{"gene":"SKAP2","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":1998,"finding":"SKAP-HOM (SKAP2) was identified as a novel adaptor protein purified via a GST-Fyn-SH2 domain affinity approach from pervanadate-treated EL4 cell lysates. Unlike the T-cell-specific SKAP55, SKAP-HOM is ubiquitously expressed. It does not constitutively associate with p59fyn in T cells but is a specific substrate for Fyn kinase in COS cells. It interacts with the adaptor polypeptide SLAP-130.","method":"GST-pulldown with Fyn-SH2 domain, N-terminal sequencing, molecular cloning, co-immunoprecipitation, COS cell transfection kinase assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal pulldown/co-IP with Fyn-SH2, substrate phosphorylation in COS cells, single lab with multiple orthogonal methods","pmids":["9755858"],"is_preprint":false},{"year":1998,"finding":"RA70 (SKAP2) associates with the SH2 domain of Fyn and interacts with Src family kinases Fyn, Hck, and Lyn during monocyte/macrophage differentiation of U937 cells, functioning as an adaptor for Src family kinases.","method":"Co-immunoprecipitation with SH2 domain of Fyn, expression analysis in differentiated U937 cells","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP with Fyn SH2 domain replicated across multiple Src family members; single lab","pmids":["9837776"],"is_preprint":false},{"year":2000,"finding":"Murine SKAP55R (mSKAP2) is phosphorylated by FYN kinase primarily at tyrosine 260, and this phosphotyrosine is essential for co-immunoprecipitation of FYN with mSKAP55R. Enforced expression of mSKAP55R inhibited in vitro growth of myeloid FDC-P1 cells and primary hematopoietic progenitors; a Y260 mutant had no effect on growth, indicating the tyrosine phosphorylation site is required for growth inhibitory function.","method":"Transient transfection in COS cells, site-directed mutagenesis of Y260, co-immunoprecipitation, retroviral overexpression in FDC-P1 and bone marrow cells, colony assays","journal":"Experimental hematology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis combined with co-IP and functional colony assay, single lab","pmids":["11063873"],"is_preprint":false},{"year":2005,"finding":"Down-regulation of SKAP-55R (SKAP2) by siRNA showed it cannot substitute for SKAP-55 in TCR-mediated LFA-1 clustering and T cell-APC conjugation, demonstrating that SKAP2 has a non-redundant but distinct function from SKAP55 in inside-out integrin signaling in T cells.","method":"siRNA knockdown of SKAP55R in T cells, LFA-1 clustering assay, T cell-APC conjugation assay","journal":"The Journal of experimental medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean siRNA loss-of-function with defined cellular phenotype, single lab, single method","pmids":["15939789"],"is_preprint":false},{"year":2005,"finding":"SKAP-HOM (SKAP2)-deficient mice show strongly attenuated BCR-mediated B cell proliferation and severely reduced adhesion of activated B cells to fibronectin (β1 integrin ligand) and ICAM-1 (β2 integrin ligand), while membrane-proximal BCR signaling (total tyrosine phosphorylation, Erk/p38/JNK phosphorylation, Ca2+ flux) is normal. This places SKAP2 downstream of membrane-proximal BCR signaling but upstream of integrin-mediated adhesion.","method":"SKAP-HOM knockout mouse analysis, BCR stimulation assays, adhesion assays to fibronectin and ICAM-1, flow cytometry, EAE model","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockout with multiple orthogonal phenotypic readouts (adhesion, proliferation, in vivo EAE), epistasis established by normal proximal signaling with impaired integrin adhesion","pmids":["16135797"],"is_preprint":false},{"year":2005,"finding":"SKAP55R (SKAP2) is expressed in myeloid cells and macrophages, is rapidly and transiently tyrosine-phosphorylated in response to M-CSF, and associates with other tyrosine-phosphorylated proteins and with actin upon M-CSF stimulation. Overexpression of SKAP55R decreased M-CSF-dependent proliferation without affecting differentiation.","method":"Western blotting for phosphorylation, co-immunoprecipitation, overexpression in myeloid cells, proliferation assays","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP and overexpression with functional readout, single lab, multiple methods","pmids":["15894167"],"is_preprint":false},{"year":2008,"finding":"Crystal structure of the Skap-hom (SKAP2) dimerization and PH domains revealed that SKAP2 is a homodimer with an N-terminal four-helix bundle dimerization domain against which two PH domains pack in a conformation incompatible with phosphoinositide binding. The isolated PH domains bind PI[3,4,5]P3. Mutations disrupting the dimerization domain or the PH domain PI[3,4,5]P3-binding pocket prevent SKAP2 localization to membrane ruffles, establishing a PI[3,4,5]P3-responsive molecular switch controlling SKAP2 function.","method":"X-ray crystallography, biochemical binding assays (phosphoinositide binding), mutagenesis, cell biology (ruffle localization assays)","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with mutagenesis and cell biological validation, multiple orthogonal methods in single rigorous study","pmids":["19026786"],"is_preprint":false},{"year":2009,"finding":"SKAP-HOM (SKAP2) in dendritic cells (DCs) is required for normal integrin-regulated DC motility and antigen-specific T cell priming in vivo. SKAP-HOM-deficient DCs show increased spontaneous motility but impaired integrin-triggered actin polymerization and reduced ability to form antigen-dependent conjugates with T cells. Immunization with SKAP-HOM-deficient BMDCs generates fewer antigen-specific T cells in vivo.","method":"SKAP-HOM knockout mouse BMDCs, in vivo LC migration assay, in vitro DC motility assay, actin polymerization assay, T cell conjugate formation assay, in vivo immunization","journal":"Journal of leukocyte biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with multiple cellular phenotypes and in vivo validation, single lab","pmids":["19369640"],"is_preprint":false},{"year":2010,"finding":"HPK1 associates with SKAP-HOM (SKAP2) to negatively regulate Rap1-mediated B-lymphocyte integrin activity and LFA-1-dependent adhesion to ICAM-1. Knockdown of HPK1 increased Rap1-GTP levels and enhanced LFA-1-dependent homotypic aggregation and adhesion, downstream of Src but independent of PI3K and PLC, via a module involving HPK1, SKAP-HOM, and RIAM.","method":"shRNA knockdown of HPK1 in Wehi 231 B cells, Rap1 activation assay, adhesion assays, HPK1-/- mouse B cells, co-immunoprecipitation","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP plus genetic KO plus functional adhesion assays, single lab, multiple orthogonal methods","pmids":["20824186"],"is_preprint":false},{"year":2011,"finding":"SKAP-HOM (SKAP2) was identified as a bona fide substrate of the lymphoid-specific tyrosine phosphatase Lyp. Crystal structures of Lyp in complex with a consensus peptide and with a phosphopeptide derived from SKAP-HOM defined the molecular determinants of Lyp substrate recognition. The Lyp dephosphorylation site on SKAP-HOM was identified through substrate specificity profiling.","method":"Combinatorial library (inverse alanine scanning) for substrate motif identification, crystal structure of Lyp/SKAP-HOM phosphopeptide complex, biochemical phosphatase assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure with biochemical validation and substrate specificity profiling in a single study with multiple orthogonal methods","pmids":["21719704"],"is_preprint":false},{"year":2011,"finding":"SKAP2 is a transcriptional target of HSF4b in lens epithelial cells and is highly expressed at the anterior tip of elongating lens fiber cells. SKAP2 localizes to actin-rich membrane ruffles and interacts with the SH2 domain of NCK2 via its N-terminus. The SKAP2-NCK2-F-actin complex accumulates at the lamellipodium leading edge. Knockdown of SKAP2 impairs disassembly of stress fibers in response to FGF-b, and overexpression of SKAP2 (but not the N-terminal deletion mutant) induces actin remodeling.","method":"Chromatin immunoprecipitation (ChIP) for HSF4b target, siRNA knockdown, co-immunoprecipitation of SKAP2 with NCK2 SH2 domain, immunofluorescence, overexpression of deletion mutants","journal":"Journal of cellular and molecular medicine","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, mutagenesis, knockdown with actin phenotype, and ChIP, single lab multiple methods","pmids":["20219016"],"is_preprint":false},{"year":2012,"finding":"Skap2 is necessary for macrophage migration, chemotaxis, global and local actin reorganization upon integrin engagement. PI[3,4,5]P3 binding to the Skap2 PH domain (relieving auto-inhibitory conformation) is critical for integrin-driven cytoskeletal response. Skap2 enables integrin-induced tyrosyl phosphorylation of SFKs, Adap, and Sirpα. Skap2 requires Sirpα for its recruitment to engaged integrins and for coordinating downstream actin rearrangement; Sirpα-deficient macrophages have identical impaired local integrin-induced responses as Skap2-/- macrophages.","method":"Skap2-/- mouse macrophage migration and chemotaxis assays, actin reorganization assays, PH domain mutants, co-immunoprecipitation/phosphorylation assays, Sirpα mutant macrophages, integrin engagement with fibronectin","journal":"Journal of cell science","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO combined with domain mutagenesis, multiple orthogonal cellular assays, epistasis with Sirpα, independently detailed mechanistic pathway","pmids":["22976304"],"is_preprint":false},{"year":2012,"finding":"SKAP2 physically associates with actin assembly factors WAVE2 and cortactin and inhibits their interaction with each other. SKAP2 suppresses WAVE2-cortactin-mediated actin polymerization in vitro. Knockdown of SKAP2 in NIH3T3 cells accelerates cell migration and enhances membrane translocation of WAVE2 in a manner dependent on SKAP2-WAVE2 binding activity.","method":"Co-immunoprecipitation of SKAP2 with WAVE2 and cortactin, in vitro actin polymerization assay, siRNA knockdown, cell migration assays, WAVE2 membrane localization assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of actin polymerization inhibition combined with co-IP and siRNA functional readout, single lab with multiple orthogonal methods","pmids":["23161539"],"is_preprint":false},{"year":2015,"finding":"SKAP2 physically interacts with Wiskott-Aldrich syndrome protein (WASP) and localizes to podosomes in macrophages. SKAP2-null macrophages rarely form podosomes, and their invasion is significantly reduced compared to wild-type. Rescue with functional SKAP2 containing an intact tyrosine phosphorylation site and WASP-binding ability restores podosome formation and invasion, while mutants lacking these features fail to rescue.","method":"Co-immunoprecipitation of SKAP2 with WASP, immunofluorescence/podosome quantification, SKAP2-/- macrophage invasion assay, rescue with SKAP2 mutants, in vivo lung metastasis model","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 2 / Strong — co-IP, KO phenotype, domain mutant rescue, in vivo model, single lab with multiple orthogonal methods","pmids":["26577701"],"is_preprint":false},{"year":2017,"finding":"Skap2 is essential for β2 integrin activation and neutrophil recruitment in vivo. Mechanistically, Skap2 regulates actin polymerization and binding of talin-1 and kindlin-3 to the β2 integrin cytoplasmic domain. The direct interaction of Skap2 with WASp via its SH3 domain is critical for integrin activation and neutrophil recruitment in vivo. Loss of Skap2 produces a LAD-like phenotype in mice.","method":"Skap2-/- mouse neutrophil studies, β2 integrin activation assays, talin-1/kindlin-3 co-immunoprecipitation, SH3 domain mutant analysis, intravital microscopy of neutrophil recruitment","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with in vivo phenotype, domain-specific mutant analysis, co-IP of integrin regulatory proteins, multiple orthogonal methods","pmids":["28183734"],"is_preprint":false},{"year":2017,"finding":"SKAP2 regulates the Arp2/3 complex and is essential for actin-mediated asymmetric cytokinesis in mouse oocytes by interacting with WAVE2. SKAP2 depletion by siRNA caused failure of spindle migration, polar body extrusion, and cytokinesis defects. SKAP2 co-localizes with actin at the oocyte cortex. Depletion reduced Arp2/3 and WAVE2 expression/localization.","method":"siRNA depletion in mouse oocytes, immunofluorescence for actin/WAVE2/Arp2/3, polar body extrusion assays, cytochalasin B colocalization","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA KD with multiple phenotypic readouts and colocalization in oocytes, single lab","pmids":["28933599"],"is_preprint":false},{"year":2018,"finding":"The SRC-family kinase HCK shapes the SKAP2 interactome. SKAP2 dimerization modulates SRC kinase binding, with dimerization indirectly affecting FYB protein binding. Domain mapping defined 14 SKAP2 interacting proteins' binding domains/motifs and identified FAM102A as a new interactor. Fine-tuning between SRC kinase binding and their activation state was identified.","method":"Yeast two-hybrid, co-immunoprecipitation, domain mutagenesis of SKAP2, protein-protein interaction mapping","journal":"Oncotarget","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — systematic interaction mapping with domain mutagenesis, single lab, multiple binding partners characterized","pmids":["29568343"],"is_preprint":false},{"year":2020,"finding":"SKAP2 is required for protection against K. pneumoniae pulmonary infection by enabling neutrophil and monocyte ROS production. SKAP2-/- neutrophils and monocytes are present in infected lungs and degranulate normally, but K. pneumoniae-stimulated ROS production in vitro is abolished. K. pneumoniae-induced neutrophil ROS requires SFKs, Syk, Btk, PLCγ2, and PKC. Loss of SKAP2 significantly impairs phosphorylation of SFKs, Syk, and Pyk2, placing SKAP2 proximal to their activation.","method":"Skap2-/- mouse infection model, ROS assays (DHR), degranulation assays, Western blotting of signaling intermediates, in vitro neutrophil stimulation with K. pneumoniae","journal":"eLife","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with in vivo infection model, multiple signaling pathway intermediates measured, functional ROS assay, multiple orthogonal methods","pmids":["32352382"],"is_preprint":false},{"year":2020,"finding":"YopH (Yersinia tyrosine phosphatase effector) dephosphorylates SKAP2 in neutrophils. SKAP2 is required for integrin receptor- and GPCR-mediated ROS production but is dispensable for degranulation under all conditions tested. YopH also blocks SKAP2-independent FcγR-stimulated phosphorylation of Syk, SLP-76, PLCγ2, and ERK1/2. These findings uncouple integrin/GPCR-dependent ROS from FcγR responses based on SKAP2 dependency.","method":"Skap2KO mouse neutrophils, YopH deletion mutant Yersinia infection, ROS assays, degranulation assays, phosphorylation analysis of signaling intermediates, Skap2KO vs WT comparison","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO combined with bacterial effector epistasis, multiple receptor stimulation conditions, multiple signaling readouts","pmids":["32392230"],"is_preprint":false},{"year":2021,"finding":"SKAP2 controls β-cell sensitivity to cytokine-induced apoptosis. Knockdown of SKAP2 aggravated cytokine-induced apoptosis in INS-1E cells and primary rat β-cells; overexpression afforded protection against cytokine-induced apoptosis. This correlated with reduced nuclear NF-κB p65 (S536-phosphorylated), lower nitric oxide production, and diminished CHOP expression. Knockdown of CHOP partially reversed the increased apoptosis caused by SKAP2 knockdown, linking SKAP2 to the NF-κB-iNOS-ER stress pathway.","method":"siRNA knockdown and overexpression in INS-1E cells and rat β-cells, apoptosis assays, NF-κB p65 nuclear translocation/phosphorylation assays, NO measurement, CHOP expression, double knockdown epistasis","journal":"Diabetes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function with epistasis (double KD with CHOP), multiple mechanistic readouts, single lab","pmids":["33203694"],"is_preprint":false},{"year":2021,"finding":"SKAP2 downregulation or complete lack impairs OPC migration and morphological maturation in oligodendrocytes. Overexpression of SKAP2 or constitutively active SKAP2 increased OPC migration, suggesting SKAP2 function depends on phosphorylation-based activation. Lack of SKAP2 enhanced the positive effect of integrin activation on OPC migration, indicating SKAP2 acts as a modulator of integrin-dependent migration in oligodendrocytes.","method":"SKAP2 KO OPCs, siRNA knockdown, overexpression of constitutively active SKAP2, migration assays, morphological maturation analysis, integrin activation experiments","journal":"Glia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO and overexpression with functional migration and differentiation readouts, single lab","pmids":["34324225"],"is_preprint":false},{"year":2021,"finding":"A de novo gain-of-function SKAP2 variant (p.Gly153Arg), located in the well-conserved lipid-binding loop of the PH domain, leads to enhanced integrin pathway activity and constitutive migratory behavior in myeloid macrophages in the absence of chemokine stimulation, consistent with constitutive SKAP2 activation.","method":"Whole-exome sequencing, monocyte-derived macrophage functional assays from patient and family members, integrin pathway activation assays, migration assays, expression of p.Gly153Arg variant in human macrophage cell line","journal":"Diabetes care","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — human variant with functional validation in primary cells and cell line, multiple assays, single lab","pmids":["34172489"],"is_preprint":false},{"year":2021,"finding":"SKAP2 is required for maximal ROS production by neutrophils in response to C-type lectin receptor (CLR) agonists and fungal pathogens (Candida glabrata and Candida albicans), and for robust killing of C. glabrata. Inside-out integrin signaling and Syk phosphorylation occur independently of SKAP2 after Candida infection. However, Pyk2, ERK1/2, and p38 phosphorylation are significantly reduced in Skap2-/- neutrophils after Candida and K. pneumoniae infection.","method":"HoxB8-immortalized Skap2-/- neutrophil progenitors, ROS assays, killing assays, phosphorylation analysis of Syk/Pyk2/ERK1/2/p38, inside-out integrin signaling assay","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO neutrophils with multiple receptor stimulation conditions and signaling readouts, single lab","pmids":["34386732"],"is_preprint":false},{"year":2022,"finding":"SKAP2 forms a complex with the Sirpα transmembrane receptor and the SHP-1 tyrosine phosphatase, and directly associates with the TIR domain of TLR4 adaptors MyD88, TIRAP, and TRAM. SKAP2-mediated recruitment of the Sirpα/SHP-1 complex to TLR4 attenuates NF-κB inflammatory signaling, while direct SKAP2 interaction with SHP-2 decreases SHP-2 activation. This dual mechanism inhibits NF-κB while promoting the TLR4-IFNβ pathway.","method":"Co-immunoprecipitation (SKAP2 with SHP-1, Sirpα, MyD88/TIRAP/TRAM, SHP-2), SKAP2 knockout mice in colitis/tumorigenesis model, NF-κB activation assays, cytokine measurements, overexpression studies","journal":"Oncogene","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple co-IPs defining complex composition, genetic KO with in vivo model, multiple signaling pathway readouts, single lab with extensive mechanistic characterization","pmids":["35034964"],"is_preprint":false},{"year":2022,"finding":"SKAP2 activates the WAVE2-ARP2/3 pathway in trophoblasts to promote cell growth and migration. SKAP2 W336K mutant (SH3 domain-blocked) cannot alter WAVE2 and ARP2 expression or HTR8/SVneo cell growth and migration, demonstrating that the SH3 domain of SKAP2 is required for its interaction with and activation of WAVE2-ARP2/3 signaling.","method":"siRNA knockdown and overexpression in HTR8/SVneo trophoblast cells, W336K SH3 domain mutant, western blotting for WAVE2/ARP2, immunofluorescence for actin-WAVE2 colocalization, cell growth (CCK8) and migration (transwell) assays","journal":"Placenta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — SH3 