{"gene":"GAB2","run_date":"2026-04-28T17:46:04","timeline":{"discoveries":[{"year":1998,"finding":"GAB2 (p97) is a scaffolding protein that, upon cytokine, growth factor, or antigen receptor stimulation, becomes tyrosyl phosphorylated and associates with SH2 domain-containing proteins including SHP2 and PI3K. Expression of p97 mutants unable to bind SHP2 blocks cytokine-induced c-fos promoter activation, inhibiting Elk1-mediated and STAT5-mediated transactivation, without inhibiting MAPK activation, revealing a novel pathway to immediate-early gene activation.","method":"Cloning, dominant-negative mutant expression, reporter gene assays, co-immunoprecipitation","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 — original cloning paper with multiple orthogonal methods (mutants, reporter assays, co-IP); foundational discovery","pmids":["9885561"],"is_preprint":false},{"year":1999,"finding":"GAB2 contains a pleckstrin homology (PH) domain and, upon tyrosine phosphorylation, physically interacts with SHP2 and GRB2. GAB2 has an inhibitory effect on Elk-1-dependent transcription triggered by oncogenic Ras or growth factors, while having a similar function to GAB1 in ERK activation, indicating distinct roles in cytoplasmic-nuclear signal transduction.","method":"Co-immunoprecipitation, reporter gene assays, overexpression with dominant-active Ras","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (Co-IP, reporter assays) in original characterization paper","pmids":["10391903"],"is_preprint":false},{"year":2001,"finding":"GAB2-deficient mast cells have defective responses to FcεRI stimulation (degranulation and cytokine gene expression), and GAB2 is the principal activator of PI3K in response to FcεRI activation, establishing that Dos/Gab family scaffolds regulate the PI3K pathway in vivo.","method":"Gab2 knockout mice, mast cell functional assays, passive cutaneous and systemic anaphylaxis models, biochemical signaling analysis","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with multiple functional readouts, published in Nature; independently replicated","pmids":["11449275"],"is_preprint":false},{"year":2001,"finding":"GAB2 associates with GRB2, SHP2, p85 subunit of PI3K, SHIP, and SHC downstream of the M-CSF receptor (Fms). Overexpression of GAB2 enhanced MAPK activity and macrophage differentiation but reduced proliferation, while a Gab2 mutant unable to bind SHP2 failed to potentiate MAPK activity and inhibited macrophage differentiation, demonstrating that GAB2-SHP2 interaction is essential for the M-CSF differentiation signal.","method":"Co-immunoprecipitation, overexpression of wild-type and SHP2-binding-defective Gab2 mutants, MAPK kinase assays, cell differentiation assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal co-IP plus functional mutant analysis with multiple readouts","pmids":["11287610"],"is_preprint":false},{"year":2001,"finding":"GAB2 is phosphorylated by ZAP-70 and co-precipitates with ZAP-70, LAT, and CD3ζ upon TCR stimulation. Overexpression of GAB2 inhibits NF-AT activation and IL-2 production; this inhibitory function requires SHP2-binding sites and the PH domain of GAB2, and depends on PI3K recruitment. GAB2 functions as a switch molecule toward inhibition of TCR signal transduction by recruiting inhibitory molecules.","method":"Co-immunoprecipitation, kinase assays, reporter gene assays (NF-AT, IL-2), Gab2 domain mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — multiple mutants and functional readouts; Tier 2 methods","pmids":["11572860"],"is_preprint":false},{"year":2002,"finding":"BCR/ABL recruits GAB2 via a GRB2/GAB2 complex through BCR/ABL phosphotyrosine 177. GAB2 mediates BCR/ABL-driven PI3K/Akt and Ras/Erk activation; Gab2-deficient mouse bone marrow myeloid progenitors are resistant to transformation by BCR/ABL, identifying GAB2 as a key determinant of BCR/ABL leukemogenesis.","method":"Gab2 knockout mouse bone marrow transformation assays, Co-immunoprecipitation, signaling pathway analysis, BCR/ABL-Y177F mutant","journal":"Cancer cell","confidence":"High","confidence_rationale":"Tier 2 — genetic knockout with BCR/ABL transformation assay, co-IP, point mutant; highly cited foundational paper","pmids":["12124177"],"is_preprint":false},{"year":2002,"finding":"PKB/AKT constitutively associates with GAB2, phosphorylates GAB2 on Ser159 in vitro, and this phosphorylation inhibits GAB2 tyrosine phosphorylation (negative feedback). The Gab2-S159A mutant enhances heregulin-induced GAB2 tyrosine phosphorylation, amplifies ERK and PKB pathway activation, and exhibits potent transforming activity, establishing a negative-feedback loop from PI3K/PKB to GAB2.","method":"In vitro kinase assay, site-directed mutagenesis (S159A), co-immunoprecipitation, transformation assay, signaling assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay plus mutagenesis plus functional transformation assay in one study","pmids":["11782427"],"is_preprint":false},{"year":2002,"finding":"GAB2 is required for Fc gamma receptor (FcγR)-initiated phagocytosis in macrophages. Upon FcγR activation, GAB2 becomes tyrosyl phosphorylated and associates with p85 and SHP-2; GAB2 is recruited to the nascent phagosome via its PH domain (requiring PI3K lipid products and facilitated by GRB2 binding), where it amplifies PI3K/Akt signaling required for phagocytosis.","method":"Gab2 knockout macrophages, phagocytosis assays, confocal fluorescence microscopy, co-immunoprecipitation, wortmannin treatment, domain mutants","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with specific phenotype, direct localization by confocal microscopy, domain mutant analysis","pmids":["12821647"],"is_preprint":false},{"year":2002,"finding":"GAB2 mediates Src phosphorylation downstream of EGF receptor signaling; Src constitutively associates with GAB2 via its SH3 domain interacting with GAB2 proline-rich sequences. Src-dependent GAB2 phosphorylation is required for EGF-induced PI3K/Akt activation and DNA synthesis in hepatocytes. Gab2 mutants with SHP2-binding-site deletions increase EGF-induced GAB2 phosphorylation and PI3K activity but block MAPK activation, demonstrating SHP2-mediated downregulation of GAB2.","method":"Src inhibitor PP1, Csk knockout cells, in vitro phosphorylation, co-immunoprecipitation, GAB2 mutants, DNA synthesis assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro phosphorylation, multiple mutants, Csk KO cells, multiple signaling readouts","pmids":["12464621"],"is_preprint":false},{"year":2003,"finding":"GAB2 interacts with GC-GAP, a novel Rho family GTPase-activating protein with activity toward RhoA, Rac1, and Cdc42, linking GAB2 scaffolding function to Rho GTPase regulation.","method":"Yeast two-hybrid screen, co-immunoprecipitation, in vitro GAP activity assay, siRNA knockdown","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — yeast two-hybrid plus in vitro GAP assay; single study","pmids":["12819203"],"is_preprint":false},{"year":2003,"finding":"GAB2 interaction with LAT upon TCR stimulation requires the c-Met binding domain (MBD) of GAB2 and a novel PXXXR Grb2/Gads SH3 binding motif. Through constitutive association with Gads/Grb2, GAB2 is recruited to lipid rafts after TCR ligation to exert its inhibitory function. Transgenic mice expressing wild-type GAB2 show impaired T cell responses, while Gab2-deficient mice show enhanced proliferative responses.","method":"Co-immunoprecipitation, GAB2 domain mutants, transgenic mice, Gab2-deficient mice, lipid raft fractionation","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 — multiple mutants, transgenic and KO mice, lipid raft localization; two orthogonal in vivo models","pmids":["12640133"],"is_preprint":false},{"year":2001,"finding":"Specific tyrosine residues on GAB2 mediate binding to distinct SH2-domain proteins: Y452, Y476, and Y584 mediate PI3K p85 binding; Y614 mediates SHP-2 binding; and Y266 and Y293 mediate CrkL SH2 binding, as established in a modified yeast two-hybrid system with inducible Lyn kinase.","method":"Modified yeast two-hybrid with inducible Lyn kinase, tyrosine mutants of GAB2","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — yeast-based phospho-dependent binding assay; site-specific mutants; single study","pmids":["11334882"],"is_preprint":false},{"year":2004,"finding":"In IL-2-stimulated T lymphocytes, SHP-2 binds tyrosine residues Y614 (via N-terminal SH2) and Y643 (via C-terminal SH2) of GAB2. Mutation of Y614 alone is sufficient to prevent SHP-2 recruitment, and this blocks ERK activation and c-fos SRE transcription, demonstrating that GAB2-SHP2 interaction is required for ERK activation in response to IL-2. SRE induction requires both ERK-dependent (via Gab2/SHP2) and Rho-dependent signals.","method":"Site-directed mutagenesis (Y614F), co-immunoprecipitation, reporter gene assays (SRE, c-fos), dominant-active/negative RhoA","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 — phosphosite mutants, co-IP, reporter assays; multiple orthogonal approaches","pmids":["15170389"],"is_preprint":false},{"year":2005,"finding":"Constitutively active STAT5 (caSTAT5) induces persistent tyrosine phosphorylation of GAB2 and formation of a complex containing STAT5, GAB2, p85 (PI3K regulatory subunit), and GRB2 (but not SHP2). A Gab2-3YF mutant incapable of binding PI3K inhibits caSTAT5-induced proliferation and survival, as well as ERK1/2 and Akt phosphorylation, demonstrating GAB2 is required for caSTAT5-mediated activation of both PI3K/Akt and Ras/MAPK pathways.","method":"Co-immunoprecipitation, GAB2 mutant (3YF) expression, proliferation/survival assays, signaling analysis","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 — co-IP with mutant validation and multiple functional readouts","pmids":["15833084"],"is_preprint":false},{"year":2005,"finding":"GAB2 overexpression in breast cancer promotes mammary cell proliferation in 3D culture; these effects require GAB2 binding to GRB2 and SHP2, and are enhanced by PI3K recruitment. GAB2 overexpression mediates hyperactivation of the SHP2-ERK pathway, and co-expression with Neu results in an invasive phenotype. Gab2 potentiates, and Gab2 deficiency ameliorates, Neu-evoked breast carcinogenesis in mice.","method":"3D Matrigel culture, Gab2 knockout mice with Neu transgene, GAB2 domain mutants (Grb2 and Shp2 binding), signaling analysis","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic KO/overexpression in mouse model, 3D culture, domain mutants; multiple orthogonal methods","pmids":["16369543"],"is_preprint":false},{"year":2005,"finding":"GAB2 associates with RANK and mediates RANK-induced activation of NF-κB, Akt, and JNK. Gab2-deficient mice develop osteopetrosis with decreased bone resorption due to defective osteoclast differentiation, establishing GAB2 as essential for RANK signaling and osteoclastogenesis.","method":"Gab2 knockout mice, osteoclastogenesis assays, co-immunoprecipitation (GAB2-RANK), signaling analysis (NF-κB, Akt, JNK), bone histomorphometry","journal":"Nature medicine","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with specific skeletal phenotype, co-IP, multiple signaling readouts","pmids":["15750601"],"is_preprint":false},{"year":2006,"finding":"PLCγ2 forms a complex with GAB2 in osteoclasts, is required for GAB2 phosphorylation, and modulates