{"gene":"ITGB1BP1","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":1997,"finding":"ICAP-1 (ITGB1BP1) specifically binds the β1 integrin cytoplasmic domain via the conserved NPXY motif; mutagenesis of Asn and Tyr of the NPXY motif and a Val residue NH2-terminal to it abrogates binding. Two isoforms (ICAP-1α, 200 aa; ICAP-1β, 150 aa) arise from alternative splicing. ICAP-1α is a phosphoprotein whose phosphorylation is enhanced by cell plating on fibronectin and reduced by constitutively active RhoA, linking its modification to integrin-mediated adhesion.","method":"Yeast two-hybrid screen, mutational analysis, cell-matrix adhesion assays with phosphorylation readout","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutational dissection of binding interface plus functional phosphorylation assays; foundational paper independently replicated by multiple subsequent studies","pmids":["9281591"],"is_preprint":false},{"year":1999,"finding":"ICAP-1 associates specifically with the β1 integrin cytoplasmic tail (not β2, β3, or β5) via the carboxyl-terminal 14 amino acids of β1. ICAP-1 overexpression markedly increases β1-dependent chemotactic migration through fibronectin-coated filters, and support of β1-dependent migration in CHO cells correlates with ICAP-1 association, establishing a functional role in β1 integrin-dependent cell migration.","method":"Yeast two-hybrid, co-immunoprecipitation in human cells, cell migration assays with wild-type and mutant β1 constructs, Triton X-100 fractionation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal binding specificity confirmed in cells, functional rescue with mutant integrins, replicated by subsequent labs","pmids":["9867804"],"is_preprint":false},{"year":2001,"finding":"ICAP-1α contains a PTB (phosphotyrosine-binding) domain (residues 58–200) that recognizes the NPXY motif of β1 integrin. Alanine-scanning and site-directed mutagenesis identified Val787, Val790, and 792NPKY795 of β1 as critical contact residues, and Leu135, Ile138, Ile139, Leu82, and Tyr144 of ICAP-1α as required for the interaction; Leu82/Tyr144 form a hydrophobic pocket that confers β1 specificity by engaging Val787.","method":"Alanine-scanning mutagenesis, site-directed mutagenesis guided by PTB-domain homology modeling","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — comprehensive mutagenesis of both binding partners with structural model validation; independently confirmed by crystal structures in 2013","pmids":["11741908"],"is_preprint":false},{"year":2002,"finding":"KRIT1 binds directly to ICAP-1 via an N-terminal NPXY-like motif in KRIT1; mutagenesis of this NPXY sequence completely abrogates the KRIT1/ICAP-1 interaction. The interaction was confirmed by GST-KRIT1 pulldown of endogenous ICAP-1 from 293T cells.","method":"Yeast two-hybrid screen of fetal brain and HeLa cDNA libraries, GST pulldown, site-directed mutagenesis","journal":"Human molecular genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — GST pulldown confirms yeast two-hybrid, mutagenesis of binding motif, replicated and extended by crystal structures in 2013","pmids":["11854171"],"is_preprint":false},{"year":2002,"finding":"ICAP-1 expression inhibits NIH3T3 cell spreading on ECM; this inhibition is counteracted by constitutively active Cdc42, placing ICAP-1 upstream of Cdc42. ICAP-1 binds Cdc42 and Rac1 in vitro, inhibits activation of these GTPases during fibronectin adhesion, reduces GDP dissociation from Cdc42 (both intrinsic and exchange-factor-stimulated), and displaces Cdc42 from cellular membranes, functioning as a guanine nucleotide dissociation inhibitor (GDI).","method":"Yeast two-hybrid, in vitro binding assay, PAK-binding GTPase activation assay, GDP dissociation assay, membrane fractionation, epistasis with constitutively active Cdc42","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro biochemical assay for GDI activity plus cell-based epistasis with multiple orthogonal methods in one study","pmids":["11807099"],"is_preprint":false},{"year":2006,"finding":"ICAP-1 binds the ROCK-I kinase via two binding sites; the proteins form complexes in cells (co-immunoprecipitation) and colocalize at the plasma membrane in lamellipodia and membrane ruffles. ICAP-1 translocates ROCK-I to the plasma membrane independently of β1 integrin ligation or ROCK kinase activity. Direct interaction in lamellipodia was confirmed by FRET between CFP-ICAP-1 and YFP-ROCK during cell spreading.","method":"Yeast two-hybrid, co-immunoprecipitation, colocalization microscopy, FRET (CFP/YFP fusion proteins), truncation mapping","journal":"Journal of cellular physiology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP plus FRET demonstrates direct in-cell interaction; single lab but multiple orthogonal methods","pmids":["16741948"],"is_preprint":false},{"year":2008,"finding":"ICAP-1 knockdown reduces β1 integrin-dependent migration of C2C12 myoblasts on laminin and endothelial cells on collagen; overexpression increases migration on laminin. Knockdown reduces central focal adhesions; overexpression increases them. ICAP-1 translocates ROCK to membrane ruffles in myoblasts, and ROCK inhibition (Y-27632) phenocopies ICAP-1 knockdown, indicating ICAP-1 regulates β1-dependent migration through ROCK translocation to integrin adhesion sites.","method":"RNAi knockdown, overexpression, migration assay, focal adhesion counting, co-immunoprecipitation, YFP-ROCK colocalization","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD and OE with defined cellular phenotype plus pharmacological epistasis; single lab","pmids":["17654484"],"is_preprint":false},{"year":2013,"finding":"Crystal structures of KRIT1 in complex with ICAP1 (2.54 Å) and ICAP1 in complex with integrin β1 cytoplasmic tail (3.0 Å) reveal that KRIT1 binds ICAP1 via a bidentate surface that directly competes with integrin β1 for the same site on the ICAP1 PTB domain. KRIT1 thereby antagonizes ICAP1-mediated suppression of β1 integrin 'inside-out' activation. Additionally, KRIT1 contains an N-terminal Nudix domain in a region previously considered unstructured.","method":"X-ray crystallography (co-crystal structures), integrin activation assays, competitive binding studies","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — co-crystal structures at near-atomic resolution with functional validation of competitive mechanism; single rigorous study with multiple orthogonal methods","pmids":["23317506"],"is_preprint":false},{"year":2013,"finding":"Co-crystal structure of the ICAP1 PTB domain with a minimal 29-amino-acid KRIT1 peptide (residues 170–198) resolved to 1.7 Å provides the highest-resolution structural detail of the ICAP1-KRIT1 interaction interface.","method":"X-ray crystallography (co-crystal structure)","journal":"Acta crystallographica. Section