domain mutagenesis combined with KD/OE and multiple functional readouts, single lab","pmids":["36126383"],"is_preprint":false},{"year":2022,"finding":"SKAP2 interacts with SRC kinases through a modular organization comprising three interacting modules: the dimerization domain, the SH3 domain, and the second interdomain (between PH and SH3). The dimerization domain is necessary and sufficient to bind most activated and myristylated SRC kinases, while all three modules are required to bind SRC kinases at steady state. SKAP2 dimerization induces increased binding for most SRC kinases. Tyrosines in the interdomains modulate these interactions.","method":"Luciferase complementation assay (NanoBiT), extensive site-directed mutagenesis of SKAP2 domains, analysis of SRC kinase family member HCK mutants (Y390, K7)","journal":"Molecular & cellular proteomics : MCP","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — luciferase complementation with extensive mutagenesis, single lab, multiple interaction modules defined","pmids":["36423812"],"is_preprint":false},{"year":2024,"finding":"SKAP2 is present in the CD11b/CD18 (Mac-1) complex at steady state in primary and NB4 neutrophils, identified by KINDLIN3 BioID proximity labeling and confirmed by CD18 immunoprecipitation. Under resting conditions (without stimulation), SKAP2 restricts CD11b/CD18-mediated adhesion. Upon stimulation, SKAP2 is required for CD18 clustering, NADPH oxidase activity, phagocytosis, and cytotoxicity against tumor cells (ADCC). SKAP2-deficient NB4 neutrophils show enhanced resting adhesion to fibronectin but strongly reduced CD18 clustering upon stimulation.","method":"BioID proximity labeling of KINDLIN3 interactome, CD18 co-immunoprecipitation, CRISPR-Cas9 KO of SKAP2/CD18/KINDLIN3 in NB4 cells, adhesion assays, CD18 clustering by microscopy, NADPH oxidase activity, phagocytosis, ADCC assays","journal":"Frontiers in immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — BioID + co-IP for complex identification, CRISPR KO with multiple functional readouts, single lab with multiple orthogonal methods","pmids":["38487529"],"is_preprint":false},{"year":2014,"finding":"Ra70/Scap2 (SKAP2) is expressed in the ependymal layer and ventricular zone of the neural tube during development (E7.5-11.5) in heterozygous LacZ-knockin mice, restricted to posterior neural tissues including neural tube and hindbrain. Homozygous Ra70/scap2 knockout mice die during embryogenesis, indicating SKAP2 is essential for embryonic development.","method":"LacZ knockin heterozygous and homozygous knockout mouse analysis, immunohistochemistry, RNA expression analysis in P19 EC cells during RA-induced neuronal differentiation","journal":"Neuroscience letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with embryonic lethality phenotype plus spatial expression mapped by reporter knockin, single lab","pmids":["24846415"],"is_preprint":false},{"year":2025,"finding":"SKAP2 is required for sperm cytoskeletal structure and mitochondrial organization during spermiogenesis. Hnrnpr mutation disrupts m6A-dependent splicing of Skap2 pre-mRNA, impairing SKAP2 protein production in sperm and causing motility decline and morphological abnormalities. Specific knockout of Skap2 in male germ cells phenocopies these defects. Extracellular vesicle-mediated delivery of SKAP2 to efferent ductules restores sperm motility and morphology, confirming the functional hnRNPR-SKAP2 axis.","method":"Hnrnpr mutant mice and human patients, germ cell-specific Skap2 KO mice, sperm motility and morphology analysis, mitochondrial organization assays, m6A-seq for splice site, extracellular vesicle delivery rescue experiment","journal":"Signal transduction and targeted therapy","confidence":"High","confidence_rationale":"Tier 2 / Strong — germ cell-specific KO with phenotype, rescue by EV-mediated delivery, upstream RNA splicing mechanism identified, multiple orthogonal methods","pmids":["41436426"],"is_preprint":false},{"year":2024,"finding":"SKAP2/PLC signaling pathway is essential for LTB4 production by neutrophils in response to bacterial T3SS stimulation, but is not required for LTB4 synthesis by macrophages (which instead requires phagocytosis and NLRP3/CASP1 inflammasome), establishing cell-type-specific pathway requirements for LTB4 synthesis.","method":"Skap2-/- mouse neutrophils and macrophages, LTB4 production assays with T3SS stimulation, pharmacological inhibitors of signaling intermediates, NLRP3/CASP1 pathway analysis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO with defined functional phenotype and cell-type epistasis, preprint not yet peer-reviewed","pmids":["bio_10.1101_2024.07.01.601466"],"is_preprint":true}],"current_model":"SKAP2 (also known as SKAP-HOM, RA70, SKAP55R, SCAP2, SAPS) is a ubiquitously expressed dimeric adaptor protein that functions as a PI[3,4,5]P3-gated molecular switch: its N-terminal four-helix bundle dimerization domain holds the PH domain in an autoinhibited conformation until PI3K-generated PI[3,4,5]P3 releases the PH domain, enabling membrane recruitment and cytoskeletal remodeling; at integrins, SKAP2 collaborates with Sirpα, SHP-1, talin-1, kindlin-3, WASP/WASp, WAVE2, cortactin, and Arp2/3 to drive actin polymerization, podosome formation, integrin clustering, and outside-in signaling in macrophages and neutrophils; it is also a substrate of Fyn/Src-family kinases (phosphorylated at a key tyrosine required for FYN association and growth inhibition), a substrate of the lymphoid phosphatase Lyp (crystal structure defined), an inhibitor of TLR4-NF-κB signaling through Sirpα/SHP-1 recruitment, and a regulator of β-cell survival through the NF-κB–iNOS–ER stress pathway; in spermatogenesis SKAP2 is regulated by hnRNPR-mediated m6A-dependent splicing and is required for sperm cytoskeletal integrity and mitochondrial organization."},"narrative":{"mechanistic_narrative":"SKAP2 is a ubiquitously expressed dimeric adaptor protein that couples membrane-proximal kinase signaling to integrin activation and actin cytoskeletal remodeling across myeloid, lymphoid, and developing cells [PMID:22976304, PMID:28183734]. Structurally, it is a homodimer in which an N-terminal four-helix bundle dimerization domain packs two PH domains in an autoinhibited conformation incompatible with phosphoinositide binding; PI3K-generated PI[3,4,5]P3 relieves this autoinhibition, driving membrane recruitment and cytoskeletal function, with mutations in either the dimerization domain or the PH binding pocket abolishing localization to membrane ruffles [PMID:19026786]. SKAP2 is a substrate of Src-family kinases, associating with Fyn, Hck, and Lyn through Fyn-SH2 recognition, and its phosphorylation at a key tyrosine is required both for Fyn association and for growth-inhibitory activity in myeloid progenitors [PMID:9755858, PMID:9837776, PMID:11063873]; its modular dimerization, SH3, and interdomain regions tune Src-family kinase binding, and it is dephosphorylated by the lymphoid phosphatase Lyp [PMID:21719704, PMID:36423812]. At engaged integrins, SKAP2 is recruited via Sirpα and orchestrates actin polymerization, podosome formation, β2-integrin activation, and integrin clustering by interacting through its SH3 domain with WASP and by regulating talin-1 and kindlin-3 loading onto the β2 cytoplasmic tail, with loss producing impaired adhesion-coupled responses and a LAD-like phenotype in mice [PMID:22976304, PMID:26577701, PMID:28183734, PMID:38487529]. SKAP2 also negatively regulates actin dynamics by binding WAVE2 and cortactin and suppressing their cooperative actin polymerization [PMID:23161539]. Genetically, SKAP2 is required for B-cell, dendritic-cell, neutrophil, and monocyte integrin-dependent adhesion and immune function, and for neutrophil/monocyte ROS production against bacterial and fungal pathogens through a SFK–Syk–Pyk2 module [PMID:16135797, PMID:19369640, PMID:28183734, PMID:32352382, PMID:34386732]. Beyond immune cells, SKAP2 inhibits TLR4–NF-κB signaling by recruiting a Sirpα/SHP-1 complex to TLR4 adaptors [PMID:35034964], protects β-cells from cytokine-induced apoptosis via the NF-κB–iNOS–ER stress (CHOP) pathway [PMID:33203694], and is required for sperm cytoskeletal integrity and mitochondrial organization downstream of an hnRNPR-controlled m6A splicing axis [PMID:41436426]. A de novo gain-of-function PH-domain variant (p.Gly153Arg) produces constitutive integrin activity and migration, and homozygous knockout is embryonic lethal in mice [PMID:34172489, PMID:24846415].","teleology":[{"year":1998,"claim":"Established SKAP2 as a Src-family-kinase-associated adaptor distinct from the T-cell-restricted SKAP55, defining its ubiquitous expression and Fyn substrate identity.","evidence":"GST-Fyn-SH2 pulldown and COS-cell kinase assays identifying SKAP-HOM/RA70 binding to Fyn, Hck, and Lyn and association with SLAP-130","pmids":["9755858","9837776"],"confidence":"Medium","gaps":["Functional consequence of Fyn association not yet determined","Phosphorylation site not mapped"]},{"year":2000,"claim":"Mapped the functional phosphotyrosine, showing tyrosine 260 is required for Fyn co-association and for SKAP2's growth-inhibitory effect in myeloid progenitors.","evidence":"Site-directed Y260 mutagenesis with co-IP and retroviral overexpression colony assays in FDC-P1 and bone marrow cells","pmids":["11063873"],"confidence":"Medium","gaps":["Mechanism linking phosphorylation to growth inhibition unresolved","Downstream effectors not identified"]},{"year":2005,"claim":"Genetic and knockdown studies placed SKAP2 downstream of membrane-proximal antigen-receptor signaling but upstream of integrin-mediated adhesion, with a function non-redundant to SKAP55.","evidence":"SKAP-HOM knockout mouse B-cell adhesion/proliferation assays and siRNA in T cells with LFA-1 clustering and conjugation readouts","pmids":["16135797","15939789","15894167"],"confidence":"High","gaps":["Molecular link to integrin activation machinery not defined","Recruitment mechanism unknown"]},{"year":2008,"claim":"Resolved the structural basis of SKAP2 regulation as a