GAB2 recruitment to RANK during RANKL-induced osteoclastogenesis. PLCgamma2 and GAB2 interact downstream of Dap12/FcRγ receptors to regulate NFATc1 activation.","method":"Co-immunoprecipitation (PLCγ2-GAB2 complex), PLCγ2 knockout mice, PLCγ inhibitor U73122, RANKL stimulation assays","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 — co-IP, genetic KO, pharmacological inhibition; multiple orthogonal methods","pmids":["17053833"],"is_preprint":false},{"year":2006,"finding":"GAB2 mediates Kit-evoked mast cell proliferation via the Rac/JNK pathway through SHP2. Kit Tyr567 (an SFK binding site) and SFK activity are required for GAB2 tyrosyl phosphorylation and GAB2-SHP2 association. GAB2 via SHP2 activates Rac/JNK and Ras to control mast cell proliferation, acting in a parallel pathway to PI3K from Kit Tyr719.","method":"Gab2 knockout mast cells, re-expression of wild-type GAB2 and SHP2-binding defective mutant, compound Gab2-/- KitY719F/Y719F mice, signaling assays (Rac, JNK, Ras), SFK inhibitors","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — genetic KO, compound mutant mice, Gab2 mutant rescue experiments; multiple orthogonal approaches","pmids":["16873377"],"is_preprint":false},{"year":2007,"finding":"GAB2 ablation severely suppresses lung metastasis of Neu-induced mammary tumors. Gab2-deficient cancer cells exhibit decreased migration and impaired ERK activation; defects are rescued by re-introduction of Gab2, establishing GAB2 as a promoter of mammary tumor metastasis via the ERK pathway.","method":"Gab2 knockout mice crossed with Neu transgenic mice, lung metastasis assays, cell migration assays, ERK signaling, Gab2 re-expression","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — genetic KO in mouse tumor model, rescue experiment, specific functional readout","pmids":["17310989"],"is_preprint":false},{"year":2007,"finding":"GAB2 was detected in neurons, tangle-bearing neurons, and dystrophic neurites in Alzheimer's disease brain; interference with GAB2 gene expression increased tau phosphorylation, suggesting GAB2 influences Alzheimer's neuropathology.","method":"Immunohistochemistry, siRNA-mediated GAB2 knockdown with tau phosphorylation readout","journal":"Neuron","confidence":"Medium","confidence_rationale":"Tier 3 — single experiment (siRNA + tau phospho assay); limited mechanistic follow-up","pmids":["17553421"],"is_preprint":false},{"year":2008,"finding":"Growth factor-induced phosphorylation of GAB2 on S210 and T391 recruits 14-3-3 proteins, which terminates GAB2 signaling by promoting dissociation of GAB2 from GRB2 and receptor complexes. GAB2-S210A/T391A double mutant exhibits sustained receptor association and signaling and promotes cell proliferation and transformation; introduction of constitutive 14-3-3 binding sites renders GAB2 refractory to receptor activation.","method":"Site-directed mutagenesis, co-immunoprecipitation, proliferation/transformation assays, constitutive 14-3-3-binding site insertions","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 — multiple mutants, co-IP, functional transformation assays; rigorous mechanistic dissection in one study","pmids":["19172738"],"is_preprint":false},{"year":2008,"finding":"In imatinib-resistant CML cells, Lyn kinase complexes with GAB2 and c-Cbl in a BCR-ABL-independent manner and mediates persistent tyrosine phosphorylation of GAB2 and BCR-ABL. Lyn silencing or inhibition is required to suppress GAB2 phosphorylation and restore imatinib sensitivity.","method":"Co-immunoprecipitation (Lyn-Gab2 complex), Lyn siRNA, kinase inhibitors, phosphorylation assays in imatinib-resistant patient samples","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP, siRNA knockdown, patient samples; single lab","pmids":["18235045"],"is_preprint":false},{"year":2008,"finding":"GAB2 is involved in differential PI3K/Akt signaling between two splice forms of c-Kit (GNNK- and GNNK+). GNNK- c-Kit mediates stronger PI3K/Akt activation through association with GAB2 and Src-mediated phosphorylation of GAB2, independent of direct PI3K binding to c-Kit. siRNA knockdown of GAB2 confirmed its role in PI3K/Akt activation downstream of c-Kit.","method":"siRNA, co-immunoprecipitation, signaling assays, c-Kit splice variant expression in Ba/F3 cells","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA validation plus co-IP; single lab","pmids":["18697750"],"is_preprint":false},{"year":2009,"finding":"Crystal structures of two GAB2 epitopes (Gab2a and Gab2b) complexed with the Grb2 SH3C domain reveal distinct binding modes: Gab2b contains a 3(10) helix positioning Arg and Lys of the RxxK motif in parallel orientation, while Gab2a has the RxxK motif in a PPII helix with staggered orientation. Two GRB2 SH3C binding sites in GAB2 are required for the GAB2-GRB2 interaction.","method":"Crystal structures, peptide arrays, isothermal titration calorimetry","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — crystal structures with biochemical validation (ITC, peptide arrays)","pmids":["19523899"],"is_preprint":false},{"year":2009,"finding":"GAB2 overexpression promotes migration and invasion of melanoma cells; Gab2 knockdown reduces these behaviors. GAB2 mediates hyperactivation of Akt signaling in the absence of growth factors. PI3K/Akt pathway inhibition decreases Gab2-mediated tumor cell migration and invasive potential. GAB2 overexpression results in enhanced tumor growth and metastatic potential in vivo.","method":"Gab2 siRNA, overexpression, PI3K inhibitor treatment, migration/invasion assays, in vivo xenograft model","journal":"The American journal of pathology","confidence":"Medium","confidence_rationale":"Tier 2 — KD and OE with functional readouts and in vivo model; single lab","pmids":["19342374"],"is_preprint":false},{"year":2010,"finding":"GAB2 overexpression in mammary epithelial cells decreases RhoA activation, reduces stress fibers and focal adhesions, and enhances cell migration via Shp2-dependent signaling. GAB2 promotes Vav2 phosphorylation and plasma membrane recruitment of p190A RhoGAP, which negatively regulates RhoA; constitutively active RhoA restores stress fibers in GAB2-expressing cells. A Gab2 mutant lacking Shp2 binding sites does not affect RhoA or cellular phenotype.","method":"Overexpression and Gab2 mutants (ΔShp2, 2xA), RhoA activity assays, p190A RhoGAP knockdown, co-immunoprecipitation, constitutively active RhoA rescue","journal":"Molecular biology of the cell","confidence":"High","confidence_rationale":"Tier 2 — multiple mutants, rescue experiments, RhoGAP knockdown, specific pathway dissection","pmids":["21118992"],"is_preprint":false},{"year":2011,"finding":"GAB2 via PI3K/ARF1 signaling regulates mast cell degranulation. Using Gab2 knock-in mice with mutations at either the PI3K or SHP2 binding sites, both binding sites are required for degranulation and anaphylaxis (but not cytokine production). The PI3K binding site of GAB2 is specifically required for granule translocation; FcεRI-stimulated ARF1 activation is dependent on Fyn and the PI3K binding site of GAB2.","method":"Gab2 knock-in mice (PI3K- and SHP2-binding site mutations), degranulation assays, ARF1 activation assay, anaphylaxis models, granule imaging","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 1–2 — knock-in mouse genetic dissection with multiple functional readouts; new ARF1 pathway identified","pmids":["21653832"],"is_preprint":false},{"year":2011,"finding":"GAB2 overexpression in ovarian cancer cells promotes migration and invasion and downregulates E-cadherin expression via PI3K pathway activation, leading to upregulation of ZEB1 (an EMT transcription factor). PI3K inhibitors reverse Gab2-induced EMT effects. GAB2 mutants defective in PI3K activation (not SHP2-ERK) abolish these effects, specifying the PI3K pathway as responsible.","method":"Overexpression, knockdown, GAB2 domain mutants (PI3K and Shp2-Erk defective), PI3K inhibitors, E-cadherin and Zeb1 expression assays, migration/invasion assays","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 — specific domain mutants dissect PI3K vs SHP2 pathways; pharmacological and genetic validation","pmids":["21996746"],"is_preprint":false},{"year":2011,"finding":"GAB2 mediates G-CSF receptor activation of the Src kinase Lyn by recruiting SHP2. After G-CSF stimulation, Lyn associates with GAB2; GAB2-recruited SHP2 dephosphorylates inhibitory pLyn-Tyr507, enabling Lyn activation. This mechanism requires the Gab2-SHP2 interaction, as a mutant Gab2 unable to bind SHP2 fails to support Tyr507 dephosphorylation.","method":"Co-immunoprecipitation, Gab2 siRNA, SHP2-deficient cells, in vitro phosphatase assay with constitutively active Shp2E76A, Lyn Tyr507/Tyr396 phosphorylation analysis, GAB2 mutants","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro phosphatase assay, GAB2 mutant, Shp2-deficient cells, Gab2 siRNA; multiple orthogonal approaches","pmids":["21636860"],"is_preprint":false},{"year":2012,"finding":"GAB2 is an A-kinase anchoring protein (AKAP) that binds the type I regulatory subunit of PKA; PKA phosphorylates GAB2 on Ser159. GAB2 is present in a preformed complex with PI3K and IRS-1 in granulosa cells. Overexpression of GAB2 enhances FSH-stimulated AKT phosphorylation, establishing GAB2 as a coordinator of PKA-to-PI3K/AKT signaling in FSH-stimulated ovarian granulosa cells.","method":"Co-immunoprecipitation, PKA in vitro phosphorylation assay, GAB2 overexpression, AKT phosphorylation assays in granulosa cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1–2 — in vitro PKA phosphorylation of GAB2, co-IP of preformed complex, functional overexpression","pmids":["23045700"],"is_preprint":false},{"year":2013,"finding":"RSK (p90 ribosomal S6 kinase) phosphorylates GAB2 on three conserved residues (in vitro and in vivo), downstream of Ras/MAPK pathway activation. RSK-mediated phosphorylation of GAB2 inhibits SHP2 recruitment without affecting GRB2 binding. An unphosphorylatable GAB2 mutant promotes invasion-like phenotype and increased cell motility, placing RSK in a negative-feedback loop restricting GAB2-dependent epithelial cell motility.","method":"In vitro RSK kinase assay, mass spectrometry phosphorylation sites, site-directed mutagenesis, co-immunoprecipitation, cell migration/invasion assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay with mutagenesis and functional validation","pmids":["23401857"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of ISIR-005 in complex with 14-3-3 and the GAB2 binding motif (Gab2pS210pT391) shows that the small molecule stabilizes the 14-3-3/GAB2 interaction at the pT391 site by occupying a pre-formed pocket at the rim of the interface. The Gab2pS210 motif binding does not create an interface pocket suitable for the molecule.","method":"Crystal structure of ternary complex, isothermal titration calorimetry, biochemical stabilization assay","journal":"ChemMedChem","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with biochemical validation","pmids":["26644359"],"is_preprint":false},{"year":2016,"finding":"GAB2 deficiency in Ptpn11E76K/+ (leukemic Shp2 gain-of-function) mice markedly attenuates myeloproliferative neoplasia, including reduced myeloid overproduction, splenomegaly, and myeloid infiltration. The interaction between leukemia-associated mutant