as a surface receptor (it does not) or an intracellular regulator of immune cell fate.","evidence":"Itfg2 knockout mice, bone marrow transplantation, immunization, in vitro migration assays, flow cytometry","pmids":["23997217"],"confidence":"High","gaps":["Molecular mechanism by which ITFG2 controls B cell migration is unknown","Whether the B cell phenotype relates to mTORC1 signaling was not tested","No interacting partners identified in this context"]},{"year":2017,"claim":"ITFG2 was identified as a subunit of the KICSTOR complex that localizes to lysosomes and recruits GATOR1 to inhibit mTORC1 upon nutrient deprivation, establishing the mechanistic basis for how upstream nutrient signals reach GATOR1 and the Rag GTPases.","evidence":"Reciprocal co-immunoprecipitation, lysosomal fractionation, genetic knockout in human cells and mouse tissues, epistasis analysis with GATOR1/GATOR2/Rag components","pmids":["28199306"],"confidence":"High","gaps":["Structural organization of KICSTOR and the ITFG2-KPTN interface were not resolved","Whether ITFG2 has functions outside the KICSTOR-mTORC1 axis was unclear","Relationship between KICSTOR and the B cell phenotype of ITFG2 deficiency was not addressed"]},{"year":2021,"claim":"A genome-wide CRISPR screen independently confirmed ITFG2 as a negative regulator of mTORC1, showing that its loss confers resistance to PI3K-AKT inhibition by sustaining mTOR signaling in cancer cells.","evidence":"Whole-genome CRISPR/Cas9 knockout screen with individual gene knockout validation and mTOR signaling readouts in cancer cell lines","pmids":["33685991"],"confidence":"Medium","gaps":["Whether resistance operates solely through KICSTOR-GATOR1 or involves additional pathways was not dissected","Clinical relevance of ITFG2 loss in drug resistance remains correlative"]},{"year":2022,"claim":"The KICSTOR complex was shown to serve as the docking platform for SAMTOR, linking S-adenosylmethionine sensing to GATOR1-mediated mTORC1 inhibition and broadening the nutrient inputs that signal through ITFG2-containing KICSTOR.","evidence":"Crystal structures of SAMTOR in apo and SAM-bound states, in vitro binding assays, mutagenesis","pmids":["35776786"],"confidence":"High","gaps":["Which KICSTOR subunit directly contacts SAMTOR was not resolved","In vivo physiological relevance of SAM sensing through KICSTOR not tested"]},{"year":2024,"claim":"A distinct mTORC1-independent function was uncovered: ITFG2 binds NEDD4-2 and inhibits its ubiquitin ligase activity toward multiple cardiac substrates (ATP5b, SERCA2a), protecting mitochondrial function and calcium homeostasis in ischemic cardiomyocytes.","evidence":"Co-immunoprecipitation, ubiquitination assays, AAV9-mediated overexpression/knockdown in myocardial infarction mouse model, primary cardiomyocyte hypoxia assays","pmids":["38848780","39477020"],"confidence":"Medium","gaps":["All NEDD4-2 studies come from a single laboratory; independent replication is needed","Whether ITFG2 acts on NEDD4-2 as part of KICSTOR or independently is unknown","Structural basis for the ITFG2-NEDD4-2 interaction has not been determined"]},{"year":2025,"claim":"Cryo-EM resolved the architecture of KICSTOR, showing that the ITFG2-KPTN heterodimer binds the C-terminal region of the SZT2 scaffold, and revealed that FBXO2-mediated ubiquitination of KPTN disrupts both the KPTN-ITFG2 and KPTN-SZT2 interfaces, providing a regulatory mechanism for KICSTOR disassembly.","evidence":"Cryo-electron microscopy, computational modeling, co-immunoprecipitation, ubiquitination assays, mTORC1 signaling readouts","pmids":["41198956","41401028"],"confidence":"High","gaps":["High-resolution structure of ITFG2 itself within the complex is not fully resolved","Whether FBXO2-mediated disassembly occurs under physiological nutrient conditions is untested"]},{"year":2025,"claim":"ITFG2 inhibition of NEDD4-2 was extended to a third substrate, Nav1.5, stabilizing sodium channel expression and current density in post-infarction cardiomyocytes and reducing arrhythmia susceptibility.","evidence":"Co-immunoprecipitation, patch-clamp electrophysiology, ubiquitination assay, AAV9 overexpression/knockdown in MI mouse model","pmids":["39864577"],"confidence":"Medium","gaps":["All three NEDD4-2 substrate studies are from one group; independent confirmation lacking","Whether ITFG2 is a general NEDD4-2 inhibitor or substrate-selective is unresolved"]},{"year":null,"claim":"Key unresolved questions include: whether the B