{"gene":"ITGA2","run_date":"2026-06-10T01:55:23","timeline":{"discoveries":[{"year":1989,"finding":"ITGA2 (VLA-2 alpha 2 subunit, GPIa) encodes a 1,181 amino acid protein with a signal peptide, long extracellular domain (1,103 aa), transmembrane domain, and short cytoplasmic segment (22 aa). The sequence contains three metal-binding domains (DXDXDGXXD), 20 cysteine residues, and a unique 191-amino acid I-domain insert (residues ~140-359) not found in other integrin alpha chains at the time, with homology to von Willebrand factor A1/A3 domains and cartilage matrix protein—regions associated with collagen binding.","method":"cDNA cloning, direct NH2-terminal protein sequencing, sequence analysis","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — primary sequence determination by cDNA cloning confirmed by direct protein sequencing; foundational structural characterization replicated across subsequent studies","pmids":["2545729"],"is_preprint":false},{"year":1989,"finding":"GPIa/IIa (integrin alpha2beta1, ITGA2/ITGB1) directly mediates platelet adhesion to collagen independently of plasma adhesive proteins. Monoclonal antibody 6F1 against GPIa/IIa blocked >95% of collagen-induced platelet adhesion in the absence of plasma and nearly completely inhibited collagen-induced platelet aggregation, establishing GPIa/IIa as a direct collagen receptor.","method":"Monoclonal antibody inhibition of platelet adhesion and aggregation assays; 6F1 affinity-purified GPIa/IIa complex; collagen-coated bead agglutination assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — antibody blockade with functional readout replicated across multiple assay systems and subsequently confirmed by many independent labs","pmids":["2546619"],"is_preprint":false},{"year":1994,"finding":"The I-domain of ITGA2 (residues 140–359) contains the collagen-binding site of integrin alpha2beta1. Mutations of Asp-151 and Asp-254 block alpha2beta1 binding to collagen, while a small region (residues 173–259) within the I-domain is recognized by function-blocking anti-alpha2 monoclonal antibodies (6F1, RMAC11, 12F1, AA10) that block both collagen and echovirus 1 binding. Collagen and echovirus 1 binding sites are adjacent or overlapping within the I-domain.","method":"Interspecies (human/bovine) alpha2 chimeras, site-directed mutagenesis, antibody epitope mapping","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — site-directed mutagenesis combined with chimera mapping in functional binding assays; independently confirmed by recombinant I-domain studies","pmids":["7511592"],"is_preprint":false},{"year":1994,"finding":"The recombinant I-domain of ITGA2 alpha2 subunit is sufficient for collagen binding, and this binding is divalent cation-independent (unlike full-length integrin binding). Thr-221 within the I-domain is a critical residue for collagen binding to both alpha2beta1 and the isolated I-domain fragment.","method":"Recombinant I-domain expression, collagen-binding assay, site-directed mutagenesis (Thr-221), divalent cation chelation experiments","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro binding with mutagenesis validation; identifies a specific residue for collagen contact","pmids":["7523399"],"is_preprint":false},{"year":1994,"finding":"GPIa/IIa (integrin alpha2beta1) is a major and universal platelet receptor mediating adhesion to collagen types I–VIII under both static conditions and flow. Monoclonal antibody 176D7 against GPIa (ITGA2) completely inhibited platelet adhesion to all collagen types tested under stasis and flow conditions.","method":"Platelet adhesion assays to multiple collagen types under static and flow conditions; monoclonal antibody inhibition studies","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic functional inhibition across eight collagen types and multiple shear rates; confirmed independently","pmids":["8118028"],"is_preprint":false},{"year":1994,"finding":"The HPA-5 alloantigen system on GPIa/IIa (ITGA2) is caused by an A→G polymorphism at base pair 1648 of the GPIa coding sequence, resulting in a Glu/Lys substitution at amino acid position 505 of the mature protein (HPA-5a = Glu505; HPA-5b = Lys505).","method":"RT-PCR, cDNA sequencing, allele-specific restriction enzyme analysis (Mnl I PCR-ASRA)","journal":"British journal of haematology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct sequencing of cDNA from genotyped individuals; confirmed by multiple independent