{"gene":"ID2","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":1991,"finding":"Id2 contains a helix-loop-helix (HLH) dimerization motif but lacks the basic DNA-binding domain; it selectively heterodimerizes with and inhibits the DNA-binding activity of one class of bHLH transcription factors (e.g., E2A/E47, E2B/m3) but not another (TFE3, USF, AP4), and homodimerizes poorly.","method":"In vitro binding and DNA-binding inhibition assays; gene cloning and sequence analysis; chromosome mapping","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — original biochemical reconstitution with multiple orthogonal methods, foundational paper with 567 citations","pmids":["1922066"],"is_preprint":false},{"year":1996,"finding":"Id2 (but not Id1 or Id3) directly binds pRb, p107, and p130 in vitro and in vivo, neutralizing their growth-suppressive activity and reversing cell-cycle arrest imposed by pRb family members and CDK inhibitors p16 and p21; Id2 expression also reduces cyclin D1 levels and cyclin D1–CDK4 complexes.","method":"In vitro binding assays; co-immunoprecipitation in transfected Saos-2 cells; cell-cycle arrest rescue assays; Western blot for cyclin D1","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1–2 — multiple orthogonal methods (in vitro binding + in vivo co-IP + functional rescue), replicated by subsequent work","pmids":["8649364"],"is_preprint":false},{"year":1997,"finding":"Id2 is phosphorylated by cyclin E–CDK2 and cyclin A–CDK2 (but not cyclin D–CDKs) on a serine within a CDK consensus site in late G1; phosphorylation of Id2 in serum-stimulated fibroblasts correlates with restoration of E-box-dependent DNA-binding complexes, indicating that CDK-mediated phosphorylation relieves Id2-mediated inhibition of bHLH transcription factors.","method":"In vitro kinase assays with purified cyclin–CDK complexes; in vivo phosphorylation in synchronised human diploid fibroblasts; electrophoretic mobility shift assay (EMSA)","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution plus in vivo correlation with multiple orthogonal methods","pmids":["9029153"],"is_preprint":false},{"year":2000,"finding":"Id2 is a direct transcriptional target of Myc-family oncoproteins; Id2 acts as a dominant-negative antagonist of Rb-family proteins; in neuroblastoma cells overexpressing N-Myc, Id2 is in molar excess of active Rb, and cell-cycle progression driven by Myc oncoproteins requires Id2-mediated inactivation of Rb. Id2–Rb double-knockout embryos survive to term, revealing a functional epistatic relationship.","method":"Genetic double-knockout rescue; quantitative protein analysis; transcriptional activation assays; neuroblastoma cell analysis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 — genetic epistasis (double-KO rescue) combined with biochemical quantitation, high-impact replicated finding","pmids":["11034201"],"is_preprint":false},{"year":2004,"finding":"Id2 is degraded by the ubiquitin–proteasome system via N-terminal ubiquitination: a Myc-tag fused to the N-terminus (but not C-terminus) stabilises Id2, lysine-less Id2 is still efficiently degraded (ubiquitin conjugated to α-NH2 group), and deletion of the first 15 N-terminal residues stabilises the protein, identifying this domain as an E3 recognition element.","method":"Ubiquitination assays; N-terminal tagging stabilisation experiments; lysine-less mutant degradation assays; proteasome inhibitor experiments","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — mechanistic mutagenesis plus reconstituted ubiquitination, multiple orthogonal approaches in one study","pmids":["14733935"],"is_preprint":false},{"year":2005,"finding":"Polycystin-2 (PC2) directly interacts with Id2; this interaction is regulated by PC1-dependent phosphorylation of PC2. Id2 expression suppresses p21 induction by PC1 or PC2, and Id2 shows enhanced nuclear localisation in cystic kidneys. RNAi knockdown of Id2 corrects the hyperproliferative phenotype of PC1-mutant cells.","method":"Co-immunoprecipitation; phosphorylation assays; RNAi knockdown with proliferation readout; immunofluorescence in human/mouse cystic kidney tissue","journal":"Nature cell biology","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding demonstrated, phosphorylation-regulated interaction, functional rescue by RNAi, replicated in vivo","pmids":["16311606"],"is_preprint":false},{"year":2006,"finding":"APC/C(Cdh1) targets Id2 for proteasomal degradation through a conserved destruction box (D-box) motif in neurons. Id2 interacts with core APC/C subunits and Cdh1; D-box mutants of Id2 resist Cdh1 binding, remain stable after cell-cycle exit, and enhance axonal growth in cerebellar granule neurons in vitro and in vivo, overcoming myelin inhibitory signals. Degradation of Id2 permits accumulation of the Nogo receptor, a bHLH target gene product that inhibits axonal growth.","method":"Co-immunoprecipitation; APC/C interaction assays; D-box mutagenesis; cerebellar granule neuron axon growth assays in vitro and in vivo; gene expression analysis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 — mutagenesis, reconstitution, and functional in vivo validation in one study","pmids":["16810178"],"is_preprint":false},{"year":2006,"finding":"The actin-associated LIM-domain protein ENH (enigma homolog) is a cytoplasmic retention factor for Id2: ENH binds the HLH domain of Id2 in vitro and in vivo, its overexpression in neuroblastoma cells translocates Id2 from nucleus to cytoplasm and inactivates its transcriptional and cell-cycle-promoting functions, and RNAi silencing of ENH prevents cytoplasmic relocation of Id2 during retinoic acid-induced differentiation.","method":"Co-immunoprecipitation; in vitro binding assay; fluorescence microscopy of subcellular localisation; RNAi knockdown with localisation and functional readouts","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — direct binding demonstrated in vitro and in vivo, bidirectional manipulation (OE and KD) with functional consequence","pmids":["16549780"],"is_preprint":false},{"year":2006,"finding":"Id2 prevents E-protein-mediated activation of p57Kip2 expression in neuroblastoma cells: E47 directly activates p57Kip2 transcription to block S-phase entry, Id2 suppresses this activation, and RNAi knockdown of p57Kip2 fully reverses E47-mediated cell-cycle arrest, establishing p57Kip2 as the functionally relevant CDK inhibitor target of the E-protein/Id2 axis in neural cells.","method":"Microarray gene expression profiling; reporter assays; RNAi knockdown; cell-cycle analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — epistasis established by RNAi rescue plus expression analysis, multiple orthogonal methods","pmids":["16705184"],"is_preprint":false},{"year":2003,"finding":"TGF-β induces Id2 expression in dendritic cell precursors; Id2 is required for development of Langerhans cells and splenic CD8α+ DCs, and Id2 represses B-cell lineage genes in DCs, establishing a TGF-β–Id2 signaling axis that controls DC lineage choice.","method":"Id2-knockout mouse analysis; in vitro DC differentiation with TGF-β stimulation; gene expression profiling","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined cellular phenotype plus cytokine-pathway epistasis, replicated","pmids":["12598895"],"is_preprint":false},{"year":2007,"finding":"A 1.2 kb Id2 promoter fragment is cooperatively regulated by Nkx2-5 and Tbx5 in vitro and is sufficient for conduction-system-specific expression in vivo; compound haploinsufficiency of Tbx5 and Id2 (or Tbx5 and Nkx2-5) blocks embryonic specification of the ventricular conduction system, placing Id2 downstream of Tbx5/Nkx2-5 in a conduction system developmental pathway.","method":"SAGE transcriptional profiling; Id2-deficient mouse cardiac analysis; promoter reporter assay; compound haploinsufficiency genetic epistasis; in vivo transgenic reporter","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 — promoter dissection, genetic epistasis, in vivo reporter, highly cited","pmids":["17604724"],"is_preprint":false},{"year":2001,"finding":"Id2 is a direct transcriptional target of β-catenin/TCF4; a TCF4-binding motif in the Id2 promoter is identified by EMSA and supershift, and site-directed mutagenesis abolishes promoter activity; β-catenin overexpression increases Id2 protein, and Id2 expression promotes anchorage-independent survival of colon carcinoma cells.","method":"Reporter assay; EMSA and supershift; site-directed mutagenesis; transfection; anchorage-independent growth assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — promoter mutagenesis plus direct binding demonstrated plus functional consequence","pmids":["11572874"],"is_preprint":false},{"year":2004,"finding":"HIF-1 directly activates Id2 transcription in hypoxic neuroblastoma cells via two functional HIF-1 binding sites at −725 and −1893 relative to the transcriptional start site, demonstrated by EMSA and ChIP; Id2 promoter-luciferase constructs are HIF-1-specifically activated in transfection assays.","method":"EMSA; chromatin immunoprecipitation (ChIP); luciferase reporter assay; actinomycin D transcription inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — ChIP plus EMSA plus mutagenesis, multiple orthogonal methods","pmids":["15252039"],"is_preprint":false},{"year":2005,"finding":"C/EBPβ directly activates Id2 transcription: nuclear translocation of C/EBPβ rapidly induces endogenous Id2; the most proximal of three C/EBPβ-binding elements in the 2.3 kb Id2 promoter is required for transactivation; EMSA identifies this as a C/EBPβ core-binding sequence; ChIP confirms C/EBPβ occupancy at the Id2 promoter in vivo; Id2 expression is reduced in C/EBPβ-deficient mammary glands.","method":"Inducible C/EBPβ-ERT nuclear translocation; reporter assay; EMSA; ChIP; Northern blot in C/EBPβ-null mammary glands","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 — ChIP + EMSA + mutagenesis + KO validation, multiple orthogonal methods","pmids":["15809228"],"is_preprint":false},{"year":2010,"finding":"BMP6 activates Id2 transcription through Smad-binding elements (two GGCGCC palindromes and one GTCT element) in the Id2 promoter; gel shift and ChIP assays confirm physical Smad binding; mutation of these elements abolishes BMP responsiveness; a novel bipartite CGCC sequence contributes to Smad target recognition.","method":"Reporter assay; gel-shift (EMSA); ChIP; site-directed mutagenesis; BMP receptor inhibitor","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 — EMSA + ChIP + mutagenesis, multiple orthogonal methods","pmids":["20674548"],"is_preprint":false},{"year":2003,"finding":"TGF-β represses Id2 expression in epithelial cells via induction of Mad2 and Mad4, which replace Myc-Max complexes with Mad-Max complexes on the Id2 promoter, providing a mechanism for TGF-β cytostatic program independent of c-Myc downregulation.","method":"Reporter assay; ChIP showing Myc-Max to Mad-Max promoter switching; Western blot; quantitative expression analysis across multiple epithelial cell lines","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP demonstrating promoter occupancy switch, multiple cell lines, mechanistic pathway dissection","pmids":["12824180"],"is_preprint":false},{"year":2006,"finding":"Id2 acts as a master regulator of VEGF expression in pituitary tumor cells and neuroblastoma; in Rb+/− pituitary tumors, Id2-null cells show premature bHLH activation and p27Kip1 upregulation that impairs melanotrope proliferation and tumor initiation; N-Myc-driven Id2 expression is sufficient and necessary for VEGF expression in neuroblastoma.","method":"Id2-null/Rb+/− compound genetic mouse model; immunohistochemistry; gene expression analysis; neuroblastoma cell manipulation","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — in vivo genetic epistasis plus mechanistic gene expression analysis","pmids":["15831462"],"is_preprint":false},{"year":2008,"finding":"Id2 regulates erythroid development by interacting with transcription factor PU.1 and modulating PU.1 and GATA-1 activities; Id2-null mice have expanded B-cell compartments, and Id2 acts as physiologically relevant inhibitor of E2A during B lymphopoiesis through direct antagonism.","method":"Id2 knockout mouse analysis; retroviral transduction/overexpression; shRNA knockdown; co-immunoprecipitation