{"gene":"SKAP1","run_date":"2026-06-10T07:46:32","timeline":{"discoveries":[{"year":1997,"finding":"SKAP55 (SKAP1) was identified as a novel adaptor protein that constitutively associates with the Src-family kinase p59(fyn) in T-lymphocytes. SKAP55 contains a pleckstrin homology domain, a C-terminal SH3 domain, and tyrosine phosphorylation sites. In vitro binding assays showed SKAP55 selectively binds SH2 domains of Lck, Lyn, Src, and Fyn but not ZAP70, Syk, Shc, SLP-76, Grb2, PI3K, or c-abl. SKAP55 is constitutively tyrosine phosphorylated in resting T-lymphocytes.","method":"GST-Fyn-SH2 domain pulldown, molecular cloning, co-immunoprecipitation, in vitro SH2 domain binding assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — initial cloning paper with multiple orthogonal biochemical methods (purification, co-IP, in vitro binding), replicated by subsequent studies","pmids":["9195899"],"is_preprint":false},{"year":1998,"finding":"SKAP55 binds FYB (ADAP/SLAP-130) through its SH3 domain and acts as a substrate for FYN kinase in T cells. FYB and SKAP55 colocalize in the perinuclear region of cells. A related protein SKAP55R also binds FYB via its SH3 domain.","method":"Yeast two-hybrid screen, co-immunoprecipitation, immunofluorescence confocal microscopy","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — yeast two-hybrid plus co-IP plus localization, replicated in subsequent papers","pmids":["9671755"],"is_preprint":false},{"year":1998,"finding":"SKAP55 directly associates with SLAP-130 (ADAP/FYB) in human T-cells. The interaction involves the SH3 domain of SKAP55 and the proline-rich sequence of SLAP-130, as demonstrated by truncation mutants and yeast two-hybrid.","method":"Co-immunoprecipitation from T cells, co-expression in COS cells, yeast two-hybrid with truncated mutants","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct interaction mapped by domain deletion in two orthogonal systems, replicated across labs","pmids":["9748251"],"is_preprint":false},{"year":2000,"finding":"The SH3 domain of FYN binds a novel proline-independent RKxxYxxY motif in SKAP55. Class I SH3 domains bound this motif while class II domains did not. Two-dimensional NMR of FYN-SH3 bound to the RKGDYASY peptide showed overlap with the proline-rich peptide binding site on the charged surface of the SH3 domain. Alanine scanning confirmed the requirement for the arginine, lysine and tandem tyrosines. Expression of the RKGDYASY peptide inhibited TcRzeta/CD3-mediated NF-AT transcription in T cells.","method":"Peptide precipitation, alanine scanning mutagenesis, 2D NMR, in vivo co-expression, NF-AT reporter assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structural analysis plus mutagenesis plus functional reporter assay in a single rigorous study","pmids":["10856234"],"is_preprint":false},{"year":2002,"finding":"SKAP55 undergoes TCR-induced translocation from cytoplasm to membrane and to lipid rafts. Upon TCR activation, SKAP55 forms homodimers through its SH3 domain and SK region, interacts with Fyn kinase and Grb-2 (dependent on phosphorylation of Y271), and its stable overexpression activates MAPK following TCR engagement.","method":"Co-immunoprecipitation, mutational analysis, subcellular fractionation, MAPK activation assays, stable overexpression","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — co-IP plus fractionation plus functional assay, single lab","pmids":["12171928"],"is_preprint":false},{"year":2002,"finding":"SKAP55 associates with CD45 in T cells via Tyr-232 of SKAP55 (identified by yeast two-hybrid and mutational analysis). Anti-CD3 stimulation promotes SKAP55 tyrosine phosphorylation and membrane translocation. Overexpression of SKAP55 induces IL-2 promoter activation, while SKAP55-Y232F mutant suppresses it and causes Fyn hyperphosphorylation with decreased kinase activity, suggesting SKAP55 couples CD45 with Src kinases for their dephosphorylation and TCR signal activation.","method":"Yeast two-hybrid, mutational analysis, in vivo co-expression, IL-2 promoter reporter assay, kinase activity assay","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — yeast two-hybrid plus mutational analysis plus functional reporter, single lab","pmids":["11909961"],"is_preprint":false},{"year":2003,"finding":"SKAP-55 (SKAP1) regulates integrin-mediated adhesion and T cell-APC conjugate formation. SKAP-55 enhances adhesion to fibronectin and ICAM-1, colocalizes with actin at the T cell-APC immunological synapse, and promotes LFA-1 clustering. This function requires the SKAP-55 SH3 domain. SKAP-55 translocates to membrane rafts upon LFA-1 and TCR co-ligation.","method":"Overexpression and dominant-negative studies, adhesion assays, confocal microscopy, membrane raft fractionation, co-localization","journal":"Nature immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (adhesion assay, microscopy, fractionation, domain deletion), replicated across labs","pmids":["12652296"],"is_preprint":false},{"year":2003,"finding":"In mast cells, SKAP55 forms an adaptor complex with SLAP-130 and MIST. SLAP-130 requires collaboration with SKAP55 for the recruitment of MIST to Lyn. MIST is preferentially recruited to Fyn (over Lyn) due to higher affinity binding of the SLAP-130/SKAP55 complex to the Fyn-SH2 domain.","method":"Co-immunoprecipitation, direct binding assays, affinity comparisons","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — co-IP plus affinity comparisons, single lab with multiple cell line validations","pmids":["12681493"],"is_preprint":false},{"year":2005,"finding":"SKAP-55 is essential for TCR-mediated 'inside-out signaling' required for LFA-1 clustering and T cell-APC conjugation. siRNA knockdown of SKAP-55 abolished LFA-1 clustering but had no effect on TCR-CD3 clustering. SKAP-55R (SKAP2) cannot substitute for SKAP-55 in this function, indicating a unique non-redundant role.","method":"siRNA knockdown, LFA-1 clustering assay, T cell-APC conjugation assay","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean siRNA knockdown with specific phenotypic readout, replicated by genetic knockout studies in other labs","pmids":["15939789"],"is_preprint":false},{"year":2005,"finding":"SKAP55 protein stability is dependent on ADAP. In ADAP-deficient Jurkat T cells, SKAP55 has a half-life of ~15-20 min (vs ~90 min in the presence of ADAP) due to increased proteolysis. ADAP restores SKAP55 stability 5-fold by decreasing its degradation rate. This protective effect requires the SKAP55 SH3 domain (which mediates SKAP55-ADAP interaction).","method":"ADAP-deficient cell line reconstitution, protein stability/pulse-chase analysis, SH3 domain inactivation mutant","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reconstitution of ADAP into deficient cells, quantitative half-life measurements, mutational validation, multiple orthogonal methods","pmids":["15849195"],"is_preprint":false},{"year":2006,"finding":"The ADAP/SKAP55 signaling module is involved in TCR-mediated inside-out signaling by recruiting activated Rap1 to the plasma membrane. Disruption of the ADAP/SKAP55 module displaces Rap1 from the plasma membrane without affecting Rap1 GTPase activity. Membrane-targeted ADAP/SKAP55 induces T-cell adhesion in the absence of TCR stimulation.","method":"Dominant-negative disruption of ADAP/SKAP55 module, membrane fractionation, Rap1 activity assays, constitutive membrane targeting constructs, adhesion assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods including dominant-negative