laboratories","pmids":["7913826"],"is_preprint":false},{"year":1994,"finding":"The Br (HPA-5) polymorphism of GPIa is encoded by a single base change at position 1648 on platelet GPIa mRNA, causing an amino acid substitution at position 505 of mature GPIa. This polymorphism is located within a 144 bp exon of the GPIa (ITGA2) gene flanked by two introns (~1.7 and ~1.9 kb).","method":"PCR of genomic DNA, RFLP analysis with MnlI endonuclease, correlation with serological MAIPA typing","journal":"Thrombosis and haemostasis","confidence":"High","confidence_rationale":"Tier 1 / Strong — genomic structure determined by PCR and confirmed by correlation with serological phenotyping","pmids":["7916494"],"is_preprint":false},{"year":1997,"finding":"The recombinant alpha2 I-domain (residues D145–S334) fused to maltose-binding protein binds immobilized collagen type I in a concentration-dependent and Mg2+-dependent manner (inhibited by EDTA or Ca2+ but sustained in Mg2+), and the I-domain alone can inhibit platelet adhesion to collagen and collagen-induced platelet aggregation (IC50 ~0.7 µM for both), confirming the I-domain as the collagen-binding site of alpha2beta1.","method":"Recombinant I-domain expression and purification, ELISA binding assay, platelet adhesion inhibition assay, platelet aggregation inhibition assay","journal":"Thrombosis and haemostasis","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted recombinant protein with functional inhibition assays; single lab but multiple orthogonal methods","pmids":["9184414"],"is_preprint":false},{"year":1999,"finding":"The C807T dimorphism (TTC/TTT in codon 224) of the GPIa (ITGA2) cDNA is associated with variation in GPIa/IIa receptor density on the platelet surface, with the 807T allele associated with higher GPIa/IIa surface density.","method":"Flow cytometry for platelet GPIa/IIa levels; PCR genotyping of C807T polymorphism","journal":"British journal of haematology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single genotype–phenotype association study; replicated in other studies linking C807T to receptor density","pmids":["10468872"],"is_preprint":false},{"year":1999,"finding":"Both the 807C/T and HPA-5 polymorphisms of GPIa (ITGA2) independently correlate with GPIa/IIa molecule number on the platelet surface, with 807T and HPA-5b alleles associated with increased receptor density. The two polymorphisms are genetically linked (HPA-5b linked to ~15.8% of 807C alleles).","method":"Flow cytometry for platelet GPIa/IIa levels; PCR-RFLP genotyping; 159 blood donors","journal":"Transfusion","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — quantitative flow cytometry phenotype-genotype correlation; single study but consistent with prior data","pmids":["10220262"],"is_preprint":false},{"year":2001,"finding":"Rhodocytin from Calloselasma rhodostoma venom directly binds to GPIa/IIa (integrin alpha2beta1, ITGA2) independently of divalent cations, induces platelet aggregation, and activates GPIa/IIa-associated Src and Lyn kinases. Src constitutively associates with GPIa/IIa and its activity transiently increases after rhodocytin stimulation, leading to Cas tyrosine phosphorylation; downstream signals include Syk and PLCγ2 phosphorylation and Ca2+ mobilization.","method":"Anti-GPIa mAb blockade, rhodocytin-coupled bead binding assay, liposome-reconstitution with recombinant GPIa/IIa, GPIa immunoprecipitation, in vitro kinase assay, Western blotting, cytochalasin D inhibition","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted direct binding to recombinant GPIa/IIa, in vitro kinase assays, immunoprecipitation; single lab with multiple orthogonal methods","pmids":["11038351"],"is_preprint":false},{"year":2001,"finding":"DX5 monoclonal antibody recognizes CD49b (ITGA2, alpha2 integrin, VLA-2), as identified by retrovirus-mediated expression cloning from an NK cell cDNA library. Binding of DX5 to NK cells and CD49b transfectants is blocked by other anti-CD49b mAbs. CD49b expression on NK cells is progressively lost upon IL-2-driven proliferation.","method":"Retrovirus-mediated expression cloning; transfection and flow cytometry; antibody competition assays","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 / Strong — expression cloning with functional antibody competition confirmation; establishes molecular identity of DX5 antigen as CD49b","pmids":["11466327"],"is_preprint":false},{"year":2003,"finding":"EMS16, a C-type lectin-like protein from Echis multisquamatus venom, is a potent and selective inhibitor