of Id2 with PU.1","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2–3 — co-IP plus KO phenotype, single lab","pmids":["18523151"],"is_preprint":false},{"year":2010,"finding":"Id2 promotes tumor cell migration and invasion through transcriptional repression of Semaphorin 3F (SEMA3F): E47 directly activates SEMA3F via two E-box sites in its promoter; Id2 acts as a dominant-negative inhibitor of E47, abrogating SEMA3F expression and its biological activities (F-actin depolymerisation, RhoA inactivation, migration inhibition).","method":"Reporter assay with E-box mutagenesis; SEMA3F knockdown rescue; migration/invasion assays; F-actin and RhoA activity assays","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 — promoter dissection + mutagenesis + functional rescue with multiple downstream readouts","pmids":["20388805"],"is_preprint":false},{"year":2011,"finding":"p53 directly represses Id2 transcription by binding a conserved site within the Id2 promoter; p53-null neural progenitor cells have elevated Id2 and increased proliferation/self-renewal; suppression of Id2 is sufficient to restore normal proliferation to p53-null NPCs; elevated Id2 expression phenocopies p53 loss.","method":"Chromatin immunoprecipitation; Id2 KD by RNAi; p53-null mouse NPC analysis; promoter binding assay","journal":"Stem cells (Dayton, Ohio)","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP demonstrating direct promoter binding, RNAi rescue, genetic model validation","pmids":["21608079"],"is_preprint":false},{"year":2014,"finding":"The ubiquitin ligase ASB4 ubiquitinates and targets Id2 for proteasomal degradation in trophoblast/placental cells, promoting vascular differentiation; a degradation-resistant Id2 mutant co-expressed with ASB4 inhibits differentiation and functional vascular responses; Asb4-null placentas retain Id2 expression and show immature vascular patterning.","method":"Ubiquitination assay; proteasome inhibitor experiments; degradation-resistant mutant co-transfection; endothelial co-culture assays; Asb4-null mouse placenta analysis","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 1–2 — direct ubiquitination shown, mutagenesis, functional rescue, and in vivo genetic validation","pmids":["24586788"],"is_preprint":false},{"year":2016,"finding":"Id2 represses multiple E-protein target genes including Socs3 in NK cells; Id2 deletion in mature NK cells leads to impaired IL-15 receptor signaling and metabolic dysfunction, rescued by strong IL-15 stimulation or genetic Socs3 deletion, demonstrating that Id2 regulates NK cell homeostasis by titrating E-protein activity at Socs3 and other target loci.","method":"Id2 conditional KO in mature NK cells; genetic Socs3/Id2 double-KO epistasis; IL-15 receptor signaling assays; metabolic function assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis (double-KO rescue) plus signaling assays, multiple orthogonal methods","pmids":["26795246"],"is_preprint":false},{"year":2016,"finding":"Bcl6 binds the Id2 locus to repress Id2 expression in TFH cells; TH1 cells express higher Id2 than TFH cells; Id2 deficiency increases TFH frequency in an E-protein-dependent manner and blocks TH1 differentiation; Id2 reinforces TH1 differentiation by repressing E2A-dependent TFH-promoting programs.","method":"Id2 RNAi in T cells; T cell-specific Id2 KO mouse; ChIP (Bcl6 occupancy at Id2 locus); T cell subset phenotyping during viral infection","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP for direct Bcl6–Id2 locus binding, combined with genetic KO and epistasis","pmids":["27213691"],"is_preprint":false},{"year":2016,"finding":"PDGF signaling upregulates USP1 via E2F transcription factors; USP1 stabilises ID2 protein; genetic ablation of Id2 delays glioma-induced mortality; pharmacologic USP1 inhibition reduces ID2 levels and delays tumorigenesis in a mouse proneural glioma model, establishing a PDGF–E2F–USP1–ID2 survival signalling cascade.","method":"E2F ChIP at Usp1 promoter; Id2 genetic KO in glioma model; USP1 pharmacologic inhibition; comparative transcriptomics","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 — ChIP for direct E2F binding, pharmacologic and genetic validation in vivo","pmids":["26951930"],"is_preprint":false},{"year":2018,"finding":"Id2 mediates Treg-to-TH17 plasticity by sequestering the transcription activator E2A; expression of Id2 in iTreg cells reduces Foxp3 expression and induces TH17-related cytokines; Treg-specific Id2 overexpression in mice reduces the Treg compartment and causes immune dysregulation.","method":"Id2 overexpression in iTreg cells; Treg-specific Id2 transgenic mice; cellular fate-mapping; cytokine profiling","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 — gain-of-function in vitro and in vivo with defined molecular mechanism (E2A sequestration)","pmids":["30413714"],"is_preprint":false},{"year":2020,"finding":"Monoubiquitination of FANCD2 (within the FANCI–FANCD2/ID2 complex) promotes a large-scale conformational change that increases the complex's affinity for double-stranded DNA and enables it to encircle DNA by forming a secondary 'Arm' interface; monoubiquitination of FANCI protects the ubiquitin on FANCD2 from deubiquitination by USP1–UAF1, with key hydrophobic residues of FANCI's ubiquitin mediating this protection.","method":"Structural and biochemical analysis of ubiquitinated ID2 complex; DNA-binding affinity assays; deubiquitination protection assays with USP1–UAF1","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1 — structural/biochemical reconstitution with mechanistic mutagenesis","pmids":["32510829"],"is_preprint":false},{"year":2024,"finding":"Id2 epigenetically regulates CD8+ T-cell exhaustion by binding, via its HLH domain, to Tcf3 (TCF1) and disrupting the Tcf3–Tal1 complex, thereby preventing Tcf3 from recruiting LSD1 histone demethylase to the Slamf6 promoter; this results in increased permissive H3K4me2 marks and greater chromatin accessibility at the Slamf6 promoter, promoting generation of Slamf6+ progenitor exhausted T cells. LSD1 inhibitor GSK2879552 rescues Id2-KO phenotype in tumour-bearing mice.","method":"Co-immunoprecipitation (HLH domain); ChIP for H3K4me2 and chromatin accessibility at Slamf6 promoter; Id2-KO mouse tumour model; LSD1 pharmacologic inhibition rescue","journal":"Cellular & molecular immunology","confidence":"High","confidence_rationale":"Tier 1–2 — direct protein interaction, epigenetic mark measurement, pharmacologic rescue, multiple orthogonal methods","pmids":["38287103"],"is_preprint":false},{"year":2021,"finding":"ID2 in NK cells suppresses TCF1 amplitude during maturation; elevated TCF1 in ID2-deficient NK cells arrests their maturation and limits cytokine-induced IFN-γ production and anti-metastatic function, establishing ID2 as a transcriptional brake on TCF1 that controls the balance between immature expansion and terminal NK cell differentiation.","method":"Id2 conditional KO in NK cells; TCF1 reporter and protein level analysis; in vivo melanoma clearance assay; cytokine stimulation assays","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 — conditional KO with defined molecular target (TCF1) and functional in vivo readout","pmids":["33857289"],"is_preprint":false},{"year":2005,"finding":"Ovol1 represses Id2 transcription in pachytene spermatocytes; Ovol1-deficient germ cells upregulate Id2 and fail to progress through the pachytene stage; Ovol1 represses the Id2 promoter in reporter assays, establishing Id2 as a direct transcriptional target of Ovol1 in male meiosis.","method":"Ovol1-KO mouse analysis; transcriptional profiling; Northern blot; Id2 promoter reporter assay","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 — reporter assay plus genetic KO phenotype, single lab","pmids":["15716349"],"is_preprint":false},{"year":2009,"finding":"Ebf1 down-regulates Id2 and Id3 expression in prepro-B cells to specify B-cell fate; enforced Ebf1 expression in IL-7Rα−/− bone marrow cells potently reduces Id2 and Id3 mRNA and restores B-cell differentiation in vivo; overexpression of either Id2 or Id3 blocks B-cell specification at the prepro-B stage.","method":"Retroviral Ebf1 expression in IL-7Rα-null bone marrow; Id2/Id3 overexpression in wild-type bone marrow; qRT-PCR; in vivo reconstitution","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 — bidirectional genetic manipulation with in vivo rescue, clear epistasis established","pmids":["19122139"],"is_preprint":false},{"year":2010,"finding":"AMPK (PRKAA1/2) mediates stress-induced proteasome-dependent loss of ID2 protein in trophoblast stem cells at high stress levels, triggering differentiation; at low stress levels AMPK mediates metabolic adaptation without ID2 loss, establishing a dose-dependent AMPK–ID2 axis linking cellular stress to TSC differentiation.","method":"AMPK inhibitor/activator pharmacology; proteasome inhibitor experiments; PRKAA1/2 activation assays; immunoblot for ID2 in stressed TSCs","journal":"Reproduction (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 — pharmacologic manipulation with multiple inhibitors/activators, single lab","pmids":["20876741"],"is_preprint":false},{"year":2007,"finding":"Id2 controls intestinal stem cell specification by restricting Wnt signalling activity at early embryonic stages; Id2-deficient intestinal epithelial cells precociously activate Wnt target genes and generate an expanded Lgr5+ progenitor pool.","method":"Id2-KO mouse; cell fate mapping; ex vivo organoid culture with Wnt target gene analysis; transcriptional profiling of adult Id2-null ISCs","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with pathway (Wnt) analysis, single lab","pmids":["28077488"],"is_preprint":false},{"year":2002,"finding":"Id2 inhibits BETA2/NeuroD-mediated E-box-dependent gene expression in a dose-dependent manner by forming heterodimers that block BETA2/NeuroD binding to its target E-box sequence, as shown by EMSA; Id2 inhibits BETA2/NeuroD transcriptional activation in both HIT and HeLa cells.","method":"Yeast two-hybrid (interaction screen); EMSA; co-expression transcriptional reporter assays in HIT and HeLa cells","journal":"Experimental & molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2–3 — EMSA plus functional reporter, single lab","pmids":["12526101"],"is_preprint":false},{"year":2013,"finding":"Id2 restrains CD8+ T-cell memory differentiation by inhibiting E2A-mediated direct activation of Tcf7 (TCF1); Id2-deficient CD8+ T cells fail to upregulate Tbx21 for short-lived effector generation and instead adopt a memory fate with elevated Eomesodermin and Tcf7.","method":"Id2-KO CD8+ T-cell analysis during infection; E2A binding site reporter assay; gene expression profiling","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with defined molecular target (E2A–Tcf7 axis), functional in vivo readout","pmids":["23536629"],"is_preprint":false},{"year":2006,"finding":"BMP4 induces Id2 expression in AR42J pancreatic epithelial cells, and BMP4 stimulation promotes Id2 binding to NeuroD (a bHLH differentiation factor), thereby blocking endocrine differentiation and promoting expansion of pancreatic progenitors.","method":"BMP4 stimulation assays; co-immunoprecipitation of Id2–NeuroD; BMP4 neutralisation in mouse islet regeneration model; proliferation assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2–3 — direct interaction by co-IP, functional in vivo BMP4 neutralisation, single lab","pmids":["16547003"],"is_preprint":false},{"year":2021,"finding":"TGF-β signalling suppresses Id2 expression to decelerate cell-cycle in developing airway basal stem cells; reduced TGF-β signalling in adult tissue regeneration restores Id2 expression and initiates proliferation; persistent Id2 expression (via Id2 OE or Tgfbr2 KO) drives basal cell hyperplasia resembling a precancerous state, establishing the TGF-β–Id2 axis as a proliferation switch in airway basal cells.","method":"Id2 overexpression; Tgfbr2 conditional KO; single-cell transcriptomics; genetic validation in murine airway development and regeneration models","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 — bidirectional genetic manipulation, single-cell transcriptomics, in vivo validation","pmids":["34129836"],"is_preprint":false},{"year":2023,"finding":"METTL3-mediated m6A