disruption, fractionation, constitutive membrane targeting, functional adhesion assays","pmids":["16980616"],"is_preprint":false},{"year":2006,"finding":"ADAP SH3c domain binds a non-canonical RKxxY294xxY297 motif in SKAP-55. FYN kinase phosphorylates Y294 in vivo, blocking ADAP-SH3c binding. Surface plasmon resonance showed phosphorylation of Y294 mediates dissociation while Y297 phosphorylation had no effect. The Y294F mutation blocked TCR-induced LFA-1-mediated adhesion to ICAM-1 and IL-2 promoter activity.","method":"In vivo phosphorylation assays, surface plasmon resonance, mutational analysis (Y294F, Y297F), adhesion assays, IL-2 promoter reporter assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — SPR quantitative binding data plus mutagenesis plus in vivo phosphorylation and functional assays","pmids":["16461356"],"is_preprint":false},{"year":2007,"finding":"SKAP55 co-immunoprecipitates with the Ras activator RasGRP1. Binding requires the C-terminus of SKAP55 and is enhanced by tyrosine phosphorylation of SKAP55. SKAP55 overexpression disrupts TCR-to-Ras-Erk-AP1 signaling, while knockdown decreases ERK phosphorylation and AP-1 activation. Constitutively active Ras or Raf-1 overcomes the inhibitory effect of SKAP55 overexpression.","method":"Co-immunoprecipitation, RNAi knockdown, overexpression, AP-1/NF-AT reporter assays, ERK phosphorylation assay, epistasis with constitutively active Ras/Raf","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — co-IP plus RNAi plus overexpression plus epistasis, single lab","pmids":["17658605"],"is_preprint":false},{"year":2008,"finding":"SKAP-55 binds RasGRP1 via its C-terminus and negatively regulates the p21(ras)-ERK pathway. SKAP-55-deficient primary T-cells show defective LFA-1 adhesion concurrent with hyper-activation of ERK. Loss of RasGRP1 binding abrogates SKAP-55 inhibition of ERK/ELK. SKAP-55-/- T-cells show increased RasGRP1 presence in the trans-Golgi network following TCR activation.","method":"Knockout primary T cells, RNAi knockdown, co-immunoprecipitation, C-terminal deletion mutants, ERK/ELK activation assays, RasGRP1 localization by microscopy","journal":"PloS one","confidence":"High","confidence_rationale":"Tier 2 / Strong — primary KO T cells plus multiple orthogonal methods including co-IP, mutants, localization, and functional assays; replicated findings from Kosco 2007","pmids":["18320039"],"is_preprint":false},{"year":2010,"finding":"SKAP1 N-terminal domain binds the C-terminal SARAH domain of RapL, forming a SKAP1-RapL-Rap1 complex that binds LFA-1. In Skap1-/- primary T cells, TCR-induced Rap1-RapL complex formation and LFA-1 binding failed to occur. A RapL mutation (L224A) that abrogated SKAP1 binding disrupted component colocalization in vesicles and T cell-DC conjugation. RapL expression slowed T cell motility in lymph nodes, an effect reversed by L224A mutation with reduced dwell times with DCs.","method":"Skap1-/- primary T cells, co-immunoprecipitation, RapL mutants, intravital two-photon imaging in lymph nodes, T cell-DC conjugation assay","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO primary T cells plus in vivo intravital imaging plus biochemical complex analysis and point mutant validation","pmids":["20346707"],"is_preprint":false},{"year":2011,"finding":"The PH domain of SKAP1 is required for RapL membrane localization and Rap1-LFA-1 complex formation. A PH domain-inactivating mutation (R131M) markedly impaired RapL translocation to membranes, Rap1 and LFA-1 binding, and LFA-1-ICAM-1 adhesion. N-terminal myristoylated SKAP1 facilitated constitutive RapL membrane and Rap1 binding, effectively substituting for PI3K and TCR ligation in LFA-1 activation.","method":"PH domain point mutation (R131M), membrane fractionation, co-immunoprecipitation, constitutive membrane-targeting (myr-SKAP1), LFA-1 adhesion assay, PI3K inhibitor studies","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — structure-function mutagenesis plus constitutive membrane targeting plus multiple functional assays, consistent with Kliche 2006","pmids":["21669874"],"is_preprint":false},{"year":2011,"finding":"The SKAP55 PH domain (specifically R131M mutation) determines the ability of the ADAP/SKAP55 module to recruit ADAP to LFA-1 integrin complexes upon TCR stimulation. Association of ADAP with SKAP55 is both sufficient and necessary for rescue of integrin function in ADAP-deficient T cells. The R131M SKAP55 mutant, while unable to restore integrin function, restored NF-κB signaling in ADAP-deficient T cells, indicating that SKAP55 association with ADAP segregates integrin and NF-κB functions of ADAP.","method":"SKAP-ADAP chimeric fusion protein, ADAP-deficient T cell reconstitution, PH domain mutation (R131M), LFA-1 co-immunoprecipitation, NF-κB reporter assay, integrin adhesion assay","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — chimeric fusion protein approach with reconstitution in deficient cells, mutagenesis, and multiple functional readouts","pmids":["21525391"],"is_preprint":false},{"year":2011,"finding":"The ADAP/SKAP55 module regulates CCR7-mediated LFA-1 activation by forming two independent pools: one interacting with a RAPL/Mst1 complex and the other linked to a RIAM/Mst1/Kindlin-3 complex. Both complexes require ADAP/SKAP55 for binding to LFA-1 upon CCR7 stimulation. Loss of the module delays T-cell homing and reduces intranodal motility in vivo.","method":"Co-immunoprecipitation, LFA-1 affinity/avidity assays, in vivo homing assays, intravital imaging","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple co-IP complexes identified plus in vivo functional assays","pmids":["22117043"],"is_preprint":false},{"year":2013,"finding":"SKAP55 is required for SLP-76 microcluster persistence and movement, junctional stabilization, and integrin-independent adhesion via the TCR. These functions require SKAP55 dimerization and ADAP interaction. The SKAP55 dimerization motif enables co-immunoprecipitation of RIAM, recruitment of talin into TCR-induced adhesive junctions, and inside-out signaling to β1 integrins. A tandem dimer with two ADAP-binding SKAP55 SH3 domains stabilized SLP-76 microclusters but could not support adhesion to integrin ligands.","method":"Fluorescence microscopy of SLP-76 microclusters, SKAP55 dimerization domain mutants, tandem dimer constructs, co-immunoprecipitation of RIAM and talin, integrin adhesion assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — live cell imaging plus domain deletion plus co-IP plus functional adhesion assays, multiple orthogonal methods","pmids":["24368808"],"is_preprint":false},{"year":2015,"finding":"The ADAP-SKAP55 signaling module promotes PD-1 expression on CD8+ T cells in a Fyn-, Ca2+-, and NFATc1-dependent manner. Knockout of SKAP55 or ADAP reduced PD-1 expression on CD8+ effector cells and enhanced anti-tumor immunity in DC vaccine models. NFATc1 inhibitor CsA also downregulated PD-1, consistent with SKAP55 acting upstream of NFATc1.","method":"Skap55-/- and Adap-/- knockout mice, DC vaccine tumor models, adoptive T cell transfer, NFATc1 inhibitor (CsA), flow cytometry for PD-1/CTLA-4/Treg","journal":"EMBO molecular medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic knockouts in primary cells and in vivo models with pharmacological validation of pathway","pmids":["25851535"],"is_preprint":false},{"year":2016,"finding":"SKAP1-deficient T cells show reduced translocation of talin and RIAM to the T cell-APC contact interface. Skap1-/- T cells show an altered pattern of talin