cell and cardiomyocyte functions of ITFG2 are mechanistically connected to KICSTOR-mTORC1 signaling or represent independent activities; the structural basis of ITFG2 interaction with NEDD4-2; and whether ITFG2 has additional NEDD4-2-independent roles outside the KICSTOR complex.","evidence":"","pmids":[],"confidence":"Low","gaps":["No study has tested whether ITFG2's immune and cardiac functions depend on KICSTOR or mTORC1","Structural basis for ITFG2-NEDD4-2 binding is unknown","Tissue-specific versus universal functions of ITFG2 have not been systematically mapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,4,5]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,6]}],"localization":[{"term_id":"GO:0005764","term_label":"lysosome","supporting_discovery_ids":[0,6]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,1,6,7]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[3,4,5]}],"complexes":["KICSTOR"],"partners":["KPTN","SZT2","C12ORF66","NEDD4L","SAMTOR"],"other_free_text":[]},"mechanistic_narrative":"ITFG2 functions as a lysosomal scaffold subunit and a cytoplasmic inhibitor of ubiquitin-mediated protein degradation. As a core component of the KICSTOR complex (with KPTN, C12orf66, and SZT2), ITFG2 forms a heterodimer with KPTN that docks onto the SZT2 crescent-shaped scaffold at lysosomes, where KICSTOR recruits the GATOR1 complex to enable nutrient-sensing (amino acid, glucose, S-adenosylmethionine) inhibition of mTORC1 via the Rag GTPases [PMID:28199306, PMID:35776786, PMID:41198956]. Independent of mTORC1, ITFG2 binds the E3 ubiquitin ligase NEDD4-2 and competitively inhibits its interaction with multiple substrates—ATP5b, SERCA2a, and Nav1.5—thereby protecting these proteins from ubiquitination and degradation in cardiomyocytes under ischemic stress [PMID:38848780, PMID:39477020, PMID:39864577]. ITFG2 also plays a cell-intrinsic role in B cell differentiation and migration, as Itfg2-deficient mice exhibit defective germinal center responses, impaired plasma cell homing to bone marrow, and reduced serum IgG [PMID:23997217]."},"prefetch_data":{"uniprot":{"accession":"Q969R8","full_name":"KICSTOR complex protein ITFG2","aliases":["Integrin-alpha FG-GAP repeat-containing protein 2"],"length_aa":447,"mass_kda":49.3,"function":"As part of the KICSTOR complex functions in the amino acid-sensing branch of the TORC1 signaling pathway. Recruits, in an amino acid-independent manner, the GATOR1 complex to the lysosomal membranes and allows its interaction with GATOR2 and the RAG GTPases. Functions upstream of the RAG GTPases and is required to negatively regulate mTORC1 signaling in absence of amino acids. In absence of the KICSTOR complex mTORC1 is constitutively localized to the lysosome and activated. The KICSTOR complex is also probably involved in the regulation of mTORC1 by glucose","subcellular_location":"Lysosome membrane","url":"https://www.uniprot.org/uniprotkb/Q969R8/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ITFG2","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ITFG2","total_profiled":1310},"omim":[{"mim_id":"617421","title":"INTEGRIN-ALPHA FG-GAP REPEAT-CONTAINING PROTEIN 2; ITFG2","url":"https://www.omim.org/entry/617421"},{"mim_id":"617420","title":"KICSTOR SUBUNIT 2; KICS2","url":"https://www.omim.org/entry/617420"},{"mim_id":"615620","title":"KAPTIN; KPTN","url":"https://www.omim.org/entry/615620"},{"mim_id":"615463","title":"SZT2 SUBUNIT OF KICSTOR COMPLEX; SZT2","url":"https://www.omim.org/entry/615463"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"},{"location":"Golgi apparatus","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ITFG2"},"hgnc":{"alias_symbol":["MDS028","KICS3"],"prev_symbol":["FGGAP1"]},"alphafold":{"accession":"Q969R8","domains":[{"cath_id":"2.130.10.10","chopping":"1-97_110-214_237-391","consensus_level":"high","plddt":92.0482,"start":1,"end":391},{"cath_id":"-","chopping":"394-425","consensus_level":"high","plddt":89.0428,"start":394,"end":425}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q969R8","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q969R8-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q969R8-F1-predicted_aligned_error_v6.png","plddt_mean":86.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ITFG2","jax_strain_url":"https://www.jax.org/strain/search?query=ITFG2"},"sequence":{"accession":"Q969R8","fasta_url":"https://rest.uniprot.org/uniprotkb/Q969R8.