of GPIa/IIa (integrin alpha2beta1). Its crystal structure at 1.9 Å resolution reveals a heterodimer with domain swapping of the central loop and a unique positively charged electrostatic patch on the concave surface that may interact with the I-domain of GPIa/IIa.","method":"X-ray crystallography at 1.9 Å resolution; structural analysis","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure determined at high resolution; single study but rigorous structural method","pmids":["14580195"],"is_preprint":false},{"year":1993,"finding":"GPIa/IIa (integrin alpha2beta1, ITGA2) specifically binds thrombospondin (TSP) in an ion-independent manner (Kd = 0.69 µM), whereas GPIIb/IIIa binding to TSP is divalent cation-dependent. Anti-GPIa/IIa antibody 6F1 inhibits GPIa/IIa binding to TSP; GPIa/IIa and GPIIb/IIIa bind to distinct sites on TSP.","method":"Saturable binding assay with purified GPIa/IIa and GPIIb/IIIa; competition experiments; antibody inhibition; ion dependence experiments","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct biochemical binding assay with purified proteins, single study","pmids":["8240284"],"is_preprint":false},{"year":2007,"finding":"The ITGA2 promoter is regulated by transcription factors including Sp1 (at SNP C-52T binding site). PARP-1 and Ku80/70 bind specifically and with enhanced affinity to the longer (CA)12 repeat allele in the 5'-regulatory region of ITGA2, coinciding with enhanced alpha2beta1 expression. A CpG-rich ITGA1 promoter region is selectively methylated in megakaryocytic cells, but ITGA2 promoter methylation does not change during megakaryocyte differentiation—indicating distinct epigenetic regulation for ITGA1 vs. ITGA2.","method":"Bisulfite genomic sequencing, promoter-luciferase reporter assay, transcriptome analysis, 5-aza-2'-deoxycytidine treatment","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (bisulfite sequencing, reporter assays, pharmacological demethylation); single lab","pmids":["17669516"],"is_preprint":false},{"year":2010,"finding":"PARP-1 and Ku80/70 bind specifically and with enhanced affinity to the longer (CA)12 repeat allele in the 5'-regulatory region of ITGA2 (beginning at -605). This enhanced binding correlates with increased ITGA2/alpha2beta1 expression. Together with SNP C-52T (Sp1 binding site), four ITGA2 haplotypes can be ranked for transcriptional activity: (CA)12/-52C > (CA)11/-52C > (CA)11/-52T > (CA)10/-52T.","method":"DNA affinity chromatography, chromatin immunoprecipitation (ChIP), promoter-luciferase reporter assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — DNA affinity chromatography and ChIP with functional reporter assays; single lab","pmids":["20090957"],"is_preprint":false},{"year":2013,"finding":"CD49b (ITGA2) is required for migration of memory CD4 T-cell precursors from blood into the bone marrow sinusoidal endothelium. CD49b-deficient or CD49b-blocked memory CD4 T-cell precursors fail to home to the bone marrow. In the marrow, memory CD4 T cells contact stromal cells expressing collagen II (a ligand for CD49b).","method":"CD49b-deficient mice, antibody blockade, adoptive transfer, in vivo migration assays, confocal imaging of stromal cell interactions","journal":"Immunology and cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout combined with antibody blockade and adoptive transfer; single lab","pmids":["23897120"],"is_preprint":false},{"year":2014,"finding":"EZH2 epigenetically regulates ITGA2 expression (via chromatin immunoprecipitation-confirmed direct targeting), and de-repression of ITGA2 following EZH2 inhibition (genetic or pharmacological with DZNep and GSK343) activates ITGA2 signaling to increase cofilin phosphorylation at Ser3, thereby reducing colorectal cancer cell migration.","method":"siRNA knockdown, pharmacological EZH2 inhibition (DZNep, GSK343), chromatin immunoprecipitation, western blotting for phospho-cofilin, cell migration assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-confirmed epigenetic regulation with pharmacological and genetic perturbation and functional migration readout; single lab","pmids":["25549357"],"is_preprint":false},{"year":2015,"finding":"ITGA2 promoter CpG island methylation inversely regulates ITGA2 expression in prostate cancer: highly methylated in non-invasive LNCaP cells (low expression) and hypomethylated in highly metastatic PC3 and 22Rv1 cells (high expression). siRNA knockdown of ITGA2 reduces prostate cancer cell migration.","method":"Bisulfite sequencing of