SHP2 and GAB2 is enhanced, and the mTOR pathway is elevated in leukemic cells. Rapamycin treatment of Ptpn11E76K/+ mice mitigates MPN phenotypes, placing GAB2-PI3K-mTOR downstream of mutant SHP2.","method":"Double mutant mice (Ptpn11E76K/+/Gab2-/-), myeloid differentiation assays, Rapamycin treatment, signaling analysis","journal":"Leukemia","confidence":"High","confidence_rationale":"Tier 2 — genetic epistasis with double-mutant mice and pharmacological rescue; multiple readouts","pmids":["27840422"],"is_preprint":false},{"year":2016,"finding":"GAB2 is essential for both myeloid and lymphoid leukemogenesis by BCR-ABL1. Gab2 knockout mice transplanted with BCR-ABL1-transduced bone marrow fail to develop CML-like disease; this is restored by wild-type GAB2 but not by GAB2 mutants lacking PI3K or SHP2 binding sites. Both PI3K and SHP2 binding sites are required for myeloid (CML) transformation, while only the SHP2 binding site is required for lymphoid (B-ALL) leukemogenesis.","method":"Mouse models of CML and B-ALL with Gab2 KO, GAB2 domain mutant rescue, signaling analysis","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with domain-specific mutant rescue in two distinct disease mouse models","pmids":["26773044"],"is_preprint":false},{"year":2017,"finding":"In zebrafish MYCN-transgenic neuroblastoma model, GAB2 overexpression activates the SHP2-Ras-ERK pathway, promotes proliferation of hyperplastic neuroblasts, and increases neuroblastoma tumor penetrance, cooperating with MYCN. This establishes GAB2 as a SHP2 activator that cooperates with MYCN in neuroblastomagenesis.","method":"Zebrafish MYCN transgenic model, GAB2 overexpression, ptpn11 gain-of-function mutants, ERK signaling analysis","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 — in vivo zebrafish model with defined genetic interactions; single lab","pmids":["28329685"],"is_preprint":false},{"year":2017,"finding":"YAP and TAZ transcriptional regulators maintain PI3K pathway activation in endometrial cancer cells by transcriptionally regulating GAB2 levels. Coordinate knockdown of YAP and TAZ markedly decreases constitutive and growth factor-induced PI3K pathway activation by reducing GAB2 protein levels.","method":"siRNA knockdown of YAP/TAZ, GAB2 protein level measurement, PI3K/AKT signaling assays, in vivo tumor growth","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — epistasis by siRNA; identifies YAP/TAZ as upstream transcriptional regulators of GAB2; single lab","pmids":["28202507"],"is_preprint":false},{"year":2017,"finding":"In IL-4/M2 macrophage polarization, GAB2 is recruited to the IL-4 receptor and synergistically enhances downstream signaling; loss of GAB2 suppresses STAT6 activation in response to IL-4, while loss of GAB1 attenuates AKT activation. GAB2 and GAB1 have non-redundant roles in M2 macrophage polarization and bleomycin-induced pulmonary fibrosis.","method":"Gab2 knockout mice, Gab1 conditional KO mice (macrophage-specific), IL-4 signaling assays, M2 polarization markers, bleomycin-induced fibrosis model, co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — two independent genetic KO models with defined signaling and phenotypic readouts","pmids":["28687632"],"is_preprint":false},{"year":2019,"finding":"Loss of PIK3R1 (p85α) in ovarian cancer cells alters GAB2 phosphorylation, relieves negative inhibition on AKT, and promotes assembly of a JAK2/STAT3 signalosome through GAB2 phosphorylation changes. This establishes GAB2 as a node linking PIK3R1 loss to both AKT and JAK2/STAT3 pathway activation.","method":"PIK3R1 siRNA knockdown, GAB2 phosphorylation analysis, AKT and STAT3 signaling assays, co-immunoprecipitation","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — siRNA epistasis with signaling pathway dissection; single lab","pmids":["30755611"],"is_preprint":false},{"year":2022,"finding":"GAB2 facilitates assembly of the CBM (CARMA3-BCL10-MALT1) signalosome in endothelial cells, which mediates Rho and NF-κB activation in response to IL-1β. GAB2 silencing reduces IL-1β-induced Rho-dependent exocytosis of P-selectin and VWF, NF-κB-dependent tissue factor expression, neutrophil adhesion, and venous thrombosis in mice.","method":"Gab2 gene silencing, MALT1 pharmacological inhibition (mepazine), inferior vena cava ligation model, P-selectin and VWF exocytosis assays, NF-κB signaling analysis","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic KD plus pharmacological inhibition with in vivo mouse thrombosis model; multiple functional readouts","pmids":["35895897"],"is_preprint":false},{"year":2009,"finding":"A unique domain in RANK (HCR, highly conserved region) recruits GAB2, which further associates with PLCγ2 in late-phase RANK signaling. HCR is dispensable for early RANK/ITAM signaling but essential for sustained NF-κB and PLCγ2/NFATc1 activation required for osteoclastogenesis.","method":"Co-immunoprecipitation (GAB2-HCR, GAB2-PLCγ2), RANK domain deletion/mutation analysis, NFATc1 reporter assays, osteoclast differentiation assays","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2 — co-IP with domain mutant analysis; single lab","pmids":["19845770"],"is_preprint":false},{"year":2008,"finding":"G-CSF stimulates Jak2-dependent phosphorylation of Gab2 on Tyr643, which promotes Shp2 binding to GAB2 and Erk1/2 activation and cell proliferation. In vitro, activated Jak2 directly phosphorylates GAB2 tyrosine residues; mutation of Y643 inhibits G-CSF-stimulated Erk1/2 activation, Shp2 binding, and Gab2-mediated cell proliferation.","method":"In vitro Jak2 kinase assay on GAB2, Jak2 antisense/dominant-negative constructs, Y643F mutagenesis, co-immunoprecipitation, Erk1/2 activation, cell proliferation assays","journal":"Cellular signalling","confidence":"High","confidence_rationale":"Tier 1 — in vitro kinase assay plus mutagenesis plus functional validation","pmids":["18644434"],"is_preprint":false}],"current_model":"GAB2 is a scaffolding/docking protein that, upon tyrosine phosphorylation by upstream kinases (including Src, ZAP-70, Jak2, Lyn, Hck, and RSK), recruits SH2-domain-containing effectors—principally SHP2, the p85 subunit of PI3K, GRB2, PLCγ, and CrkL—through defined phosphotyrosine motifs (Y452/Y476/Y584 for PI3K; Y614/Y643 for SHP2; Y266/Y293 for CrkL) to amplify PI3K/AKT/mTOR and SHP2/Ras/ERK signaling downstream of receptor tyrosine kinases, cytokine receptors, antigen receptors (FcεRI, TCR, FcγR), and non-receptor oncoproteins (BCR/ABL); it is negatively regulated by PKB/AKT phosphorylation at Ser159 and by 14-3-3 recruitment to phospho-Ser210/Thr391 (which uncouples GAB2 from GRB2-receptor complexes) and by RSK phosphorylation (which inhibits SHP2 recruitment), and it controls diverse cellular processes including mast cell degranulation (via Fyn/Gab2/PI3K/ARF1 for granule translocation), osteoclastogenesis (via RANK-GAB2-NF-κB/Akt/JNK and GAB2-PLCγ2/NFATc1), macrophage M2 polarization (via GAB2-STAT6), endothelial thromboinflammation (via Gab2-MALT1/CBM signalosome), cell migration and invasion (via SHP2-dependent suppression of RhoA through p190A RhoGAP/Vav2), and leukemic transformation (via distinct GAB2-PI3K and GAB2-SHP2 pathways for myeloid and lymphoid BCR/ABL leukemogenesis, respectively)."},"narrative":{"teleology":[{"year":1998,"claim":"Identification of GAB2 as a cytokine-responsive scaffolding protein that recruits SHP2 and PI3K resolved how Dos/Gab-family docking proteins diversify downstream signaling from receptor complexes, revealing a novel SHP2-dependent pathway to immediate-early gene activation distinct from classical MAPK signaling.","evidence":"Cloning, dominant-negative mutant expression, reporter gene assays, and co-immunoprecipitation in cytokine-stimulated cells","pmids":["9885561"],"confidence":"High","gaps":["Identity of upstream kinase(s) phosphorylating GAB2 not determined","Physiological role in vivo not established"]},{"year":2001,"claim":"Mapping of specific GAB2 phosphotyrosine residues to distinct SH2 partners (Y452/Y476/Y584 for PI3K p85; Y614 for SHP2; Y266/Y293 for CrkL) established GAB2 as a modular signaling platform where individual phosphosites independently recruit effectors, and genetic ablation in mice revealed that GAB2 is the principal PI3K activator downstream of FcεRI, essential for mast cell degranulation and anaphylaxis.","evidence":"Modified yeast two-hybrid with Lyn kinase and tyrosine mutants; Gab2 knockout mice with mast cell functional assays and anaphylaxis models","pmids":["11334882","11449275"],"confidence":"High","gaps":["Structural basis of phosphosite–SH2 domain selectivity not resolved","Redundancy with GAB1 in mast cells not fully assessed"]},{"year":2001,"claim":"Demonstration that GAB2–SHP2 interaction is required for M-CSF-driven macrophage differentiation and that GAB2 inhibits TCR-mediated NF-AT activation via SHP2 and PI3K extended GAB2 function beyond growth factor signaling to lineage specification and T cell inhibition.","evidence":"SHP2-binding-defective GAB2 mutants in macrophage differentiation; GAB2 domain mutants, ZAP-70 kinase assays, and NF-AT reporter assays in T cells; transgenic and KO mice","pmids":["11287610","11572860","12640133"],"confidence":"High","gaps":["How GAB2 switches between activating (macrophage) and inhibitory (T cell) outputs not resolved","Quantitative contribution of Gads vs GRB2 in T cell recruitment unclear"]},{"year":2002,"claim":"Identification of GAB2 as an essential mediator of BCR-ABL leukemogenesis—recruited via GRB2 to BCR-ABL pY177 to activate PI3K/Akt and Ras/ERK—and of negative feedback from AKT via Ser159 phosphorylation that restrains GAB2 tyrosine phosphorylation and transforming activity established GAB2 as both a critical oncogenic intermediary and a regulated signaling node.","evidence":"Gab2 KO bone marrow transformation by BCR-ABL, BCR-ABL Y177F mutant; in vitro AKT kinase assay on Ser159, S159A mutant with enhanced transformation","pmids":["12124177","11782427"],"confidence":"High","gaps":["Relative contributions of PI3K vs SHP2 arms to myeloid vs lymphoid BCR-ABL transformation not yet distinguished","Structural basis of Ser159-mediated inhibition unknown"]},{"year":2002,"claim":"Establishing that Src constitutively associates with GAB2 and is required for EGF-induced PI3K/Akt activation, and that GAB2 PH domain–dependent recruitment to nascent phagosomes amplifies PI3K signaling for FcγR-mediated phagocytosis, broadened the upstream kinase repertoire and defined a spatially restricted scaffolding role at membrane compartments.","evidence":"Src inhibitor PP1, Csk KO cells, in vitro phosphorylation; Gab2 KO macrophages, confocal imaging of phagosome recruitment, PH domain mutants","pmids":["12464621","12821647"],"confidence":"High","gaps":["Lipid species binding the PH domain in phagosomes not identified","Whether GAB2 PH domain localization is PI(3,4,5)P3-specific not confirmed"]},{"year":2005,"claim":"Demonstration that GAB2 mediates RANK-induced NF-κB/Akt/JNK activation and that Gab2 KO mice develop osteopetrosis, alongside evidence that GAB2 cooperates with ErbB2/Neu in breast carcinogenesis via SHP2-ERK, established GAB2 as essential for osteoclastogenesis and a driver of solid tumor progression.","evidence":"Gab2 KO mice bone histomorphometry and osteoclast assays; Gab2 KO crossed with Neu