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q969R8/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q969R8"}},"corpus_meta":[{"pmid":"28199306","id":"PMC_28199306","title":"KICSTOR recruits GATOR1 to the lysosome and is necessary for nutrients to regulate mTORC1.","date":"2017","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/28199306","citation_count":267,"is_preprint":false},{"pmid":"33685991","id":"PMC_33685991","title":"Genomic Alterations in PIK3CA-Mutated Breast Cancer Result in mTORC1 Activation and Limit the Sensitivity to PI3Kα Inhibitors.","date":"2021","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/33685991","citation_count":32,"is_preprint":false},{"pmid":"35776786","id":"PMC_35776786","title":"Molecular mechanism of S-adenosylmethionine sensing by SAMTOR in mTORC1 signaling.","date":"2022","source":"Science advances","url":"https://pubmed.ncbi.nlm.nih.gov/35776786","citation_count":32,"is_preprint":false},{"pmid":"33083013","id":"PMC_33083013","title":"Genomic testing in 1019 individuals from 349 Pakistani families results in high diagnostic yield and clinical utility.","date":"2020","source":"NPJ genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33083013","citation_count":31,"is_preprint":false},{"pmid":"16734683","id":"PMC_16734683","title":"Radiation hybrid mapping of 18 positional and physiological candidate genes for arthrogryposis multiplex congenita on porcine chromosome 5.","date":"2006","source":"Animal genetics","url":"https://pubmed.ncbi.nlm.nih.gov/16734683","citation_count":15,"is_preprint":false},{"pmid":"23997217","id":"PMC_23997217","title":"Integrin-α FG-GAP repeat-containing protein 2 is critical for normal B cell differentiation and controls disease development in a lupus model.","date":"2013","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/23997217","citation_count":10,"is_preprint":false},{"pmid":"38848780","id":"PMC_38848780","title":"ITFG2, an immune-modulatory protein, targets ATP 5b to maintain mitochondrial function in myocardial infarction.","date":"2024","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/38848780","citation_count":4,"is_preprint":false},{"pmid":"38142287","id":"PMC_38142287","title":"Co-methylation analyses identify CpGs associated with lipid traits in Chinese discordant monozygotic twins.","date":"2024","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/38142287","citation_count":3,"is_preprint":false},{"pmid":"39864577","id":"PMC_39864577","title":"A New target of ischemic ventricular arrhythmias-ITFG2.","date":"2025","source":"European journal of pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/39864577","citation_count":1,"is_preprint":false},{"pmid":"39477020","id":"PMC_39477020","title":"ITFG2 as a NEDD4-2 inhibitor: Preserving calcium homeostasis to prevent myocardial ischemic injury.","date":"2024","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/39477020","citation_count":1,"is_preprint":false},{"pmid":"41401028","id":"PMC_41401028","title":"FBXO2-mediated KPTN ubiquitination promotes amino acid-dependent mTORC1 signaling and tumor growth.","date":"2025","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/41401028","citation_count":1,"is_preprint":false},{"pmid":"41198956","id":"PMC_41198956","title":"Architecture of the human KICSTOR and GATOR1-KICSTOR complexes.","date":"2025","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/41198956","citation_count":0,"is_preprint":false},{"pmid":"41041534","id":"PMC_41041534","title":"Genomic relationship between polycystic ovary syndrome and bipolar disorder.","date":"2025","source":"Research square","url":"https://pubmed.ncbi.nlm.nih.gov/41041534","citation_count":0,"is_preprint":false},{"pmid":"41158364","id":"PMC_41158364","title":"The potential of circITFG2 as a therapeutic target in lung squamous cell carcinoma.","date":"2025","source":"Journal of thoracic disease","url":"https://pubmed.ncbi.nlm.nih.gov/41158364","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8880,"output_tokens":2202,"usd":0.029835},"stage2":{"model":"claude-opus-4-6","input_tokens":5480,"output_tokens":2512,"usd":0.1353},"total_usd":0.165135,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"ITFG2 is a component of the KICSTOR complex (together with KPTN, C12orf66, and SZT2) that localizes to lysosomes, recruits GATOR1 (but not GATOR2) to the lysosomal surface, and is required for amino acid or glucose deprivation to inhibit mTORC1; KICSTOR is necessary for GATOR1 to interact with its substrates the Rag GTPases and with GATOR2.