F","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution crystal structure; complements and extends the 2013 Molecular Cell structural study","pmids":["23695561"],"is_preprint":false},{"year":2016,"finding":"ICAP1 contains a functional nuclear localization signal (NLS); nuclear localization impairs ICAP1's ability to suppress β1 integrin activation. ICAP1 drives nuclear localization of KRIT1 in a manner dependent on direct ICAP1/KRIT1 interaction, establishing that nuclear-cytoplasmic shuttling of ICAP1 controls both integrin activation state and KRIT1 subcellular distribution.","method":"Overexpression, NLS mutagenesis, flow cytometry (integrin activation assay), fluorescence microscopy of nuclear localization","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis of NLS with functional readout; single lab, two orthogonal methods (localization + activation assay)","pmids":["28003363"],"is_preprint":false},{"year":2017,"finding":"ICAP-1 is monoubiquitylated by Smurf1; this modification prevents ICAP-1 binding to β1 integrin and alters focal adhesion organization. Non-ubiquitylatable ICAP-1 interferes with fibronectin density sensing. ICAP-1 monoubiquitylation regulates rigidity sensing by increasing MRCKα-dependent cell contractility via myosin phosphorylation independently of substrate rigidity, and acts as a molecular switch from ROCK2-mediated to MRCKα-mediated cell contractility.","method":"Ubiquitylation assays (Smurf1 as E3 ligase), non-ubiquitylatable mutant expression, focal adhesion analysis, myosin phosphorylation assays, cell migration on substrates of varying density/stiffness","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — identification of E3 ligase with functional consequences via mutant rescue; single lab, multiple cellular readouts","pmids":["28049720"],"is_preprint":false},{"year":2020,"finding":"ICAP1 nuclear accumulation is inhibited by serine phosphorylation at Ser-10 (and to a lesser extent Ser-25) within its unstructured N-terminal region; phosphorylation-blocking substitutions enhance nuclear accumulation. PAK4 phosphorylates ICAP1 at Ser-10 both in vitro and in cultured cells, and active PAK4 inhibits ICAP1 nuclear accumulation in a Ser-10-dependent manner. This phosphorylation controls nuclear localization of the ICAP1–KRIT1 complex.","method":"Phosphorylation-mimicking and phosphorylation-blocking mutagenesis, quantitative fluorescence microscopy, in vitro kinase assay (PAK4), cell-based kinase assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay plus cell-based validation with mutagenesis; single lab but multiple orthogonal methods with rigorous controls","pmids":["32005669"],"is_preprint":false},{"year":2022,"finding":"ICAP-1 loss in mice causes defective single-positive CD8+ thymocyte generation without affecting integrin α4β1-dependent adhesion in thymocytes; ICAP-1 displays strong nuclear distribution in thymocytes and its absence correlates with reduced Runx3 levels in SP CD8+ thymocytes. In spleen, ICAP-1 loss upregulates α4β1-mediated adhesion of T and B cells and reduces proliferation, with a decrease in marginal zone B cells.","method":"ICAP-1 knockout mice, flow cytometry, nuclear/cytoplasmic fractionation, adhesion assays, proliferation assays","journal":"European journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean KO with defined phenotypes but single lab, no direct mechanistic link between nuclear ICAP-1 and Runx3 regulation established","pmids":["35491946"],"is_preprint":false},{"year":2024,"finding":"ICAP-1 knockdown in primary human T cells impairs LFA-1 (αLβ2 integrin)-directed cell polarity, velocity, and transmigration toward SDF-1, revealing a role for ICAP-1 in β2 integrin-mediated T cell migration in addition to its established β1 integrin functions.","method":"RNAi screen, primary T cell knockdown, cell polarity/morphology assay, transmigration assay","journal":"Immunology and cell biology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, knockdown phenotype with no molecular mechanism established for the β2 integrin connection","pmids":["39607284"],"is_preprint":false},{"year":2026,"finding":"ICAP-1α isoform (but not ICAP-1β) reduces aggressiveness and directionality of NSCLC cells on stiffness-gradient substrates; ICAP-1α has extensive subcellular distribution, inhibits integrin activity and talin tension. Matrix stiffening triggers a shift in ICAP-1 isoform expression, positioning ICAP-1 as a mechanotransducer relaying signals from β1 integrin to talin.","method":"Isoform-specific expression, cell-directed matrix (CDM) migration assays, talin tension sensor (FRET-based), integrin activity assays","journal":"Biochemical pharmacology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — FRET-based talin tension measurement plus functional migration assay; single lab, novel finding not yet replicated","pmids":["41617095"],"is_preprint":false}],"current_model":"ITGB1BP1/ICAP-1 is a PTB-domain phosphoprotein that specifically binds the NPXY motif of the β1 integrin cytoplasmic tail to suppress integrin 'inside-out' activation; KRIT1 competitively displaces ICAP-1 from β1 integrin (as revealed by co-crystal structures) to relieve this suppression, while nuclear-cytoplasmic shuttling of ICAP-1—controlled by PAK4-mediated Ser-10 phosphorylation and Smurf1-mediated monoubiquitylation—regulates both integrin activation state and KRIT1 nuclear localization; additionally, ICAP-1 modulates cell migration and mechanosensing by acting as a GDI for Cdc42/Rac1, translocating ROCK-I to β1 integrin adhesion sites, and switching between ROCK2- and MRCKα-dependent contractility pathways in response to matrix density and rigidity."},"narrative":{"mechanistic_narrative":"ITGB1BP1 (ICAP-1) is a PTB-domain phosphoprotein that governs the activation state of β1 integrin and thereby controls cell adhesion, migration, and mechanosensing [PMID:9281591, PMID:9867804]. Its PTB domain (residues 58–200) recognizes the NPXY motif of the β1 integrin cytoplasmic tail with strict β1 selectivity, conferred by a hydrophobic pocket (Leu82/Tyr144) that engages Val787 of the integrin [PMID:9281591, PMID:11741908], and this binding suppresses 'inside-out' integrin activation. The cerebral cavernous malformation protein KRIT1 binds the same PTB surface through an N-terminal NPXY-like motif, and co-crystal structures show that KRIT1 directly competes with β1 integrin for ICAP-1, relieving its suppressive effect on integrin activation [PMID:11854171, PMID:23317506, PMID:23695561]. ICAP-1 shuttles between cytoplasm and nucleus via a functional NLS, with nuclear localization disabling its integrin-suppressive activity while simultaneously driving KRIT1 into the nucleus; this shuttling is controlled by PAK4-mediated Ser-10 phosphorylation, which restrains nuclear accumulation, and by