cleavage (by calpain). Expression of a calpain-cleavage-resistant talin mutant (L432G) rescued the impaired adhesion of Skap1-/- T cells with DCs.","method":"Skap1-/- T cells, confocal microscopy of contact interface, talin/RIAM localization, talin cleavage assay, non-cleavable talin (L432G) reconstitution, T cell-DC conjugation assay","journal":"Immunology letters","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — KO cells with localization and functional rescue, single lab","pmids":["26905930"],"is_preprint":false},{"year":2017,"finding":"LFA-1 cross-linking activates FAK1/PYK2 which phosphorylate LAT selectively on Y171, leading to formation of LAT-GRB2-SKAP1 complexes distinct from canonical LAT-GADs-SLP-76 complexes. LFA-1 cross-linking increased LAT-GRB2-SKAP1 relative to LAT-GADs-SLP-76 complexes and decreased T cell-DC dwell times dependent on LAT-Y171, reducing T cell binding to DCs and proliferation.","method":"Co-immunoprecipitation, LAT Y171 mutant, FAK1/PYK2 activation assays, T cell-DC dwell time analysis, T cell proliferation assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical complex identification plus phosphorylation site mutants plus in vivo functional assays for dwell time and proliferation","pmids":["28699640"],"is_preprint":false},{"year":2017,"finding":"Within the SKAP55 PH domain, D120 facilitates cytoplasmic retention of SKAP55 in non-stimulated T cells, while K152 promotes membrane recruitment via actin binding upon TCR triggering. K152-dependent PH domain interaction with actin promotes talin binding to LFA-1, facilitating LFA-1 activation.","method":"PH domain point mutations (D120, K152), subcellular fractionation, actin co-immunoprecipitation, talin-LFA-1 binding assay, LFA-1 activation assay","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — structure-function mutagenesis with co-IP and functional assays, single lab","pmids":["28052935"],"is_preprint":false},{"year":2018,"finding":"SKAP1 forms homodimers mediated by residues A17 to L21 in the N-terminal region. SKAP1 dimerization is not required for its binding to RapL.","method":"Co-immunoprecipitation of truncation/deletion mutants, N-terminal deletion mapping","journal":"BMC research notes","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP with deletion mutants, single lab, consistent with earlier dimerization observations","pmids":["30522503"],"is_preprint":false},{"year":2019,"finding":"SKAP1 is phosphorylated by and binds to PLK1 at N-terminal serine 31 (S31). This interaction is needed for optimal PLK1 kinase activity. siRNA knockdown of SKAP1 reduced T-cell division and delayed expression of PLK1, Cyclin A and pH3. Reconstitution with WT SKAP1 but not the S31 mutant restored normal cell division. SKAP1-PLK1 binding is dynamically regulated during the T-cell cycle.","method":"siRNA knockdown, co-immunoprecipitation, in vitro phosphorylation assay, S31 point mutation reconstitution, cell cycle analysis (Cyclin A, pH3, PLK1 expression)","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — co-IP plus mutagenesis plus KD/reconstitution, single lab","pmids":["31320682"],"is_preprint":false},{"year":2024,"finding":"Two modules control SKAP1 interaction with SRC kinases: one composed of two conserved motifs in the second interdomain that interact with the SH2 domain of SRC kinases, and a second module composed of the DIM (dimerization) domain modulated by the SH3 domain and SRC kinase activation state. These binding properties differ between SKAP1 and its paralog SKAP2.","method":"Domain dissection/truncation analysis, binding comparisons between SKAP1 and SKAP2 modules","journal":"PloS one","confidence":"Low","confidence_rationale":"Tier 3 / Weak — modular dissection analysis, single lab, limited orthogonal validation described in abstract","pmids":["38483858"],"is_preprint":false}],"current_model":"SKAP1 (SKAP55) is a T cell-specific adaptor protein that couples the TCR to LFA-1 inside-out signaling by forming a constitutive complex with ADAP (stabilized through mutual SH3-domain interactions), recruiting activated Rap1 to the plasma membrane via its PH domain and a direct N-terminal/SARAH-domain interaction with RapL, thereby assembling a SKAP1-RapL-Rap1-LFA-1 complex that promotes integrin clustering and T cell-APC conjugation; additionally, SKAP1 modulates the Ras-ERK pathway by binding RasGRP1, regulates PD-1 expression via an NFATc1-dependent pathway, forms LAT-GRB2-SKAP1 complexes downstream of LFA-1/FAK1 signaling to promote T cell de-adhesion, and acts as a scaffold for PLK1 at serine 31 to support optimal T cell cycling."},"narrative":{"mechanistic_narrative":"SKAP1 (SKAP55) is a T cell-restricted cytosolic adaptor that couples T-cell receptor (TCR) engagement to integrin-mediated adhesion through 'inside-out' signaling, controlling LFA-1 clustering and the formation of stable T cell-antigen-presenting cell conjugates [PMID:12652296, PMID:15939789]. It functions as part of a constitutive module with the adaptor ADAP (FYB/SLAP-130), an interaction mediated by the SKAP1 SH3 domain binding a proline-rich region of ADAP and reciprocally stabilizing SKAP1 against proteolytic degradation [PMID:9748251, PMID:15849195]. The ADAP/SKAP1 module recruits activated Rap1 to the plasma membrane, where SKAP1 bridges Rap1 to its effector RapL via a direct N-terminal interaction with the RapL SARAH domain, assembling a SKAP1-RapL-Rap1 complex that engages LFA-1 and drives integrin activation [PMID:16980616, PMID:20346707]. Membrane localization of this module requires the SKAP1 PH domain, which directs RapL membrane translocation and, through residue-specific actin binding, promotes talin recruitment to LFA-1 [PMID:21669874, PMID:28052935]; SKAP1 loss alters calpain-mediated talin cleavage and impairs talin/RIAM delivery to the contact interface [PMID:24368808, PMID:26905930]. Beyond adhesion, SKAP1 binds the Ras activator RasGRP1 through its C-terminus to negatively regulate the Ras-ERK pathway [PMID:18320039], and the ADAP/SKAP1 module promotes PD-1 expression on CD8+ T cells via an NFATc1-dependent pathway, with its deletion enhancing anti-tumor immunity [PMID:25851535]. SKAP1 was first identified as a constitutive partner of the Src-family kinase Fyn and a Fyn substrate, with Fyn-mediated phosphorylation of a non-canonical RKxxYxxY motif controlling its interactions [PMID:9195899, PMID:10856234, PMID:16461356].","teleology":[{"year":1997,"claim":"Established SKAP1 as a Src-kinase-associated adaptor, defining its domain architecture and placing it within proximal TCR signaling.","evidence":"GST-SH2 pulldown, molecular cloning, and in vitro SH2 binding assays in T-lymphocytes","pmids":["9195899"],"confidence":"High","gaps":["Functional consequence of Fyn association not established","Downstream effectors unknown at this stage"]},{"year":1998,"claim":"Identified ADAP (FYB/SLAP-130) as the principal SH3-domain partner of SKAP1, defining the core adaptor module.","evidence":"Yeast two-hybrid, co-IP, and truncation mapping in T and COS cells","pmids":["9671755","9748251"],"confidence":"High","gaps":["Functional output of the ADAP-SKAP1 complex not yet defined","Whether the interaction is constitutive or regulated unclear"]},{"year":2000,"claim":"Defined a proline-independent RKxxYxxY motif as the structural basis for Fyn-SH3 recognition of SKAP1, linking the interaction to TCR-driven transcription.","evidence":"Peptide precipitation, alanine scanning, 2D NMR, and NF-AT reporter assay","pmids":["10856234"],"confidence":"High","gaps":["Physiological