transgenic, 3D culture, domain mutants","pmids":["15750601","16369543"],"confidence":"High","gaps":["Direct RANK–GAB2 binding interface not structurally characterized","Whether GAB2 functions in osteoblasts is unknown"]},{"year":2006,"claim":"PLCγ2 was found to complex with GAB2 and modulate its phosphorylation during RANKL-stimulated osteoclastogenesis, and GAB2 via SHP2 was shown to activate Rac/JNK for Kit-evoked mast cell proliferation, revealing cell-type-specific effector partnerships that diversify GAB2 output.","evidence":"PLCγ2 KO mice and co-IP of PLCγ2–GAB2; compound Gab2 KO/Kit mutant mice, SHP2-binding-defective GAB2 rescue, Rac/JNK assays","pmids":["17053833","16873377"],"confidence":"High","gaps":["Whether PLCγ2–GAB2 interaction is direct or bridged by phosphotyrosine motifs not established","GAB2 role in non-mast cell Kit signaling (e.g., melanocytes, ICCs) unexplored"]},{"year":2008,"claim":"Discovery that 14-3-3 recruitment to phospho-Ser210/Thr391 dissociates GAB2 from GRB2/receptor complexes to terminate signaling, and that Jak2 directly phosphorylates GAB2 Tyr643 to promote SHP2 binding and ERK activation, defined a second negative regulatory mechanism and a new upstream kinase.","evidence":"S210A/T391A double mutant with sustained signaling and transformation; constitutive 14-3-3 binding site insertion; in vitro Jak2 kinase assay on GAB2, Y643F mutagenesis","pmids":["19172738","18644434"],"confidence":"High","gaps":["Kinase(s) responsible for Ser210/Thr391 phosphorylation in vivo not identified","Whether 14-3-3 binding affects GAB2 subcellular localization not determined"]},{"year":2009,"claim":"Crystal structures of GAB2 peptides complexed with the GRB2 C-SH3 domain revealed two distinct binding modes (PPII helix vs 3₁₀ helix) for the RxxK motif, providing the first atomic-resolution view of GAB2–effector recognition.","evidence":"X-ray crystallography, isothermal titration calorimetry, peptide arrays","pmids":["19523899"],"confidence":"High","gaps":["No full-length or larger-fragment GAB2 structure exists","Whether both SH3 sites are simultaneously occupied in cells unknown"]},{"year":2010,"claim":"GAB2 was shown to promote cell migration by SHP2-dependent activation of Vav2 and plasma membrane recruitment of p190A RhoGAP, suppressing RhoA and reducing stress fibers, providing the first mechanistic link from GAB2 to Rho GTPase regulation and cytoskeletal remodeling.","evidence":"GAB2 ΔShp2 mutants, RhoA activity assays, p190A RhoGAP knockdown, constitutively active RhoA rescue in mammary epithelial cells","pmids":["21118992"],"confidence":"High","gaps":["Direct SHP2 substrate(s) mediating Vav2 phosphorylation not identified","In vivo relevance of Gab2–RhoA axis in metastasis not tested"]},{"year":2011,"claim":"Knock-in mice with PI3K- or SHP2-binding site mutations in GAB2 dissected effector-specific outputs in mast cells, showing PI3K is required for ARF1-dependent granule translocation while both PI3K and SHP2 sites are needed for degranulation and anaphylaxis, establishing the first genetically separated effector arms in vivo.","evidence":"Gab2 knock-in mice (PI3K-binding and SHP2-binding site mutations), ARF1 activation assays, granule translocation imaging, anaphylaxis models","pmids":["21653832"],"confidence":"High","gaps":["GEF linking PI3K to ARF1 downstream of GAB2 not identified","Whether ARF1 pathway operates in non-mast cell GAB2-expressing contexts unknown"]},{"year":2013,"claim":"RSK was identified as a third negative-feedback kinase phosphorylating GAB2 on conserved residues to inhibit SHP2 recruitment without affecting GRB2 binding, selectively restricting GAB2-SHP2-dependent cell motility, revealing pathway-selective feedback regulation.","evidence":"In vitro RSK kinase assay, mass spectrometry, site-directed mutagenesis, co-IP, migration/invasion assays","pmids":["23401857"],"confidence":"High","gaps":["Identity of the specific RSK-phosphorylated residues that block SHP2 SH2 binding not structurally explained","In vivo validation of RSK–GAB2 feedback in tumors not reported"]},{"year":2016,"claim":"Genetic epistasis in BCR-ABL leukemia models demonstrated that myeloid (CML) transformation requires both GAB2–PI3K and GAB2–SHP2 arms, while lymphoid (B-ALL) transformation depends primarily on GAB2–SHP2, providing lineage-specific pathway assignments within a single oncogene system.","evidence":"Gab2 KO mice with BCR-ABL1 transduction, domain-specific mutant rescue in CML and B-ALL models","pmids":["26773044"],"confidence":"High","gaps":["Why lymphoid transformation is SHP2-dependent but PI3K-independent not mechanistically explained","Whether these distinctions hold in human CML/B-ALL not confirmed"]},{"year":2017,"claim":"GAB2 was found to have non-redundant roles with GAB1 in macrophage polarization—GAB2 activates STAT6 for M2 polarization while GAB1 activates AKT—and was placed downstream of YAP/TAZ transcriptional regulation in endometrial cancer, integrating GAB2 into Hippo pathway cross-talk.","evidence":"Gab2 KO and Gab1 conditional KO mice, IL-4/STAT6 signaling, bleomycin fibrosis model; YAP/TAZ siRNA with GAB2 protein and PI3K readouts in endometrial cancer cells","pmids":["28687632","28202507"],"confidence":"High","gaps":["Direct mechanism of GAB2-dependent STAT6 activation not resolved","Whether YAP/TAZ directly bind GAB2 promoter not shown"]},{"year":2022,"claim":"GAB2 was discovered to facilitate assembly of the CARMA3–BCL10–MALT1 (CBM) signalosome in endothelial cells, mediating IL-1β-induced Rho activation, NF-κB-dependent tissue factor expression, P-selectin/VWF exocytosis, and venous thrombosis, extending GAB2 function to endothelial thromboinflammation.","evidence":"Gab2 silencing, MALT1 inhibitor mepazine, IVC ligation thrombosis model, P-selectin/VWF exocytosis assays, NF-κB signaling","pmids":["35895897"],"confidence":"High","gaps":["How GAB2 physically connects to MALT1/CBM complex not defined","Whether GAB2 scaffolding of CBM occurs in non-endothelial cell types unknown"]},{"year":null,"claim":"A full-length structural model of GAB2 and the mechanism by which its intrinsically disordered regions coordinate simultaneous effector binding remain unknown; the GEF connecting GAB2–PI3K to ARF1, the structural basis of 14-3-3/RSK-mediated negative regulation, and the in vivo significance of GAB2 in neurodegeneration are also unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No full-length GAB2 structure","GEF for PI3K-ARF1 link unidentified","Neurodegeneration role based on single siRNA study"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,1,5,7,15,29]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[6,20,30]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,1,5]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[7,10,25]}],"pathway":[{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,2,5,6,8,15,17,26,36]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[2,4,7,10,26,36,38]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[5,14,21,33,34]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[13]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,15]}],"complexes":["GRB2/GAB2 complex","CBM signalosome (CARMA3-BCL10-MALT1)"],"partners":["GRB2","SHP2","PIK3R1","PLCG2","CRKL","LYN","SRC","JAK2"],"other_free_text":[]},"mechanistic_narrative":"GAB2 is a multi-site docking/scaffolding protein that amplifies PI3K/AKT and SHP2/Ras/ERK signaling downstream of receptor tyrosine kinases, cytokine receptors, antigen receptors, and oncoproteins by recruiting SH2-domain effectors—principally the p85 subunit of PI3K, SHP2, GRB2, PLCγ2, and CrkL—to specific phosphotyrosine motifs upon phosphorylation by kinases including Src, ZAP-70, Jak2, and Lyn [PMID:9885561, PMID:11334882, PMID:12464621, PMID:18644434]. GAB2 is negatively regulated through AKT-mediated Ser159 phosphorylation, RSK-mediated phosphorylation that uncouples SHP2, and 14-3-3 recruitment to phospho-Ser210/Thr391 that dissociates GAB2 from GRB2–receptor complexes, establishing multiple feedback loops that restrain its signaling output [PMID:11782427, PMID:19172738, PMID:23401857]. Genetic ablation of GAB2 in mice reveals essential, non-redundant roles in mast cell degranulation via PI3K/ARF1 [PMID:11449275, PMID:21653832], osteoclastogenesis via RANK–NF-κB/Akt/JNK and PLCγ2/NFATc1 [PMID:15750601, PMID:17053833], Fcγ receptor–mediated phagocytosis [PMID:12821647], M2 macrophage polarization via STAT6 [PMID:28687632], endothelial thromboinflammation via the CBM signalosome [PMID:35895897], and BCR-ABL–driven myeloid and lymphoid leukemogenesis through distinct PI3K- and SHP2-dependent pathways [PMID:12124177, PMID:26773044]. GAB2 also promotes tumor cell migration and invasion by SHP2-dependent suppression of RhoA through p190A RhoGAP and Vav2 [PMID:21118992], and cooperates with ErbB2/Neu in mammary carcinogenesis and metastasis [PMID:16369543, PMID:17310989]."},"prefetch_data":{"uniprot":{"accession":"Q9UQC2","full_name":"GRB2-associated-binding protein 2","aliases":["GRB2-associated binder 2","Growth factor receptor bound protein 2-associated protein 2","pp100"],"length_aa":676,"mass_kda":74.5,"function":"Adapter protein which acts downstream of several membrane receptors including cytokine, antigen, hormone, cell matrix and growth factor receptors to regulate multiple signaling pathways. Regulates osteoclast differentiation mediating the TNFRSF11A/RANK signaling. In allergic response, it plays a role in mast cells activation and degranulation through PI-3-kinase regulation. Also involved in the regulation of cell proliferation and hematopoiesis","subcellular_location":"Cytoplasm; Cell membrane; Membrane raft","url":"https://www.uniprot.org/uniprotkb/Q9UQC2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/GAB2","classification":"Not Classified","n_dependent_lines":90,"n_total_lines":1208,"dependency_fraction":0.07450331125827815},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/GAB2","total_profiled":1310},"omim":[{"mim_id":"621356","title":"SH3 AND CYSTEINE-RICH DOMAINS 2; STAC2","url":"https://www.omim.org/entry/621356"},{"mim_id":"620029","title":"NEURODEVELOPMENTAL DISORDER WITH HYPOTONIA, LANGUAGE DELAY, AND SKELETAL DEFECTS WITH OR WITHOUT SEIZURES; NEDHLSS","url":"https://www.omim.org/entry/620029"},{"mim_id":"618447","title":"LONG QT SYNDROME 8; LQT8","url":"https://www.omim.org/entry/618447"},{"mim_id":"611875","title":"BRUGADA SYNDROME 3; BRGDA3","url":"https://www.omim.org/entry/611875"},{"mim_id":"608360","title":"LEUCINE-RICH REPEAT-CONTAINING PROTEIN 8A; LRRC8A","url":"https://www.omim.org/entry/608360"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Plasma membrane","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"brain","ntpm":54.0}],"url":"https://www.proteinatlas.org/search/GAB2"},"hgnc":{"alias_symbol":["KIAA0571"],"prev_symbol":[]},"alphafold":{"accession":"Q9UQC2","domains":[{"cath_id":"2.30.29.30","chopping":"7-119","consensus_level":"high","plddt":83.6504,"start":7,"end":119}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UQC2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UQC2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UQC2-F1-predicted_aligned_error_v6.png","plddt_mean":51.91},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=GAB2","jax_strain_url":"https://www.jax.org/strain/search?query=GAB2"},"sequence":{"accession":"Q9UQC2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UQC2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UQC2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UQC2"}},"corpus_meta":[{"pmid":"17553421","id":"PMC_17553421","title":"GAB2 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stimulation, becomes tyrosyl phosphorylated and associates with SH2 domain-containing proteins including SHP2 and PI3K. Expression of p97 mutants unable to bind SHP2 blocks cytokine-induced c-fos promoter activation, inhibiting Elk1-mediated and STAT5-mediated transactivation, without inhibiting MAPK activation, revealing a novel pathway to immediate-early gene activation.