Smurf1-mediated monoubiquitylation, which blocks β1 binding [PMID:28003363, PMID:28049720, PMID:32005669]. Beyond integrin binding, ICAP-1 acts as a guanine nucleotide dissociation inhibitor for Cdc42 and Rac1 and recruits ROCK-I to β1 integrin adhesion sites, integrating these activities into mechanotransduction—including a Smurf1-controlled switch between ROCK2- and MRCKα-dependent contractility and isoform-specific (ICAP-1α) tuning of talin tension on stiff matrices [PMID:11807099, PMID:16741948, PMID:17654484, PMID:28049720, PMID:41617095]. In vivo, ICAP-1 loss in mice disrupts CD8+ single-positive thymocyte generation and dysregulates β4β1-mediated lymphocyte adhesion [PMID:35491946].","teleology":[{"year":1997,"claim":"Established the founding molecular interaction—that ICAP-1 specifically engages the β1 integrin cytoplasmic tail via its NPXY motif and is regulated by adhesion-dependent phosphorylation—defining ICAP-1 as an integrin-tail-binding adaptor.","evidence":"Yeast two-hybrid, NPXY mutagenesis, and adhesion/phosphorylation assays on fibronectin","pmids":["9281591"],"confidence":"High","gaps":["Functional consequence of the interaction for integrin activation not yet defined","Kinase responsible for ICAP-1 phosphorylation unidentified"]},{"year":1999,"claim":"Demonstrated that the ICAP-1/β1 interaction is functionally consequential, linking it to β1-dependent chemotactic migration and confirming binding specificity for β1 over other β subunits.","evidence":"Yeast two-hybrid, co-IP in human cells, and migration assays with wild-type/mutant β1 in CHO cells","pmids":["9867804"],"confidence":"High","gaps":["Whether ICAP-1 activates or suppresses integrin not resolved","Downstream effectors of migration phenotype unknown"]},{"year":2001,"claim":"Mapped the binding interface to the PTB domain at residue resolution, explaining the structural basis of β1 specificity through identified contact residues on both partners.","evidence":"Alanine-scanning and site-directed mutagenesis guided by PTB homology modeling","pmids":["11741908"],"confidence":"High","gaps":["Lacked a crystal structure to confirm the modeled interface","Regulation of the interface in cells unaddressed"]},{"year":2002,"claim":"Identified KRIT1 as a second NPXY-motif partner of ICAP-1, foreshadowing a competition between two distinct ligands for the same adaptor.","evidence":"Yeast two-hybrid screen and GST-KRIT1 pulldown of endogenous ICAP-1, with NPXY mutagenesis","pmids":["11854171"],"confidence":"High","gaps":["Whether KRIT1 and β1 bind the same ICAP-1 surface not yet shown","Functional outcome of KRIT1 binding undefined"]},{"year":2002,"claim":"Revealed an integrin-independent activity, showing ICAP-1 functions as a GDI for Cdc42/Rac1 to restrain cell spreading, broadening its role into Rho-family GTPase regulation.","evidence":"In vitro binding and GDP-dissociation assays, GTPase activation assays, membrane fractionation, and epistasis with constitutively active Cdc42","pmids":["11807099"],"confidence":"High","gaps":["Integration of GDI activity with integrin-tail binding unclear","In vivo relevance of GDI function not tested"]},{"year":2006,"claim":"Connected ICAP-1 to actomyosin regulation by showing it binds and translocates ROCK-I to the plasma membrane independently of integrin ligation or kinase activity.","evidence":"Yeast two-hybrid, reciprocal co-IP, FRET between CFP-ICAP-1 and YFP-ROCK, and truncation mapping","pmids":["16741948"],"confidence":"High","gaps":["Functional consequence of ROCK translocation not yet shown","Relationship to GDI and integrin functions unresolved"]},{"year":2008,"claim":"Linked ROCK translocation to physiology, showing ICAP-1 regulates β1-dependent migration and focal adhesion organization through ROCK recruitment to adhesion sites.","evidence":"RNAi, overexpression, migration and focal-adhesion assays, and pharmacological ROCK inhibition (Y-27632) in myoblasts and endothelial cells","pmids":["17654484"],"confidence":"Medium","gaps":["Single lab","Direct molecular link between ICAP-1 and adhesion-site ROCK localization not structurally defined"]},{"year":2013,"claim":"Resolved the central mechanistic question by crystallography, proving that KRIT1 competes with β1 integrin for the same ICAP-1 PTB surface to antagonize ICAP-1-mediated suppression of integrin activation.","evidence":"Co-crystal structures of KRIT1–ICAP1 and ICAP1–β1 tail (and a 1.7 Å ICAP1–KRIT1 peptide structure), with integrin activation and competitive binding assays","pmids":["23317506","23695561"],"confidence":"High","gaps":["How the competition is regulated dynamically in cells not addressed","Spatial coordination of the two ligand pools unknown"]},{"year":2016,"claim":"Established nuclear-cytoplasmic shuttling as a regulatory layer, showing ICAP-1 has an NLS whose use both disables integrin suppression and drives KRIT1 into the nucleus.","evidence":"NLS mutagenesis with integrin activation flow cytometry and fluorescence microscopy","pmids":["28003363"],"confidence":"Medium","gaps":["Signals triggering shuttling not identified here","Nuclear function of ICAP-1/KRIT1 undefined"]},{"year":2017,"claim":"Identified monoubiquitylation as a switch, showing Smurf1 modifies ICAP-1 to block β1 binding and toggle contractility from ROCK2- to MRCKα-dependent, coupling ICAP-1 to rigidity sensing.","evidence":"Ubiquitylation assays with Smurf1, non-ubiquitylatable mutant rescue, focal-adhesion and myosin-phosphorylation assays, migration on varying density/stiffness substrates","pmids":["28049720"],"confidence":"Medium","gaps":["Single lab","Ubiquitylation site(s) and deubiquitylase not defined"]},{"year":2020,"claim":"Defined the kinase input controlling shuttling, showing PAK4 phosphorylates ICAP-1 at Ser-10 to inhibit nuclear accumulation of the ICAP1–KRIT1 complex.","evidence":"Phosphomimetic/blocking mutagenesis, quantitative microscopy, and in vitro plus cell-based PAK4 kinase assays","pmids":["32005669"],"confidence":"High","gaps":["Upstream signals activating PAK4 toward ICAP-1 unknown","Phosphatase reversing Ser-10 unidentified"]},{"year":2022,"claim":"Provided in vivo physiological context, showing ICAP-1 loss disrupts CD8+ thymocyte generation and dysregulates β4β1-mediated lymphocyte adhesion, with strong nuclear ICAP-1 in thymocytes.","evidence":"ICAP-1 knockout mice with flow cytometry, nuclear/cytoplasmic fractionation, and adhesion/proliferation assays","pmids":["35491946"],"confidence":"Medium","gaps":["No direct mechanistic link between nuclear ICAP-1 and Runx3 established","Single lab"]},{"year":2024,"claim":"Extended ICAP-1 function beyond β1 integrins, implicating it in LFA-1 (β2 integrin)-directed T cell polarity and transmigration.","evidence":"RNAi knockdown in primary human T cells with polarity and transmigration assays toward