PI[3,4,5]P3-gated molecular switch in which dimerization autoinhibits the PH domain until lipid binding releases it for membrane recruitment.","evidence":"X-ray crystallography of dimerization and PH domains plus phosphoinositide binding assays and ruffle-localization mutants","pmids":["19026786"],"confidence":"High","gaps":["Kinetics of in vivo switching not measured","Effectors engaged after membrane recruitment not defined structurally"]},{"year":2009,"claim":"Extended SKAP2's integrin-adhesion role to dendritic cells, linking it to integrin-triggered actin polymerization and in vivo T-cell priming.","evidence":"SKAP-HOM knockout BMDC motility, actin polymerization, conjugate formation, and in vivo immunization assays","pmids":["19369640"],"confidence":"Medium","gaps":["Direct actin-regulatory partners in DCs not identified"]},{"year":2010,"claim":"Defined an HPK1–SKAP2–RIAM module negatively regulating Rap1-driven integrin activation in B cells, situating SKAP2 in a defined signaling complex.","evidence":"shRNA/knockout of HPK1, Rap1 activation and adhesion assays, and co-IP in B cells","pmids":["20824186"],"confidence":"Medium","gaps":["Direct vs indirect SKAP2-HPK1 contact not resolved","Mechanism of Rap1 control unclear"]},{"year":2011,"claim":"Identified SKAP2 as a substrate of the lymphoid phosphatase Lyp and as an HSF4b-regulated actin remodeler interacting with NCK2, establishing both its dephosphorylation and an actin-localized effector partner.","evidence":"Crystal structures of Lyp/SKAP-HOM phosphopeptide with specificity profiling; ChIP, co-IP with NCK2 SH2, and actin-remodeling knockdown in lens cells","pmids":["21719704","20219016"],"confidence":"High","gaps":["Physiological setting of Lyp-mediated dephosphorylation not defined","NCK2 interaction tested largely outside immune cells"]},{"year":2012,"claim":"Established the integrin actin-remodeling mechanism: SKAP2 requires PI[3,4,5]P3 binding and Sirpα for recruitment, while also directly binding and inhibiting WAVE2-cortactin actin polymerization, revealing dual positive and negative actin control.","evidence":"Skap2-/- macrophage migration with PH-domain and Sirpα mutants; co-IP and in vitro reconstitution of WAVE2-cortactin polymerization inhibition with knockdown migration assays","pmids":["22976304","23161539"],"confidence":"High","gaps":["How positive (Sirpα/integrin) and negative (WAVE2-cortactin) functions are spatially balanced unresolved"]},{"year":2015,"claim":"Demonstrated SKAP2's SH3-mediated WASP interaction and phosphotyrosine site are jointly required for podosome formation and macrophage invasion.","evidence":"Co-IP with WASP, podosome quantification, Skap2-/- invasion with domain-mutant rescue and in vivo metastasis model","pmids":["26577701"],"confidence":"High","gaps":["Relationship between WASP and WAVE2 engagement not reconciled"]},{"year":2017,"claim":"Identified SKAP2 as essential for β2-integrin activation and neutrophil recruitment by regulating talin-1/kindlin-3 loading and acting through SH3-mediated WASp binding, producing a LAD-like phenotype; also extended its actin role to Arp2/3-dependent oocyte cytokinesis.","evidence":"Skap2-/- neutrophil integrin activation, talin-1/kindlin-3 co-IP, SH3 mutant analysis, intravital microscopy; siRNA depletion in oocytes with WAVE2/Arp2/3 colocalization","pmids":["28183734","28933599"],"confidence":"High","gaps":["Direct vs indirect control of talin-1/kindlin-3 binding not biochemically resolved"]},{"year":2018,"claim":"Systematically mapped the SKAP2 interactome, showing dimerization modulates Src-family kinase binding and indirectly affects FYB binding, and identified FAM102A as a new partner.","evidence":"Yeast two-hybrid, co-IP, and domain mutagenesis defining binding domains of 14 interactors","pmids":["29568343"],"confidence":"Medium","gaps":["Functional roles of newly mapped interactors not tested"]},{"year":2020,"claim":"Positioned SKAP2 proximal to SFK/Syk/Pyk2 activation as essential for receptor-specific neutrophil/monocyte ROS production, dissociating ROS from degranulation and Fcγ-receptor responses.","evidence":"Skap2-/- infection models (K. pneumoniae), ROS and degranulation assays, signaling intermediate phosphorylation; YopH phosphatase epistasis distinguishing integrin/GPCR vs Fcγ pathways","pmids":["32352382","32392230"],"confidence":"High","gaps":["Direct substrate/partner mediating ROS activation not pinpointed","How SKAP2 selectively gates integrin/GPCR vs Fcγ pathways unclear"]},{"year":2021,"claim":"Broadened SKAP2 to a tissue-spanning modulator: protecting β-cells via NF-κB–iNOS–CHOP, modulating oligodendrocyte/OPC integrin-dependent migration, with a de novo PH-domain gain-of-function variant causing constitutive migration, and a further ROS role against fungal pathogens.","evidence":"INS-1E/β-cell knockdown-overexpression with CHOP epistasis; OPC KO/overexpression migration; whole-exome sequencing of p.Gly153Arg with macrophage assays; Skap2-/- neutrophil anti-Candida ROS and signaling","pmids":["33203694","34324225","34172489","34386732"],"confidence":"Medium","gaps":["Whether β-cell and neuronal roles share the integrin/actin mechanism unresolved","Mechanism by which Gly153Arg constitutively activates not structurally confirmed"]},{"year":2022,"claim":"Defined SKAP2 as a negative regulator of TLR4-NF-κB inflammation via Sirpα/SHP-1 recruitment to TLR4 adaptors, and confirmed SH3-dependent WAVE2-ARP2/3 activation drives trophoblast growth/migration.","evidence":"Co-IPs of SKAP2 with SHP-1/Sirpα/MyD88/TIRAP/TRAM/SHP-2 with KO colitis model; W336K SH3 mutant with WAVE2/ARP2 readouts in trophoblasts; NanoBiT modular mapping of Src-family kinase binding","pmids":["35034964","36126383","36423812"],"confidence":"High","gaps":["How the same protein switches between actin scaffolding and TLR4 inhibition is unresolved"]},{"year":2024,"claim":"Placed SKAP2 within the resting Mac-1 (CD11b/CD18) complex where it restricts adhesion at rest but enables CD18 clustering, NADPH oxidase, phagocytosis, and ADCC upon stimulation; preprint data add cell-type-specific LTB4 control.","evidence":"KINDLIN3 BioID and CD18 co-IP, CRISPR KO of SKAP2/CD18/KINDLIN3 in NB4 neutrophils with adhesion/clustering/oxidase/phagocytosis/ADCC assays; Skap2-/- LTB4 neutrophil vs macrophage comparison (preprint)","pmids":["38487529","bio_10.1101_2024.07.01.601466"],"confidence":"High","gaps":["Molecular trigger switching SKAP2 from adhesion-restricting to clustering-promoting not defined"]},{"year":2025,"claim":"Revealed an hnRNPR–m6A–SKAP2 axis required for sperm cytoskeletal integrity and mitochondrial organization, extending SKAP2 to spermiogenesis with rescue by EV-mediated protein delivery.","evidence":"Hnrnpr mutant and germ-cell-specific Skap2 KO mice, m6A-seq, sperm morphology/motility/mitochondrial assays, EV delivery rescue","pmids":["41436426"],"confidence":"High","gaps":["Whether sperm role uses the integrin/actin switch mechanism not established","Direct SKAP2 cytoskeletal partners in sperm not identified"]},{"year":null,"claim":"How a single autoinhibited adaptor is selectively deployed across distinct contexts — positive actin/integrin assembly, negative WAVE2-cortactin and adhesion restriction, and TLR4-NF-κB inhibition — remains mechanistically unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model explaining context-dependent switching between opposing SKAP2 functions","The direct effector immediately downstream of PI[3,4,5]P3-triggered recruitment not defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,14,23]},{"term_id":"GO:0008289","term_label":"lipid binding","supporting_discovery_ids":[6,11]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[12,13,15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[12,23,26]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[6,11,26]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[10,12,13]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5,11]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,14,17,23]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6,11,23]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[11,14,26]}],"complexes":["CD11b/CD18 (Mac-1) complex","Sirpα/SHP-1 complex"],"partners":["FYN","WASP","WAVE2","SIRPA","TLN1","FERMT3","CTTN","NCK2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O75563","full_name":"Src kinase-associated phosphoprotein 2","aliases":["Pyk2/RAFTK-associated protein","Retinoic acid-induced protein 70","SKAP55 homolog","SKAP-55HOM","SKAP-HOM","Src family-associated phosphoprotein 2","Src kinase-associated phosphoprotein 55-related protein","Src-associated adapter protein with PH and SH3 domains"],"length_aa":359,"mass_kda":41.2,"function":"May be involved in B-cell and macrophage adhesion processes. In B-cells, may act by coupling the B-cell receptor (BCR) to integrin activation. May play a role in src signaling pathway","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/O75563/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SKAP2","classification":"Not Classified","n_dependent_lines":7,"n_total_lines":1208,"dependency_fraction":0.005794701986754967},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SKAP2","total_profiled":1310},"omim":[{"mim_id":"605215","title":"SRC KINASE-ASSOCIATED PHOSPHOPROTEIN 2; SKAP2","url":"https://www.omim.org/entry/605215"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SKAP2"},"hgnc":{"alias_symbol":["RA70","SKAP-HOM","SKAP55R","SAPS"],"prev_symbol":["SCAP2"]},"alphafold":{"accession":"O75563","domains":[{"cath_id":"2.30.29.30","chopping":"118-223","consensus_level":"high","plddt":90.1946,"start":118,"end":223},{"cath_id":"2.30.30.40","chopping":"299-356","consensus_level":"high","plddt":91.3224,"start":299,"end":356},{"cath_id":"1.10.287","chopping":"16-63","consensus_level":"high","plddt":83.8121,"start":16,"end":63}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75563","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75563-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75563-F1-predicted_aligned_error_v6.png","plddt_mean":74.