\",\n      \"method\": \"Cloning, dominant-negative mutant expression, reporter gene assays, co-immunoprecipitation\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — original cloning paper with multiple orthogonal methods (mutants, reporter assays, co-IP); foundational discovery\",\n      \"pmids\": [\"9885561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"GAB2 contains a pleckstrin homology (PH) domain and, upon tyrosine phosphorylation, physically interacts with SHP2 and GRB2. GAB2 has an inhibitory effect on Elk-1-dependent transcription triggered by oncogenic Ras or growth factors, while having a similar function to GAB1 in ERK activation, indicating distinct roles in cytoplasmic-nuclear signal transduction.\",\n      \"method\": \"Co-immunoprecipitation, reporter gene assays, overexpression with dominant-active Ras\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (Co-IP, reporter assays) in original characterization paper\",\n      \"pmids\": [\"10391903\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"GAB2-deficient mast cells have defective responses to FcεRI stimulation (degranulation and cytokine gene expression), and GAB2 is the principal activator of PI3K in response to FcεRI activation, establishing that Dos/Gab family scaffolds regulate the PI3K pathway in vivo.\",\n      \"method\": \"Gab2 knockout mice, mast cell functional assays, passive cutaneous and systemic anaphylaxis models, biochemical signaling analysis\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with multiple functional readouts, published in Nature; independently replicated\",\n      \"pmids\": [\"11449275\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"GAB2 associates with GRB2, SHP2, p85 subunit of PI3K, SHIP, and SHC downstream of the M-CSF receptor (Fms). Overexpression of GAB2 enhanced MAPK activity and macrophage differentiation but reduced proliferation, while a Gab2 mutant unable to bind SHP2 failed to potentiate MAPK activity and inhibited macrophage differentiation, demonstrating that GAB2-SHP2 interaction is essential for the M-CSF differentiation signal.\",\n      \"method\": \"Co-immunoprecipitation, overexpression of wild-type and SHP2-binding-defective Gab2 mutants, MAPK kinase assays, cell differentiation assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal co-IP plus functional mutant analysis with multiple readouts\",\n      \"pmids\": [\"11287610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"GAB2 is phosphorylated by ZAP-70 and co-precipitates with ZAP-70, LAT, and CD3ζ upon TCR stimulation. Overexpression of GAB2 inhibits NF-AT activation and IL-2 production; this inhibitory function requires SHP2-binding sites and the PH domain of GAB2, and depends on PI3K recruitment. GAB2 functions as a switch molecule toward inhibition of TCR signal transduction by recruiting inhibitory molecules.\",\n      \"method\": \"Co-immunoprecipitation, kinase assays, reporter gene assays (NF-AT, IL-2), Gab2 domain mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants and functional readouts; Tier 2 methods\",\n      \"pmids\": [\"11572860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"BCR/ABL recruits GAB2 via a GRB2/GAB2 complex through BCR/ABL phosphotyrosine 177. GAB2 mediates BCR/ABL-driven PI3K/Akt and Ras/Erk activation; Gab2-deficient mouse bone marrow myeloid progenitors are resistant to transformation by BCR/ABL, identifying GAB2 as a key determinant of BCR/ABL leukemogenesis.\",\n      \"method\": \"Gab2 knockout mouse bone marrow transformation assays, Co-immunoprecipitation, signaling pathway analysis, BCR/ABL-Y177F mutant\",\n      \"journal\": \"Cancer cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic knockout with BCR/ABL transformation assay, co-IP, point mutant; highly cited foundational paper\",\n      \"pmids\": [\"12124177\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"PKB/AKT constitutively associates with GAB2, phosphorylates GAB2 on Ser159 in vitro, and this phosphorylation inhibits GAB2 tyrosine phosphorylation (negative feedback). The Gab2-S159A mutant enhances heregulin-induced GAB2 tyrosine phosphorylation, amplifies ERK and PKB pathway activation, and exhibits potent transforming activity, establishing a negative-feedback loop from PI3K/PKB to GAB2.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis (S159A), co-immunoprecipitation, transformation assay, signaling assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay plus mutagenesis plus functional transformation assay in one study\",\n      \"pmids\": [\"11782427\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"GAB2 is required for Fc gamma receptor (FcγR)-initiated phagocytosis in macrophages. Upon FcγR activation, GAB2 becomes tyrosyl phosphorylated and associates with p85 and SHP-2; GAB2 is recruited to the nascent phagosome via its PH domain (requiring PI3K lipid products and facilitated by GRB2 binding), where it amplifies PI3K/Akt signaling required for phagocytosis.\",\n      \"method\": \"Gab2 knockout macrophages, phagocytosis assays, confocal fluorescence microscopy, co-immunoprecipitation, wortmannin treatment, domain mutants\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with specific phenotype, direct localization by confocal microscopy, domain mutant analysis\",\n      \"pmids\": [\"12821647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"GAB2 mediates Src phosphorylation downstream of EGF receptor signaling; Src constitutively associates with GAB2 via its SH3 domain interacting with GAB2 proline-rich sequences. Src-dependent GAB2 phosphorylation is required for EGF-induced PI3K/Akt activation and DNA synthesis in hepatocytes. Gab2 mutants with SHP2-binding-site deletions increase EGF-induced GAB2 phosphorylation and PI3K activity but block MAPK activation, demonstrating SHP2-mediated downregulation of GAB2.\",\n      \"method\": \"Src inhibitor PP1, Csk knockout cells, in vitro phosphorylation, co-immunoprecipitation, GAB2 mutants, DNA synthesis assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro phosphorylation, multiple mutants, Csk KO cells, multiple signaling readouts\",\n      \"pmids\": [\"12464621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GAB2 interacts with GC-GAP, a novel Rho family GTPase-activating protein with activity toward RhoA, Rac1, and Cdc42, linking GAB2 scaffolding function to Rho GTPase regulation.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, in vitro GAP activity assay, siRNA knockdown\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — yeast two-hybrid plus in vitro GAP assay; single study\",\n      \"pmids\": [\"12819203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"GAB2 interaction with LAT upon TCR stimulation requires the c-Met binding domain (MBD) of GAB2 and a novel PXXXR Grb2/Gads SH3 binding motif. Through constitutive association with Gads/Grb2, GAB2 is recruited to lipid rafts after TCR ligation to exert its inhibitory function. Transgenic mice expressing wild-type GAB2 show impaired T cell responses, while Gab2-deficient mice show enhanced proliferative responses.\",\n      \"method\": \"Co-immunoprecipitation, GAB2 domain mutants, transgenic mice, Gab2-deficient mice, lipid raft fractionation\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants, transgenic and KO mice, lipid raft localization; two orthogonal in vivo models\",\n      \"pmids\": [\"12640133\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Specific tyrosine residues on GAB2 mediate binding to distinct SH2-domain proteins: Y452, Y476, and Y584 mediate PI3K p85 binding; Y614 mediates SHP-2 binding; and Y266 and Y293 mediate CrkL SH2 binding, as established in a modified yeast two-hybrid system with inducible Lyn kinase.\",\n      \"method\": \"Modified yeast two-hybrid with inducible Lyn kinase, tyrosine mutants of GAB2\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — yeast-based phospho-dependent binding assay; site-specific mutants; single study\",\n      \"pmids\": [\"11334882\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In IL-2-stimulated T lymphocytes, SHP-2 binds tyrosine residues Y614 (via N-terminal SH2) and Y643 (via C-terminal SH2) of GAB2. Mutation of Y614 alone is sufficient to prevent SHP-2 recruitment, and this blocks ERK activation and c-fos SRE transcription, demonstrating that GAB2-SHP2 interaction is required for ERK activation in response to IL-2. SRE induction requires both ERK-dependent (via Gab2/SHP2) and Rho-dependent signals.\",\n      \"method\": \"Site-directed mutagenesis (Y614F), co-immunoprecipitation, reporter gene assays (SRE, c-fos), dominant-active/negative RhoA\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — phosphosite mutants, co-IP, reporter assays; multiple orthogonal approaches\",\n      \"pmids\": [\"15170389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Constitutively active STAT5 (caSTAT5) induces persistent tyrosine phosphorylation of GAB2 and formation of a complex containing STAT5, GAB2, p85 (PI3K regulatory subunit), and GRB2 (but not SHP2). A Gab2-3YF mutant incapable of binding PI3K inhibits caSTAT5-induced proliferation and survival, as well as ERK1/2 and Akt phosphorylation, demonstrating GAB2 is required for caSTAT5-mediated activation of both PI3K/Akt and Ras/MAPK pathways.\",\n      \"method\": \"Co-immunoprecipitation, GAB2 mutant (3YF) expression, proliferation/survival assays, signaling analysis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP with mutant validation and multiple functional readouts\",\n      \"pmids\": [\"15833084\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GAB2 overexpression in breast cancer promotes mammary cell proliferation in 3D culture; these effects require GAB2 binding to GRB2 and SHP2, and are enhanced by PI3K recruitment. GAB2 overexpression mediates hyperactivation of the SHP2-ERK pathway, and co-expression with Neu results in an invasive phenotype. Gab2 potentiates, and Gab2 deficiency ameliorates, Neu-evoked breast carcinogenesis in mice.\",\n      \"method\": \"3D Matrigel culture, Gab2 knockout mice with Neu transgene, GAB2 domain mutants (Grb2 and Shp2 binding), signaling analysis\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO/overexpression in mouse model, 3D culture, domain mutants; multiple orthogonal methods\",\n      \"pmids\": [\"16369543\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"GAB2 associates with RANK and mediates RANK-induced activation of NF-κB, Akt, and JNK. Gab2-deficient mice develop osteopetrosis with decreased bone resorption due to defective osteoclast differentiation, establishing GAB2 as essential for RANK signaling and osteoclastogenesis.