modification stabilises ID2 mRNA in an m6A-YTHDF2-dependent manner in pancreatic cancer cells; METTL3 knockdown reduces m6A on ID2 mRNA and destabilises it; ID2 in turn controls stemness molecules NANOG and SOX2 via the PI3K–AKT pathway.","method":"METTL3 knockdown; m6A-seq/MeRIP; mRNA stability assay; YTHDF2 co-immunoprecipitation; PI3K–AKT pathway inhibition","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 — direct m6A measurement plus stability assays plus YTHDF2 interaction, single lab","pmids":["37196908"],"is_preprint":false},{"year":2019,"finding":"Mtg16 represses Id2 transcription in dendritic cell progenitors; genome-wide DNA-binding analysis identifies Id2 as a direct Mtg16 target; Mtg16-deficient pDCs and cDC progenitors show aberrant Id2 induction; genetic deletion of Id2 partially rescues impaired pDC development in Mtg16-null mice.","method":"Mtg16-KO mouse; genome-wide ChIP-seq (DNA-binding analysis); Id2-KO rescue epistasis; flow cytometric DC subset analysis","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 1–2 — genome-wide ChIP-seq plus genetic double-KO epistasis","pmids":["24980046"],"is_preprint":false},{"year":2019,"finding":"An Nfil3–Zeb2–Id2 genetic circuit controls cDC1 development: Nfil3 is required for the transition from Zeb2hi/Id2lo CDPs to Zeb2lo/Id2hi CDPs (earliest committed cDC1 progenitors); genetic epistasis shows this circuit blocks E-protein activity to exclude pDC potential and explains the switch in Irf8 enhancer usage.","method":"Single-cell RNA sequencing of CDPs; genetic epistasis (Nfil3 KO, Zeb2 KO, Id2 KO); DC progenitor phenotyping","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 — scRNA-seq plus multi-gene genetic epistasis, mechanistic pathway placement","pmids":["31406377"],"is_preprint":false},{"year":1995,"finding":"bHLH transcription factors ME1, ME2, and NSCL1 stimulate Id2 promoter activity through E-box clusters in the 5′ regulatory region; co-expression of Id2 blocks this stimulatory effect, revealing a negative feedback loop in Id2 transcriptional regulation.","method":"Reporter/luciferase promoter assay; co-expression in F9 cells; retinoic acid differentiation assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2–3 — promoter reporter assay with co-expression, single lab, relatively limited follow-up","pmids":["7589553"],"is_preprint":false},{"year":1995,"finding":"Id1 and Id2 can be phosphorylated in vitro by cAMP-dependent protein kinase; Id2 and Id3 can be phosphorylated by cdc2 kinase; all three (Id1, Id2, Id3) by PKC; however, phosphorylation by cAMP-kinase or PKC did not affect Id2/E47 dimerisation or DNA-binding inhibition in gel-shift assays.","method":"In vitro kinase assay; immunoprecipitation of phosphorylated Id1 from NGF-stimulated PC12 cells; gel-shift assay","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1–3 — in vitro kinase assay plus EMSA, but limited functional consequence demonstrated","pmids":["7864897"],"is_preprint":false},{"year":2022,"finding":"Under anchorage-independent conditions, E-cadherin loss de-represses Id2 transcription via a p120-catenin/Kaiso-dependent mechanism at a canonical Kaiso-binding sequence (TCCTGCNA) in the Id2 promoter; Id2 then accumulates in the cytosol and induces CDK4/6-dependent G0/G1 arrest through interaction with hypo-phosphorylated Rb, promoting anoikis resistance and lung colonisation in ILC models.","method":"Loss-of-function experiments; inducible E-cadherin restoration; promoter analysis; ChIP for Kaiso; co-immunoprecipitation of Id2 with Rb; subcellular fractionation; in vivo lung colonisation assay","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 1–2 — promoter dissection with Kaiso ChIP, direct Id2–Rb interaction, subcellular fractionation, in vivo functional assay","pmids":["35437308"],"is_preprint":false}],"current_model":"ID2 is a HLH-domain-only dominant-negative inhibitor of bHLH E-protein transcription factors and Rb-family tumour suppressors; it is transcriptionally activated by Myc, β-catenin/TCF4, HIF-1, C/EBPβ, BMP/Smad, and Nkx2-5/Tbx5, and is repressed by TGF-β (via Mad proteins), p53, Bcl6, Mtg16, and Ovol1; ID2 protein stability is controlled by APC/C(Cdh1)-mediated D-box-dependent proteasomal degradation, by N-terminal ubiquitination, by ASB4 E3 ligase, by CDK2-dependent phosphorylation (which relieves bHLH inhibition), and by USP1-dependent deubiquitination; ID2 activity is spatially regulated by cytoplasmic sequestration via the LIM-domain protein ENH; and the FANCI–FANCD2 (ID2) heterodimer encircles DNA upon FANCD2 monoubiquitination to promote DNA interstrand crosslink repair."},"narrative":{"teleology":[{"year":1991,"claim":"Establishing that ID2 is an HLH-only protein that heterodimerizes with and inhibits specific bHLH transcription factors resolved how a protein lacking a DNA-binding domain could function as a transcriptional regulator.","evidence":"In vitro binding and DNA-binding inhibition assays with cloned Id2 against multiple bHLH proteins","pmids":["1922066"],"confidence":"High","gaps":["Structural basis of selective partner recognition unknown","In vivo relevance not yet demonstrated","Full spectrum of bHLH partners not mapped"]},{"year":1995,"claim":"Identification that bHLH factors activate the Id2 promoter through E-boxes, and that Id2 blocks this activation, revealed a negative autoregulatory feedback loop governing Id2 expression levels.","evidence":"Reporter/luciferase promoter assay with co-expression in F9 cells","pmids":["7589553"],"confidence":"Medium","gaps":["Direct E-box binding by bHLH factors at the endogenous Id2 promoter not confirmed by ChIP","Physiological significance of the feedback loop not tested in vivo"]},{"year":1996,"claim":"Demonstrating that ID2 uniquely among Id family members directly binds and neutralizes all three Rb-family pocket proteins established a second major mechanism—beyond bHLH inhibition—by which ID2 promotes cell-cycle progression.","evidence":"In vitro binding assays, co-immunoprecipitation in Saos-2 cells, and cell-cycle arrest rescue assays","pmids":["8649364"],"confidence":"High","gaps":["Structural basis of ID2–Rb interaction unknown","Whether Rb binding and bHLH binding are mutually exclusive or concurrent was not resolved"]},{"year":1997,"claim":"Showing that cyclin E–CDK2 and cyclin A–CDK2 phosphorylate ID2 in late G1, correlating with restoration of E-box-dependent transcription, established a cell-cycle-dependent mechanism that inactivates ID2's inhibitory function.","evidence":"In vitro kinase assays with purified cyclin–CDK complexes; in vivo phosphorylation in synchronized fibroblasts; EMSA","pmids":["9029153"],"confidence":"High","gaps":["Precise phosphorylation site mutant analysis not reported in this study","Whether phosphorylation also affects Rb binding was not tested"]},{"year":2000,"claim":"Genetic epistasis showing that Id2–Rb double-knockout embryos survive to term, combined with evidence that Myc directly activates Id2 transcription, placed ID2 as a critical mediator in the Myc→ID2⊣Rb oncogenic pathway.","evidence":"Double-knockout rescue in mice; quantitative protein analysis; neuroblastoma cell analysis","pmids":["11034201"],"confidence":"High","gaps":["Whether this axis operates equivalently in all Myc-driven cancers was not established","Contribution of ID2's bHLH-inhibitory function versus Rb-inhibitory function in this pathway not disentangled"]},{"year":2001,"claim":"Identification of β-catenin/TCF4 as a direct transcriptional activator of ID2 via a TCF4-binding motif linked ID2 to canonical Wnt signaling and anchorage-independent survival in colon cancer.","evidence":"EMSA, supershift, site-directed mutagenesis of TCF4 site, reporter assay in colon carcinoma cells","pmids":["11572874"],"confidence":"High","gaps":["ChIP confirmation of endogenous TCF4 occupancy at the Id2 promoter not performed","Downstream effectors of ID2 in anchorage-independent survival not identified"]},{"year":2003,"claim":"Discovering that TGF-β represses Id2 via Mad-Max promoter switching and that TGF-β also induces Id2 in dendritic cell precursors revealed context-dependent transcriptional regulation of Id2, with TGF-β repressing Id2 in epithelial cells to enable cytostasis but inducing it in immune progenitors to control DC lineage choice.","evidence":"ChIP showing Myc-Max to Mad-Max switch at Id2 promoter in epithelial cells; Id2-KO mouse DC analysis with TGF-β stimulation","pmids":["12824180","12598895"],"confidence":"High","gaps":["Molecular basis of context-dependent TGF-β regulation (repression vs. activation) not resolved","Whether Smad proteins directly bind the Id2 promoter in DC progenitors was not shown"]},{"year":2004,"claim":"Demonstrating that ID2 is degraded via N-terminal ubiquitination (conjugation to the α-NH2 group rather than internal lysines) and that the first 15 N-terminal residues serve as an E3 recognition element revealed an unconventional proteolytic control mechanism, while HIF-1 was shown to directly activate Id2 transcription under hypoxia.","evidence":"Lysine-less mutant degradation assays and N-terminal tagging stabilization experiments; ChIP and EMSA identifying HIF-1 binding sites in the Id2 promoter","pmids":["14733935","15252039"],"confidence":"High","gaps":["The specific E3 ligase mediating N-terminal ubiquitination was not identified","Physiological relevance of HIF-1–Id2 axis beyond neuroblastoma not explored"]},{"year":2005,"claim":"C/EBPβ was identified as a direct transcriptional activator of Id2 via ChIP-confirmed promoter occupancy, while Ovol1 was shown to repress Id2 in spermatocytes, and polycystin-2 (PC2) was found to physically interact with ID2 in a phosphorylation-dependent manner relevant to cystic kidney disease.","evidence":"ChIP, EMSA, mutagenesis, and C/EBPβ-null mammary analysis; Ovol1-KO mouse spermatocyte analysis; PC2 co-immunoprecipitation and RNAi rescue in PKD cells","pmids":["15809228","15716349","16311606"],"confidence":"High","gaps":["Direct mechanism by which PC2 sequesters ID2 not structurally resolved","Whether PC2–ID2 interaction is relevant beyond cystic kidney disease not tested"]},{"year":2006,"claim":"Multiple discoveries converged to show how ID2 protein is spatially and temporally controlled: APC/C(Cdh1) targets ID2 for D-box-dependent degradation in post-mitotic neurons (controlling axon growth via Nogo receptor), ENH sequesters ID2 in the cytoplasm during differentiation, and E47–ID2 antagonism regulates p57Kip2 in neuroblastoma, building a comprehensive picture of multi-layered ID2 regulation in neural cells.","evidence":"D-box mutagenesis and APC/C interaction assays with in vivo axon growth readout; ENH co-IP with bidirectional manipulation and subcellular localization; E47-driven p57Kip2 reporter with RNAi rescue","pmids":["16810178","16549780","16705184"],"confidence":"High","gaps":["Whether APC/C(Cdh1) and ENH pathways cooperate or act independently not addressed","Whether p57Kip2 is the sole E-protein target mediating cell-cycle arrest in neural progenitors unknown"]},{"year":2007,"claim":"Placing Id2 downstream of the cardiac transcription factors Nkx2-5 and Tbx5 in ventricular conduction system specification broadened ID2's developmental role beyond immune and neural tissues to cardiac morphogenesis.","evidence":"Id2 promoter reporter in vivo; compound haploinsufficiency genetic epistasis in mouse heart","pmids":["17604724"],"confidence":"High","gaps":["Direct bHLH targets of ID2 in conduction system cells not identified","Whether ID2 acts via Rb or bHLH inhibition in this context not resolved"]},{"year":2010,"claim":"BMP/Smad-binding elements in the Id2 promoter were biochemically mapped, and ID2 was shown to promote tumor cell migration by repressing SEMA3F through E47 antagonism, linking ID2 to invasion beyond its established role in proliferation.","evidence":"ChIP and EMSA for Smad binding at Id2 promoter; E-box mutagenesis at SEMA3F promoter with migration/invasion assays","pmids":["20674548","20388805"],"confidence":"High","gaps":["In vivo validation of SEMA3F-dependent invasion pathway not performed","Whether other semaphorins are similarly regulated by E47/ID2 not tested"]},{"year":2011,"claim":"Demonstrating that p53 directly represses Id2 transcription established ID2 as a node integrating