\",\n      \"method\": \"Co-immunoprecipitation, lysosomal fractionation/localization, genetic knockout in cultured human cells and mouse tissues, epistasis with GATOR1/GATOR2/Rag GTPase components\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, fractionation, KO phenotype, pathway epistasis; replicated across multiple orthogonal methods in a highly-cited foundational study\",\n      \"pmids\": [\"28199306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The KICSTOR complex (including ITFG2) serves as the docking platform through which SAMTOR (an S-adenosylmethionine sensor) communicates with GATOR1 to regulate mTORC1; SAM-induced conformational change in SAMTOR's helical domain modulates its interaction with the GATOR1-KICSTOR complex.\",\n      \"method\": \"Crystal structure of SAMTOR in apo and SAM-bound forms, in vitro binding/functional assays, mutagenesis\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with functional validation and mutagenesis; KICSTOR/ITFG2 role confirmed biochemically\",\n      \"pmids\": [\"35776786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"ITFG2 (Itfg2) is an intracellular protein (not surface-expressed) that plays a critical role in B cell differentiation: Itfg2-deficient mice retain B cells in the spleen, show reduced serum IgG, defective B cell migration in vitro, a shift from germinal center to extrafollicular B cell maturation, and failure of antigen-specific plasma cell homing to bone marrow; bone marrow transplantation confirmed hematopoietic cell-intrinsic activity.\",\n      \"method\": \"Itfg2 knockout mouse model, bone marrow transplantation, immunization with thymus-dependent antigen, in vitro migration assays, flow cytometry\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO with multiple defined cellular phenotypes, bone marrow transplant epistasis, replicated across multiple readouts\",\n      \"pmids\": [\"23997217\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ITFG2 forms a complex with NEDD4-2 and ATP5b (mitochondrial ATP synthase β-subunit), inhibiting the binding of NEDD4-2 to ATP5b and thereby reducing ubiquitination and degradation of ATP5b; this protects mitochondrial function (ATP production, ROS, membrane potential) in cardiomyocytes under hypoxia/ischemia.\",\n      \"method\": \"Co-immunoprecipitation, AAV9-mediated overexpression and shRNA knockdown in vivo (MI mouse model), primary cardiomyocyte hypoxia assays, ubiquitination assays\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and ubiquitination assays with in vivo validation; single lab, moderate orthogonal support\",\n      \"pmids\": [\"38848780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ITFG2 binds NEDD4-2 and reduces its interaction with SERCA2a, preventing NEDD4-2-mediated ubiquitination and degradation of SERCA2a, thereby stabilizing calcium homeostasis in cardiomyocytes under ischemic conditions.\",\n      \"method\": \"Co-immunoprecipitation, AAV9 overexpression and knockdown in MI mouse model, primary cardiomyocyte hypoxia model, ubiquitination assay, echocardiography\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP, ubiquitination assay, in vivo functional readout; single lab\",\n      \"pmids\": [\"39477020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ITFG2 inhibits NEDD4-2-mediated ubiquitination of Nav1.5 by reducing the binding affinity between NEDD4-2 and Nav1.5, thereby upregulating Nav1.5 protein levels and sodium current in ventricular cardiomyocytes after myocardial infarction, reducing susceptibility to ischemic ventricular arrhythmias.\",\n      \"method\": \"Co-immunoprecipitation, AAV9 overexpression and shRNA knockdown in MI mouse model, patch-clamp electrophysiology, ubiquitination assay in neonatal cardiomyocytes under hypoxia\",\n      \"journal\": \"European journal of pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP, patch-clamp, ubiquitination assay, in vivo phenotype; single lab\",\n      \"pmids\": [\"39864577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Cryo-EM structural analysis revealed that within the KICSTOR complex, SZT2 forms a crescent-shaped scaffold that binds the ITFG2-KPTN heterodimer at its C terminus; FBXO2-mediated ubiquitination of KPTN (at K49, K67, K262, K265) disrupts the KPTN-ITFG2 and KPTN-SZT2 interactions, impairing KICSTOR's ability to recruit GATOR1 to the lysosomal surface.