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SKAP2","jax_strain_url":"https://www.jax.org/strain/search?query=SKAP2"},"sequence":{"accession":"O75563","fasta_url":"https://rest.uniprot.org/uniprotkb/O75563.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75563/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75563"}},"corpus_meta":[{"pmid":"14657016","id":"PMC_14657016","title":"The 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Unlike the T-cell-specific SKAP55, SKAP-HOM is ubiquitously expressed. It does not constitutively associate with p59fyn in T cells but is a specific substrate for Fyn kinase in COS cells. It interacts with the adaptor polypeptide SLAP-130.\",\n      \"method\": \"GST-pulldown with Fyn-SH2 domain, N-terminal sequencing, molecular cloning, co-immunoprecipitation, COS cell transfection kinase assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal pulldown/co-IP with Fyn-SH2, substrate phosphorylation in COS cells, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"9755858\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"RA70 (SKAP2) associates with the SH2 domain of Fyn and interacts with Src family kinases Fyn, Hck, and Lyn during monocyte/macrophage differentiation of U937 cells, functioning as an adaptor for Src family kinases.\",\n      \"method\": \"Co-immunoprecipitation with SH2 domain of Fyn, expression analysis in differentiated U937 cells\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP with Fyn SH2 domain replicated across multiple Src family members; single lab\",\n      \"pmids\": [\"9837776\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Murine SKAP55R (mSKAP2) is phosphorylated by FYN kinase primarily at tyrosine 260, and this phosphotyrosine is essential for co-immunoprecipitation of FYN with mSKAP55R. Enforced expression of mSKAP55R inhibited in vitro growth of myeloid FDC-P1 cells and primary hematopoietic progenitors; a Y260 mutant had no effect on growth, indicating the tyrosine phosphorylation site is required for growth inhibitory function.\",\n      \"method\": \"Transient transfection in COS cells, site-directed mutagenesis of Y260, co-immunoprecipitation, retroviral overexpression in FDC-P1 and bone marrow cells, colony assays\",\n      \"journal\": \"Experimental hematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis combined with co-IP and functional colony assay, single lab\",\n      \"pmids\": [\"11063873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Down-regulation of SKAP-55R (SKAP2) by siRNA showed it cannot substitute for SKAP-55 in TCR-mediated LFA-1 clustering and T cell-APC conjugation, demonstrating that SKAP2 has a non-redundant but distinct function from SKAP55 in inside-out integrin signaling in T cells.\",\n      \"method\": \"siRNA knockdown of SKAP55R in T cells, LFA-1 clustering assay, T cell-APC conjugation assay\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean siRNA loss-of-function with defined cellular phenotype, single lab, single method\",\n      \"pmids\": [\"15939789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SKAP-HOM (SKAP2)-deficient mice show strongly attenuated BCR-mediated B cell proliferation and severely reduced adhesion of activated B cells to fibronectin (β1 integrin ligand) and ICAM-1 (β2 integrin ligand), while membrane-proximal BCR signaling (total tyrosine phosphorylation, Erk/p38/JNK phosphorylation, Ca2+ flux) is normal. This places SKAP2 downstream of membrane-proximal BCR signaling but upstream of integrin-mediated adhesion.\",\n      \"method\": \"SKAP-HOM knockout mouse analysis, BCR stimulation assays, adhesion assays to fibronectin and ICAM-1, flow cytometry, EAE model\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockout with multiple orthogonal phenotypic readouts (adhesion, proliferation, in vivo EAE), epistasis established by normal proximal signaling with impaired integrin adhesion\",\n      \"pmids\": [\"16135797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SKAP55R (SKAP2) is expressed in myeloid cells and macrophages, is rapidly and transiently tyrosine-phosphorylated in response to M-CSF, and associates with other tyrosine-phosphorylated proteins and with actin upon M-CSF stimulation. Overexpression of SKAP55R decreased M-CSF-dependent proliferation without affecting differentiation.\",\n      \"method\": \"Western blotting for phosphorylation, co-immunoprecipitation, overexpression in myeloid cells, proliferation assays\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP and overexpression with functional readout, single lab, multiple methods\",\n      \"pmids\": [\"15894167\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Crystal structure of the Skap-hom (SKAP2) dimerization and PH domains revealed that SKAP2 is a homodimer with an N-terminal four-helix bundle dimerization domain against which two PH domains pack in a conformation incompatible with phosphoinositide binding. The isolated PH domains bind PI[3,4,5]P3. Mutations disrupting the dimerization domain or the PH domain PI[3,4,5]P3-binding pocket prevent SKAP2 localization to membrane ruffles, establishing a PI[3,4,5]P3-responsive molecular switch controlling SKAP2 function.\",\n      \"method\": \"X-ray crystallography, biochemical binding assays (phosphoinositide binding), mutagenesis, cell biology (ruffle localization assays)\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with mutagenesis and cell biological validation, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"19026786\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SKAP-HOM (SKAP2) in dendritic cells (DCs) is required for normal integrin-regulated DC motility and antigen-specific T cell priming in vivo. SKAP-HOM-deficient DCs show increased spontaneous motility but impaired integrin-triggered actin polymerization and reduced ability to form antigen-dependent conjugates with T cells. Immunization with SKAP-HOM-deficient BMDCs generates fewer antigen-specific T cells in vivo.\",\n      \"method\": \"SKAP-HOM knockout mouse BMDCs, in vivo LC migration assay, in vitro DC motility assay, actin polymerization assay, T cell conjugate formation assay, in vivo immunization\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with multiple cellular phenotypes and in vivo validation, single lab\",\n      \"pmids\": [\"19369640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"HPK1 associates with SKAP-HOM (SKAP2) to negatively regulate Rap1-mediated B-lymphocyte integrin activity and LFA-1-dependent adhesion to ICAM-1. Knockdown of HPK1 increased Rap1-GTP levels and enhanced LFA-1-dependent homotypic aggregation and adhesion, downstream of Src but independent of PI3K and PLC, via a module involving HPK1, SKAP-HOM, and RIAM.\",\n      \"method\": \"shRNA knockdown of HPK1 in Wehi 231 B cells, Rap1 activation assay, adhesion assays, HPK1-/- mouse B cells, co-immunoprecipitation\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP plus genetic KO plus functional adhesion assays, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"20824186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SKAP-HOM (SKAP2) was identified as a bona fide substrate of the lymphoid-specific tyrosine phosphatase Lyp. Crystal structures of Lyp in complex with a consensus peptide and with a phosphopeptide derived from SKAP-HOM defined the molecular determinants of Lyp substrate recognition. The Lyp dephosphorylation site on SKAP-HOM was identified through substrate specificity profiling.\",\n      \"method\": \"Combinatorial library (inverse alanine scanning) for substrate motif identification, crystal structure of Lyp/SKAP-HOM phosphopeptide complex, biochemical phosphatase assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure with biochemical validation and substrate specificity profiling in a single study with multiple orthogonal methods\",\n      \"pmids\": [\"21719704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"SKAP2 is a transcriptional target of HSF4b in lens epithelial cells and is highly expressed at the anterior tip of elongating lens fiber cells. SKAP2 localizes to actin-rich membrane ruffles and interacts with the SH2 domain of NCK2 via its N-terminus. The SKAP2-NCK2-F-actin complex accumulates at the lamellipodium leading edge. Knockdown of SKAP2 impairs disassembly of stress fibers in response to FGF-b, and overexpression of SKAP2 (but not the N-terminal deletion mutant) induces actin remodeling.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for HSF4b target, siRNA knockdown, co-immunoprecipitation of SKAP2 with NCK2 SH2 domain, immunofluorescence, overexpression of deletion mutants\",\n      \"journal\": \"Journal of cellular and molecular medicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, mutagenesis, knockdown with actin phenotype, and ChIP, single lab multiple methods\",\n      \"pmids\": [\"20219016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Skap2 is necessary for macrophage migration, chemotaxis, global and local actin reorganization upon integrin engagement. PI[3,4,5]P3 binding to the Skap2 PH domain (relieving auto-inhibitory conformation) is critical for integrin-driven cytoskeletal response. Skap2 enables integrin-induced tyrosyl phosphorylation of SFKs, Adap, and Sirpα. Skap2 requires Sirpα for its recruitment to engaged integrins and for coordinating downstream actin rearrangement; Sirpα-deficient macrophages have identical impaired local integrin-induced responses as Skap2-/- macrophages.\",\n      \"method\": \"Skap2-/- mouse macrophage migration and chemotaxis assays, actin reorganization assays, PH domain mutants, co-immunoprecipitation/phosphorylation assays, Sirpα mutant macrophages, integrin engagement with fibronectin\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO combined with domain mutagenesis, multiple orthogonal cellular assays, epistasis with Sirpα, independently detailed mechanistic pathway\",\n      \"pmids\": [\"22976304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"SKAP2 physically associates with actin assembly factors WAVE2 and cortactin and inhibits their interaction with each other. SKAP2 suppresses WAVE2-cortactin-mediated actin polymerization in vitro. Knockdown of SKAP2 in NIH3T3 cells accelerates cell migration and enhances membrane translocation of WAVE2 in a manner dependent on SKAP2-WAVE2 binding activity.