tumor-suppressor and oncogenic signals: Myc activates and p53 represses the same gene, with the balance determining neural progenitor proliferation.","evidence":"ChIP for p53 at Id2 promoter; Id2 knockdown rescue in p53-null NPCs","pmids":["21608079"],"confidence":"High","gaps":["Whether p53-mediated Id2 repression operates in non-neural tissues not addressed","Mechanism by which p53 binding leads to transcriptional repression not dissected"]},{"year":2013,"claim":"Showing that ID2 restrains CD8+ T-cell memory differentiation by blocking E2A-mediated Tcf7 (TCF1) activation established ID2 as a molecular switch between effector and memory T-cell fates.","evidence":"Id2-KO CD8+ T-cell analysis during infection; E2A binding site reporter assay; gene expression profiling","pmids":["23536629"],"confidence":"High","gaps":["Whether ID2 affects TCF1 protein stability in addition to transcription not tested","Relative contribution of ID2 versus ID3 in memory/effector balance not resolved"]},{"year":2014,"claim":"Identification of ASB4 as an E3 ubiquitin ligase that targets ID2 for proteasomal degradation in trophoblasts provided a tissue-specific degradation mechanism controlling vascular differentiation in the placenta.","evidence":"Direct ubiquitination assay; degradation-resistant ID2 mutant; Asb4-null mouse placenta analysis","pmids":["24586788"],"confidence":"High","gaps":["Whether ASB4 ubiquitinates ID2 at the N-terminus or at lysine residues not determined","Relationship between ASB4 and APC/C(Cdh1)-mediated degradation pathways not examined"]},{"year":2016,"claim":"Three concurrent advances revealed that: USP1 deubiquitinase stabilizes ID2 to drive glioma survival (PDGF–E2F–USP1–ID2 axis); ID2 controls NK cell homeostasis by repressing E-protein target Socs3; and Bcl6 represses Id2 to promote TFH over TH1 differentiation, firmly establishing ID2 as a central integrator of immune lineage decisions.","evidence":"USP1 pharmacologic inhibition and Id2 KO in glioma model with ChIP; Id2 conditional KO in NK cells with Socs3 double-KO epistasis; Bcl6 ChIP at Id2 locus with T-cell subset phenotyping","pmids":["26951930","26795246","27213691"],"confidence":"High","gaps":["Whether USP1 deubiquitinates ID2 at the N-terminal ubiquitin or at lysine-linked chains not resolved","How Bcl6 mechanistically represses the Id2 locus (co-repressor identity) not identified"]},{"year":2019,"claim":"Genome-wide binding analysis of Mtg16 at the Id2 locus, combined with an Nfil3–Zeb2–Id2 genetic circuit controlling cDC1 specification, consolidated ID2 as the key node in a multi-factor transcriptional network governing dendritic cell lineage commitment.","evidence":"Mtg16 ChIP-seq with Id2/Mtg16 double-KO epistasis; scRNA-seq of CDPs with Nfil3/Zeb2/Id2 genetic epistasis","pmids":["24980046","31406377"],"confidence":"High","gaps":["How Mtg16 mechanistically represses the Id2 promoter (direct or indirect DNA binding) not fully resolved","Whether the Nfil3–Zeb2–Id2 circuit operates in human DC development not confirmed"]},{"year":2020,"claim":"Structural and biochemical reconstitution of the monoubiquitinated FANCI–FANCD2 (ID2) complex showed that FANCD2 ubiquitination drives a conformational change enabling the complex to encircle DNA, clarifying the molecular basis of DNA interstrand crosslink repair activation (note: this concerns the FANCI–FANCD2 complex, distinct from the HLH protein ID2).","evidence":"Structural analysis of ubiquitinated ID2 complex; DNA-binding affinity assays; deubiquitination protection assays with USP1–UAF1","pmids":["32510829"],"confidence":"High","gaps":["This finding pertains to the FANCI–FANCD2 heterodimer, not the HLH protein ID2; included here because both share the 'ID2' acronym in the literature"]},{"year":2021,"claim":"Demonstrating that TGF-β suppresses Id2 in developing airway basal stem cells and that persistent Id2 expression drives basal cell hyperplasia established the TGF-β–ID2 axis as a proliferation switch with precancerous implications, while ID2 was also shown to suppress TCF1 amplitude to control terminal NK cell maturation.","evidence":"Bidirectional genetic manipulation (Id2 OE, Tgfbr2 KO) in murine airways with scRNA-seq; Id2 conditional KO in NK cells with in vivo melanoma clearance assay","pmids":["34129836","33857289"],"confidence":"High","gaps":["Whether TGF-β–ID2 axis directly causes malignant transformation or only a precancerous state not resolved","Mechanism by which ID2 suppresses TCF1 (direct E-protein sequestration vs. other) not fully dissected"]},{"year":2022,"claim":"E-cadherin loss was shown to de-repress Id2 via a p120-catenin/Kaiso pathway, with cytosolic ID2 inducing G0/G1 arrest through hypo-phosphorylated Rb interaction, unexpectedly demonstrating that ID2 can promote quiescence and anoikis resistance rather than proliferation depending on subcellular context.","evidence":"ChIP for Kaiso at Id2 promoter; co-IP of ID2 with Rb; subcellular fractionation; in vivo lung colonization assay in ILC models","pmids":["35437308"],"confidence":"High","gaps":["How cytosolic ID2 preferentially binds hypo-phosphorylated Rb while nuclear ID2 antagonizes Rb growth suppression is paradoxical and not mechanistically reconciled","Generalizability beyond invasive lobular carcinoma not tested"]},{"year":2024,"claim":"Elucidating that ID2 disrupts a Tcf3–Tal1 complex to prevent LSD1 recruitment to the Slamf6 promoter, thereby maintaining permissive H3K4me2 marks, revealed an epigenetic mechanism through which ID2 sustains progenitor exhausted CD8+ T cells—extending its function beyond simple bHLH sequestration to chromatin remodeling.","evidence":"Co-IP of ID2 HLH domain with Tcf3; ChIP for H3K4me2 at Slamf6 promoter; LSD1 inhibitor rescue in Id2-KO tumor-bearing mice","pmids":["38287103"],"confidence":"High","gaps":["Whether ID2-mediated disruption of LSD1 recruitment occurs at other loci genome-wide not tested","Direct structural basis of how ID2 HLH domain disrupts the Tcf3–Tal1 interface unknown"]},{"year":null,"claim":"Key unresolved questions include: the structural basis of ID2's selective partner recognition (bHLH vs. Rb vs. PC2); how nuclear vs. cytosolic ID2 exerts opposing effects on Rb-mediated cell-cycle control; the identity of the E3 ligase mediating N-terminal ubiquitination; and comprehensive mapping of the chromatin landscape changes driven by ID2 across immune and non-immune lineages.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of ID2 in complex with any partner","Nuclear vs. cytosolic ID2 function on Rb not mechanistically reconciled","Genome-wide ID2-dependent chromatin remodeling not systematically mapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,8,18,21,26,32]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,8,18,26,33]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5,7,26]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[7,41]}],"pathway":[{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1,2,3,41]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,11,14,35]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[10,20,38]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[9,21,22,24,27,33,37,38]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,11,12,13,15,19]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,6,20,23]}],"complexes":["APC/C(Cdh1) (as substrate)"],"partners":["E2A","RB1","ENH","CDH1","USP1","ASB4","PU.1","TCF3"],"other_free_text":[]},"mechanistic_narrative":"ID2 is a helix-loop-helix (HLH) protein that lacks a basic DNA-binding domain and functions as a dominant-negative inhibitor of basic HLH (bHLH) transcription factors and Rb-family tumor suppressors, thereby controlling cell proliferation, differentiation, and lineage commitment across diverse tissues including the immune, nervous, cardiovascular, and intestinal systems. ID2 heterodimerizes with E-proteins (E47, E2A) to block their DNA-binding activity and downstream target gene expression—including p57Kip2, Socs3, SEMA3F, and Tcf7—while also directly binding and neutralizing pRb, p107, and p130 to promote cell-cycle progression [PMID:1922066, PMID:8649364, PMID:16705184, PMID:26795246]. ID2 protein stability is tightly regulated by APC/C(Cdh1)-dependent D-box-mediated degradation in neurons, N-terminal ubiquitination, ASB4 E3 ligase activity in trophoblasts, USP1-mediated deubiquitination in glioma, and CDK2-dependent phosphorylation that relieves bHLH inhibition in late G1 [PMID:16810178, PMID:14733935, PMID:24586788, PMID:26951930, PMID:9029153]. ID2 transcription is activated by Myc, β-catenin/TCF4, HIF-1, C/EBPβ, BMP/Smad, and Nkx2-5/Tbx5, and repressed by TGF-β (via Mad-Max promoter switching), p53, Bcl6, Mtg16, and Ovol1, integrating multiple developmental and stress signals into a single dominant-negative output [PMID:11034201, PMID:11572874, PMID:15252039, PMID:15809228, PMID:12824180, PMID:21608079, PMID:27213691]."},"prefetch_data":{"uniprot":{"accession":"Q02363","full_name":"DNA-binding protein inhibitor ID-2","aliases":["Class B basic helix-loop-helix protein 26","bHLHb26","Inhibitor of DNA binding 2","Inhibitor of differentiation 2"],"length_aa":134,"mass_kda":14.9,"function":"Transcriptional regulator (lacking a basic DNA binding domain) which negatively regulates the basic helix-loop-helix (bHLH) transcription factors by forming heterodimers and inhibiting their DNA binding and transcriptional activity. Implicated in regulating a variety of cellular processes, including cellular growth, senescence, differentiation, apoptosis, angiogenesis, and neoplastic transformation. Inhibits skeletal muscle and cardiac myocyte differentiation. Regulates the circadian clock by repressing the transcriptional activator activity of the CLOCK-BMAL1 heterodimer. Restricts the CLOCK and BMAL1 localization to the cytoplasm. Plays a role in both the input and output pathways of the circadian clock: in the input component, is involved in modulating the magnitude of photic entrainment and in the output component, contributes to the regulation of a variety of liver clock-controlled genes involved in lipid metabolism","subcellular_location":"Cytoplasm; Nucleus","url":"https://www.uniprot.org/uniprotkb/Q02363/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ID2","classification":"Not Classified","n_dependent_lines":39,"n_total_lines":1208,"dependency_fraction":0.03228476821192053},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ID2","total_profiled":1310},"omim":[{"mim_id":"620305","title":"NEUROOCULORENAL SYNDROME; NORS","url":"https://www.omim.org/entry/620305"},{"mim_id":"614041","title":"RB TRANSCRIPTIONAL COREPRESSOR 1; RB1","url":"https://www.omim.org/entry/614041"},{"mim_id":"609946","title":"DEAFNESS, AUTOSOMAL RECESSIVE 47; DFNB47","url":"https://www.omim.org/entry/609946"},{"mim_id":"609602","title":"KLF TRANSCRIPTION FACTOR 17; KLF17","url":"https://www.omim.org/entry/609602"},{"mim_id":"608433","title":"ZINC FINGER- AND BTB DOMAIN-CONTAINING PROTEIN 18; ZBTB18","url":"https://www.omim.org/entry/608433"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Nuclear bodies","reliability":"Approved"},{"location":"Centrosome","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"blood vessel","ntpm":790.2},{"tissue":"parathyroid gland","ntpm":1136.9}],"url":"https://www.proteinatlas.org/search/ID2"},"hgnc":{"alias_symbol":["GIG8","bHLHb26"],"prev_symbol":[]},"alphafold":{"accession":"Q02363","domains":[{"cath_id":"4.10.280.10","chopping":"31-85","consensus_level":"medium","plddt":90.2402,"start":31,"end":85}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q02363","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q02363-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q02363-F1-predicted_aligned_error_v6.png","plddt_mean":68.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ID2","jax_strain_url":"https://www.jax.org/strain/search?query=ID2"},"sequence":{"accession":"Q02363","fasta_url":"https://rest.uniprot.org/uniprotkb/Q02363.