\",\n      \"method\": \"Cryo-electron microscopy, computational modeling, biochemical binding assays, co-immunoprecipitation, ubiquitination assay, mTORC1 signaling readouts\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structure plus biochemical validation and mutagenesis in a single rigorous study\",\n      \"pmids\": [\"41198956\", \"41401028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Loss of ITFG2 (identified in a genome-wide CRISPR/Cas9 knockout screen) results in sustained mTOR signaling under pharmacologic inhibition of PI3K-AKT, confirming ITFG2 as a negative regulator of mTORC1 in cancer cells; resistance could be reversed by mTOR inhibition.\",\n      \"method\": \"Whole genome CRISPR/Cas9 knockout screen, validated by individual gene knockout with mTOR signaling readouts\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genome-wide CRISPR screen with individual validation; confirms mTORC1-negative regulator role in cancer context\",\n      \"pmids\": [\"33685991\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ITFG2 is a core subunit of the KICSTOR complex (with KPTN, C12orf66, and SZT2) that localizes to lysosomes where it recruits GATOR1 to enable nutrient-sensing inhibition of mTORC1; outside of mTORC1 regulation, ITFG2 acts as an inhibitor of the E3 ubiquitin ligase NEDD4-2, protecting multiple substrates (ATP5b, SERCA2a, Nav1.5) from ubiquitin-mediated degradation in cardiomyocytes, and plays a cell-intrinsic role in B cell differentiation and migration.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ITFG2 functions as a lysosomal scaffold subunit and a cytoplasmic inhibitor of ubiquitin-mediated protein degradation. As a core component of the KICSTOR complex (with KPTN, C12orf66, and SZT2), ITFG2 forms a heterodimer with KPTN that docks onto the SZT2 crescent-shaped scaffold at lysosomes, where KICSTOR recruits the GATOR1 complex to enable nutrient-sensing (amino acid, glucose, S-adenosylmethionine) inhibition of mTORC1 via the Rag GTPases [PMID:28199306, PMID:35776786, PMID:41198956]. Independent of mTORC1, ITFG2 binds the E3 ubiquitin ligase NEDD4-2 and competitively inhibits its interaction with multiple substrates—ATP5b, SERCA2a, and Nav1.5—thereby protecting these proteins from ubiquitination and degradation in cardiomyocytes under ischemic stress [PMID:38848780, PMID:39477020, PMID:39864577]. ITFG2 also plays a cell-intrinsic role in B cell differentiation and migration, as Itfg2-deficient mice exhibit defective germinal center responses, impaired plasma cell homing to bone marrow, and reduced serum IgG [PMID:23997217].\",\n  \"teleology\": [\n    {\n      \"year\": 2013,\n      \"claim\": \"The first in vivo function of ITFG2 was established: it is required cell-intrinsically for B cell differentiation, germinal center maturation, and plasma cell migration to bone marrow, resolving whether it acts as a surface receptor (it does not) or an intracellular regulator of immune cell fate.\",\n      \"evidence\": \"Itfg2 knockout mice, bone marrow transplantation, immunization, in vitro migration assays, flow cytometry\",\n      \"pmids\": [\"23997217\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Molecular mechanism by which ITFG2 controls B cell migration is unknown\",\n        \"Whether the B cell phenotype relates to mTORC1 signaling was not tested\",\n        \"No interacting partners identified in this context\"\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"ITFG2 was identified as a subunit of the KICSTOR complex that localizes to lysosomes and recruits GATOR1 to inhibit mTORC1 upon nutrient deprivation, establishing the mechanistic basis for how upstream nutrient signals reach GATOR1 and the Rag GTPases.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation, lysosomal fractionation, genetic knockout in human cells and mouse tissues, epistasis analysis with GATOR1/GATOR2/Rag components\",\n      \"pmids\": [\"28199306\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Structural organization of KICSTOR and the ITFG2-KPTN interface were not resolved\",\n        \"Whether ITFG2 has functions outside the KICSTOR-mTORC1 axis was unclear\",\n        \"Relationship between KICSTOR and the B cell phenotype of ITFG2 deficiency was not addressed\"\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"A genome-wide CRISPR screen independently confirmed ITFG2 as a negative regulator of mTORC1, showing that its loss confers resistance to PI3K-AKT inhibition by sustaining mTOR signaling in cancer cells.