\",\n      \"method\": \"Gab2 knockout mice, osteoclastogenesis assays, co-immunoprecipitation (GAB2-RANK), signaling analysis (NF-κB, Akt, JNK), bone histomorphometry\",\n      \"journal\": \"Nature medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with specific skeletal phenotype, co-IP, multiple signaling readouts\",\n      \"pmids\": [\"15750601\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"PLCγ2 forms a complex with GAB2 in osteoclasts, is required for GAB2 phosphorylation, and modulates GAB2 recruitment to RANK during RANKL-induced osteoclastogenesis. PLCgamma2 and GAB2 interact downstream of Dap12/FcRγ receptors to regulate NFATc1 activation.\",\n      \"method\": \"Co-immunoprecipitation (PLCγ2-GAB2 complex), PLCγ2 knockout mice, PLCγ inhibitor U73122, RANKL stimulation assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — co-IP, genetic KO, pharmacological inhibition; multiple orthogonal methods\",\n      \"pmids\": [\"17053833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"GAB2 mediates Kit-evoked mast cell proliferation via the Rac/JNK pathway through SHP2. Kit Tyr567 (an SFK binding site) and SFK activity are required for GAB2 tyrosyl phosphorylation and GAB2-SHP2 association. GAB2 via SHP2 activates Rac/JNK and Ras to control mast cell proliferation, acting in a parallel pathway to PI3K from Kit Tyr719.\",\n      \"method\": \"Gab2 knockout mast cells, re-expression of wild-type GAB2 and SHP2-binding defective mutant, compound Gab2-/- KitY719F/Y719F mice, signaling assays (Rac, JNK, Ras), SFK inhibitors\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO, compound mutant mice, Gab2 mutant rescue experiments; multiple orthogonal approaches\",\n      \"pmids\": [\"16873377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GAB2 ablation severely suppresses lung metastasis of Neu-induced mammary tumors. Gab2-deficient cancer cells exhibit decreased migration and impaired ERK activation; defects are rescued by re-introduction of Gab2, establishing GAB2 as a promoter of mammary tumor metastasis via the ERK pathway.\",\n      \"method\": \"Gab2 knockout mice crossed with Neu transgenic mice, lung metastasis assays, cell migration assays, ERK signaling, Gab2 re-expression\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO in mouse tumor model, rescue experiment, specific functional readout\",\n      \"pmids\": [\"17310989\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"GAB2 was detected in neurons, tangle-bearing neurons, and dystrophic neurites in Alzheimer's disease brain; interference with GAB2 gene expression increased tau phosphorylation, suggesting GAB2 influences Alzheimer's neuropathology.\",\n      \"method\": \"Immunohistochemistry, siRNA-mediated GAB2 knockdown with tau phosphorylation readout\",\n      \"journal\": \"Neuron\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single experiment (siRNA + tau phospho assay); limited mechanistic follow-up\",\n      \"pmids\": [\"17553421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Growth factor-induced phosphorylation of GAB2 on S210 and T391 recruits 14-3-3 proteins, which terminates GAB2 signaling by promoting dissociation of GAB2 from GRB2 and receptor complexes. GAB2-S210A/T391A double mutant exhibits sustained receptor association and signaling and promotes cell proliferation and transformation; introduction of constitutive 14-3-3 binding sites renders GAB2 refractory to receptor activation.\",\n      \"method\": \"Site-directed mutagenesis, co-immunoprecipitation, proliferation/transformation assays, constitutive 14-3-3-binding site insertions\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants, co-IP, functional transformation assays; rigorous mechanistic dissection in one study\",\n      \"pmids\": [\"19172738\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In imatinib-resistant CML cells, Lyn kinase complexes with GAB2 and c-Cbl in a BCR-ABL-independent manner and mediates persistent tyrosine phosphorylation of GAB2 and BCR-ABL. Lyn silencing or inhibition is required to suppress GAB2 phosphorylation and restore imatinib sensitivity.\",\n      \"method\": \"Co-immunoprecipitation (Lyn-Gab2 complex), Lyn siRNA, kinase inhibitors, phosphorylation assays in imatinib-resistant patient samples\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP, siRNA knockdown, patient samples; single lab\",\n      \"pmids\": [\"18235045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"GAB2 is involved in differential PI3K/Akt signaling between two splice forms of c-Kit (GNNK- and GNNK+). GNNK- c-Kit mediates stronger PI3K/Akt activation through association with GAB2 and Src-mediated phosphorylation of GAB2, independent of direct PI3K binding to c-Kit. siRNA knockdown of GAB2 confirmed its role in PI3K/Akt activation downstream of c-Kit.\",\n      \"method\": \"siRNA, co-immunoprecipitation, signaling assays, c-Kit splice variant expression in Ba/F3 cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA validation plus co-IP; single lab\",\n      \"pmids\": [\"18697750\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystal structures of two GAB2 epitopes (Gab2a and Gab2b) complexed with the Grb2 SH3C domain reveal distinct binding modes: Gab2b contains a 3(10) helix positioning Arg and Lys of the RxxK motif in parallel orientation, while Gab2a has the RxxK motif in a PPII helix with staggered orientation. Two GRB2 SH3C binding sites in GAB2 are required for the GAB2-GRB2 interaction.\",\n      \"method\": \"Crystal structures, peptide arrays, isothermal titration calorimetry\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures with biochemical validation (ITC, peptide arrays)\",\n      \"pmids\": [\"19523899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"GAB2 overexpression promotes migration and invasion of melanoma cells; Gab2 knockdown reduces these behaviors. GAB2 mediates hyperactivation of Akt signaling in the absence of growth factors. PI3K/Akt pathway inhibition decreases Gab2-mediated tumor cell migration and invasive potential. GAB2 overexpression results in enhanced tumor growth and metastatic potential in vivo.\",\n      \"method\": \"Gab2 siRNA, overexpression, PI3K inhibitor treatment, migration/invasion assays, in vivo xenograft model\",\n      \"journal\": \"The American journal of pathology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — KD and OE with functional readouts and in vivo model; single lab\",\n      \"pmids\": [\"19342374\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"GAB2 overexpression in mammary epithelial cells decreases RhoA activation, reduces stress fibers and focal adhesions, and enhances cell migration via Shp2-dependent signaling. GAB2 promotes Vav2 phosphorylation and plasma membrane recruitment of p190A RhoGAP, which negatively regulates RhoA; constitutively active RhoA restores stress fibers in GAB2-expressing cells. A Gab2 mutant lacking Shp2 binding sites does not affect RhoA or cellular phenotype.\",\n      \"method\": \"Overexpression and Gab2 mutants (ΔShp2, 2xA), RhoA activity assays, p190A RhoGAP knockdown, co-immunoprecipitation, constitutively active RhoA rescue\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple mutants, rescue experiments, RhoGAP knockdown, specific pathway dissection\",\n      \"pmids\": [\"21118992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GAB2 via PI3K/ARF1 signaling regulates mast cell degranulation. Using Gab2 knock-in mice with mutations at either the PI3K or SHP2 binding sites, both binding sites are required for degranulation and anaphylaxis (but not cytokine production). The PI3K binding site of GAB2 is specifically required for granule translocation; FcεRI-stimulated ARF1 activation is dependent on Fyn and the PI3K binding site of GAB2.\",\n      \"method\": \"Gab2 knock-in mice (PI3K- and SHP2-binding site mutations), degranulation assays, ARF1 activation assay, anaphylaxis models, granule imaging\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — knock-in mouse genetic dissection with multiple functional readouts; new ARF1 pathway identified\",\n      \"pmids\": [\"21653832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GAB2 overexpression in ovarian cancer cells promotes migration and invasion and downregulates E-cadherin expression via PI3K pathway activation, leading to upregulation of ZEB1 (an EMT transcription factor). PI3K inhibitors reverse Gab2-induced EMT effects. GAB2 mutants defective in PI3K activation (not SHP2-ERK) abolish these effects, specifying the PI3K pathway as responsible.\",\n      \"method\": \"Overexpression, knockdown, GAB2 domain mutants (PI3K and Shp2-Erk defective), PI3K inhibitors, E-cadherin and Zeb1 expression assays, migration/invasion assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — specific domain mutants dissect PI3K vs SHP2 pathways; pharmacological and genetic validation\",\n      \"pmids\": [\"21996746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"GAB2 mediates G-CSF receptor activation of the Src kinase Lyn by recruiting SHP2. After G-CSF stimulation, Lyn associates with GAB2; GAB2-recruited SHP2 dephosphorylates inhibitory pLyn-Tyr507, enabling Lyn activation. This mechanism requires the Gab2-SHP2 interaction, as a mutant Gab2 unable to bind SHP2 fails to support Tyr507 dephosphorylation.\",\n      \"method\": \"Co-immunoprecipitation, Gab2 siRNA, SHP2-deficient cells, in vitro phosphatase assay with constitutively active Shp2E76A, Lyn Tyr507/Tyr396 phosphorylation analysis, GAB2 mutants\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro phosphatase assay, GAB2 mutant, Shp2-deficient cells, Gab2 siRNA; multiple orthogonal approaches\",\n      \"pmids\": [\"21636860\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"GAB2 is an A-kinase anchoring protein (AKAP) that binds the type I regulatory subunit of PKA; PKA phosphorylates GAB2 on Ser159. GAB2 is present in a preformed complex with PI3K and IRS-1 in granulosa cells. Overexpression of GAB2 enhances FSH-stimulated AKT phosphorylation, establishing GAB2 as a coordinator of PKA-to-PI3K/AKT signaling in FSH-stimulated ovarian granulosa cells.\",\n      \"method\": \"Co-immunoprecipitation, PKA in vitro phosphorylation assay, GAB2 overexpression, AKT phosphorylation assays in granulosa cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — in vitro PKA phosphorylation of GAB2, co-IP of preformed complex, functional overexpression\",\n      \"pmids\": [\"23045700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RSK (p90 ribosomal S6 kinase) phosphorylates GAB2 on three conserved residues (in vitro and in vivo), downstream of Ras/MAPK pathway activation. RSK-mediated phosphorylation of GAB2 inhibits SHP2 recruitment without affecting GRB2 binding. An unphosphorylatable GAB2 mutant promotes invasion-like phenotype and increased cell motility, placing RSK in a negative-feedback loop restricting GAB2-dependent epithelial cell motility.