role of Fyn-SKAP1 binding in adhesion not yet connected"]},{"year":2003,"claim":"Showed SKAP1 controls integrin-mediated adhesion and immunological synapse formation, defining its core cellular function in inside-out signaling.","evidence":"Overexpression/dominant-negative studies, adhesion assays, confocal microscopy, raft fractionation","pmids":["12652296"],"confidence":"High","gaps":["Molecular link from SKAP1 to LFA-1 not yet identified","SH3-domain dependence implicated but mechanism unresolved"]},{"year":2005,"claim":"Demonstrated SKAP1 is non-redundantly required for TCR-induced LFA-1 clustering and that its stability depends on ADAP, establishing the module as a functional unit.","evidence":"siRNA knockdown with LFA-1 clustering/conjugation readouts; ADAP-deficient cell reconstitution with pulse-chase half-life analysis","pmids":["15939789","15849195"],"confidence":"High","gaps":["The membrane effector bridging SKAP1 to integrin still unidentified","Mechanism of SKAP1 proteolysis in absence of ADAP unknown"]},{"year":2006,"claim":"Identified Rap1 membrane recruitment as the output of the ADAP/SKAP1 module and mapped Fyn phosphorylation of Y294 as a regulatory switch for the ADAP-SKAP1 interaction.","evidence":"Dominant-negative module disruption, Rap1 activity/fractionation assays, SPR binding, and Y294F/Y297F mutagenesis with functional readouts","pmids":["16980616","16461356"],"confidence":"High","gaps":["How Rap1 connects to LFA-1 downstream not yet defined","Effector linking Rap1 to integrin still unknown"]},{"year":2008,"claim":"Established a second SKAP1 function as a negative regulator of the Ras-ERK pathway through C-terminal binding of RasGRP1.","evidence":"Knockout primary T cells, RNAi, co-IP, C-terminal deletion mutants, ERK/ELK assays, RasGRP1 localization","pmids":["17658605","18320039"],"confidence":"High","gaps":["Mechanism by which SKAP1 controls RasGRP1 Golgi localization unresolved","Integration of adhesion and Ras-regulatory roles unclear"]},{"year":2011,"claim":"Resolved the SKAP1-RapL-Rap1-LFA-1 connectivity, showing the N-terminus binds the RapL SARAH domain and the PH domain drives RapL membrane localization to assemble the integrin-activating complex.","evidence":"Skap1-/- primary T cells, co-IP, RapL L224A and PH-domain R131M mutants, intravital two-photon imaging, membrane fractionation","pmids":["20346707","21669874","21525391"],"confidence":"High","gaps":["PH-domain lipid/membrane ligand not directly identified at this stage","Distinction between integrin and NF-kB arms of ADAP only partially mapped"]},{"year":2013,"claim":"Showed SKAP1 dimerization and ADAP binding are required for SLP-76 microcluster stabilization and recruitment of RIAM/talin, extending its scaffolding role to junctional stability and beta1 integrins.","evidence":"Live-cell SLP-76 microcluster imaging, dimerization mutants, tandem-dimer constructs, RIAM/talin co-IP, adhesion assays","pmids":["24368808"],"confidence":"High","gaps":["How dimerization couples to talin recruitment mechanistically unresolved"]},{"year":2016,"claim":"Linked SKAP1 to talin processing, showing it controls calpain-mediated talin cleavage and talin/RIAM delivery to the contact interface.","evidence":"Skap1-/- T cells, talin/RIAM localization, talin cleavage assay, non-cleavable talin L432G rescue","pmids":["26905930"],"confidence":"Medium","gaps":["Single lab; direct biochemical link between SKAP1 and calpain not established","How SKAP1 modulates cleavage mechanistically unknown"]},{"year":2017,"claim":"Defined SKAP1 in an LFA-1/FAK1-driven de-adhesion pathway via LAT-GRB2-SKAP1 complexes, and refined PH-domain control of cytoplasmic versus membrane localization.","evidence":"Co-IP, LAT Y171 mutant, FAK1/PYK2 assays, T cell-DC dwell time and proliferation assays; PH-domain D120/K152 mutants with actin co-IP","pmids":["28699640","28052935"],"confidence":"High","gaps":["Switch between adhesion-promoting and de-adhesion complexes not fully mapped","K152-actin functional data from single lab (Medium)"]},{"year":2019,"claim":"Extended SKAP1 function beyond adhesion to T-cell cycle control as a scaffold for PLK1 at serine 31, with PD-1 regulation establishing immunoregulatory roles.","evidence":"siRNA knockdown, co-IP, in vitro phosphorylation, S31 mutant reconstitution, cell cycle analysis; plus Skap55-/- DC vaccine tumor models for PD-1/NFATc1","pmids":["31320682","25851535"],"confidence":"Medium","gaps":["PLK1-scaffolding data from single lab","Mechanistic link between adhesion-adaptor and cell-cycle roles unresolved"]},{"year":2024,"claim":"Began dissecting the modular determinants distinguishing SKAP1 from its paralog SKAP2 in Src-kinase binding.","evidence":"Domain dissection and binding comparisons between SKAP1 and SKAP2 modules","pmids":["38483858"],"confidence":"Low","gaps":["Low-confidence modular dissection, single lab with limited orthogonal validation","Functional consequences of paralog-specific binding not established"]},{"year":null,"claim":"How SKAP1's distinct roles — integrin inside-out signaling, Ras-ERK regulation, de-adhesion, PD-1 control, and PLK1-dependent cell cycling — are coordinated within a single T cell remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model integrating adhesion and cell-cycle functions","Structural basis of PH-domain membrane/lipid engagement undefined","Temporal switching between adhesion and de-adhesion complexes unmapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[2,9,10,14]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[6,22]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[13,24]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4,22]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[4,6,10,15]}],"pathway":[{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[6,8,14,19]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[10,13,21]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[6,18,20]}],"complexes":["ADAP-SKAP1 module","SKAP1-RapL-Rap1-LFA-1 complex","LAT-GRB2-SKAP1 complex"],"partners":["FYB","FYN","RAPL","RAP1","RASGRP1","GRB2","LAT","PLK1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q86WV1","full_name":"Src kinase-associated phosphoprotein 1","aliases":["Src family-associated phosphoprotein 1","Src kinase-associated phosphoprotein of 55 kDa","SKAP-55","pp55"],"length_aa":359,"mass_kda":41.4,"function":"Positively regulates T-cell receptor signaling by enhancing the MAP kinase pathway. Required for optimal conjugation between T-cells and antigen-presenting cells by promoting the clustering of integrin ITGAL on the surface of T-cells. May be involved in high affinity immunoglobulin epsilon receptor signaling in mast cells","subcellular_location":"Cytoplasm; Nucleus; Cell membrane","url":"https://www.uniprot.org/uniprotkb/Q86WV1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/SKAP1","classification":"Not Classified","n_dependent_lines":14,"n_total_lines":1208,"dependency_fraction":0.011589403973509934},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/SKAP1","total_profiled":1310},"omim":[{"mim_id":"618478","title":"FYN-BINDING PROTEIN 2; FYB2","url":"https://www.omim.org/entry/618478"},{"mim_id":"604969","title":"SRC KINASE-ASSOCIATED PHOSPHOPROTEIN 1; 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 \"finding\": \"SKAP55 (SKAP1) was identified as a novel adaptor protein that constitutively associates with the Src-family kinase p59(fyn) in T-lymphocytes. SKAP55 contains a pleckstrin homology domain, a C-terminal SH3 domain, and tyrosine phosphorylation sites. In vitro binding assays showed SKAP55 selectively binds SH2 domains of Lck, Lyn, Src, and Fyn but not ZAP70, Syk, Shc, SLP-76, Grb2, PI3K, or c-abl. SKAP55 is constitutively tyrosine phosphorylated in resting T-lymphocytes.