ITGA2 promoter CpG island, qPCR, siRNA knockdown, cell migration scratch assay","journal":"The Prostate","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bisulfite sequencing correlated with expression and confirmed functionally by siRNA knockdown; single lab","pmids":["25662931"],"is_preprint":false},{"year":2015,"finding":"Human Th17 cells co-express IL-7R and the collagen-binding integrin alpha2beta1 (CD49b/ITGA2). IL-7 increases Th17 adhesion to collagen via alpha2beta1. Co-engagement of IL-7R and alpha2beta1 cooperatively enhances IL-17 production and osteoclastogenic function via JAK/PI3K/AKT and MAPK/ERK pathways. Blockade of alpha2beta1 with a neutralizing mAb inhibited IL-7-induced bone loss in vivo.","method":"Flow cytometry, adhesion assays to collagen, neutralizing antibody blockade in vivo, ELISA for IL-17, osteoclast differentiation assay, signaling pathway inhibition","journal":"Journal of immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays in vitro and in vivo; single lab with functional antibody blockade","pmids":["26408663"],"is_preprint":false},{"year":2019,"finding":"ITGA2 interacts with STAT3 (demonstrated by co-immunoprecipitation) and upregulates STAT3 phosphorylation, which transcriptionally increases PD-L1 expression in pancreatic cancer cells. ITGA2 overexpression promotes cancer cell proliferation and invasion; ITGA2 knockdown inhibits these processes.","method":"Co-immunoprecipitation, Western blot, RT-qPCR, RNA-seq, MTS assay, colony formation assay, transwell assay, immunohistochemistry","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP establishes protein-protein interaction; multiple functional assays; single lab","pmids":["31818309"],"is_preprint":false},{"year":2018,"finding":"Blockade of ITGA2 with a specific antibody induces apoptosis in ITGA2-overexpressing gastric cancer cells by upregulating RhoA-p38 MAPK signaling and promoting expression of Bim, Apaf-1, and Caspase-9. At lower doses, anti-ITGA2 antibody inhibits gastric cancer cell migration by downregulating N-WASP, PAK, and LIMK, thereby impairing actin organization.","method":"Anti-ITGA2 antibody treatment, Western blot, flow cytometry apoptosis assay, cell migration assay","journal":"Biological procedures online","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — antibody-mediated functional blockade with pathway-level Western blot validation; single lab","pmids":["29743821"],"is_preprint":false},{"year":2021,"finding":"Cyclic mechanical stretch promotes proliferation and inhibits apoptosis of nucleus pulposus cells via the ITGA2/PI3K/AKT signaling pathway. Downregulation of ITGA2 by RNA interference abrogates stretch-induced PI3K/AKT activation and blocks stretch-induced COL2A1 expression and cell proliferation.","method":"Cyclic tensile stress application, microarray gene expression analysis, Western blot, RNA interference (siRNA), MTT assay, flow cytometry","journal":"Oxidative medicine and cellular longevity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA interference validates pathway dependency; single lab with multiple orthogonal methods","pmids":["33815660"],"is_preprint":false},{"year":2022,"finding":"ITGA2 localizes to the nucleus in pancreatic cancer cells and inhibits the non-homologous end joining (NHEJ) DNA repair pathway by restraining recruitment of DNA-PKcs to the Ku70/80 heterodimer during DNA damage response, thereby sensitizing cells to radiotherapy.","method":"Nuclear fractionation, TCGA data analysis (genome stability parameters), NHEJ activity assay, DNA-PKcs/Ku70/80 immunoprecipitation, radiation sensitivity assays","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct biochemical demonstration of impaired DNA-PKcs recruitment to Ku70/80 with functional radiation sensitivity readout; single lab","pmids":["35998796"],"is_preprint":false},{"year":2021,"finding":"ITGA2 overexpression promotes esophageal squamous cell carcinoma cell invasion and migration via FAK/AKT pathway activation and EMT induction. Treatment with AKT inhibitor MK-2206 rescues the ESCC progression caused by ITGA2 overexpression, placing ITGA2 upstream of FAK/AKT in this context.","method":"siRNA knockdown, overexpression, Western blot, Transwell assay, wound healing assay, xenograft tumor model, AKT inhibitor (MK-2206) rescue experiment","journal":"OncoTargets and therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological rescue places ITGA2 upstream of FAK/AKT; multiple functional assays; single