\",\n      \"method\": \"In vitro RSK kinase assay, mass spectrometry phosphorylation sites, site-directed mutagenesis, co-immunoprecipitation, cell migration/invasion assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay with mutagenesis and functional validation\",\n      \"pmids\": [\"23401857\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of ISIR-005 in complex with 14-3-3 and the GAB2 binding motif (Gab2pS210pT391) shows that the small molecule stabilizes the 14-3-3/GAB2 interaction at the pT391 site by occupying a pre-formed pocket at the rim of the interface. The Gab2pS210 motif binding does not create an interface pocket suitable for the molecule.\",\n      \"method\": \"Crystal structure of ternary complex, isothermal titration calorimetry, biochemical stabilization assay\",\n      \"journal\": \"ChemMedChem\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with biochemical validation\",\n      \"pmids\": [\"26644359\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GAB2 deficiency in Ptpn11E76K/+ (leukemic Shp2 gain-of-function) mice markedly attenuates myeloproliferative neoplasia, including reduced myeloid overproduction, splenomegaly, and myeloid infiltration. The interaction between leukemia-associated mutant SHP2 and GAB2 is enhanced, and the mTOR pathway is elevated in leukemic cells. Rapamycin treatment of Ptpn11E76K/+ mice mitigates MPN phenotypes, placing GAB2-PI3K-mTOR downstream of mutant SHP2.\",\n      \"method\": \"Double mutant mice (Ptpn11E76K/+/Gab2-/-), myeloid differentiation assays, Rapamycin treatment, signaling analysis\",\n      \"journal\": \"Leukemia\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis with double-mutant mice and pharmacological rescue; multiple readouts\",\n      \"pmids\": [\"27840422\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"GAB2 is essential for both myeloid and lymphoid leukemogenesis by BCR-ABL1. Gab2 knockout mice transplanted with BCR-ABL1-transduced bone marrow fail to develop CML-like disease; this is restored by wild-type GAB2 but not by GAB2 mutants lacking PI3K or SHP2 binding sites. Both PI3K and SHP2 binding sites are required for myeloid (CML) transformation, while only the SHP2 binding site is required for lymphoid (B-ALL) leukemogenesis.\",\n      \"method\": \"Mouse models of CML and B-ALL with Gab2 KO, GAB2 domain mutant rescue, signaling analysis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with domain-specific mutant rescue in two distinct disease mouse models\",\n      \"pmids\": [\"26773044\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In zebrafish MYCN-transgenic neuroblastoma model, GAB2 overexpression activates the SHP2-Ras-ERK pathway, promotes proliferation of hyperplastic neuroblasts, and increases neuroblastoma tumor penetrance, cooperating with MYCN. This establishes GAB2 as a SHP2 activator that cooperates with MYCN in neuroblastomagenesis.\",\n      \"method\": \"Zebrafish MYCN transgenic model, GAB2 overexpression, ptpn11 gain-of-function mutants, ERK signaling analysis\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — in vivo zebrafish model with defined genetic interactions; single lab\",\n      \"pmids\": [\"28329685\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"YAP and TAZ transcriptional regulators maintain PI3K pathway activation in endometrial cancer cells by transcriptionally regulating GAB2 levels. Coordinate knockdown of YAP and TAZ markedly decreases constitutive and growth factor-induced PI3K pathway activation by reducing GAB2 protein levels.\",\n      \"method\": \"siRNA knockdown of YAP/TAZ, GAB2 protein level measurement, PI3K/AKT signaling assays, in vivo tumor growth\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — epistasis by siRNA; identifies YAP/TAZ as upstream transcriptional regulators of GAB2; single lab\",\n      \"pmids\": [\"28202507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In IL-4/M2 macrophage polarization, GAB2 is recruited to the IL-4 receptor and synergistically enhances downstream signaling; loss of GAB2 suppresses STAT6 activation in response to IL-4, while loss of GAB1 attenuates AKT activation. GAB2 and GAB1 have non-redundant roles in M2 macrophage polarization and bleomycin-induced pulmonary fibrosis.\",\n      \"method\": \"Gab2 knockout mice, Gab1 conditional KO mice (macrophage-specific), IL-4 signaling assays, M2 polarization markers, bleomycin-induced fibrosis model, co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — two independent genetic KO models with defined signaling and phenotypic readouts\",\n      \"pmids\": [\"28687632\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss of PIK3R1 (p85α) in ovarian cancer cells alters GAB2 phosphorylation, relieves negative inhibition on AKT, and promotes assembly of a JAK2/STAT3 signalosome through GAB2 phosphorylation changes. This establishes GAB2 as a node linking PIK3R1 loss to both AKT and JAK2/STAT3 pathway activation.\",\n      \"method\": \"PIK3R1 siRNA knockdown, GAB2 phosphorylation analysis, AKT and STAT3 signaling assays, co-immunoprecipitation\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — siRNA epistasis with signaling pathway dissection; single lab\",\n      \"pmids\": [\"30755611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"GAB2 facilitates assembly of the CBM (CARMA3-BCL10-MALT1) signalosome in endothelial cells, which mediates Rho and NF-κB activation in response to IL-1β. GAB2 silencing reduces IL-1β-induced Rho-dependent exocytosis of P-selectin and VWF, NF-κB-dependent tissue factor expression, neutrophil adhesion, and venous thrombosis in mice.\",\n      \"method\": \"Gab2 gene silencing, MALT1 pharmacological inhibition (mepazine), inferior vena cava ligation model, P-selectin and VWF exocytosis assays, NF-κB signaling analysis\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KD plus pharmacological inhibition with in vivo mouse thrombosis model; multiple functional readouts\",\n      \"pmids\": [\"35895897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"A unique domain in RANK (HCR, highly conserved region) recruits GAB2, which further associates with PLCγ2 in late-phase RANK signaling. HCR is dispensable for early RANK/ITAM signaling but essential for sustained NF-κB and PLCγ2/NFATc1 activation required for osteoclastogenesis.\",\n      \"method\": \"Co-immunoprecipitation (GAB2-HCR, GAB2-PLCγ2), RANK domain deletion/mutation analysis, NFATc1 reporter assays, osteoclast differentiation assays\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — co-IP with domain mutant analysis; single lab\",\n      \"pmids\": [\"19845770\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"G-CSF stimulates Jak2-dependent phosphorylation of Gab2 on Tyr643, which promotes Shp2 binding to GAB2 and Erk1/2 activation and cell proliferation. In vitro, activated Jak2 directly phosphorylates GAB2 tyrosine residues; mutation of Y643 inhibits G-CSF-stimulated Erk1/2 activation, Shp2 binding, and Gab2-mediated cell proliferation.\",\n      \"method\": \"In vitro Jak2 kinase assay on GAB2, Jak2 antisense/dominant-negative constructs, Y643F mutagenesis, co-immunoprecipitation, Erk1/2 activation, cell proliferation assays\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro kinase assay plus mutagenesis plus functional validation\",\n      \"pmids\": [\"18644434\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"GAB2 is a scaffolding/docking protein that, upon tyrosine phosphorylation by upstream kinases (including Src, ZAP-70, Jak2, Lyn, Hck, and RSK), recruits SH2-domain-containing effectors—principally SHP2, the p85 subunit of PI3K, GRB2, PLCγ, and CrkL—through defined phosphotyrosine motifs (Y452/Y476/Y584 for PI3K; Y614/Y643 for SHP2; Y266/Y293 for CrkL) to amplify PI3K/AKT/mTOR and SHP2/Ras/ERK signaling downstream of receptor tyrosine kinases, cytokine receptors, antigen receptors (FcεRI, TCR, FcγR), and non-receptor oncoproteins (BCR/ABL); it is negatively regulated by PKB/AKT phosphorylation at Ser159 and by 14-3-3 recruitment to phospho-Ser210/Thr391 (which uncouples GAB2 from GRB2-receptor complexes) and by RSK phosphorylation (which inhibits SHP2 recruitment), and it controls diverse cellular processes including mast cell degranulation (via Fyn/Gab2/PI3K/ARF1 for granule translocation), osteoclastogenesis (via RANK-GAB2-NF-κB/Akt/JNK and GAB2-PLCγ2/NFATc1), macrophage M2 polarization (via GAB2-STAT6), endothelial thromboinflammation (via Gab2-MALT1/CBM signalosome), cell migration and invasion (via SHP2-dependent suppression of RhoA through p190A RhoGAP/Vav2), and leukemic transformation (via distinct GAB2-PI3K and GAB2-SHP2 pathways for myeloid and lymphoid BCR/ABL leukemogenesis, respectively).\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"GAB2 is a multi-site docking/scaffolding protein that amplifies PI3K/AKT and SHP2/Ras/ERK signaling downstream of receptor tyrosine kinases, cytokine receptors, antigen receptors, and oncoproteins by recruiting SH2-domain effectors—principally the p85 subunit of PI3K, SHP2, GRB2, PLCγ2, and CrkL—to specific phosphotyrosine motifs upon phosphorylation by kinases including Src, ZAP-70, Jak2, and Lyn [PMID:9885561, PMID:11334882, PMID:12464621, PMID:18644434]. GAB2 is negatively regulated through AKT-mediated Ser159 phosphorylation, RSK-mediated phosphorylation that uncouples SHP2, and 14-3-3 recruitment to phospho-Ser210/Thr391 that dissociates GAB2 from GRB2–receptor complexes, establishing multiple feedback loops that restrain its signaling output [PMID:11782427, PMID:19172738, PMID:23401857]. Genetic ablation of GAB2 in mice reveals essential, non-redundant roles in mast cell degranulation via PI3K/ARF1 [PMID:11449275, PMID:21653832], osteoclastogenesis via RANK–NF-κB/Akt/JNK and PLCγ2/NFATc1 [PMID:15750601, PMID:17053833], Fcγ receptor–mediated phagocytosis [PMID:12821647], M2 macrophage polarization via STAT6 [PMID:28687632], endothelial thromboinflammation via the CBM signalosome [PMID:35895897], and BCR-ABL–driven myeloid and lymphoid leukemogenesis through distinct PI3K- and SHP2-dependent pathways [PMID:12124177, PMID:26773044]. GAB2 also promotes tumor cell migration and invasion by SHP2-dependent suppression of RhoA through p190A RhoGAP and Vav2 [PMID:21118992], and cooperates with ErbB2/Neu in mammary carcinogenesis and metastasis [PMID:16369543, PMID:17310989].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of GAB2 as a cytokine-responsive scaffolding protein that recruits SHP2 and PI3K resolved how Dos/Gab-family docking proteins diversify downstream signaling from receptor complexes, revealing a novel SHP2-dependent pathway to immediate-early gene activation distinct from classical MAPK signaling.\",\n      \"evidence\": \"Cloning, dominant-negative mutant expression, reporter gene assays, and co-immunoprecipitation in cytokine-stimulated cells\",\n      \"pmids\": [\"9885561\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of upstream kinase(s) phosphorylating GAB2 not determined\", \"Physiological role in vivo not established\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Mapping of specific GAB2 phosphotyrosine residues to distinct SH2 partners (Y452/Y476/Y584 for PI3K p85; Y614 for SHP2; Y266/Y293 for CrkL) established GAB2 as a modular signaling platform where individual phosphosites independently recruit effectors, and genetic ablation in mice revealed that GAB2 is the principal PI3K activator downstream of FcεRI, essential for mast cell degranulation and anaphylaxis.