SDF-1","pmids":["39607284"],"confidence":"Low","gaps":["No molecular mechanism established for the β2 integrin connection","Single lab, knockdown only"]},{"year":2026,"claim":"Cast ICAP-1 as an isoform-specific mechanotransducer, showing ICAP-1α (not β) reduces cancer cell aggressiveness and dampens talin tension on stiffness gradients.","evidence":"Isoform-specific expression, cell-derived matrix migration assays, FRET talin tension sensor, and integrin activity assays in NSCLC cells","pmids":["41617095"],"confidence":"Medium","gaps":["Single lab, not replicated","Mechanism by which stiffness shifts isoform expression undefined"]},{"year":null,"claim":"How the multiple regulatory inputs—phosphorylation, monoubiquitylation, nuclear shuttling, and isoform switching—are integrated in real time at adhesion sites, and what ICAP-1/KRIT1 does in the nucleus, remain open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Nuclear function of the ICAP-1/KRIT1 complex uncharacterized","Quantitative hierarchy of competing regulatory modifications not established","Mechanism coupling β2 integrin function to known β1/KRIT1 biology unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[4,7,9]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,2,5]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,6]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9,11,12]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[9]}],"pathway":[{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[0,1,7]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[4,7,10]}],"complexes":[],"partners":["ITGB1","KRIT1","CDC42","RAC1","ROCK1","PAK4","SMURF1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O14713","full_name":"Integrin beta-1-binding protein 1","aliases":["Integrin cytoplasmic domain-associated protein 1","ICAP-1"],"length_aa":200,"mass_kda":21.8,"function":"Key regulator of the integrin-mediated cell-matrix interaction signaling by binding to the ITGB1 cytoplasmic tail and preventing the activation of integrin alpha-5/beta-1 (heterodimer of ITGA5 and ITGB1) by talin or FERMT1. Plays a role in cell proliferation, differentiation, spreading, adhesion and migration in the context of mineralization and bone development and angiogenesis. Stimulates cellular proliferation in a fibronectin-dependent manner. Involved in the regulation of beta-1 integrin-containing focal adhesion (FA) site dynamics by controlling its assembly rate during cell adhesion; inhibits beta-1 integrin clustering within FA by directly competing with talin TLN1, and hence stimulates osteoblast spreading and migration in a fibronectin- and/or collagen-dependent manner. Acts as a guanine nucleotide dissociation inhibitor (GDI) by regulating Rho family GTPases during integrin-mediated cell matrix adhesion; reduces the level of active GTP-bound form of both CDC42 and RAC1 GTPases upon cell adhesion to fibronectin. Stimulates the release of active CDC42 from the membranes to maintain it in an inactive cytoplasmic pool. Participates in the translocation of the Rho-associated protein kinase ROCK1 to membrane ruffles at cell leading edges of the cell membrane, leading to an increase of myoblast cell migration on laminin. Plays a role in bone mineralization at a late stage of osteoblast differentiation; modulates the dynamic formation of focal adhesions into fibrillar adhesions, which are adhesive structures responsible for fibronectin deposition and fibrillogenesis. Plays a role in blood vessel development; acts as a negative regulator of angiogenesis by attenuating endothelial cell proliferation and migration, lumen formation and sprouting angiogenesis by promoting AKT phosphorylation and inhibiting ERK1/2 phosphorylation through activation of the Notch signaling pathway. Promotes transcriptional activity of the MYC promoter","subcellular_location":"Nucleus; Cytoplasm; Cytoplasm, cytoskeleton; Cell membrane; Cell projection, lamellipodium; Cell projection, ruffle","url":"https://www.uniprot.org/uniprotkb/O14713/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ITGB1BP1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ITGB1BP1","total_profiled":1310},"omim":[{"mim_id":"607153","title":"INTEGRIN, BETA-1, BINDING PROTEIN OF, 1; ITGB1BP1","url":"https://www.omim.org/entry/607153"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nuclear bodies","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ITGB1BP1"},"hgnc":{"alias_symbol":["ICAP-1A","ICAP-1B","ICAP1","ICAP1A","ICAP1B","ICAP-1alpha"],"prev_symbol":[]},"alphafold":{"accession":"O14713","domains":[{"cath_id":"2.30.29.30","chopping":"60-195","consensus_level":"high","plddt":93.8981,"start":60,"end":195}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O14713","model_url":"https://alphafold.ebi.ac.uk/files/AF-O14713-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O14713-F1-predicted_aligned_error_v6.png","plddt_mean":79.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ITGB1BP1","jax_strain_url":"https://www.jax.org/strain/search?query=ITGB1BP1"},"sequence":{"accession":"O14713","fasta_url":"https://rest.uniprot.org/uniprotkb/O14713.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O14713/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O14713"}},"corpus_meta":[{"pmid":"11854171","id":"PMC_11854171","title":"KRIT1 association with the integrin-binding protein ICAP-1: a new direction in the elucidation of cerebral cavernous malformations (CCM1) pathogenesis.","date":"2002","source":"Human molecular genetics","url":"https://pubmed.ncbi.nlm.nih.gov/11854171","citation_count":160,"is_preprint":false},{"pmid":"9281591","id":"PMC_9281591","title":"ICAP-1, a novel beta1 integrin cytoplasmic domain-associated protein, binds to a conserved and functionally important NPXY sequence motif of beta1 integrin.","date":"1997","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/9281591","citation_count":146,"is_preprint":false},{"pmid":"9867804","id":"PMC_9867804","title":"Interaction of the integrin beta1 cytoplasmic domain with ICAP-1 protein.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/9867804","citation_count":91,"is_preprint":false},{"pmid":"23317506","id":"PMC_23317506","title":"Mechanism for KRIT1 release of ICAP1-mediated suppression of integrin activation.","date":"2013","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/23317506","citation_count":72,"is_preprint":false},{"pmid":"11807099","id":"PMC_11807099","title":"The integrin cytoplasmic domain-associated protein ICAP-1 binds and regulates Rho family GTPases during cell spreading.","date":"2002","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/11807099","citation_count":51,"is_preprint":false},{"pmid":"11741908","id":"PMC_11741908","title":"Molecular basis for interaction between Icap1 alpha PTB domain and beta 1 integrin.