lab","pmids":["34113124"],"is_preprint":false},{"year":2023,"finding":"BACH1 transcription factor directly binds the upstream promoter region of ITGA2 (confirmed by ChIP and dual-luciferase reporter assay) to transcriptionally activate ITGA2 expression, and the BACH1-ITGA2 axis promotes lung adenocarcinoma cell migration and invasion by activating the FAK-RAC1-PAK signaling pathway and regulating cytoskeletal organization.","method":"Chromatin immunoprecipitation (ChIP), dual-luciferase reporter assay, RNA sequencing, Western blot, cell adhesion assay, migration/invasion assays","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct promoter binding confirmed by ChIP and luciferase reporter; downstream signaling validated by Western blot; single lab","pmids":["37311571"],"is_preprint":false},{"year":2022,"finding":"Elevated ITGA2 expression in intrahepatic cholangiocarcinoma cells promotes clonogenic growth induced by collagen type I. ITGA2 depletion or integrin alpha2beta1-selective inhibitor treatment abolishes robust iCCA cell interaction with collagen type I and blocks collagen type I-induced colony growth (3–6 fold enhancement).","method":"ITGA2 siRNA depletion, integrin alpha2beta1-selective inhibitor, cell adhesion assay, colony formation assay in 4 iCCA cell lines vs. non-cancerous cholangiocyte line","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic and pharmacological inhibition with functional colony growth readout; four cell lines compared; single lab","pmids":["36575207"],"is_preprint":false},{"year":2024,"finding":"Loss of both ITGA1 and ITGA2 (via genomic deletion or TEAD1 loss) activates epithelial-to-mesenchymal transition in benign prostate epithelial cells via enhanced secretion and autocrine activation of TGFβ1 and nuclear targeting of YAP1, converting cells to tumorigenic in vivo. TEAD1 is identified as a key transcriptional regulator of ITGA1 and ITGA2 expression.","method":"Genomic deletion (CRISPR-Cas9), in vitro invasion assays, in vivo tumorigenicity assay, genome-wide co-expression analysis, EMT marker Western blot, TGFβ1 ELISA","journal":"Advanced science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR-mediated loss-of-function with in vitro and in vivo functional readout; mechanistic pathway placement via TGFβ1/YAP1; single lab","pmids":["38169150"],"is_preprint":false},{"year":2020,"finding":"ITGA2 promotes breast cancer stemness and metastasis downstream of miR-206 (direct miR-206 target). ITGA2 knockdown suppresses mammosphere formation, pluripotency marker expression, cell cycling (G1 arrest), migration, and invasion, and reduces lung metastasis. ITGA2 overexpression reverses miR-206-induced G1 arrest. RNA-seq reveals ITGA2 regulates CCND1 (cell cycle) and ACLY (lipid metabolism) as downstream targets.","method":"siRNA knockdown, miRNA overexpression/inhibition, RNA sequencing, mammosphere formation assay, flow cytometry cell cycle analysis, Transwell migration/invasion, lung metastasis in vivo model","journal":"Genes & diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic rescue experiments with RNA-seq for downstream target identification; multiple functional assays; single lab","pmids":["34179312"],"is_preprint":false},{"year":2019,"finding":"ADAR1 p110 enhances adhesion of hepatocellular carcinoma cells to extracellular matrix by upregulating ITGA2 at both mRNA and protein levels. ADAR1 p110 overexpression promotes HCC metastasis in an orthotopic xenograft mouse model, and positive correlation between ADAR1 and ITGA2 was confirmed in patient HCC specimens.","method":"Lentivirus-mediated ADAR1 overexpression/knockdown, in vitro cell adhesion assay, Western blot, RT-PCR, orthotopic xenograft mouse model, IHC of patient samples","journal":"Medical science monitor","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — lentiviral gain/loss-of-function with functional adhesion assay and in vivo validation; single lab","pmids":["30798327"],"is_preprint":false},{"year":2021,"finding":"miR-99a-3p suppresses PTC metastasis by targeting GRP94; GRP94 overexpression reverses miR-99a-3p inhibition of metastasis. The miR-99a-3p/GRP94 axis exerts its effect by inhibiting the expression and cytoplasmic relocation of ITGA2, implicating ITGA2 localization (cytoplasmic vs. membrane) as functionally important for metastasis.","method":"miRNA overexpression/inhibition, siRNA knockdown, subcellular fractionation/localization, EMT markers, invasion assay, in vivo xenograft model","journal":"Acta biochimica et