\",\n      \"method\": \"Co-immunoprecipitation of SKAP2 with WAVE2 and cortactin, in vitro actin polymerization assay, siRNA knockdown, cell migration assays, WAVE2 membrane localization assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of actin polymerization inhibition combined with co-IP and siRNA functional readout, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"23161539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SKAP2 physically interacts with Wiskott-Aldrich syndrome protein (WASP) and localizes to podosomes in macrophages. SKAP2-null macrophages rarely form podosomes, and their invasion is significantly reduced compared to wild-type. Rescue with functional SKAP2 containing an intact tyrosine phosphorylation site and WASP-binding ability restores podosome formation and invasion, while mutants lacking these features fail to rescue.\",\n      \"method\": \"Co-immunoprecipitation of SKAP2 with WASP, immunofluorescence/podosome quantification, SKAP2-/- macrophage invasion assay, rescue with SKAP2 mutants, in vivo lung metastasis model\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — co-IP, KO phenotype, domain mutant rescue, in vivo model, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"26577701\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Skap2 is essential for β2 integrin activation and neutrophil recruitment in vivo. Mechanistically, Skap2 regulates actin polymerization and binding of talin-1 and kindlin-3 to the β2 integrin cytoplasmic domain. The direct interaction of Skap2 with WASp via its SH3 domain is critical for integrin activation and neutrophil recruitment in vivo. Loss of Skap2 produces a LAD-like phenotype in mice.\",\n      \"method\": \"Skap2-/- mouse neutrophil studies, β2 integrin activation assays, talin-1/kindlin-3 co-immunoprecipitation, SH3 domain mutant analysis, intravital microscopy of neutrophil recruitment\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with in vivo phenotype, domain-specific mutant analysis, co-IP of integrin regulatory proteins, multiple orthogonal methods\",\n      \"pmids\": [\"28183734\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SKAP2 regulates the Arp2/3 complex and is essential for actin-mediated asymmetric cytokinesis in mouse oocytes by interacting with WAVE2. SKAP2 depletion by siRNA caused failure of spindle migration, polar body extrusion, and cytokinesis defects. SKAP2 co-localizes with actin at the oocyte cortex. Depletion reduced Arp2/3 and WAVE2 expression/localization.\",\n      \"method\": \"siRNA depletion in mouse oocytes, immunofluorescence for actin/WAVE2/Arp2/3, polar body extrusion assays, cytochalasin B colocalization\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA KD with multiple phenotypic readouts and colocalization in oocytes, single lab\",\n      \"pmids\": [\"28933599\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The SRC-family kinase HCK shapes the SKAP2 interactome. SKAP2 dimerization modulates SRC kinase binding, with dimerization indirectly affecting FYB protein binding. Domain mapping defined 14 SKAP2 interacting proteins' binding domains/motifs and identified FAM102A as a new interactor. Fine-tuning between SRC kinase binding and their activation state was identified.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, domain mutagenesis of SKAP2, protein-protein interaction mapping\",\n      \"journal\": \"Oncotarget\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — systematic interaction mapping with domain mutagenesis, single lab, multiple binding partners characterized\",\n      \"pmids\": [\"29568343\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"SKAP2 is required for protection against K. pneumoniae pulmonary infection by enabling neutrophil and monocyte ROS production. SKAP2-/- neutrophils and monocytes are present in infected lungs and degranulate normally, but K. pneumoniae-stimulated ROS production in vitro is abolished. K. pneumoniae-induced neutrophil ROS requires SFKs, Syk, Btk, PLCγ2, and PKC. Loss of SKAP2 significantly impairs phosphorylation of SFKs, Syk, and Pyk2, placing SKAP2 proximal to their activation.\",\n      \"method\": \"Skap2-/- mouse infection model, ROS assays (DHR), degranulation assays, Western blotting of signaling intermediates, in vitro neutrophil stimulation with K. pneumoniae\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with in vivo infection model, multiple signaling pathway intermediates measured, functional ROS assay, multiple orthogonal methods\",\n      \"pmids\": [\"32352382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"YopH (Yersinia tyrosine phosphatase effector) dephosphorylates SKAP2 in neutrophils. SKAP2 is required for integrin receptor- and GPCR-mediated ROS production but is dispensable for degranulation under all conditions tested. YopH also blocks SKAP2-independent FcγR-stimulated phosphorylation of Syk, SLP-76, PLCγ2, and ERK1/2. These findings uncouple integrin/GPCR-dependent ROS from FcγR responses based on SKAP2 dependency.\",\n      \"method\": \"Skap2KO mouse neutrophils, YopH deletion mutant Yersinia infection, ROS assays, degranulation assays, phosphorylation analysis of signaling intermediates, Skap2KO vs WT comparison\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO combined with bacterial effector epistasis, multiple receptor stimulation conditions, multiple signaling readouts\",\n      \"pmids\": [\"32392230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SKAP2 controls β-cell sensitivity to cytokine-induced apoptosis. Knockdown of SKAP2 aggravated cytokine-induced apoptosis in INS-1E cells and primary rat β-cells; overexpression afforded protection against cytokine-induced apoptosis. This correlated with reduced nuclear NF-κB p65 (S536-phosphorylated), lower nitric oxide production, and diminished CHOP expression. Knockdown of CHOP partially reversed the increased apoptosis caused by SKAP2 knockdown, linking SKAP2 to the NF-κB-iNOS-ER stress pathway.\",\n      \"method\": \"siRNA knockdown and overexpression in INS-1E cells and rat β-cells, apoptosis assays, NF-κB p65 nuclear translocation/phosphorylation assays, NO measurement, CHOP expression, double knockdown epistasis\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function with epistasis (double KD with CHOP), multiple mechanistic readouts, single lab\",\n      \"pmids\": [\"33203694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SKAP2 downregulation or complete lack impairs OPC migration and morphological maturation in oligodendrocytes. Overexpression of SKAP2 or constitutively active SKAP2 increased OPC migration, suggesting SKAP2 function depends on phosphorylation-based activation. Lack of SKAP2 enhanced the positive effect of integrin activation on OPC migration, indicating SKAP2 acts as a modulator of integrin-dependent migration in oligodendrocytes.\",\n      \"method\": \"SKAP2 KO OPCs, siRNA knockdown, overexpression of constitutively active SKAP2, migration assays, morphological maturation analysis, integrin activation experiments\",\n      \"journal\": \"Glia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO and overexpression with functional migration and differentiation readouts, single lab\",\n      \"pmids\": [\"34324225\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A de novo gain-of-function SKAP2 variant (p.Gly153Arg), located in the well-conserved lipid-binding loop of the PH domain, leads to enhanced integrin pathway activity and constitutive migratory behavior in myeloid macrophages in the absence of chemokine stimulation, consistent with constitutive SKAP2 activation.\",\n      \"method\": \"Whole-exome sequencing, monocyte-derived macrophage functional assays from patient and family members, integrin pathway activation assays, migration assays, expression of p.Gly153Arg variant in human macrophage cell line\",\n      \"journal\": \"Diabetes care\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — human variant with functional validation in primary cells and cell line, multiple assays, single lab\",\n      \"pmids\": [\"34172489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SKAP2 is required for maximal ROS production by neutrophils in response to C-type lectin receptor (CLR) agonists and fungal pathogens (Candida glabrata and Candida albicans), and for robust killing of C. glabrata. Inside-out integrin signaling and Syk phosphorylation occur independently of SKAP2 after Candida infection. However, Pyk2, ERK1/2, and p38 phosphorylation are significantly reduced in Skap2-/- neutrophils after Candida and K. pneumoniae infection.\",\n      \"method\": \"HoxB8-immortalized Skap2-/- neutrophil progenitors, ROS assays, killing assays, phosphorylation analysis of Syk/Pyk2/ERK1/2/p38, inside-out integrin signaling assay\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO neutrophils with multiple receptor stimulation conditions and signaling readouts, single lab\",\n      \"pmids\": [\"34386732\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SKAP2 forms a complex with the Sirpα transmembrane receptor and the SHP-1 tyrosine phosphatase, and directly associates with the TIR domain of TLR4 adaptors MyD88, TIRAP, and TRAM. SKAP2-mediated recruitment of the Sirpα/SHP-1 complex to TLR4 attenuates NF-κB inflammatory signaling, while direct SKAP2 interaction with SHP-2 decreases SHP-2 activation. This dual mechanism inhibits NF-κB while promoting the TLR4-IFNβ pathway.\",\n      \"method\": \"Co-immunoprecipitation (SKAP2 with SHP-1, Sirpα, MyD88/TIRAP/TRAM, SHP-2), SKAP2 knockout mice in colitis/tumorigenesis model, NF-κB activation assays, cytokine measurements, overexpression studies\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple co-IPs defining complex composition, genetic KO with in vivo model, multiple signaling pathway readouts, single lab with extensive mechanistic characterization\",\n      \"pmids\": [\"35034964\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SKAP2 activates the WAVE2-ARP2/3 pathway in trophoblasts to promote cell growth and migration. SKAP2 W336K mutant (SH3 domain-blocked) cannot alter WAVE2 and ARP2 expression or HTR8/SVneo cell growth and migration, demonstrating that the SH3 domain of SKAP2 is required for its interaction with and activation of WAVE2-ARP2/3 signaling.