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11741908","citation_count":45,"is_preprint":false},{"pmid":"16741948","id":"PMC_16741948","title":"Integrin cytoplasmic domain-associated protein-1 (ICAP-1) interacts with the ROCK-I kinase at the plasma membrane.","date":"2006","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/16741948","citation_count":22,"is_preprint":false},{"pmid":"28003363","id":"PMC_28003363","title":"Nuclear Localization of Integrin Cytoplasmic Domain-associated Protein-1 (ICAP1) Influences β1 Integrin Activation and Recruits Krev/Interaction Trapped-1 (KRIT1) to the Nucleus.","date":"2016","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28003363","citation_count":21,"is_preprint":false},{"pmid":"16546571","id":"PMC_16546571","title":"Unraveling ICAP-1 function: toward a new direction?","date":"2005","source":"European journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/16546571","citation_count":18,"is_preprint":false},{"pmid":"17654484","id":"PMC_17654484","title":"Integrin Cytoplasmic domain-Associated Protein-1 (ICAP-1) promotes migration of myoblasts and affects focal adhesions.","date":"2008","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/17654484","citation_count":14,"is_preprint":false},{"pmid":"23695561","id":"PMC_23695561","title":"Cocrystal structure of the ICAP1 PTB domain in complex with a KRIT1 peptide.","date":"2013","source":"Acta crystallographica. Section F, Structural biology and crystallization communications","url":"https://pubmed.ncbi.nlm.nih.gov/23695561","citation_count":11,"is_preprint":false},{"pmid":"28049720","id":"PMC_28049720","title":"ICAP-1 monoubiquitylation coordinates matrix density and rigidity sensing for cell migration through ROCK2-MRCKα balance.","date":"2017","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/28049720","citation_count":10,"is_preprint":false},{"pmid":"32005669","id":"PMC_32005669","title":"Serine phosphorylation of the small phosphoprotein ICAP1 inhibits its nuclear accumulation.","date":"2020","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/32005669","citation_count":7,"is_preprint":false},{"pmid":"37252376","id":"PMC_37252376","title":"ITGB1BP1, a Novel Transcriptional Target of CD44-Downstream Signaling Promoting Cancer Cell Invasion.","date":"2023","source":"Breast cancer (Dove Medical Press)","url":"https://pubmed.ncbi.nlm.nih.gov/37252376","citation_count":5,"is_preprint":false},{"pmid":"22711159","id":"PMC_22711159","title":"Concepts and hypothesis: integrin cytoplasmic domain-associated protein-1 (ICAP-1) as a potential player in cerebral cavernous malformation.","date":"2012","source":"Journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/22711159","citation_count":3,"is_preprint":false},{"pmid":"35491946","id":"PMC_35491946","title":"ICAP-1 loss impairs CD8+ thymocyte development and leads to reduced marginal zone B cells in mice.","date":"2022","source":"European journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/35491946","citation_count":1,"is_preprint":false},{"pmid":"39607284","id":"PMC_39607284","title":"RNAi library screening reveals Gβ1, Casein Kinase 2 and ICAP-1 as novel regulators of LFA-1-mediated T cell polarity and migration.","date":"2024","source":"Immunology and cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/39607284","citation_count":0,"is_preprint":false},{"pmid":"41617095","id":"PMC_41617095","title":"ICAP-1 alternative splicing regulates Talin tension polarization in NSCLC durotaxis.","date":"2026","source":"Biochemical pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/41617095","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":10568,"output_tokens":4298,"usd":0.048087,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12358,"output_tokens":4505,"usd":0.087207,"stage2_stop_reason":"end_turn"},"total_usd":0.135294,"stage1_batch_id":"msgbatch_01DUPACZi7AAWwuZiUjseQF4","stage2_batch_id":"msgbatch_018yt7chE3f48PEFtDwtj6AE","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1997,\n      \"finding\": \"ICAP-1 (ITGB1BP1) specifically binds the β1 integrin cytoplasmic domain via the conserved NPXY motif; mutagenesis of Asn and Tyr of the NPXY motif and a Val residue NH2-terminal to it abrogates binding. Two isoforms (ICAP-1α, 200 aa; ICAP-1β, 150 aa) arise from alternative splicing. ICAP-1α is a phosphoprotein whose phosphorylation is enhanced by cell plating on fibronectin and reduced by constitutively active RhoA, linking its modification to integrin-mediated adhesion.\",\n      \"method\": \"Yeast two-hybrid screen, mutational analysis, cell-matrix adhesion assays with phosphorylation readout\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutational dissection of binding interface plus functional phosphorylation assays; foundational paper independently replicated by multiple subsequent studies\",\n      \"pmids\": [\"9281591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"ICAP-1 associates specifically with the β1 integrin cytoplasmic tail (not β2, β3, or β5) via the carboxyl-terminal 14 amino acids of β1. ICAP-1 overexpression markedly increases β1-dependent chemotactic migration through fibronectin-coated filters, and support of β1-dependent migration in CHO cells correlates with ICAP-1 association, establishing a functional role in β1 integrin-dependent cell migration.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation in human cells, cell migration assays with wild-type and mutant β1 constructs, Triton X-100 fractionation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal binding specificity confirmed in cells, functional rescue with mutant integrins, replicated by subsequent labs\",\n      \"pmids\": [\"9867804\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"ICAP-1α contains a PTB (phosphotyrosine-binding) domain (residues 58–200) that recognizes the NPXY motif of β1 integrin. Alanine-scanning and site-directed mutagenesis identified Val787, Val790, and 792NPKY795 of β1 as critical contact residues, and Leu135, Ile138, Ile139, Leu82, and Tyr144 of ICAP-1α as required for the interaction; Leu82/Tyr144 form a hydrophobic pocket that confers β1 specificity by engaging Val787.\",\n      \"method\": \"Alanine-scanning mutagenesis, site-directed mutagenesis guided by PTB-domain homology modeling\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — comprehensive mutagenesis of both binding partners with structural model validation; independently confirmed by crystal structures in 2013\",\n      \"pmids\": [\"11741908\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"KRIT1 binds directly to ICAP-1 via an N-terminal NPXY-like motif in KRIT1; mutagenesis of this NPXY sequence completely abrogates the KRIT1/ICAP-1 interaction. The interaction was confirmed by GST-KRIT1 pulldown of endogenous ICAP-1 from 293T cells.