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q02363/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q02363"}},"corpus_meta":[{"pmid":"1922066","id":"PMC_1922066","title":"Id proteins Id1 and Id2 selectively inhibit DNA binding by one class of helix-loop-helix proteins.","date":"1991","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/1922066","citation_count":567,"is_preprint":false},{"pmid":"11034201","id":"PMC_11034201","title":"Id2 is a retinoblastoma protein target and mediates signalling by Myc oncoproteins.","date":"2000","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/11034201","citation_count":421,"is_preprint":false},{"pmid":"12598895","id":"PMC_12598895","title":"Transcriptional profiling identifies Id2 function in dendritic cell development.","date":"2003","source":"Nature immunology","url":"https://pubmed.ncbi.nlm.nih.gov/12598895","citation_count":403,"is_preprint":false},{"pmid":"22057289","id":"PMC_22057289","title":"The transcriptional regulators Id2 and Id3 control the formation of distinct memory CD8+ T cell subsets.","date":"2011","source":"Nature immunology","url":"https://pubmed.ncbi.nlm.nih.gov/22057289","citation_count":347,"is_preprint":false},{"pmid":"11120774","id":"PMC_11120774","title":"Id2 and Id3 inhibit development of CD34(+) stem cells into predendritic cell (pre-DC)2 but not into pre-DC1. 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mapping\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — original biochemical reconstitution with multiple orthogonal methods, foundational paper with 567 citations\",\n      \"pmids\": [\"1922066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Id2 (but not Id1 or Id3) directly binds pRb, p107, and p130 in vitro and in vivo, neutralizing their growth-suppressive activity and reversing cell-cycle arrest imposed by pRb family members and CDK inhibitors p16 and p21; Id2 expression also reduces cyclin D1 levels and cyclin D1–CDK4 complexes.\",\n      \"method\": \"In vitro binding assays; co-immunoprecipitation in transfected Saos-2 cells; cell-cycle arrest rescue assays; Western blot for cyclin D1\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — multiple orthogonal methods (in vitro binding + in vivo co-IP + functional rescue), replicated by subsequent work\",\n      \"pmids\": [\"8649364\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Id2 is phosphorylated by cyclin E–CDK2 and cyclin A–CDK2 (but not cyclin D–CDKs) on a serine within a CDK consensus site in late G1; phosphorylation of Id2 in serum-stimulated fibroblasts correlates with restoration of E-box-dependent DNA-binding complexes, indicating that CDK-mediated phosphorylation relieves Id2-mediated inhibition of bHLH transcription factors.\",\n      \"method\": \"In vitro kinase assays with purified cyclin–CDK complexes; in vivo phosphorylation in synchronised human diploid fibroblasts; electrophoretic mobility shift assay (EMSA)\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution plus in vivo correlation with multiple orthogonal methods\",\n      \"pmids\": [\"9029153\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Id2 is a direct transcriptional target of Myc-family oncoproteins; Id2 acts as a dominant-negative antagonist of Rb-family proteins; in neuroblastoma cells overexpressing N-Myc, Id2 is in molar excess of active Rb, and cell-cycle progression driven by Myc oncoproteins requires Id2-mediated inactivation of Rb. Id2–Rb double-knockout embryos survive to term, revealing a functional epistatic relationship.\",\n      \"method\": \"Genetic double-knockout rescue; quantitative protein analysis; transcriptional activation assays; neuroblastoma cell analysis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genetic epistasis (double-KO rescue) combined with biochemical quantitation, high-impact replicated finding\",\n      \"pmids\": [\"11034201\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Id2 is degraded by the ubiquitin–proteasome system via N-terminal ubiquitination: a Myc-tag fused to the N-terminus (but not C-terminus) stabilises Id2, lysine-less Id2 is still efficiently degraded (ubiquitin conjugated to α-NH2 group), and deletion of the first 15 N-terminal residues stabilises the protein, identifying this domain as an E3 recognition element.\",\n      \"method\": \"Ubiquitination assays; N-terminal tagging stabilisation experiments; lysine-less mutant degradation assays; proteasome inhibitor experiments\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mechanistic mutagenesis plus reconstituted ubiquitination, multiple orthogonal approaches in one study\",\n      \"pmids\": [\"14733935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Polycystin-2 (PC2) directly interacts with Id2; this interaction is regulated by PC1-dependent phosphorylation of PC2. Id2 expression suppresses p21 induction by PC1 or PC2, and Id2 shows enhanced nuclear localisation in cystic kidneys. RNAi knockdown of Id2 corrects the hyperproliferative phenotype of PC1-mutant cells.\",\n      \"method\": \"Co-immunoprecipitation; phosphorylation assays; RNAi knockdown with proliferation readout; immunofluorescence in human/mouse cystic kidney tissue\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding demonstrated, phosphorylation-regulated interaction, functional rescue by RNAi, replicated in vivo\",\n      \"pmids\": [\"16311606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"APC/C(Cdh1) targets Id2 for proteasomal degradation through a conserved destruction box (D-box) motif in neurons. Id2 interacts with core APC/C subunits and Cdh1; D-box mutants of Id2 resist Cdh1 binding, remain stable after cell-cycle exit, and enhance axonal growth in cerebellar granule neurons in vitro and in vivo, overcoming myelin inhibitory signals. Degradation of Id2 permits accumulation of the Nogo receptor, a bHLH target gene product that inhibits axonal growth.\",\n      \"method\": \"Co-immunoprecipitation; APC/C interaction assays; D-box mutagenesis; cerebellar granule neuron axon growth assays in vitro and in vivo; gene expression analysis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — mutagenesis, reconstitution, and functional in vivo validation in one study\",\n      \"pmids\": [\"16810178\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The actin-associated LIM-domain protein ENH (enigma homolog) is a cytoplasmic retention factor for Id2: ENH binds the HLH domain of Id2 in vitro and in vivo, its overexpression in neuroblastoma cells translocates Id2 from nucleus to cytoplasm and inactivates its transcriptional and cell-cycle-promoting functions, and RNAi silencing of ENH prevents cytoplasmic relocation of Id2 during retinoic acid-induced differentiation.\",\n      \"method\": \"Co-immunoprecipitation; in vitro binding assay; fluorescence microscopy of subcellular localisation; RNAi knockdown with localisation and functional readouts\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct binding demonstrated in vitro and in vivo, bidirectional manipulation (OE and KD) with functional consequence\",\n      \"pmids\": [\"16549780\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Id2 prevents E-protein-mediated activation of p57Kip2 expression in neuroblastoma cells: E47 directly activates p57Kip2 transcription to block S-phase entry, Id2 suppresses this activation, and RNAi knockdown of p57Kip2 fully reverses E47-mediated cell-cycle arrest, establishing p57Kip2 as the functionally relevant CDK inhibitor target of the E-protein/Id2 axis in neural cells.\",\n      \"method\": \"Microarray gene expression profiling; reporter assays; RNAi knockdown; cell-cycle analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — epistasis established by RNAi rescue plus expression analysis, multiple orthogonal methods\",\n      \"pmids\": [\"16705184\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"TGF-β induces Id2 expression in dendritic cell precursors; Id2 is required for development of Langerhans cells and splenic CD8α+ DCs, and Id2 represses B-cell lineage genes in DCs, establishing a TGF-β–Id2 signaling axis that controls DC lineage choice.\",\n      \"method\": \"Id2-knockout mouse analysis; in vitro DC differentiation with TGF-β stimulation; gene expression profiling\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined cellular phenotype plus cytokine-pathway epistasis, replicated\",\n      \"pmids\": [\"12598895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"A 1.2 kb Id2 promoter fragment is cooperatively regulated by Nkx2-5 and Tbx5 in vitro and is sufficient for conduction-system-specific expression in vivo; compound haploinsufficiency of Tbx5 and Id2 (or Tbx5 and Nkx2-5) blocks embryonic specification of the ventricular conduction system, placing Id2 downstream of Tbx5/Nkx2-5 in a conduction system developmental pathway.\",\n      \"method\": \"SAGE transcriptional profiling; Id2-deficient mouse cardiac analysis; promoter reporter assay; compound haploinsufficiency genetic epistasis; in vivo transgenic reporter\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — promoter dissection, genetic epistasis, in vivo reporter, highly cited\",\n      \"pmids\": [\"17604724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Id2 is a direct transcriptional target of β-catenin/TCF4; a TCF4-binding motif in the Id2 promoter is identified by EMSA and supershift, and site-directed mutagenesis abolishes promoter activity; β-catenin overexpression increases Id2 protein, and Id2 expression promotes anchorage-independent survival of colon carcinoma cells.\",\n      \"method\": \"Reporter assay; EMSA and supershift; site-directed mutagenesis; transfection; anchorage-independent growth assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — promoter mutagenesis plus direct binding demonstrated plus functional consequence\",\n      \"pmids\": [\"11572874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"HIF-1 directly activates Id2 transcription in hypoxic neuroblastoma cells via two functional HIF-1 binding sites at −725 and −1893 relative to the transcriptional start site, demonstrated by EMSA and ChIP; Id2 promoter-luciferase constructs are HIF-1-specifically activated in transfection assays.\",\n      \"method\": \"EMSA; chromatin immunoprecipitation (ChIP); luciferase reporter assay; actinomycin D transcription inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — ChIP plus EMSA plus mutagenesis, multiple orthogonal methods\",\n      \"pmids\": [\"15252039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"C/EBPβ directly activates Id2 transcription: nuclear translocation of C/EBPβ rapidly induces endogenous Id2; the most proximal of three C/EBPβ-binding elements in the 2.3 kb Id2 promoter is required for transactivation; EMSA identifies this as a C/EBPβ core-binding sequence; ChIP confirms C/EBPβ occupancy at the Id2 promoter in vivo; Id2 expression is reduced in C/EBPβ-deficient mammary glands.\",\n      \"method\": \"Inducible C/EBPβ-ERT nuclear translocation; reporter assay; EMSA; ChIP; Northern blot in C/EBPβ-null mammary glands\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — ChIP + EMSA + mutagenesis + KO validation, multiple orthogonal methods\",\n      \"pmids\": [\"15809228\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"BMP6 activates Id2 transcription through Smad-binding elements (two GGCGCC palindromes and one GTCT element) in the Id2 promoter; gel shift and ChIP assays confirm physical Smad binding; mutation of these elements abolishes BMP responsiveness; a novel bipartite CGCC sequence contributes to Smad target recognition.\",\n      \"method\": \"Reporter assay; gel-shift (EMSA); ChIP; site-directed mutagenesis; BMP receptor inhibitor\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — EMSA + ChIP + mutagenesis, multiple orthogonal methods\",\n      \"pmids\": [\"20674548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"TGF-β represses Id2 expression in epithelial cells via induction of Mad2 and Mad4, which replace Myc-Max complexes with Mad-Max complexes on the Id2 promoter, providing a mechanism for TGF-β cytostatic program independent of c-Myc downregulation.\",\n      \"method\": \"Reporter assay; ChIP showing Myc-Max to Mad-Max promoter switching; Western blot; quantitative expression analysis across multiple epithelial cell lines\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP demonstrating promoter occupancy switch, multiple cell lines, mechanistic pathway dissection\",\n      \"pmids\": [\"12824180\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Id2 acts as a master regulator of VEGF expression in pituitary tumor cells and neuroblastoma; in Rb+/− pituitary tumors, Id2-null cells show premature bHLH activation and p27Kip1 upregulation that impairs melanotrope proliferation and tumor initiation; N-Myc-driven Id2 expression is sufficient and necessary for VEGF expression in neuroblastoma.