\",\n      \"method\": \"GST-Fyn-SH2 domain pulldown, molecular cloning, co-immunoprecipitation, in vitro SH2 domain binding assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — initial cloning paper with multiple orthogonal biochemical methods (purification, co-IP, in vitro binding), replicated by subsequent studies\",\n      \"pmids\": [\"9195899\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SKAP55 binds FYB (ADAP/SLAP-130) through its SH3 domain and acts as a substrate for FYN kinase in T cells. FYB and SKAP55 colocalize in the perinuclear region of cells. A related protein SKAP55R also binds FYB via its SH3 domain.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, immunofluorescence confocal microscopy\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — yeast two-hybrid plus co-IP plus localization, replicated in subsequent papers\",\n      \"pmids\": [\"9671755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"SKAP55 directly associates with SLAP-130 (ADAP/FYB) in human T-cells. The interaction involves the SH3 domain of SKAP55 and the proline-rich sequence of SLAP-130, as demonstrated by truncation mutants and yeast two-hybrid.\",\n      \"method\": \"Co-immunoprecipitation from T cells, co-expression in COS cells, yeast two-hybrid with truncated mutants\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct interaction mapped by domain deletion in two orthogonal systems, replicated across labs\",\n      \"pmids\": [\"9748251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"The SH3 domain of FYN binds a novel proline-independent RKxxYxxY motif in SKAP55. Class I SH3 domains bound this motif while class II domains did not. Two-dimensional NMR of FYN-SH3 bound to the RKGDYASY peptide showed overlap with the proline-rich peptide binding site on the charged surface of the SH3 domain. Alanine scanning confirmed the requirement for the arginine, lysine and tandem tyrosines. Expression of the RKGDYASY peptide inhibited TcRzeta/CD3-mediated NF-AT transcription in T cells.\",\n      \"method\": \"Peptide precipitation, alanine scanning mutagenesis, 2D NMR, in vivo co-expression, NF-AT reporter assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structural analysis plus mutagenesis plus functional reporter assay in a single rigorous study\",\n      \"pmids\": [\"10856234\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SKAP55 undergoes TCR-induced translocation from cytoplasm to membrane and to lipid rafts. Upon TCR activation, SKAP55 forms homodimers through its SH3 domain and SK region, interacts with Fyn kinase and Grb-2 (dependent on phosphorylation of Y271), and its stable overexpression activates MAPK following TCR engagement.\",\n      \"method\": \"Co-immunoprecipitation, mutational analysis, subcellular fractionation, MAPK activation assays, stable overexpression\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — co-IP plus fractionation plus functional assay, single lab\",\n      \"pmids\": [\"12171928\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"SKAP55 associates with CD45 in T cells via Tyr-232 of SKAP55 (identified by yeast two-hybrid and mutational analysis). Anti-CD3 stimulation promotes SKAP55 tyrosine phosphorylation and membrane translocation. Overexpression of SKAP55 induces IL-2 promoter activation, while SKAP55-Y232F mutant suppresses it and causes Fyn hyperphosphorylation with decreased kinase activity, suggesting SKAP55 couples CD45 with Src kinases for their dephosphorylation and TCR signal activation.\",\n      \"method\": \"Yeast two-hybrid, mutational analysis, in vivo co-expression, IL-2 promoter reporter assay, kinase activity assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — yeast two-hybrid plus mutational analysis plus functional reporter, single lab\",\n      \"pmids\": [\"11909961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SKAP-55 (SKAP1) regulates integrin-mediated adhesion and T cell-APC conjugate formation. SKAP-55 enhances adhesion to fibronectin and ICAM-1, colocalizes with actin at the T cell-APC immunological synapse, and promotes LFA-1 clustering. This function requires the SKAP-55 SH3 domain. SKAP-55 translocates to membrane rafts upon LFA-1 and TCR co-ligation.\",\n      \"method\": \"Overexpression and dominant-negative studies, adhesion assays, confocal microscopy, membrane raft fractionation, co-localization\",\n      \"journal\": \"Nature immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (adhesion assay, microscopy, fractionation, domain deletion), replicated across labs\",\n      \"pmids\": [\"12652296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"In mast cells, SKAP55 forms an adaptor complex with SLAP-130 and MIST. SLAP-130 requires collaboration with SKAP55 for the recruitment of MIST to Lyn. MIST is preferentially recruited to Fyn (over Lyn) due to higher affinity binding of the SLAP-130/SKAP55 complex to the Fyn-SH2 domain.\",\n      \"method\": \"Co-immunoprecipitation, direct binding assays, affinity comparisons\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — co-IP plus affinity comparisons, single lab with multiple cell line validations\",\n      \"pmids\": [\"12681493\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SKAP-55 is essential for TCR-mediated 'inside-out signaling' required for LFA-1 clustering and T cell-APC conjugation. siRNA knockdown of SKAP-55 abolished LFA-1 clustering but had no effect on TCR-CD3 clustering. SKAP-55R (SKAP2) cannot substitute for SKAP-55 in this function, indicating a unique non-redundant role.\",\n      \"method\": \"siRNA knockdown, LFA-1 clustering assay, T cell-APC conjugation assay\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean siRNA knockdown with specific phenotypic readout, replicated by genetic knockout studies in other labs\",\n      \"pmids\": [\"15939789\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"SKAP55 protein stability is dependent on ADAP. In ADAP-deficient Jurkat T cells, SKAP55 has a half-life of ~15-20 min (vs ~90 min in the presence of ADAP) due to increased proteolysis. ADAP restores SKAP55 stability 5-fold by decreasing its degradation rate. This protective effect requires the SKAP55 SH3 domain (which mediates SKAP55-ADAP interaction).\",\n      \"method\": \"ADAP-deficient cell line reconstitution, protein stability/pulse-chase analysis, SH3 domain inactivation mutant\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reconstitution of ADAP into deficient cells, quantitative half-life measurements, mutational validation, multiple orthogonal methods\",\n      \"pmids\": [\"15849195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The ADAP/SKAP55 signaling module is involved in TCR-mediated inside-out signaling by recruiting activated Rap1 to the plasma membrane. Disruption of the ADAP/SKAP55 module displaces Rap1 from the plasma membrane without affecting Rap1 GTPase activity. Membrane-targeted ADAP/SKAP55 induces T-cell adhesion in the absence of TCR stimulation.