\",\n      \"method\": \"siRNA knockdown and overexpression in HTR8/SVneo trophoblast cells, W336K SH3 domain mutant, western blotting for WAVE2/ARP2, immunofluorescence for actin-WAVE2 colocalization, cell growth (CCK8) and migration (transwell) assays\",\n      \"journal\": \"Placenta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — SH3 domain mutagenesis combined with KD/OE and multiple functional readouts, single lab\",\n      \"pmids\": [\"36126383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"SKAP2 interacts with SRC kinases through a modular organization comprising three interacting modules: the dimerization domain, the SH3 domain, and the second interdomain (between PH and SH3). The dimerization domain is necessary and sufficient to bind most activated and myristylated SRC kinases, while all three modules are required to bind SRC kinases at steady state. SKAP2 dimerization induces increased binding for most SRC kinases. Tyrosines in the interdomains modulate these interactions.\",\n      \"method\": \"Luciferase complementation assay (NanoBiT), extensive site-directed mutagenesis of SKAP2 domains, analysis of SRC kinase family member HCK mutants (Y390, K7)\",\n      \"journal\": \"Molecular & cellular proteomics : MCP\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — luciferase complementation with extensive mutagenesis, single lab, multiple interaction modules defined\",\n      \"pmids\": [\"36423812\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SKAP2 is present in the CD11b/CD18 (Mac-1) complex at steady state in primary and NB4 neutrophils, identified by KINDLIN3 BioID proximity labeling and confirmed by CD18 immunoprecipitation. Under resting conditions (without stimulation), SKAP2 restricts CD11b/CD18-mediated adhesion. Upon stimulation, SKAP2 is required for CD18 clustering, NADPH oxidase activity, phagocytosis, and cytotoxicity against tumor cells (ADCC). SKAP2-deficient NB4 neutrophils show enhanced resting adhesion to fibronectin but strongly reduced CD18 clustering upon stimulation.\",\n      \"method\": \"BioID proximity labeling of KINDLIN3 interactome, CD18 co-immunoprecipitation, CRISPR-Cas9 KO of SKAP2/CD18/KINDLIN3 in NB4 cells, adhesion assays, CD18 clustering by microscopy, NADPH oxidase activity, phagocytosis, ADCC assays\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — BioID + co-IP for complex identification, CRISPR KO with multiple functional readouts, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"38487529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ra70/Scap2 (SKAP2) is expressed in the ependymal layer and ventricular zone of the neural tube during development (E7.5-11.5) in heterozygous LacZ-knockin mice, restricted to posterior neural tissues including neural tube and hindbrain. Homozygous Ra70/scap2 knockout mice die during embryogenesis, indicating SKAP2 is essential for embryonic development.\",\n      \"method\": \"LacZ knockin heterozygous and homozygous knockout mouse analysis, immunohistochemistry, RNA expression analysis in P19 EC cells during RA-induced neuronal differentiation\",\n      \"journal\": \"Neuroscience letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with embryonic lethality phenotype plus spatial expression mapped by reporter knockin, single lab\",\n      \"pmids\": [\"24846415\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SKAP2 is required for sperm cytoskeletal structure and mitochondrial organization during spermiogenesis. Hnrnpr mutation disrupts m6A-dependent splicing of Skap2 pre-mRNA, impairing SKAP2 protein production in sperm and causing motility decline and morphological abnormalities. Specific knockout of Skap2 in male germ cells phenocopies these defects. Extracellular vesicle-mediated delivery of SKAP2 to efferent ductules restores sperm motility and morphology, confirming the functional hnRNPR-SKAP2 axis.\",\n      \"method\": \"Hnrnpr mutant mice and human patients, germ cell-specific Skap2 KO mice, sperm motility and morphology analysis, mitochondrial organization assays, m6A-seq for splice site, extracellular vesicle delivery rescue experiment\",\n      \"journal\": \"Signal transduction and targeted therapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — germ cell-specific KO with phenotype, rescue by EV-mediated delivery, upstream RNA splicing mechanism identified, multiple orthogonal methods\",\n      \"pmids\": [\"41436426\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SKAP2/PLC signaling pathway is essential for LTB4 production by neutrophils in response to bacterial T3SS stimulation, but is not required for LTB4 synthesis by macrophages (which instead requires phagocytosis and NLRP3/CASP1 inflammasome), establishing cell-type-specific pathway requirements for LTB4 synthesis.\",\n      \"method\": \"Skap2-/- mouse neutrophils and macrophages, LTB4 production assays with T3SS stimulation, pharmacological inhibitors of signaling intermediates, NLRP3/CASP1 pathway analysis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO with defined functional phenotype and cell-type epistasis, preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.07.01.601466\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"SKAP2 (also known as SKAP-HOM, RA70, SKAP55R, SCAP2, SAPS) is a ubiquitously expressed dimeric adaptor protein that functions as a PI[3,4,5]P3-gated molecular switch: its N-terminal four-helix bundle dimerization domain holds the PH domain in an autoinhibited conformation until PI3K-generated PI[3,4,5]P3 releases the PH domain, enabling membrane recruitment and cytoskeletal remodeling; at integrins, SKAP2 collaborates with Sirpα, SHP-1, talin-1, kindlin-3, WASP/WASp, WAVE2, cortactin, and Arp2/3 to drive actin polymerization, podosome formation, integrin clustering, and outside-in signaling in macrophages and neutrophils; it is also a substrate of Fyn/Src-family kinases (phosphorylated at a key tyrosine required for FYN association and growth inhibition), a substrate of the lymphoid phosphatase Lyp (crystal structure defined), an inhibitor of TLR4-NF-κB signaling through Sirpα/SHP-1 recruitment, and a regulator of β-cell survival through the NF-κB–iNOS–ER stress pathway; in spermatogenesis SKAP2 is regulated by hnRNPR-mediated m6A-dependent splicing and is required for sperm cytoskeletal integrity and mitochondrial organization.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SKAP2 is a ubiquitously expressed dimeric adaptor protein that couples membrane-proximal kinase signaling to integrin activation and actin cytoskeletal remodeling across myeloid, lymphoid, and developing cells [#11, #14]. Structurally, it is a homodimer in which an N-terminal four-helix bundle dimerization domain packs two PH domains in an autoinhibited conformation incompatible with phosphoinositide binding; PI3K-generated PI[3,4,5]P3 relieves this autoinhibition, driving membrane recruitment and cytoskeletal function, with mutations in either the dimerization domain or the PH binding pocket abolishing localization to membrane ruffles [#6]. SKAP2 is a substrate of Src-family kinases, associating with Fyn, Hck, and Lyn through Fyn-SH2 recognition, and its phosphorylation at a key tyrosine is required both for Fyn association and for growth-inhibitory activity in myeloid progenitors [#0, #1, #2]; its modular dimerization, SH3, and interdomain regions tune Src-family kinase binding, and it is dephosphorylated by the lymphoid phosphatase Lyp [#9, #25]. At engaged integrins, SKAP2 is recruited via Sirpα and orchestrates actin polymerization, podosome formation, β2-integrin activation, and integrin clustering by interacting through its SH3 domain with WASP and by regulating talin-1 and kindlin-3 loading onto the β2 cytoplasmic tail, with loss producing impaired adhesion-coupled responses and a LAD-like phenotype in mice [#11, #13, #14, #26]. SKAP2 also negatively regulates actin dynamics by binding WAVE2 and cortactin and suppressing their cooperative actin polymerization [#12]. Genetically, SKAP2 is required for B-cell, dendritic-cell, neutrophil, and monocyte integrin-dependent adhesion and immune function, and for neutrophil/monocyte ROS production against bacterial and fungal pathogens through a SFK–Syk–Pyk2 module [#4, #7, #14, #17, #22]. Beyond immune cells, SKAP2 inhibits TLR4–NF-κB signaling by recruiting a Sirpα/SHP-1 complex to TLR4 adaptors [#23], protects β-cells from cytokine-induced apoptosis via the NF-κB–iNOS–ER stress (CHOP) pathway [#19], and is required for sperm cytoskeletal integrity and mitochondrial organization downstream of an hnRNPR-controlled m6A splicing axis [#28]. A de novo gain-of-function PH-domain variant (p.Gly153Arg) produces constitutive integrin activity and migration, and homozygous knockout is embryonic lethal in mice [#21, #27].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Established SKAP2 as a Src-family-kinase-associated adaptor distinct from the T-cell-restricted SKAP55, defining its ubiquitous expression and Fyn substrate identity.\",\n      \"evidence\": \"GST-Fyn-SH2 pulldown and COS-cell kinase assays identifying SKAP-HOM/RA70 binding to Fyn, Hck, and Lyn and association with SLAP-130\",\n      \"pmids\": [\"9755858\", \"9837776\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of Fyn association not yet determined\", \"Phosphorylation site not mapped\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Mapped the functional phosphotyrosine, showing tyrosine 260 is required for Fyn co-association and for SKAP2's growth-inhibitory effect in myeloid progenitors.