\",\n      \"method\": \"Id2-null/Rb+/− compound genetic mouse model; immunohistochemistry; gene expression analysis; neuroblastoma cell manipulation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vivo genetic epistasis plus mechanistic gene expression analysis\",\n      \"pmids\": [\"15831462\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Id2 regulates erythroid development by interacting with transcription factor PU.1 and modulating PU.1 and GATA-1 activities; Id2-null mice have expanded B-cell compartments, and Id2 acts as physiologically relevant inhibitor of E2A during B lymphopoiesis through direct antagonism.\",\n      \"method\": \"Id2 knockout mouse analysis; retroviral transduction/overexpression; shRNA knockdown; co-immunoprecipitation of Id2 with PU.1\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — co-IP plus KO phenotype, single lab\",\n      \"pmids\": [\"18523151\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Id2 promotes tumor cell migration and invasion through transcriptional repression of Semaphorin 3F (SEMA3F): E47 directly activates SEMA3F via two E-box sites in its promoter; Id2 acts as a dominant-negative inhibitor of E47, abrogating SEMA3F expression and its biological activities (F-actin depolymerisation, RhoA inactivation, migration inhibition).\",\n      \"method\": \"Reporter assay with E-box mutagenesis; SEMA3F knockdown rescue; migration/invasion assays; F-actin and RhoA activity assays\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — promoter dissection + mutagenesis + functional rescue with multiple downstream readouts\",\n      \"pmids\": [\"20388805\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"p53 directly represses Id2 transcription by binding a conserved site within the Id2 promoter; p53-null neural progenitor cells have elevated Id2 and increased proliferation/self-renewal; suppression of Id2 is sufficient to restore normal proliferation to p53-null NPCs; elevated Id2 expression phenocopies p53 loss.\",\n      \"method\": \"Chromatin immunoprecipitation; Id2 KD by RNAi; p53-null mouse NPC analysis; promoter binding assay\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP demonstrating direct promoter binding, RNAi rescue, genetic model validation\",\n      \"pmids\": [\"21608079\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The ubiquitin ligase ASB4 ubiquitinates and targets Id2 for proteasomal degradation in trophoblast/placental cells, promoting vascular differentiation; a degradation-resistant Id2 mutant co-expressed with ASB4 inhibits differentiation and functional vascular responses; Asb4-null placentas retain Id2 expression and show immature vascular patterning.\",\n      \"method\": \"Ubiquitination assay; proteasome inhibitor experiments; degradation-resistant mutant co-transfection; endothelial co-culture assays; Asb4-null mouse placenta analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct ubiquitination shown, mutagenesis, functional rescue, and in vivo genetic validation\",\n      \"pmids\": [\"24586788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Id2 represses multiple E-protein target genes including Socs3 in NK cells; Id2 deletion in mature NK cells leads to impaired IL-15 receptor signaling and metabolic dysfunction, rescued by strong IL-15 stimulation or genetic Socs3 deletion, demonstrating that Id2 regulates NK cell homeostasis by titrating E-protein activity at Socs3 and other target loci.\",\n      \"method\": \"Id2 conditional KO in mature NK cells; genetic Socs3/Id2 double-KO epistasis; IL-15 receptor signaling assays; metabolic function assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis (double-KO rescue) plus signaling assays, multiple orthogonal methods\",\n      \"pmids\": [\"26795246\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Bcl6 binds the Id2 locus to repress Id2 expression in TFH cells; TH1 cells express higher Id2 than TFH cells; Id2 deficiency increases TFH frequency in an E-protein-dependent manner and blocks TH1 differentiation; Id2 reinforces TH1 differentiation by repressing E2A-dependent TFH-promoting programs.\",\n      \"method\": \"Id2 RNAi in T cells; T cell-specific Id2 KO mouse; ChIP (Bcl6 occupancy at Id2 locus); T cell subset phenotyping during viral infection\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP for direct Bcl6–Id2 locus binding, combined with genetic KO and epistasis\",\n      \"pmids\": [\"27213691\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PDGF signaling upregulates USP1 via E2F transcription factors; USP1 stabilises ID2 protein; genetic ablation of Id2 delays glioma-induced mortality; pharmacologic USP1 inhibition reduces ID2 levels and delays tumorigenesis in a mouse proneural glioma model, establishing a PDGF–E2F–USP1–ID2 survival signalling cascade.\",\n      \"method\": \"E2F ChIP at Usp1 promoter; Id2 genetic KO in glioma model; USP1 pharmacologic inhibition; comparative transcriptomics\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — ChIP for direct E2F binding, pharmacologic and genetic validation in vivo\",\n      \"pmids\": [\"26951930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Id2 mediates Treg-to-TH17 plasticity by sequestering the transcription activator E2A; expression of Id2 in iTreg cells reduces Foxp3 expression and induces TH17-related cytokines; Treg-specific Id2 overexpression in mice reduces the Treg compartment and causes immune dysregulation.\",\n      \"method\": \"Id2 overexpression in iTreg cells; Treg-specific Id2 transgenic mice; cellular fate-mapping; cytokine profiling\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — gain-of-function in vitro and in vivo with defined molecular mechanism (E2A sequestration)\",\n      \"pmids\": [\"30413714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Monoubiquitination of FANCD2 (within the FANCI–FANCD2/ID2 complex) promotes a large-scale conformational change that increases the complex's affinity for double-stranded DNA and enables it to encircle DNA by forming a secondary 'Arm' interface; monoubiquitination of FANCI protects the ubiquitin on FANCD2 from deubiquitination by USP1–UAF1, with key hydrophobic residues of FANCI's ubiquitin mediating this protection.\",\n      \"method\": \"Structural and biochemical analysis of ubiquitinated ID2 complex; DNA-binding affinity assays; deubiquitination protection assays with USP1–UAF1\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural/biochemical reconstitution with mechanistic mutagenesis\",\n      \"pmids\": [\"32510829\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Id2 epigenetically regulates CD8+ T-cell exhaustion by binding, via its HLH domain, to Tcf3 (TCF1) and disrupting the Tcf3–Tal1 complex, thereby preventing Tcf3 from recruiting LSD1 histone demethylase to the Slamf6 promoter; this results in increased permissive H3K4me2 marks and greater chromatin accessibility at the Slamf6 promoter, promoting generation of Slamf6+ progenitor exhausted T cells. LSD1 inhibitor GSK2879552 rescues Id2-KO phenotype in tumour-bearing mice.\",\n      \"method\": \"Co-immunoprecipitation (HLH domain); ChIP for H3K4me2 and chromatin accessibility at Slamf6 promoter; Id2-KO mouse tumour model; LSD1 pharmacologic inhibition rescue\",\n      \"journal\": \"Cellular & molecular immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — direct protein interaction, epigenetic mark measurement, pharmacologic rescue, multiple orthogonal methods\",\n      \"pmids\": [\"38287103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ID2 in NK cells suppresses TCF1 amplitude during maturation; elevated TCF1 in ID2-deficient NK cells arrests their maturation and limits cytokine-induced IFN-γ production and anti-metastatic function, establishing ID2 as a transcriptional brake on TCF1 that controls the balance between immature expansion and terminal NK cell differentiation.\",\n      \"method\": \"Id2 conditional KO in NK cells; TCF1 reporter and protein level analysis; in vivo melanoma clearance assay; cytokine stimulation assays\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — conditional KO with defined molecular target (TCF1) and functional in vivo readout\",\n      \"pmids\": [\"33857289\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ovol1 represses Id2 transcription in pachytene spermatocytes; Ovol1-deficient germ cells upregulate Id2 and fail to progress through the pachytene stage; Ovol1 represses the Id2 promoter in reporter assays, establishing Id2 as a direct transcriptional target of Ovol1 in male meiosis.\",\n      \"method\": \"Ovol1-KO mouse analysis; transcriptional profiling; Northern blot; Id2 promoter reporter assay\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reporter assay plus genetic KO phenotype, single lab\",\n      \"pmids\": [\"15716349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Ebf1 down-regulates Id2 and Id3 expression in prepro-B cells to specify B-cell fate; enforced Ebf1 expression in IL-7Rα−/− bone marrow cells potently reduces Id2 and Id3 mRNA and restores B-cell differentiation in vivo; overexpression of either Id2 or Id3 blocks B-cell specification at the prepro-B stage.\",\n      \"method\": \"Retroviral Ebf1 expression in IL-7Rα-null bone marrow; Id2/Id3 overexpression in wild-type bone marrow; qRT-PCR; in vivo reconstitution\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional genetic manipulation with in vivo rescue, clear epistasis established\",\n      \"pmids\": [\"19122139\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"AMPK (PRKAA1/2) mediates stress-induced proteasome-dependent loss of ID2 protein in trophoblast stem cells at high stress levels, triggering differentiation; at low stress levels AMPK mediates metabolic adaptation without ID2 loss, establishing a dose-dependent AMPK–ID2 axis linking cellular stress to TSC differentiation.\",\n      \"method\": \"AMPK inhibitor/activator pharmacology; proteasome inhibitor experiments; PRKAA1/2 activation assays; immunoblot for ID2 in stressed TSCs\",\n      \"journal\": \"Reproduction (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — pharmacologic manipulation with multiple inhibitors/activators, single lab\",\n      \"pmids\": [\"20876741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Id2 controls intestinal stem cell specification by restricting Wnt signalling activity at early embryonic stages; Id2-deficient intestinal epithelial cells precociously activate Wnt target genes and generate an expanded Lgr5+ progenitor pool.\",\n      \"method\": \"Id2-KO mouse; cell fate mapping; ex vivo organoid culture with Wnt target gene analysis; transcriptional profiling of adult Id2-null ISCs\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with pathway (Wnt) analysis, single lab\",\n      \"pmids\": [\"28077488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Id2 inhibits BETA2/NeuroD-mediated E-box-dependent gene expression in a dose-dependent manner by forming heterodimers that block BETA2/NeuroD binding to its target E-box sequence, as shown by EMSA; Id2 inhibits BETA2/NeuroD transcriptional activation in both HIT and HeLa cells.\",\n      \"method\": \"Yeast two-hybrid (interaction screen); EMSA; co-expression transcriptional reporter assays in HIT and HeLa cells\",\n      \"journal\": \"Experimental & molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — EMSA plus functional reporter, single lab\",\n      \"pmids\": [\"12526101\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Id2 restrains CD8+ T-cell memory differentiation by inhibiting E2A-mediated direct activation of Tcf7 (TCF1); Id2-deficient CD8+ T cells fail to upregulate Tbx21 for short-lived effector generation and instead adopt a memory fate with elevated Eomesodermin and Tcf7.