\",\n      \"method\": \"Dominant-negative disruption of ADAP/SKAP55 module, membrane fractionation, Rap1 activity assays, constitutive membrane targeting constructs, adhesion assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods including dominant-negative disruption, fractionation, constitutive membrane targeting, functional adhesion assays\",\n      \"pmids\": [\"16980616\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ADAP SH3c domain binds a non-canonical RKxxY294xxY297 motif in SKAP-55. FYN kinase phosphorylates Y294 in vivo, blocking ADAP-SH3c binding. Surface plasmon resonance showed phosphorylation of Y294 mediates dissociation while Y297 phosphorylation had no effect. The Y294F mutation blocked TCR-induced LFA-1-mediated adhesion to ICAM-1 and IL-2 promoter activity.\",\n      \"method\": \"In vivo phosphorylation assays, surface plasmon resonance, mutational analysis (Y294F, Y297F), adhesion assays, IL-2 promoter reporter assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — SPR quantitative binding data plus mutagenesis plus in vivo phosphorylation and functional assays\",\n      \"pmids\": [\"16461356\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"SKAP55 co-immunoprecipitates with the Ras activator RasGRP1. Binding requires the C-terminus of SKAP55 and is enhanced by tyrosine phosphorylation of SKAP55. SKAP55 overexpression disrupts TCR-to-Ras-Erk-AP1 signaling, while knockdown decreases ERK phosphorylation and AP-1 activation. Constitutively active Ras or Raf-1 overcomes the inhibitory effect of SKAP55 overexpression.\",\n      \"method\": \"Co-immunoprecipitation, RNAi knockdown, overexpression, AP-1/NF-AT reporter assays, ERK phosphorylation assay, epistasis with constitutively active Ras/Raf\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — co-IP plus RNAi plus overexpression plus epistasis, single lab\",\n      \"pmids\": [\"17658605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"SKAP-55 binds RasGRP1 via its C-terminus and negatively regulates the p21(ras)-ERK pathway. SKAP-55-deficient primary T-cells show defective LFA-1 adhesion concurrent with hyper-activation of ERK. Loss of RasGRP1 binding abrogates SKAP-55 inhibition of ERK/ELK. SKAP-55-/- T-cells show increased RasGRP1 presence in the trans-Golgi network following TCR activation.\",\n      \"method\": \"Knockout primary T cells, RNAi knockdown, co-immunoprecipitation, C-terminal deletion mutants, ERK/ELK activation assays, RasGRP1 localization by microscopy\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — primary KO T cells plus multiple orthogonal methods including co-IP, mutants, localization, and functional assays; replicated findings from Kosco 2007\",\n      \"pmids\": [\"18320039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"SKAP1 N-terminal domain binds the C-terminal SARAH domain of RapL, forming a SKAP1-RapL-Rap1 complex that binds LFA-1. In Skap1-/- primary T cells, TCR-induced Rap1-RapL complex formation and LFA-1 binding failed to occur. A RapL mutation (L224A) that abrogated SKAP1 binding disrupted component colocalization in vesicles and T cell-DC conjugation. RapL expression slowed T cell motility in lymph nodes, an effect reversed by L224A mutation with reduced dwell times with DCs.\",\n      \"method\": \"Skap1-/- primary T cells, co-immunoprecipitation, RapL mutants, intravital two-photon imaging in lymph nodes, T cell-DC conjugation assay\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO primary T cells plus in vivo intravital imaging plus biochemical complex analysis and point mutant validation\",\n      \"pmids\": [\"20346707\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The PH domain of SKAP1 is required for RapL membrane localization and Rap1-LFA-1 complex formation. A PH domain-inactivating mutation (R131M) markedly impaired RapL translocation to membranes, Rap1 and LFA-1 binding, and LFA-1-ICAM-1 adhesion. N-terminal myristoylated SKAP1 facilitated constitutive RapL membrane and Rap1 binding, effectively substituting for PI3K and TCR ligation in LFA-1 activation.\",\n      \"method\": \"PH domain point mutation (R131M), membrane fractionation, co-immunoprecipitation, constitutive membrane-targeting (myr-SKAP1), LFA-1 adhesion assay, PI3K inhibitor studies\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — structure-function mutagenesis plus constitutive membrane targeting plus multiple functional assays, consistent with Kliche 2006\",\n      \"pmids\": [\"21669874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The SKAP55 PH domain (specifically R131M mutation) determines the ability of the ADAP/SKAP55 module to recruit ADAP to LFA-1 integrin complexes upon TCR stimulation. Association of ADAP with SKAP55 is both sufficient and necessary for rescue of integrin function in ADAP-deficient T cells. The R131M SKAP55 mutant, while unable to restore integrin function, restored NF-κB signaling in ADAP-deficient T cells, indicating that SKAP55 association with ADAP segregates integrin and NF-κB functions of ADAP.\",\n      \"method\": \"SKAP-ADAP chimeric fusion protein, ADAP-deficient T cell reconstitution, PH domain mutation (R131M), LFA-1 co-immunoprecipitation, NF-κB reporter assay, integrin adhesion assay\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — chimeric fusion protein approach with reconstitution in deficient cells, mutagenesis, and multiple functional readouts\",\n      \"pmids\": [\"21525391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The ADAP/SKAP55 module regulates CCR7-mediated LFA-1 activation by forming two independent pools: one interacting with a RAPL/Mst1 complex and the other linked to a RIAM/Mst1/Kindlin-3 complex. Both complexes require ADAP/SKAP55 for binding to LFA-1 upon CCR7 stimulation. Loss of the module delays T-cell homing and reduces intranodal motility in vivo.\",\n      \"method\": \"Co-immunoprecipitation, LFA-1 affinity/avidity assays, in vivo homing assays, intravital imaging\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple co-IP complexes identified plus in vivo functional assays\",\n      \"pmids\": [\"22117043\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"SKAP55 is required for SLP-76 microcluster persistence and movement, junctional stabilization, and integrin-independent adhesion via the TCR. These functions require SKAP55 dimerization and ADAP interaction. The SKAP55 dimerization motif enables co-immunoprecipitation of RIAM, recruitment of talin into TCR-induced adhesive junctions, and inside-out signaling to β1 integrins. A tandem dimer with two ADAP-binding SKAP55 SH3 domains stabilized SLP-76 microclusters but could not support adhesion to integrin ligands.\",\n      \"method\": \"Fluorescence microscopy of SLP-76 microclusters, SKAP55 dimerization domain mutants, tandem dimer constructs, co-immunoprecipitation of RIAM and talin, integrin adhesion assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — live cell imaging plus domain deletion plus co-IP plus functional adhesion assays, multiple orthogonal methods\",\n      \"pmids\": [\"24368808\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The ADAP-SKAP55 signaling module promotes PD-1 expression on CD8+ T cells in a Fyn-, Ca2+-, and NFATc1-dependent manner. Knockout of SKAP55 or ADAP reduced PD-1 expression on CD8+ effector cells and enhanced anti-tumor immunity in DC vaccine models. NFATc1 inhibitor CsA also downregulated PD-1, consistent with SKAP55 acting upstream of NFATc1.