\",\n      \"evidence\": \"Whole-genome CRISPR/Cas9 knockout screen with individual gene knockout validation and mTOR signaling readouts in cancer cell lines\",\n      \"pmids\": [\"33685991\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Whether resistance operates solely through KICSTOR-GATOR1 or involves additional pathways was not dissected\",\n        \"Clinical relevance of ITFG2 loss in drug resistance remains correlative\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The KICSTOR complex was shown to serve as the docking platform for SAMTOR, linking S-adenosylmethionine sensing to GATOR1-mediated mTORC1 inhibition and broadening the nutrient inputs that signal through ITFG2-containing KICSTOR.\",\n      \"evidence\": \"Crystal structures of SAMTOR in apo and SAM-bound states, in vitro binding assays, mutagenesis\",\n      \"pmids\": [\"35776786\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Which KICSTOR subunit directly contacts SAMTOR was not resolved\",\n        \"In vivo physiological relevance of SAM sensing through KICSTOR not tested\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"A distinct mTORC1-independent function was uncovered: ITFG2 binds NEDD4-2 and inhibits its ubiquitin ligase activity toward multiple cardiac substrates (ATP5b, SERCA2a), protecting mitochondrial function and calcium homeostasis in ischemic cardiomyocytes.\",\n      \"evidence\": \"Co-immunoprecipitation, ubiquitination assays, AAV9-mediated overexpression/knockdown in myocardial infarction mouse model, primary cardiomyocyte hypoxia assays\",\n      \"pmids\": [\"38848780\", \"39477020\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"All NEDD4-2 studies come from a single laboratory; independent replication is needed\",\n        \"Whether ITFG2 acts on NEDD4-2 as part of KICSTOR or independently is unknown\",\n        \"Structural basis for the ITFG2-NEDD4-2 interaction has not been determined\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Cryo-EM resolved the architecture of KICSTOR, showing that the ITFG2-KPTN heterodimer binds the C-terminal region of the SZT2 scaffold, and revealed that FBXO2-mediated ubiquitination of KPTN disrupts both the KPTN-ITFG2 and KPTN-SZT2 interfaces, providing a regulatory mechanism for KICSTOR disassembly.\",\n      \"evidence\": \"Cryo-electron microscopy, computational modeling, co-immunoprecipitation, ubiquitination assays, mTORC1 signaling readouts\",\n      \"pmids\": [\"41198956\", \"41401028\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"High-resolution structure of ITFG2 itself within the complex is not fully resolved\",\n        \"Whether FBXO2-mediated disassembly occurs under physiological nutrient conditions is untested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"ITFG2 inhibition of NEDD4-2 was extended to a third substrate, Nav1.5, stabilizing sodium channel expression and current density in post-infarction cardiomyocytes and reducing arrhythmia susceptibility.\",\n      \"evidence\": \"Co-immunoprecipitation, patch-clamp electrophysiology, ubiquitination assay, AAV9 overexpression/knockdown in MI mouse model\",\n      \"pmids\": [\"39864577\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"All three NEDD4-2 substrate studies are from one group; independent confirmation lacking\",\n        \"Whether ITFG2 is a general NEDD4-2 inhibitor or substrate-selective is unresolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: whether the B cell and cardiomyocyte functions of ITFG2 are mechanistically connected to KICSTOR-mTORC1 signaling or represent independent activities; the structural basis of ITFG2 interaction with NEDD4-2; and whether ITFG2 has additional NEDD4-2-independent roles outside the KICSTOR complex.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No study has tested whether ITFG2's immune and cardiac functions depend on KICSTOR or mTORC1\",\n        \"Structural basis for ITFG2-NEDD4-2 binding is unknown\",\n        \"Tissue-specific versus universal functions of ITFG2 have not been systematically mapped\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 4, 5]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005764\", \"supporting_discovery_ids\": [0, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 1, 6, 7]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [3, 4, 5]}\n    ],\n    \"complexes\": [\n      \"KICSTOR\"\n    ],\n    \"partners\": [\n      \"KPTN\",\n      \"SZT2\",\n      \"C12orf66\",\n      \"NEDD4L\",\n      \"SAMTOR\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}