\",\n      \"evidence\": \"Site-directed Y260 mutagenesis with co-IP and retroviral overexpression colony assays in FDC-P1 and bone marrow cells\",\n      \"pmids\": [\"11063873\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking phosphorylation to growth inhibition unresolved\", \"Downstream effectors not identified\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Genetic and knockdown studies placed SKAP2 downstream of membrane-proximal antigen-receptor signaling but upstream of integrin-mediated adhesion, with a function non-redundant to SKAP55.\",\n      \"evidence\": \"SKAP-HOM knockout mouse B-cell adhesion/proliferation assays and siRNA in T cells with LFA-1 clustering and conjugation readouts\",\n      \"pmids\": [\"16135797\", \"15939789\", \"15894167\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link to integrin activation machinery not defined\", \"Recruitment mechanism unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Resolved the structural basis of SKAP2 regulation as a PI[3,4,5]P3-gated molecular switch in which dimerization autoinhibits the PH domain until lipid binding releases it for membrane recruitment.\",\n      \"evidence\": \"X-ray crystallography of dimerization and PH domains plus phosphoinositide binding assays and ruffle-localization mutants\",\n      \"pmids\": [\"19026786\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinetics of in vivo switching not measured\", \"Effectors engaged after membrane recruitment not defined structurally\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Extended SKAP2's integrin-adhesion role to dendritic cells, linking it to integrin-triggered actin polymerization and in vivo T-cell priming.\",\n      \"evidence\": \"SKAP-HOM knockout BMDC motility, actin polymerization, conjugate formation, and in vivo immunization assays\",\n      \"pmids\": [\"19369640\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct actin-regulatory partners in DCs not identified\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined an HPK1–SKAP2–RIAM module negatively regulating Rap1-driven integrin activation in B cells, situating SKAP2 in a defined signaling complex.\",\n      \"evidence\": \"shRNA/knockout of HPK1, Rap1 activation and adhesion assays, and co-IP in B cells\",\n      \"pmids\": [\"20824186\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect SKAP2-HPK1 contact not resolved\", \"Mechanism of Rap1 control unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Identified SKAP2 as a substrate of the lymphoid phosphatase Lyp and as an HSF4b-regulated actin remodeler interacting with NCK2, establishing both its dephosphorylation and an actin-localized effector partner.\",\n      \"evidence\": \"Crystal structures of Lyp/SKAP-HOM phosphopeptide with specificity profiling; ChIP, co-IP with NCK2 SH2, and actin-remodeling knockdown in lens cells\",\n      \"pmids\": [\"21719704\", \"20219016\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological setting of Lyp-mediated dephosphorylation not defined\", \"NCK2 interaction tested largely outside immune cells\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established the integrin actin-remodeling mechanism: SKAP2 requires PI[3,4,5]P3 binding and Sirpα for recruitment, while also directly binding and inhibiting WAVE2-cortactin actin polymerization, revealing dual positive and negative actin control.\",\n      \"evidence\": \"Skap2-/- macrophage migration with PH-domain and Sirpα mutants; co-IP and in vitro reconstitution of WAVE2-cortactin polymerization inhibition with knockdown migration assays\",\n      \"pmids\": [\"22976304\", \"23161539\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How positive (Sirpα/integrin) and negative (WAVE2-cortactin) functions are spatially balanced unresolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrated SKAP2's SH3-mediated WASP interaction and phosphotyrosine site are jointly required for podosome formation and macrophage invasion.\",\n      \"evidence\": \"Co-IP with WASP, podosome quantification, Skap2-/- invasion with domain-mutant rescue and in vivo metastasis model\",\n      \"pmids\": [\"26577701\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship between WASP and WAVE2 engagement not reconciled\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified SKAP2 as essential for β2-integrin activation and neutrophil recruitment by regulating talin-1/kindlin-3 loading and acting through SH3-mediated WASp binding, producing a LAD-like phenotype; also extended its actin role to Arp2/3-dependent oocyte cytokinesis.\",\n      \"evidence\": \"Skap2-/- neutrophil integrin activation, talin-1/kindlin-3 co-IP, SH3 mutant analysis, intravital microscopy; siRNA depletion in oocytes with WAVE2/Arp2/3 colocalization\",\n      \"pmids\": [\"28183734\", \"28933599\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs indirect control of talin-1/kindlin-3 binding not biochemically resolved\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Systematically mapped the SKAP2 interactome, showing dimerization modulates Src-family kinase binding and indirectly affects FYB binding, and identified FAM102A as a new partner.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, and domain mutagenesis defining binding domains of 14 interactors\",\n      \"pmids\": [\"29568343\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional roles of newly mapped interactors not tested\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Positioned SKAP2 proximal to SFK/Syk/Pyk2 activation as essential for receptor-specific neutrophil/monocyte ROS production, dissociating ROS from degranulation and Fcγ-receptor responses.\",\n      \"evidence\": \"Skap2-/- infection models (K. pneumoniae), ROS and degranulation assays, signaling intermediate phosphorylation; YopH phosphatase epistasis distinguishing integrin/GPCR vs Fcγ pathways\",\n      \"pmids\": [\"32352382\", \"32392230\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct substrate/partner mediating ROS activation not pinpointed\", \"How SKAP2 selectively gates integrin/GPCR vs Fcγ pathways unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Broadened SKAP2 to a tissue-spanning modulator: protecting β-cells via NF-κB–iNOS–CHOP, modulating oligodendrocyte/OPC integrin-dependent migration, with a de novo PH-domain gain-of-function variant causing constitutive migration, and a further ROS role against fungal pathogens.\",\n      \"evidence\": \"INS-1E/β-cell knockdown-overexpression with CHOP epistasis; OPC KO/overexpression migration; whole-exome sequencing of p.Gly153Arg with macrophage assays; Skap2-/- neutrophil anti-Candida ROS and signaling\",\n      \"pmids\": [\"33203694\", \"34324225\", \"34172489\", \"34386732\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether β-cell and neuronal roles share the integrin/actin mechanism unresolved\", \"Mechanism by which Gly153Arg constitutively activates not structurally confirmed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined SKAP2 as a negative regulator of TLR4-NF-κB inflammation via Sirpα/SHP-1 recruitment to TLR4 adaptors, and confirmed SH3-dependent WAVE2-ARP2/3 activation drives trophoblast growth/migration.\",\n      \"evidence\": \"Co-IPs of SKAP2 with SHP-1/Sirpα/MyD88/TIRAP/TRAM/SHP-2 with KO colitis model; W336K SH3 mutant with WAVE2/ARP2 readouts in trophoblasts; NanoBiT modular mapping of Src-family kinase binding\",\n      \"pmids\": [\"35034964\", \"36126383\", \"36423812\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the same protein switches between actin scaffolding and TLR4 inhibition is unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placed SKAP2 within the resting Mac-1 (CD11b/CD18) complex where it restricts adhesion at rest but enables CD18 clustering, NADPH oxidase, phagocytosis, and ADCC upon stimulation; preprint data add cell-type-specific LTB4 control.\",\n      \"evidence\": \"KINDLIN3 BioID and CD18 co-IP, CRISPR KO of SKAP2/CD18/KINDLIN3 in NB4 neutrophils with adhesion/clustering/oxidase/phagocytosis/ADCC assays; Skap2-/- LTB4 neutrophil vs macrophage comparison (preprint)\",\n      \"pmids\": [\"38487529\", \"bio_10.1101_2024.07.01.601466\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular trigger switching SKAP2 from adhesion-restricting to clustering-promoting not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed an hnRNPR–m6A–SKAP2 axis required for sperm cytoskeletal integrity and mitochondrial organization, extending SKAP2 to spermiogenesis with rescue by EV-mediated protein delivery.\",\n      \"evidence\": \"Hnrnpr mutant and germ-cell-specific Skap2 KO mice, m6A-seq, sperm morphology/motility/mitochondrial assays, EV delivery rescue\",\n      \"pmids\": [\"41436426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether sperm role uses the integrin/actin switch mechanism not established\", \"Direct SKAP2 cytoskeletal partners in sperm not identified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How a single autoinhibited adaptor is selectively deployed across distinct contexts — positive actin/integrin assembly, negative WAVE2-cortactin and adhesion restriction, and TLR4-NF-κB inhibition — remains mechanistically unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model explaining context-dependent switching between opposing SKAP2 functions\", \"The direct effector immediately downstream of PI[3,4,5]P3-triggered recruitment not defined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 14, 23]},\n      {\"term_id\": \"GO:0008289\", \"supporting_discovery_ids\": [6, 11]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [12, 13, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [12, 23, 26]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [6, 11, 26]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [10, 12, 13]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5, 11]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 14, 17, 23]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6, 11, 23]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [11, 14, 26]}\n    ],\n    \"complexes\": [\"CD11b/CD18 (Mac-1) complex\", \"Sirpα/SHP-1 complex\"],\n    \"partners\": [\"FYN\", \"WASP\", \"WAVE2\", \"SIRPA\", \"TLN1\", \"FERMT3\", \"CTTN\", \"NCK2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":8,"faith_pct":87.5}}