\",\n      \"method\": \"Skap55-/- and Adap-/- knockout mice, DC vaccine tumor models, adoptive T cell transfer, NFATc1 inhibitor (CsA), flow cytometry for PD-1/CTLA-4/Treg\",\n      \"journal\": \"EMBO molecular medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic knockouts in primary cells and in vivo models with pharmacological validation of pathway\",\n      \"pmids\": [\"25851535\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SKAP1-deficient T cells show reduced translocation of talin and RIAM to the T cell-APC contact interface. Skap1-/- T cells show an altered pattern of talin cleavage (by calpain). Expression of a calpain-cleavage-resistant talin mutant (L432G) rescued the impaired adhesion of Skap1-/- T cells with DCs.\",\n      \"method\": \"Skap1-/- T cells, confocal microscopy of contact interface, talin/RIAM localization, talin cleavage assay, non-cleavable talin (L432G) reconstitution, T cell-DC conjugation assay\",\n      \"journal\": \"Immunology letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — KO cells with localization and functional rescue, single lab\",\n      \"pmids\": [\"26905930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"LFA-1 cross-linking activates FAK1/PYK2 which phosphorylate LAT selectively on Y171, leading to formation of LAT-GRB2-SKAP1 complexes distinct from canonical LAT-GADs-SLP-76 complexes. LFA-1 cross-linking increased LAT-GRB2-SKAP1 relative to LAT-GADs-SLP-76 complexes and decreased T cell-DC dwell times dependent on LAT-Y171, reducing T cell binding to DCs and proliferation.\",\n      \"method\": \"Co-immunoprecipitation, LAT Y171 mutant, FAK1/PYK2 activation assays, T cell-DC dwell time analysis, T cell proliferation assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical complex identification plus phosphorylation site mutants plus in vivo functional assays for dwell time and proliferation\",\n      \"pmids\": [\"28699640\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Within the SKAP55 PH domain, D120 facilitates cytoplasmic retention of SKAP55 in non-stimulated T cells, while K152 promotes membrane recruitment via actin binding upon TCR triggering. K152-dependent PH domain interaction with actin promotes talin binding to LFA-1, facilitating LFA-1 activation.\",\n      \"method\": \"PH domain point mutations (D120, K152), subcellular fractionation, actin co-immunoprecipitation, talin-LFA-1 binding assay, LFA-1 activation assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — structure-function mutagenesis with co-IP and functional assays, single lab\",\n      \"pmids\": [\"28052935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SKAP1 forms homodimers mediated by residues A17 to L21 in the N-terminal region. SKAP1 dimerization is not required for its binding to RapL.\",\n      \"method\": \"Co-immunoprecipitation of truncation/deletion mutants, N-terminal deletion mapping\",\n      \"journal\": \"BMC research notes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP with deletion mutants, single lab, consistent with earlier dimerization observations\",\n      \"pmids\": [\"30522503\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SKAP1 is phosphorylated by and binds to PLK1 at N-terminal serine 31 (S31). This interaction is needed for optimal PLK1 kinase activity. siRNA knockdown of SKAP1 reduced T-cell division and delayed expression of PLK1, Cyclin A and pH3. Reconstitution with WT SKAP1 but not the S31 mutant restored normal cell division. SKAP1-PLK1 binding is dynamically regulated during the T-cell cycle.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, in vitro phosphorylation assay, S31 point mutation reconstitution, cell cycle analysis (Cyclin A, pH3, PLK1 expression)\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — co-IP plus mutagenesis plus KD/reconstitution, single lab\",\n      \"pmids\": [\"31320682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Two modules control SKAP1 interaction with SRC kinases: one composed of two conserved motifs in the second interdomain that interact with the SH2 domain of SRC kinases, and a second module composed of the DIM (dimerization) domain modulated by the SH3 domain and SRC kinase activation state. These binding properties differ between SKAP1 and its paralog SKAP2.\",\n      \"method\": \"Domain dissection/truncation analysis, binding comparisons between SKAP1 and SKAP2 modules\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — modular dissection analysis, single lab, limited orthogonal validation described in abstract\",\n      \"pmids\": [\"38483858\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SKAP1 (SKAP55) is a T cell-specific adaptor protein that couples the TCR to LFA-1 inside-out signaling by forming a constitutive complex with ADAP (stabilized through mutual SH3-domain interactions), recruiting activated Rap1 to the plasma membrane via its PH domain and a direct N-terminal/SARAH-domain interaction with RapL, thereby assembling a SKAP1-RapL-Rap1-LFA-1 complex that promotes integrin clustering and T cell-APC conjugation; additionally, SKAP1 modulates the Ras-ERK pathway by binding RasGRP1, regulates PD-1 expression via an NFATc1-dependent pathway, forms LAT-GRB2-SKAP1 complexes downstream of LFA-1/FAK1 signaling to promote T cell de-adhesion, and acts as a scaffold for PLK1 at serine 31 to support optimal T cell cycling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SKAP1 (SKAP55) is a T cell-restricted cytosolic adaptor that couples T-cell receptor (TCR) engagement to integrin-mediated adhesion through 'inside-out' signaling, controlling LFA-1 clustering and the formation of stable T cell-antigen-presenting cell conjugates [#6, #8]. It functions as part of a constitutive module with the adaptor ADAP (FYB/SLAP-130), an interaction mediated by the SKAP1 SH3 domain binding a proline-rich region of ADAP and reciprocally stabilizing SKAP1 against proteolytic degradation [#2, #9]. The ADAP/SKAP1 module recruits activated Rap1 to the plasma membrane, where SKAP1 bridges Rap1 to its effector RapL via a direct N-terminal interaction with the RapL SARAH domain, assembling a SKAP1-RapL-Rap1 complex that engages LFA-1 and drives integrin activation [#10, #14]. Membrane localization of this module requires the SKAP1 PH domain, which directs RapL membrane translocation and, through residue-specific actin binding, promotes talin recruitment to LFA-1 [#15, #22]; SKAP1 loss alters calpain-mediated talin cleavage and impairs talin/RIAM delivery to the contact interface [#18, #20]. Beyond adhesion, SKAP1 binds the Ras activator RasGRP1 through its C-terminus to negatively regulate the Ras-ERK pathway [#13], and the ADAP/SKAP1 module promotes PD-1 expression on CD8+ T cells via an NFATc1-dependent pathway, with its deletion enhancing anti-tumor immunity [#19]. SKAP1 was first identified as a constitutive partner of the Src-family kinase Fyn and a Fyn substrate, with Fyn-mediated phosphorylation of a non-canonical RKxxYxxY motif controlling its interactions [#0, #3, #11].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established SKAP1 as a Src-kinase-associated adaptor, defining its domain architecture and placing it within proximal TCR signaling.\",\n      \"evidence\": \"GST-SH2 pulldown, molecular cloning, and in vitro SH2 binding assays in T-lymphocytes\",\n      \"pmids\": [\"9195899\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of Fyn association not established\", \"Downstream effectors unknown at this stage\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identified ADAP (FYB/SLAP-130) as the principal SH3-domain partner of SKAP1, defining the core adaptor module.