\",\n      \"method\": \"Yeast two-hybrid screen of fetal brain and HeLa cDNA libraries, GST pulldown, site-directed mutagenesis\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — GST pulldown confirms yeast two-hybrid, mutagenesis of binding motif, replicated and extended by crystal structures in 2013\",\n      \"pmids\": [\"11854171\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"ICAP-1 expression inhibits NIH3T3 cell spreading on ECM; this inhibition is counteracted by constitutively active Cdc42, placing ICAP-1 upstream of Cdc42. ICAP-1 binds Cdc42 and Rac1 in vitro, inhibits activation of these GTPases during fibronectin adhesion, reduces GDP dissociation from Cdc42 (both intrinsic and exchange-factor-stimulated), and displaces Cdc42 from cellular membranes, functioning as a guanine nucleotide dissociation inhibitor (GDI).\",\n      \"method\": \"Yeast two-hybrid, in vitro binding assay, PAK-binding GTPase activation assay, GDP dissociation assay, membrane fractionation, epistasis with constitutively active Cdc42\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro biochemical assay for GDI activity plus cell-based epistasis with multiple orthogonal methods in one study\",\n      \"pmids\": [\"11807099\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"ICAP-1 binds the ROCK-I kinase via two binding sites; the proteins form complexes in cells (co-immunoprecipitation) and colocalize at the plasma membrane in lamellipodia and membrane ruffles. ICAP-1 translocates ROCK-I to the plasma membrane independently of β1 integrin ligation or ROCK kinase activity. Direct interaction in lamellipodia was confirmed by FRET between CFP-ICAP-1 and YFP-ROCK during cell spreading.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation, colocalization microscopy, FRET (CFP/YFP fusion proteins), truncation mapping\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP plus FRET demonstrates direct in-cell interaction; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"16741948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ICAP-1 knockdown reduces β1 integrin-dependent migration of C2C12 myoblasts on laminin and endothelial cells on collagen; overexpression increases migration on laminin. Knockdown reduces central focal adhesions; overexpression increases them. ICAP-1 translocates ROCK to membrane ruffles in myoblasts, and ROCK inhibition (Y-27632) phenocopies ICAP-1 knockdown, indicating ICAP-1 regulates β1-dependent migration through ROCK translocation to integrin adhesion sites.\",\n      \"method\": \"RNAi knockdown, overexpression, migration assay, focal adhesion counting, co-immunoprecipitation, YFP-ROCK colocalization\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD and OE with defined cellular phenotype plus pharmacological epistasis; single lab\",\n      \"pmids\": [\"17654484\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structures of KRIT1 in complex with ICAP1 (2.54 Å) and ICAP1 in complex with integrin β1 cytoplasmic tail (3.0 Å) reveal that KRIT1 binds ICAP1 via a bidentate surface that directly competes with integrin β1 for the same site on the ICAP1 PTB domain. KRIT1 thereby antagonizes ICAP1-mediated suppression of β1 integrin 'inside-out' activation. Additionally, KRIT1 contains an N-terminal Nudix domain in a region previously considered unstructured.\",\n      \"method\": \"X-ray crystallography (co-crystal structures), integrin activation assays, competitive binding studies\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — co-crystal structures at near-atomic resolution with functional validation of competitive mechanism; single rigorous study with multiple orthogonal methods\",\n      \"pmids\": [\"23317506\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Co-crystal structure of the ICAP1 PTB domain with a minimal 29-amino-acid KRIT1 peptide (residues 170–198) resolved to 1.7 Å provides the highest-resolution structural detail of the ICAP1-KRIT1 interaction interface.\",\n      \"method\": \"X-ray crystallography (co-crystal structure)\",\n      \"journal\": \"Acta crystallographica. Section F\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution crystal structure; complements and extends the 2013 Molecular Cell structural study\",\n      \"pmids\": [\"23695561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"ICAP1 contains a functional nuclear localization signal (NLS); nuclear localization impairs ICAP1's ability to suppress β1 integrin activation. ICAP1 drives nuclear localization of KRIT1 in a manner dependent on direct ICAP1/KRIT1 interaction, establishing that nuclear-cytoplasmic shuttling of ICAP1 controls both integrin activation state and KRIT1 subcellular distribution.\",\n      \"method\": \"Overexpression, NLS mutagenesis, flow cytometry (integrin activation assay), fluorescence microscopy of nuclear localization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis of NLS with functional readout; single lab, two orthogonal methods (localization + activation assay)\",\n      \"pmids\": [\"28003363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"ICAP-1 is monoubiquitylated by Smurf1; this modification prevents ICAP-1 binding to β1 integrin and alters focal adhesion organization. Non-ubiquitylatable ICAP-1 interferes with fibronectin density sensing. ICAP-1 monoubiquitylation regulates rigidity sensing by increasing MRCKα-dependent cell contractility via myosin phosphorylation independently of substrate rigidity, and acts as a molecular switch from ROCK2-mediated to MRCKα-mediated cell contractility.\",\n      \"method\": \"Ubiquitylation assays (Smurf1 as E3 ligase), non-ubiquitylatable mutant expression, focal adhesion analysis, myosin phosphorylation assays, cell migration on substrates of varying density/stiffness\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — identification of E3 ligase with functional consequences via mutant rescue; single lab, multiple cellular readouts\",\n      \"pmids\": [\"28049720\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ICAP1 nuclear accumulation is inhibited by serine phosphorylation at Ser-10 (and to a lesser extent Ser-25) within its unstructured N-terminal region; phosphorylation-blocking substitutions enhance nuclear accumulation. PAK4 phosphorylates ICAP1 at Ser-10 both in vitro and in cultured cells, and active PAK4 inhibits ICAP1 nuclear accumulation in a Ser-10-dependent manner. This phosphorylation controls nuclear localization of the ICAP1–KRIT1 complex.