\",\n      \"method\": \"Id2-KO CD8+ T-cell analysis during infection; E2A binding site reporter assay; gene expression profiling\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with defined molecular target (E2A–Tcf7 axis), functional in vivo readout\",\n      \"pmids\": [\"23536629\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"BMP4 induces Id2 expression in AR42J pancreatic epithelial cells, and BMP4 stimulation promotes Id2 binding to NeuroD (a bHLH differentiation factor), thereby blocking endocrine differentiation and promoting expansion of pancreatic progenitors.\",\n      \"method\": \"BMP4 stimulation assays; co-immunoprecipitation of Id2–NeuroD; BMP4 neutralisation in mouse islet regeneration model; proliferation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — direct interaction by co-IP, functional in vivo BMP4 neutralisation, single lab\",\n      \"pmids\": [\"16547003\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"TGF-β signalling suppresses Id2 expression to decelerate cell-cycle in developing airway basal stem cells; reduced TGF-β signalling in adult tissue regeneration restores Id2 expression and initiates proliferation; persistent Id2 expression (via Id2 OE or Tgfbr2 KO) drives basal cell hyperplasia resembling a precancerous state, establishing the TGF-β–Id2 axis as a proliferation switch in airway basal cells.\",\n      \"method\": \"Id2 overexpression; Tgfbr2 conditional KO; single-cell transcriptomics; genetic validation in murine airway development and regeneration models\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — bidirectional genetic manipulation, single-cell transcriptomics, in vivo validation\",\n      \"pmids\": [\"34129836\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"METTL3-mediated m6A modification stabilises ID2 mRNA in an m6A-YTHDF2-dependent manner in pancreatic cancer cells; METTL3 knockdown reduces m6A on ID2 mRNA and destabilises it; ID2 in turn controls stemness molecules NANOG and SOX2 via the PI3K–AKT pathway.\",\n      \"method\": \"METTL3 knockdown; m6A-seq/MeRIP; mRNA stability assay; YTHDF2 co-immunoprecipitation; PI3K–AKT pathway inhibition\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct m6A measurement plus stability assays plus YTHDF2 interaction, single lab\",\n      \"pmids\": [\"37196908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Mtg16 represses Id2 transcription in dendritic cell progenitors; genome-wide DNA-binding analysis identifies Id2 as a direct Mtg16 target; Mtg16-deficient pDCs and cDC progenitors show aberrant Id2 induction; genetic deletion of Id2 partially rescues impaired pDC development in Mtg16-null mice.\",\n      \"method\": \"Mtg16-KO mouse; genome-wide ChIP-seq (DNA-binding analysis); Id2-KO rescue epistasis; flow cytometric DC subset analysis\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — genome-wide ChIP-seq plus genetic double-KO epistasis\",\n      \"pmids\": [\"24980046\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"An Nfil3–Zeb2–Id2 genetic circuit controls cDC1 development: Nfil3 is required for the transition from Zeb2hi/Id2lo CDPs to Zeb2lo/Id2hi CDPs (earliest committed cDC1 progenitors); genetic epistasis shows this circuit blocks E-protein activity to exclude pDC potential and explains the switch in Irf8 enhancer usage.\",\n      \"method\": \"Single-cell RNA sequencing of CDPs; genetic epistasis (Nfil3 KO, Zeb2 KO, Id2 KO); DC progenitor phenotyping\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — scRNA-seq plus multi-gene genetic epistasis, mechanistic pathway placement\",\n      \"pmids\": [\"31406377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"bHLH transcription factors ME1, ME2, and NSCL1 stimulate Id2 promoter activity through E-box clusters in the 5′ regulatory region; co-expression of Id2 blocks this stimulatory effect, revealing a negative feedback loop in Id2 transcriptional regulation.\",\n      \"method\": \"Reporter/luciferase promoter assay; co-expression in F9 cells; retinoic acid differentiation assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 — promoter reporter assay with co-expression, single lab, relatively limited follow-up\",\n      \"pmids\": [\"7589553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Id1 and Id2 can be phosphorylated in vitro by cAMP-dependent protein kinase; Id2 and Id3 can be phosphorylated by cdc2 kinase; all three (Id1, Id2, Id3) by PKC; however, phosphorylation by cAMP-kinase or PKC did not affect Id2/E47 dimerisation or DNA-binding inhibition in gel-shift assays.\",\n      \"method\": \"In vitro kinase assay; immunoprecipitation of phosphorylated Id1 from NGF-stimulated PC12 cells; gel-shift assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–3 — in vitro kinase assay plus EMSA, but limited functional consequence demonstrated\",\n      \"pmids\": [\"7864897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Under anchorage-independent conditions, E-cadherin loss de-represses Id2 transcription via a p120-catenin/Kaiso-dependent mechanism at a canonical Kaiso-binding sequence (TCCTGCNA) in the Id2 promoter; Id2 then accumulates in the cytosol and induces CDK4/6-dependent G0/G1 arrest through interaction with hypo-phosphorylated Rb, promoting anoikis resistance and lung colonisation in ILC models.\",\n      \"method\": \"Loss-of-function experiments; inducible E-cadherin restoration; promoter analysis; ChIP for Kaiso; co-immunoprecipitation of Id2 with Rb; subcellular fractionation; in vivo lung colonisation assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — promoter dissection with Kaiso ChIP, direct Id2–Rb interaction, subcellular fractionation, in vivo functional assay\",\n      \"pmids\": [\"35437308\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ID2 is a HLH-domain-only dominant-negative inhibitor of bHLH E-protein transcription factors and Rb-family tumour suppressors; it is transcriptionally activated by Myc, β-catenin/TCF4, HIF-1, C/EBPβ, BMP/Smad, and Nkx2-5/Tbx5, and is repressed by TGF-β (via Mad proteins), p53, Bcl6, Mtg16, and Ovol1; ID2 protein stability is controlled by APC/C(Cdh1)-mediated D-box-dependent proteasomal degradation, by N-terminal ubiquitination, by ASB4 E3 ligase, by CDK2-dependent phosphorylation (which relieves bHLH inhibition), and by USP1-dependent deubiquitination; ID2 activity is spatially regulated by cytoplasmic sequestration via the LIM-domain protein ENH; and the FANCI–FANCD2 (ID2) heterodimer encircles DNA upon FANCD2 monoubiquitination to promote DNA interstrand crosslink repair.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"ID2 is a helix-loop-helix (HLH) protein that lacks a basic DNA-binding domain and functions as a dominant-negative inhibitor of basic HLH (bHLH) transcription factors and Rb-family tumor suppressors, thereby controlling cell proliferation, differentiation, and lineage commitment across diverse tissues including the immune, nervous, cardiovascular, and intestinal systems. ID2 heterodimerizes with E-proteins (E47, E2A) to block their DNA-binding activity and downstream target gene expression—including p57Kip2, Socs3, SEMA3F, and Tcf7—while also directly binding and neutralizing pRb, p107, and p130 to promote cell-cycle progression [PMID:1922066, PMID:8649364, PMID:16705184, PMID:26795246]. ID2 protein stability is tightly regulated by APC/C(Cdh1)-dependent D-box-mediated degradation in neurons, N-terminal ubiquitination, ASB4 E3 ligase activity in trophoblasts, USP1-mediated deubiquitination in glioma, and CDK2-dependent phosphorylation that relieves bHLH inhibition in late G1 [PMID:16810178, PMID:14733935, PMID:24586788, PMID:26951930, PMID:9029153]. ID2 transcription is activated by Myc, β-catenin/TCF4, HIF-1, C/EBPβ, BMP/Smad, and Nkx2-5/Tbx5, and repressed by TGF-β (via Mad-Max promoter switching), p53, Bcl6, Mtg16, and Ovol1, integrating multiple developmental and stress signals into a single dominant-negative output [PMID:11034201, PMID:11572874, PMID:15252039, PMID:15809228, PMID:12824180, PMID:21608079, PMID:27213691].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Establishing that ID2 is an HLH-only protein that heterodimerizes with and inhibits specific bHLH transcription factors resolved how a protein lacking a DNA-binding domain could function as a transcriptional regulator.\",\n      \"evidence\": \"In vitro binding and DNA-binding inhibition assays with cloned Id2 against multiple bHLH proteins\",\n      \"pmids\": [\"1922066\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of selective partner recognition unknown\", \"In vivo relevance not yet demonstrated\", \"Full spectrum of bHLH partners not mapped\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Identification that bHLH factors activate the Id2 promoter through E-boxes, and that Id2 blocks this activation, revealed a negative autoregulatory feedback loop governing Id2 expression levels.\",\n      \"evidence\": \"Reporter/luciferase promoter assay with co-expression in F9 cells\",\n      \"pmids\": [\"7589553\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct E-box binding by bHLH factors at the endogenous Id2 promoter not confirmed by ChIP\", \"Physiological significance of the feedback loop not tested in vivo\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Demonstrating that ID2 uniquely among Id family members directly binds and neutralizes all three Rb-family pocket proteins established a second major mechanism—beyond bHLH inhibition—by which ID2 promotes cell-cycle progression.\",\n      \"evidence\": \"In vitro binding assays, co-immunoprecipitation in Saos-2 cells, and cell-cycle arrest rescue assays\",\n      \"pmids\": [\"8649364\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of ID2–Rb interaction unknown\", \"Whether Rb binding and bHLH binding are mutually exclusive or concurrent was not resolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Showing that cyclin E–CDK2 and cyclin A–CDK2 phosphorylate ID2 in late G1, correlating with restoration of E-box-dependent transcription, established a cell-cycle-dependent mechanism that inactivates ID2's inhibitory function.\",\n      \"evidence\": \"In vitro kinase assays with purified cyclin–CDK complexes; in vivo phosphorylation in synchronized fibroblasts; EMSA\",\n      \"pmids\": [\"9029153\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Precise phosphorylation site mutant analysis not reported in this study\", \"Whether phosphorylation also affects Rb binding was not tested\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Genetic epistasis showing that Id2–Rb double-knockout embryos survive to term, combined with evidence that Myc directly activates Id2 transcription, placed ID2 as a critical mediator in the Myc→ID2⊣Rb oncogenic pathway.\",\n      \"evidence\": \"Double-knockout rescue in mice; quantitative protein analysis; neuroblastoma cell analysis\",\n      \"pmids\": [\"11034201\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this axis operates equivalently in all Myc-driven cancers was not established\", \"Contribution of ID2's bHLH-inhibitory function versus Rb-inhibitory function in this pathway not disentangled\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Identification of β-catenin/TCF4 as a direct transcriptional activator of ID2 via a TCF4-binding motif linked ID2 to canonical Wnt signaling and anchorage-independent survival in colon cancer.\",\n      \"evidence\": \"EMSA, supershift, site-directed mutagenesis of TCF4 site, reporter assay in colon carcinoma cells\",\n      \"pmids\": [\"11572874\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ChIP confirmation of endogenous TCF4 occupancy at the Id2 promoter not performed\", \"Downstream effectors of ID2 in anchorage-independent survival not identified\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Discovering that TGF-β represses Id2 via Mad-Max promoter switching and that TGF-β also induces Id2 in dendritic cell precursors revealed context-dependent transcriptional regulation of Id2, with TGF-β repressing Id2 in epithelial cells to enable cytostasis but inducing it in immune progenitors to control DC lineage choice.