\",\n      \"evidence\": \"Modified yeast two-hybrid with Lyn kinase and tyrosine mutants; Gab2 knockout mice with mast cell functional assays and anaphylaxis models\",\n      \"pmids\": [\"11334882\", \"11449275\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of phosphosite–SH2 domain selectivity not resolved\", \"Redundancy with GAB1 in mast cells not fully assessed\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Demonstration that GAB2–SHP2 interaction is required for M-CSF-driven macrophage differentiation and that GAB2 inhibits TCR-mediated NF-AT activation via SHP2 and PI3K extended GAB2 function beyond growth factor signaling to lineage specification and T cell inhibition.\",\n      \"evidence\": \"SHP2-binding-defective GAB2 mutants in macrophage differentiation; GAB2 domain mutants, ZAP-70 kinase assays, and NF-AT reporter assays in T cells; transgenic and KO mice\",\n      \"pmids\": [\"11287610\", \"11572860\", \"12640133\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How GAB2 switches between activating (macrophage) and inhibitory (T cell) outputs not resolved\", \"Quantitative contribution of Gads vs GRB2 in T cell recruitment unclear\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identification of GAB2 as an essential mediator of BCR-ABL leukemogenesis—recruited via GRB2 to BCR-ABL pY177 to activate PI3K/Akt and Ras/ERK—and of negative feedback from AKT via Ser159 phosphorylation that restrains GAB2 tyrosine phosphorylation and transforming activity established GAB2 as both a critical oncogenic intermediary and a regulated signaling node.\",\n      \"evidence\": \"Gab2 KO bone marrow transformation by BCR-ABL, BCR-ABL Y177F mutant; in vitro AKT kinase assay on Ser159, S159A mutant with enhanced transformation\",\n      \"pmids\": [\"12124177\", \"11782427\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contributions of PI3K vs SHP2 arms to myeloid vs lymphoid BCR-ABL transformation not yet distinguished\", \"Structural basis of Ser159-mediated inhibition unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing that Src constitutively associates with GAB2 and is required for EGF-induced PI3K/Akt activation, and that GAB2 PH domain–dependent recruitment to nascent phagosomes amplifies PI3K signaling for FcγR-mediated phagocytosis, broadened the upstream kinase repertoire and defined a spatially restricted scaffolding role at membrane compartments.\",\n      \"evidence\": \"Src inhibitor PP1, Csk KO cells, in vitro phosphorylation; Gab2 KO macrophages, confocal imaging of phagosome recruitment, PH domain mutants\",\n      \"pmids\": [\"12464621\", \"12821647\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Lipid species binding the PH domain in phagosomes not identified\", \"Whether GAB2 PH domain localization is PI(3,4,5)P3-specific not confirmed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstration that GAB2 mediates RANK-induced NF-κB/Akt/JNK activation and that Gab2 KO mice develop osteopetrosis, alongside evidence that GAB2 cooperates with ErbB2/Neu in breast carcinogenesis via SHP2-ERK, established GAB2 as essential for osteoclastogenesis and a driver of solid tumor progression.\",\n      \"evidence\": \"Gab2 KO mice bone histomorphometry and osteoclast assays; Gab2 KO crossed with Neu transgenic, 3D culture, domain mutants\",\n      \"pmids\": [\"15750601\", \"16369543\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct RANK–GAB2 binding interface not structurally characterized\", \"Whether GAB2 functions in osteoblasts is unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"PLCγ2 was found to complex with GAB2 and modulate its phosphorylation during RANKL-stimulated osteoclastogenesis, and GAB2 via SHP2 was shown to activate Rac/JNK for Kit-evoked mast cell proliferation, revealing cell-type-specific effector partnerships that diversify GAB2 output.\",\n      \"evidence\": \"PLCγ2 KO mice and co-IP of PLCγ2–GAB2; compound Gab2 KO/Kit mutant mice, SHP2-binding-defective GAB2 rescue, Rac/JNK assays\",\n      \"pmids\": [\"17053833\", \"16873377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether PLCγ2–GAB2 interaction is direct or bridged by phosphotyrosine motifs not established\", \"GAB2 role in non-mast cell Kit signaling (e.g., melanocytes, ICCs) unexplored\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery that 14-3-3 recruitment to phospho-Ser210/Thr391 dissociates GAB2 from GRB2/receptor complexes to terminate signaling, and that Jak2 directly phosphorylates GAB2 Tyr643 to promote SHP2 binding and ERK activation, defined a second negative regulatory mechanism and a new upstream kinase.\",\n      \"evidence\": \"S210A/T391A double mutant with sustained signaling and transformation; constitutive 14-3-3 binding site insertion; in vitro Jak2 kinase assay on GAB2, Y643F mutagenesis\",\n      \"pmids\": [\"19172738\", \"18644434\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase(s) responsible for Ser210/Thr391 phosphorylation in vivo not identified\", \"Whether 14-3-3 binding affects GAB2 subcellular localization not determined\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Crystal structures of GAB2 peptides complexed with the GRB2 C-SH3 domain revealed two distinct binding modes (PPII helix vs 3₁₀ helix) for the RxxK motif, providing the first atomic-resolution view of GAB2–effector recognition.\",\n      \"evidence\": \"X-ray crystallography, isothermal titration calorimetry, peptide arrays\",\n      \"pmids\": [\"19523899\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No full-length or larger-fragment GAB2 structure exists\", \"Whether both SH3 sites are simultaneously occupied in cells unknown\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"GAB2 was shown to promote cell migration by SHP2-dependent activation of Vav2 and plasma membrane recruitment of p190A RhoGAP, suppressing RhoA and reducing stress fibers, providing the first mechanistic link from GAB2 to Rho GTPase regulation and cytoskeletal remodeling.\",\n      \"evidence\": \"GAB2 ΔShp2 mutants, RhoA activity assays, p190A RhoGAP knockdown, constitutively active RhoA rescue in mammary epithelial cells\",\n      \"pmids\": [\"21118992\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SHP2 substrate(s) mediating Vav2 phosphorylation not identified\", \"In vivo relevance of Gab2–RhoA axis in metastasis not tested\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Knock-in mice with PI3K- or SHP2-binding site mutations in GAB2 dissected effector-specific outputs in mast cells, showing PI3K is required for ARF1-dependent granule translocation while both PI3K and SHP2 sites are needed for degranulation and anaphylaxis, establishing the first genetically separated effector arms in vivo.\",\n      \"evidence\": \"Gab2 knock-in mice (PI3K-binding and SHP2-binding site mutations), ARF1 activation assays, granule translocation imaging, anaphylaxis models\",\n      \"pmids\": [\"21653832\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"GEF linking PI3K to ARF1 downstream of GAB2 not identified\", \"Whether ARF1 pathway operates in non-mast cell GAB2-expressing contexts unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"RSK was identified as a third negative-feedback kinase phosphorylating GAB2 on conserved residues to inhibit SHP2 recruitment without affecting GRB2 binding, selectively restricting GAB2-SHP2-dependent cell motility, revealing pathway-selective feedback regulation.\",\n      \"evidence\": \"In vitro RSK kinase assay, mass spectrometry, site-directed mutagenesis, co-IP, migration/invasion assays\",\n      \"pmids\": [\"23401857\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the specific RSK-phosphorylated residues that block SHP2 SH2 binding not structurally explained\", \"In vivo validation of RSK–GAB2 feedback in tumors not reported\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Genetic epistasis in BCR-ABL leukemia models demonstrated that myeloid (CML) transformation requires both GAB2–PI3K and GAB2–SHP2 arms, while lymphoid (B-ALL) transformation depends primarily on GAB2–SHP2, providing lineage-specific pathway assignments within a single oncogene system.\",\n      \"evidence\": \"Gab2 KO mice with BCR-ABL1 transduction, domain-specific mutant rescue in CML and B-ALL models\",\n      \"pmids\": [\"26773044\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why lymphoid transformation is SHP2-dependent but PI3K-independent not mechanistically explained\", \"Whether these distinctions hold in human CML/B-ALL not confirmed\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"GAB2 was found to have non-redundant roles with GAB1 in macrophage polarization—GAB2 activates STAT6 for M2 polarization while GAB1 activates AKT—and was placed downstream of YAP/TAZ transcriptional regulation in endometrial cancer, integrating GAB2 into Hippo pathway cross-talk.\",\n      \"evidence\": \"Gab2 KO and Gab1 conditional KO mice, IL-4/STAT6 signaling, bleomycin fibrosis model; YAP/TAZ siRNA with GAB2 protein and PI3K readouts in endometrial cancer cells\",\n      \"pmids\": [\"28687632\", \"28202507\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct mechanism of GAB2-dependent STAT6 activation not resolved\", \"Whether YAP/TAZ directly bind GAB2 promoter not shown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"GAB2 was discovered to facilitate assembly of the CARMA3–BCL10–MALT1 (CBM) signalosome in endothelial cells, mediating IL-1β-induced Rho activation, NF-κB-dependent tissue factor expression, P-selectin/VWF exocytosis, and venous thrombosis, extending GAB2 function to endothelial thromboinflammation.\",\n      \"evidence\": \"Gab2 silencing, MALT1 inhibitor mepazine, IVC ligation thrombosis model, P-selectin/VWF exocytosis assays, NF-κB signaling\",\n      \"pmids\": [\"35895897\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How GAB2 physically connects to MALT1/CBM complex not defined\", \"Whether GAB2 scaffolding of CBM occurs in non-endothelial cell types unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full-length structural model of GAB2 and the mechanism by which its intrinsically disordered regions coordinate simultaneous effector binding remain unknown; the GEF connecting GAB2–PI3K to ARF1, the structural basis of 14-3-3/RSK-mediated negative regulation, and the in vivo significance of GAB2 in neurodegeneration are also unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No full-length GAB2 structure\", \"GEF for PI3K-ARF1 link unidentified\", \"Neurodegeneration role based on single siRNA study\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 1, 5, 7, 15, 29]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [6, 20, 30]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [7, 10, 25]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 2, 5, 6, 8, 15, 17, 26, 36]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [2, 4, 7, 10, 26, 36, 38]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [5, 14, 21, 33, 34]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 15]}\n    ],\n    \"complexes\": [\n      \"GRB2/GAB2 complex\",\n      \"CBM signalosome (CARMA3-BCL10-MALT1)\"\n    ],\n    \"partners\": [\n      \"GRB2\",\n      \"SHP2\",\n      \"PIK3R1\",\n      \"PLCG2\",\n      \"CRKL\",\n      \"LYN\",\n      \"SRC\",\n      \"JAK2\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}