\",\n      \"method\": \"Phosphorylation-mimicking and phosphorylation-blocking mutagenesis, quantitative fluorescence microscopy, in vitro kinase assay (PAK4), cell-based kinase assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay plus cell-based validation with mutagenesis; single lab but multiple orthogonal methods with rigorous controls\",\n      \"pmids\": [\"32005669\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ICAP-1 loss in mice causes defective single-positive CD8+ thymocyte generation without affecting integrin α4β1-dependent adhesion in thymocytes; ICAP-1 displays strong nuclear distribution in thymocytes and its absence correlates with reduced Runx3 levels in SP CD8+ thymocytes. In spleen, ICAP-1 loss upregulates α4β1-mediated adhesion of T and B cells and reduces proliferation, with a decrease in marginal zone B cells.\",\n      \"method\": \"ICAP-1 knockout mice, flow cytometry, nuclear/cytoplasmic fractionation, adhesion assays, proliferation assays\",\n      \"journal\": \"European journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean KO with defined phenotypes but single lab, no direct mechanistic link between nuclear ICAP-1 and Runx3 regulation established\",\n      \"pmids\": [\"35491946\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"ICAP-1 knockdown in primary human T cells impairs LFA-1 (αLβ2 integrin)-directed cell polarity, velocity, and transmigration toward SDF-1, revealing a role for ICAP-1 in β2 integrin-mediated T cell migration in addition to its established β1 integrin functions.\",\n      \"method\": \"RNAi screen, primary T cell knockdown, cell polarity/morphology assay, transmigration assay\",\n      \"journal\": \"Immunology and cell biology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, knockdown phenotype with no molecular mechanism established for the β2 integrin connection\",\n      \"pmids\": [\"39607284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"ICAP-1α isoform (but not ICAP-1β) reduces aggressiveness and directionality of NSCLC cells on stiffness-gradient substrates; ICAP-1α has extensive subcellular distribution, inhibits integrin activity and talin tension. Matrix stiffening triggers a shift in ICAP-1 isoform expression, positioning ICAP-1 as a mechanotransducer relaying signals from β1 integrin to talin.\",\n      \"method\": \"Isoform-specific expression, cell-directed matrix (CDM) migration assays, talin tension sensor (FRET-based), integrin activity assays\",\n      \"journal\": \"Biochemical pharmacology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — FRET-based talin tension measurement plus functional migration assay; single lab, novel finding not yet replicated\",\n      \"pmids\": [\"41617095\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ITGB1BP1/ICAP-1 is a PTB-domain phosphoprotein that specifically binds the NPXY motif of the β1 integrin cytoplasmic tail to suppress integrin 'inside-out' activation; KRIT1 competitively displaces ICAP-1 from β1 integrin (as revealed by co-crystal structures) to relieve this suppression, while nuclear-cytoplasmic shuttling of ICAP-1—controlled by PAK4-mediated Ser-10 phosphorylation and Smurf1-mediated monoubiquitylation—regulates both integrin activation state and KRIT1 nuclear localization; additionally, ICAP-1 modulates cell migration and mechanosensing by acting as a GDI for Cdc42/Rac1, translocating ROCK-I to β1 integrin adhesion sites, and switching between ROCK2- and MRCKα-dependent contractility pathways in response to matrix density and rigidity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ITGB1BP1 (ICAP-1) is a PTB-domain phosphoprotein that governs the activation state of β1 integrin and thereby controls cell adhesion, migration, and mechanosensing [#0, #1]. Its PTB domain (residues 58–200) recognizes the NPXY motif of the β1 integrin cytoplasmic tail with strict β1 selectivity, conferred by a hydrophobic pocket (Leu82/Tyr144) that engages Val787 of the integrin [#0, #2], and this binding suppresses 'inside-out' integrin activation. The cerebral cavernous malformation protein KRIT1 binds the same PTB surface through an N-terminal NPXY-like motif, and co-crystal structures show that KRIT1 directly competes with β1 integrin for ICAP-1, relieving its suppressive effect on integrin activation [#3, #7, #8]. ICAP-1 shuttles between cytoplasm and nucleus via a functional NLS, with nuclear localization disabling its integrin-suppressive activity while simultaneously driving KRIT1 into the nucleus; this shuttling is controlled by PAK4-mediated Ser-10 phosphorylation, which restrains nuclear accumulation, and by Smurf1-mediated monoubiquitylation, which blocks β1 binding [#9, #10, #11]. Beyond integrin binding, ICAP-1 acts as a guanine nucleotide dissociation inhibitor for Cdc42 and Rac1 and recruits ROCK-I to β1 integrin adhesion sites, integrating these activities into mechanotransduction—including a Smurf1-controlled switch between ROCK2- and MRCKα-dependent contractility and isoform-specific (ICAP-1α) tuning of talin tension on stiff matrices [#4, #5, #6, #10, #14]. In vivo, ICAP-1 loss in mice disrupts CD8+ single-positive thymocyte generation and dysregulates β4β1-mediated lymphocyte adhesion [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established the founding molecular interaction—that ICAP-1 specifically engages the β1 integrin cytoplasmic tail via its NPXY motif and is regulated by adhesion-dependent phosphorylation—defining ICAP-1 as an integrin-tail-binding adaptor.\",\n      \"evidence\": \"Yeast two-hybrid, NPXY mutagenesis, and adhesion/phosphorylation assays on fibronectin\",\n      \"pmids\": [\"9281591\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the interaction for integrin activation not yet defined\", \"Kinase responsible for ICAP-1 phosphorylation unidentified\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Demonstrated that the ICAP-1/β1 interaction is functionally consequential, linking it to β1-dependent chemotactic migration and confirming binding specificity for β1 over other β subunits.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP in human cells, and migration assays with wild-type/mutant β1 in CHO cells\",\n      \"pmids\": [\"9867804\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether ICAP-1 activates or suppresses integrin not resolved\", \"Downstream effectors of migration phenotype unknown\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Mapped the binding interface to the PTB domain at residue resolution, explaining the structural basis of β1 specificity through identified contact residues on both partners.\",\n      \"evidence\": \"Alanine-scanning and site-directed mutagenesis guided by PTB homology modeling\",\n      \"pmids\": [\"11741908\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Lacked a crystal structure to confirm the modeled interface\", \"Regulation of the interface in cells unaddressed\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identified KRIT1 as a second NPXY-motif partner of ICAP-1, foreshadowing a competition between two distinct ligands for the same adaptor.