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, and truncation mapping in T and COS cells\",\n      \"pmids\": [\"9671755\", \"9748251\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional output of the ADAP-SKAP1 complex not yet defined\", \"Whether the interaction is constitutive or regulated unclear\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined a proline-independent RKxxYxxY motif as the structural basis for Fyn-SH3 recognition of SKAP1, linking the interaction to TCR-driven transcription.\",\n      \"evidence\": \"Peptide precipitation, alanine scanning, 2D NMR, and NF-AT reporter assay\",\n      \"pmids\": [\"10856234\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological role of Fyn-SKAP1 binding in adhesion not yet connected\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showed SKAP1 controls integrin-mediated adhesion and immunological synapse formation, defining its core cellular function in inside-out signaling.\",\n      \"evidence\": \"Overexpression/dominant-negative studies, adhesion assays, confocal microscopy, raft fractionation\",\n      \"pmids\": [\"12652296\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular link from SKAP1 to LFA-1 not yet identified\", \"SH3-domain dependence implicated but mechanism unresolved\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Demonstrated SKAP1 is non-redundantly required for TCR-induced LFA-1 clustering and that its stability depends on ADAP, establishing the module as a functional unit.\",\n      \"evidence\": \"siRNA knockdown with LFA-1 clustering/conjugation readouts; ADAP-deficient cell reconstitution with pulse-chase half-life analysis\",\n      \"pmids\": [\"15939789\", \"15849195\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The membrane effector bridging SKAP1 to integrin still unidentified\", \"Mechanism of SKAP1 proteolysis in absence of ADAP unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified Rap1 membrane recruitment as the output of the ADAP/SKAP1 module and mapped Fyn phosphorylation of Y294 as a regulatory switch for the ADAP-SKAP1 interaction.\",\n      \"evidence\": \"Dominant-negative module disruption, Rap1 activity/fractionation assays, SPR binding, and Y294F/Y297F mutagenesis with functional readouts\",\n      \"pmids\": [\"16980616\", \"16461356\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Rap1 connects to LFA-1 downstream not yet defined\", \"Effector linking Rap1 to integrin still unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established a second SKAP1 function as a negative regulator of the Ras-ERK pathway through C-terminal binding of RasGRP1.\",\n      \"evidence\": \"Knockout primary T cells, RNAi, co-IP, C-terminal deletion mutants, ERK/ELK assays, RasGRP1 localization\",\n      \"pmids\": [\"17658605\", \"18320039\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which SKAP1 controls RasGRP1 Golgi localization unresolved\", \"Integration of adhesion and Ras-regulatory roles unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Resolved the SKAP1-RapL-Rap1-LFA-1 connectivity, showing the N-terminus binds the RapL SARAH domain and the PH domain drives RapL membrane localization to assemble the integrin-activating complex.\",\n      \"evidence\": \"Skap1-/- primary T cells, co-IP, RapL L224A and PH-domain R131M mutants, intravital two-photon imaging, membrane fractionation\",\n      \"pmids\": [\"20346707\", \"21669874\", \"21525391\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"PH-domain lipid/membrane ligand not directly identified at this stage\", \"Distinction between integrin and NF-kB arms of ADAP only partially mapped\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Showed SKAP1 dimerization and ADAP binding are required for SLP-76 microcluster stabilization and recruitment of RIAM/talin, extending its scaffolding role to junctional stability and beta1 integrins.\",\n      \"evidence\": \"Live-cell SLP-76 microcluster imaging, dimerization mutants, tandem-dimer constructs, RIAM/talin co-IP, adhesion assays\",\n      \"pmids\": [\"24368808\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How dimerization couples to talin recruitment mechanistically unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Linked SKAP1 to talin processing, showing it controls calpain-mediated talin cleavage and talin/RIAM delivery to the contact interface.\",\n      \"evidence\": \"Skap1-/- T cells, talin/RIAM localization, talin cleavage assay, non-cleavable talin L432G rescue\",\n      \"pmids\": [\"26905930\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; direct biochemical link between SKAP1 and calpain not established\", \"How SKAP1 modulates cleavage mechanistically unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Defined SKAP1 in an LFA-1/FAK1-driven de-adhesion pathway via LAT-GRB2-SKAP1 complexes, and refined PH-domain control of cytoplasmic versus membrane localization.\",\n      \"evidence\": \"Co-IP, LAT Y171 mutant, FAK1/PYK2 assays, T cell-DC dwell time and proliferation assays; PH-domain D120/K152 mutants with actin co-IP\",\n      \"pmids\": [\"28699640\", \"28052935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Switch between adhesion-promoting and de-adhesion complexes not fully mapped\", \"K152-actin functional data from single lab (Medium)\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Extended SKAP1 function beyond adhesion to T-cell cycle control as a scaffold for PLK1 at serine 31, with PD-1 regulation establishing immunoregulatory roles.\",\n      \"evidence\": \"siRNA knockdown, co-IP, in vitro phosphorylation, S31 mutant reconstitution, cell cycle analysis; plus Skap55-/- DC vaccine tumor models for PD-1/NFATc1\",\n      \"pmids\": [\"31320682\", \"25851535\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"PLK1-scaffolding data from single lab\", \"Mechanistic link between adhesion-adaptor and cell-cycle roles unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Began dissecting the modular determinants distinguishing SKAP1 from its paralog SKAP2 in Src-kinase binding.\",\n      \"evidence\": \"Domain dissection and binding comparisons between SKAP1 and SKAP2 modules\",\n      \"pmids\": [\"38483858\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Low-confidence modular dissection, single lab with limited orthogonal validation\", \"Functional consequences of paralog-specific binding not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How SKAP1's distinct roles — integrin inside-out signaling, Ras-ERK regulation, de-adhesion, PD-1 control, and PLK1-dependent cell cycling — are coordinated within a single T cell remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model integrating adhesion and cell-cycle functions\", \"Structural basis of PH-domain membrane/lipid engagement undefined\", \"Temporal switching between adhesion and de-adhesion complexes unmapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2, 9, 10, 14]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [6, 22]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [13, 24]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4, 22]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [4, 6, 10, 15]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [6, 8, 14, 19]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [10, 13, 21]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [6, 18, 20]}\n    ],\n    \"complexes\": [\"ADAP-SKAP1 module\", \"SKAP1-RapL-Rap1-LFA-1 complex\", \"LAT-GRB2-SKAP1 complex\"],\n    \"partners\": [\"FYB\", \"FYN\", \"RAPL\", \"RAP1\", \"RASGRP1\", \"GRB2\", \"LAT\", \"PLK1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":6,"faith_total":6,"faith_pct":100.0}}