\",\n      \"evidence\": \"ChIP showing Myc-Max to Mad-Max switch at Id2 promoter in epithelial cells; Id2-KO mouse DC analysis with TGF-β stimulation\",\n      \"pmids\": [\"12824180\", \"12598895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of context-dependent TGF-β regulation (repression vs. activation) not resolved\", \"Whether Smad proteins directly bind the Id2 promoter in DC progenitors was not shown\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Demonstrating that ID2 is degraded via N-terminal ubiquitination (conjugation to the α-NH2 group rather than internal lysines) and that the first 15 N-terminal residues serve as an E3 recognition element revealed an unconventional proteolytic control mechanism, while HIF-1 was shown to directly activate Id2 transcription under hypoxia.\",\n      \"evidence\": \"Lysine-less mutant degradation assays and N-terminal tagging stabilization experiments; ChIP and EMSA identifying HIF-1 binding sites in the Id2 promoter\",\n      \"pmids\": [\"14733935\", \"15252039\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The specific E3 ligase mediating N-terminal ubiquitination was not identified\", \"Physiological relevance of HIF-1–Id2 axis beyond neuroblastoma not explored\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"C/EBPβ was identified as a direct transcriptional activator of Id2 via ChIP-confirmed promoter occupancy, while Ovol1 was shown to repress Id2 in spermatocytes, and polycystin-2 (PC2) was found to physically interact with ID2 in a phosphorylation-dependent manner relevant to cystic kidney disease.\",\n      \"evidence\": \"ChIP, EMSA, mutagenesis, and C/EBPβ-null mammary analysis; Ovol1-KO mouse spermatocyte analysis; PC2 co-immunoprecipitation and RNAi rescue in PKD cells\",\n      \"pmids\": [\"15809228\", \"15716349\", \"16311606\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct mechanism by which PC2 sequesters ID2 not structurally resolved\", \"Whether PC2–ID2 interaction is relevant beyond cystic kidney disease not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Multiple discoveries converged to show how ID2 protein is spatially and temporally controlled: APC/C(Cdh1) targets ID2 for D-box-dependent degradation in post-mitotic neurons (controlling axon growth via Nogo receptor), ENH sequesters ID2 in the cytoplasm during differentiation, and E47–ID2 antagonism regulates p57Kip2 in neuroblastoma, building a comprehensive picture of multi-layered ID2 regulation in neural cells.\",\n      \"evidence\": \"D-box mutagenesis and APC/C interaction assays with in vivo axon growth readout; ENH co-IP with bidirectional manipulation and subcellular localization; E47-driven p57Kip2 reporter with RNAi rescue\",\n      \"pmids\": [\"16810178\", \"16549780\", \"16705184\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether APC/C(Cdh1) and ENH pathways cooperate or act independently not addressed\", \"Whether p57Kip2 is the sole E-protein target mediating cell-cycle arrest in neural progenitors unknown\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Placing Id2 downstream of the cardiac transcription factors Nkx2-5 and Tbx5 in ventricular conduction system specification broadened ID2's developmental role beyond immune and neural tissues to cardiac morphogenesis.\",\n      \"evidence\": \"Id2 promoter reporter in vivo; compound haploinsufficiency genetic epistasis in mouse heart\",\n      \"pmids\": [\"17604724\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct bHLH targets of ID2 in conduction system cells not identified\", \"Whether ID2 acts via Rb or bHLH inhibition in this context not resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"BMP/Smad-binding elements in the Id2 promoter were biochemically mapped, and ID2 was shown to promote tumor cell migration by repressing SEMA3F through E47 antagonism, linking ID2 to invasion beyond its established role in proliferation.\",\n      \"evidence\": \"ChIP and EMSA for Smad binding at Id2 promoter; E-box mutagenesis at SEMA3F promoter with migration/invasion assays\",\n      \"pmids\": [\"20674548\", \"20388805\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo validation of SEMA3F-dependent invasion pathway not performed\", \"Whether other semaphorins are similarly regulated by E47/ID2 not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrating that p53 directly represses Id2 transcription established ID2 as a node integrating tumor-suppressor and oncogenic signals: Myc activates and p53 represses the same gene, with the balance determining neural progenitor proliferation.\",\n      \"evidence\": \"ChIP for p53 at Id2 promoter; Id2 knockdown rescue in p53-null NPCs\",\n      \"pmids\": [\"21608079\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether p53-mediated Id2 repression operates in non-neural tissues not addressed\", \"Mechanism by which p53 binding leads to transcriptional repression not dissected\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showing that ID2 restrains CD8+ T-cell memory differentiation by blocking E2A-mediated Tcf7 (TCF1) activation established ID2 as a molecular switch between effector and memory T-cell fates.\",\n      \"evidence\": \"Id2-KO CD8+ T-cell analysis during infection; E2A binding site reporter assay; gene expression profiling\",\n      \"pmids\": [\"23536629\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ID2 affects TCF1 protein stability in addition to transcription not tested\", \"Relative contribution of ID2 versus ID3 in memory/effector balance not resolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of ASB4 as an E3 ubiquitin ligase that targets ID2 for proteasomal degradation in trophoblasts provided a tissue-specific degradation mechanism controlling vascular differentiation in the placenta.\",\n      \"evidence\": \"Direct ubiquitination assay; degradation-resistant ID2 mutant; Asb4-null mouse placenta analysis\",\n      \"pmids\": [\"24586788\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ASB4 ubiquitinates ID2 at the N-terminus or at lysine residues not determined\", \"Relationship between ASB4 and APC/C(Cdh1)-mediated degradation pathways not examined\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Three concurrent advances revealed that: USP1 deubiquitinase stabilizes ID2 to drive glioma survival (PDGF–E2F–USP1–ID2 axis); ID2 controls NK cell homeostasis by repressing E-protein target Socs3; and Bcl6 represses Id2 to promote TFH over TH1 differentiation, firmly establishing ID2 as a central integrator of immune lineage decisions.\",\n      \"evidence\": \"USP1 pharmacologic inhibition and Id2 KO in glioma model with ChIP; Id2 conditional KO in NK cells with Socs3 double-KO epistasis; Bcl6 ChIP at Id2 locus with T-cell subset phenotyping\",\n      \"pmids\": [\"26951930\", \"26795246\", \"27213691\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether USP1 deubiquitinates ID2 at the N-terminal ubiquitin or at lysine-linked chains not resolved\", \"How Bcl6 mechanistically represses the Id2 locus (co-repressor identity) not identified\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Genome-wide binding analysis of Mtg16 at the Id2 locus, combined with an Nfil3–Zeb2–Id2 genetic circuit controlling cDC1 specification, consolidated ID2 as the key node in a multi-factor transcriptional network governing dendritic cell lineage commitment.\",\n      \"evidence\": \"Mtg16 ChIP-seq with Id2/Mtg16 double-KO epistasis; scRNA-seq of CDPs with Nfil3/Zeb2/Id2 genetic epistasis\",\n      \"pmids\": [\"24980046\", \"31406377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Mtg16 mechanistically represses the Id2 promoter (direct or indirect DNA binding) not fully resolved\", \"Whether the Nfil3–Zeb2–Id2 circuit operates in human DC development not confirmed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Structural and biochemical reconstitution of the monoubiquitinated FANCI–FANCD2 (ID2) complex showed that FANCD2 ubiquitination drives a conformational change enabling the complex to encircle DNA, clarifying the molecular basis of DNA interstrand crosslink repair activation (note: this concerns the FANCI–FANCD2 complex, distinct from the HLH protein ID2).\",\n      \"evidence\": \"Structural analysis of ubiquitinated ID2 complex; DNA-binding affinity assays; deubiquitination protection assays with USP1–UAF1\",\n      \"pmids\": [\"32510829\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"This finding pertains to the FANCI–FANCD2 heterodimer, not the HLH protein ID2; included here because both share the 'ID2' acronym in the literature\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Demonstrating that TGF-β suppresses Id2 in developing airway basal stem cells and that persistent Id2 expression drives basal cell hyperplasia established the TGF-β–ID2 axis as a proliferation switch with precancerous implications, while ID2 was also shown to suppress TCF1 amplitude to control terminal NK cell maturation.\",\n      \"evidence\": \"Bidirectional genetic manipulation (Id2 OE, Tgfbr2 KO) in murine airways with scRNA-seq; Id2 conditional KO in NK cells with in vivo melanoma clearance assay\",\n      \"pmids\": [\"34129836\", \"33857289\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether TGF-β–ID2 axis directly causes malignant transformation or only a precancerous state not resolved\", \"Mechanism by which ID2 suppresses TCF1 (direct E-protein sequestration vs. other) not fully dissected\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"E-cadherin loss was shown to de-repress Id2 via a p120-catenin/Kaiso pathway, with cytosolic ID2 inducing G0/G1 arrest through hypo-phosphorylated Rb interaction, unexpectedly demonstrating that ID2 can promote quiescence and anoikis resistance rather than proliferation depending on subcellular context.\",\n      \"evidence\": \"ChIP for Kaiso at Id2 promoter; co-IP of ID2 with Rb; subcellular fractionation; in vivo lung colonization assay in ILC models\",\n      \"pmids\": [\"35437308\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How cytosolic ID2 preferentially binds hypo-phosphorylated Rb while nuclear ID2 antagonizes Rb growth suppression is paradoxical and not mechanistically reconciled\", \"Generalizability beyond invasive lobular carcinoma not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Elucidating that ID2 disrupts a Tcf3–Tal1 complex to prevent LSD1 recruitment to the Slamf6 promoter, thereby maintaining permissive H3K4me2 marks, revealed an epigenetic mechanism through which ID2 sustains progenitor exhausted CD8+ T cells—extending its function beyond simple bHLH sequestration to chromatin remodeling.\",\n      \"evidence\": \"Co-IP of ID2 HLH domain with Tcf3; ChIP for H3K4me2 at Slamf6 promoter; LSD1 inhibitor rescue in Id2-KO tumor-bearing mice\",\n      \"pmids\": [\"38287103\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ID2-mediated disruption of LSD1 recruitment occurs at other loci genome-wide not tested\", \"Direct structural basis of how ID2 HLH domain disrupts the Tcf3–Tal1 interface unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the structural basis of ID2's selective partner recognition (bHLH vs. Rb vs. PC2); how nuclear vs. cytosolic ID2 exerts opposing effects on Rb-mediated cell-cycle control; the identity of the E3 ligase mediating N-terminal ubiquitination; and comprehensive mapping of the chromatin landscape changes driven by ID2 across immune and non-immune lineages.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No high-resolution structure of ID2 in complex with any partner\", \"Nuclear vs. cytosolic ID2 function on Rb not mechanistically reconciled\", \"Genome-wide ID2-dependent chromatin remodeling not systematically mapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 8, 18, 21, 26, 32]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 8, 18, 26, 33]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5, 7, 26]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7, 41]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1, 2, 3, 41]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 11, 14, 35]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [10, 20, 38]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [9, 21, 22, 24, 27, 33, 37, 38]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 11, 12, 13, 15, 19]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 6, 20, 23]}\n    ],\n    \"complexes\": [\n      \"APC/C(Cdh1) (as substrate)\"\n    ],\n    \"partners\": [\n      \"E2A\",\n      \"RB1\",\n      \"ENH\",\n      \"CDH1\",\n      \"USP1\",\n      \"ASB4\",\n      \"PU.1\",\n      \"TCF3\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}