\",\n      \"evidence\": \"Yeast two-hybrid screen and GST-KRIT1 pulldown of endogenous ICAP-1, with NPXY mutagenesis\",\n      \"pmids\": [\"11854171\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether KRIT1 and β1 bind the same ICAP-1 surface not yet shown\", \"Functional outcome of KRIT1 binding undefined\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Revealed an integrin-independent activity, showing ICAP-1 functions as a GDI for Cdc42/Rac1 to restrain cell spreading, broadening its role into Rho-family GTPase regulation.\",\n      \"evidence\": \"In vitro binding and GDP-dissociation assays, GTPase activation assays, membrane fractionation, and epistasis with constitutively active Cdc42\",\n      \"pmids\": [\"11807099\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Integration of GDI activity with integrin-tail binding unclear\", \"In vivo relevance of GDI function not tested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Connected ICAP-1 to actomyosin regulation by showing it binds and translocates ROCK-I to the plasma membrane independently of integrin ligation or kinase activity.\",\n      \"evidence\": \"Yeast two-hybrid, reciprocal co-IP, FRET between CFP-ICAP-1 and YFP-ROCK, and truncation mapping\",\n      \"pmids\": [\"16741948\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of ROCK translocation not yet shown\", \"Relationship to GDI and integrin functions unresolved\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Linked ROCK translocation to physiology, showing ICAP-1 regulates β1-dependent migration and focal adhesion organization through ROCK recruitment to adhesion sites.\",\n      \"evidence\": \"RNAi, overexpression, migration and focal-adhesion assays, and pharmacological ROCK inhibition (Y-27632) in myoblasts and endothelial cells\",\n      \"pmids\": [\"17654484\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Direct molecular link between ICAP-1 and adhesion-site ROCK localization not structurally defined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Resolved the central mechanistic question by crystallography, proving that KRIT1 competes with β1 integrin for the same ICAP-1 PTB surface to antagonize ICAP-1-mediated suppression of integrin activation.\",\n      \"evidence\": \"Co-crystal structures of KRIT1–ICAP1 and ICAP1–β1 tail (and a 1.7 Å ICAP1–KRIT1 peptide structure), with integrin activation and competitive binding assays\",\n      \"pmids\": [\"23317506\", \"23695561\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the competition is regulated dynamically in cells not addressed\", \"Spatial coordination of the two ligand pools unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Established nuclear-cytoplasmic shuttling as a regulatory layer, showing ICAP-1 has an NLS whose use both disables integrin suppression and drives KRIT1 into the nucleus.\",\n      \"evidence\": \"NLS mutagenesis with integrin activation flow cytometry and fluorescence microscopy\",\n      \"pmids\": [\"28003363\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signals triggering shuttling not identified here\", \"Nuclear function of ICAP-1/KRIT1 undefined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified monoubiquitylation as a switch, showing Smurf1 modifies ICAP-1 to block β1 binding and toggle contractility from ROCK2- to MRCKα-dependent, coupling ICAP-1 to rigidity sensing.\",\n      \"evidence\": \"Ubiquitylation assays with Smurf1, non-ubiquitylatable mutant rescue, focal-adhesion and myosin-phosphorylation assays, migration on varying density/stiffness substrates\",\n      \"pmids\": [\"28049720\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Ubiquitylation site(s) and deubiquitylase not defined\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined the kinase input controlling shuttling, showing PAK4 phosphorylates ICAP-1 at Ser-10 to inhibit nuclear accumulation of the ICAP1–KRIT1 complex.\",\n      \"evidence\": \"Phosphomimetic/blocking mutagenesis, quantitative microscopy, and in vitro plus cell-based PAK4 kinase assays\",\n      \"pmids\": [\"32005669\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Upstream signals activating PAK4 toward ICAP-1 unknown\", \"Phosphatase reversing Ser-10 unidentified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Provided in vivo physiological context, showing ICAP-1 loss disrupts CD8+ thymocyte generation and dysregulates β4β1-mediated lymphocyte adhesion, with strong nuclear ICAP-1 in thymocytes.\",\n      \"evidence\": \"ICAP-1 knockout mice with flow cytometry, nuclear/cytoplasmic fractionation, and adhesion/proliferation assays\",\n      \"pmids\": [\"35491946\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct mechanistic link between nuclear ICAP-1 and Runx3 established\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended ICAP-1 function beyond β1 integrins, implicating it in LFA-1 (β2 integrin)-directed T cell polarity and transmigration.\",\n      \"evidence\": \"RNAi knockdown in primary human T cells with polarity and transmigration assays toward SDF-1\",\n      \"pmids\": [\"39607284\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No molecular mechanism established for the β2 integrin connection\", \"Single lab, knockdown only\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Cast ICAP-1 as an isoform-specific mechanotransducer, showing ICAP-1α (not β) reduces cancer cell aggressiveness and dampens talin tension on stiffness gradients.\",\n      \"evidence\": \"Isoform-specific expression, cell-derived matrix migration assays, FRET talin tension sensor, and integrin activity assays in NSCLC cells\",\n      \"pmids\": [\"41617095\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab, not replicated\", \"Mechanism by which stiffness shifts isoform expression undefined\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple regulatory inputs—phosphorylation, monoubiquitylation, nuclear shuttling, and isoform switching—are integrated in real time at adhesion sites, and what ICAP-1/KRIT1 does in the nucleus, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Nuclear function of the ICAP-1/KRIT1 complex uncharacterized\", \"Quantitative hierarchy of competing regulatory modifications not established\", \"Mechanism coupling β2 integrin function to known β1/KRIT1 biology unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [4, 7, 9]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 2, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 6]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9, 11, 12]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [0, 1, 7]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [4, 7, 10]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"ITGB1\", \"KRIT1\", \"CDC42\", \"RAC1\", \"ROCK1\", \"PAK4\", \"SMURF1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}