biophysica Sinica","confidence":"Low","confidence_rationale":"Tier 3 / Weak — indirect evidence for ITGA2 localization; single lab, no direct imaging of ITGA2 trafficking mechanism","pmids":["34687203"],"is_preprint":false},{"year":2023,"finding":"In ovarian cancer metastasis, macrophage-stimulated mesothelial cells upregulate ITGA2 expression via JNK and Akt signaling pathways; knockdown of ITGA2 in macrophage-conditioned mesothelial cells significantly reduces ovarian cancer cell adhesion to mesothelial cells.","method":"mRNA sequencing, siRNA knockdown, signaling pathway inhibition (JNK, Akt inhibitors), cell adhesion assay","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with functional adhesion readout; pathway inhibitors identify upstream regulators; single lab","pmids":["36766725"],"is_preprint":false},{"year":2025,"finding":"LncRNA-ITGA2 is an enhancer-associated lncRNA that, in a NONO-dependent manner, mediates chromatin looping interactions between the ITGA2 enhancer and ITGA2 promoter, increases H3K27 acetylation at both the enhancer and promoter, and thereby upregulates ITGA2 expression to promote vascular smooth muscle cell proliferation and migration.","method":"CUT&Tag, promoter capture Hi-C, microarray, CRISPR-Cas9 knockout of lncRNA-ITGA2 and NONO, RNA sequencing, chromatin immunoprecipitation sequencing (ChIP-seq), CHIRP, RIP, carotid artery wire injury mouse model","journal":"Circulation research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiomics approach with CRISPR knockout validation and in vivo model; mechanistic regulation of ITGA2 expression established; single lab","pmids":["40321134"],"is_preprint":false}],"current_model":"ITGA2 encodes the alpha2 subunit of integrin alpha2beta1 (GPIa/IIa, VLA-2, CD49b), which functions as a direct collagen receptor via its I-domain (residues ~140–359), with Thr-221, Asp-151, and Asp-254 being critical for collagen binding; the receptor mediates platelet adhesion to collagen types I–VIII under static and flow conditions, constitutively associates with Src/Lyn kinases to transduce activation signals upon ligand engagement, binds thrombospondin independently of divalent cations, regulates cancer cell migration, invasion, and stemness through FAK/AKT, RhoA-p38 MAPK, STAT3-PD-L1, and PI3K/AKT pathways, and in the nucleus inhibits NHEJ DNA repair by blocking DNA-PKcs recruitment to Ku70/80; its expression is regulated transcriptionally by TEAD1, BACH1, HOXD3, and PARP-1/Ku80 binding to a CA-repeat promoter element, and epigenetically by CpG methylation and EZH2-mediated histone modification."},"narrative":{"mechanistic_narrative":"ITGA2 encodes the alpha2 subunit of integrin alpha2beta1 (GPIa/IIa, VLA-2, CD49b), a heterodimeric cell-surface receptor whose principal function is direct, high-affinity binding to collagen and related matrix ligands to mediate cell adhesion, signaling, and motility [PMID:2545729, PMID:2546619, PMID:8118028]. The collagen-binding activity resides in a unique 191-residue I-domain insert (~residues 140–359) homologous to von Willebrand factor A domains; the recombinant I-domain alone is sufficient for collagen binding, with Asp-151, Asp-254 and Thr-221 critical for ligand contact, and this isolated-domain binding is divalent-cation-independent in contrast to the Mg2+-dependence of the intact receptor [PMID:2545729, PMID:7511592, PMID:7523399, PMID:9184414]. On platelets, alpha2beta1 is the major universal receptor for collagen types I–VIII under both static and flow conditions and additionally binds thrombospondin at a distinct, ion-independent site [PMID:2546619, PMID:8118028, PMID:8240284]. Ligand engagement triggers outside-in signaling through a constitutively associated Src/Lyn module, leading to Cas, Syk and PLCgamma2 phosphorylation and Ca2+ mobilization, as revealed by the snake-venom agonist rhodocytin [PMID:11038351]. Beyond platelets, ITGA2 drives leukocyte trafficking and inflammatory function—homing of memory CD4 T-cell precursors to bone marrow and IL-7-cooperative Th17 osteoclastogenesis—and in epithelial and cancer cells it controls adhesion, migration, invasion, EMT and stemness through FAK/AKT, RhoA-p38 MAPK, STAT3–PD-L1 and PI3K/AKT signaling [PMID:23897120, PMID:26408663, PMID:31818309, PMID:29743821, PMID:34113124, PMID:34179312]. A non-canonical nuclear pool of ITGA2 inhibits non-homologous end-joining by restraining DNA-PKcs recruitment to the Ku70/80 heterodimer, sensitizing cells to radiotherapy [PMID:35998796]. ITGA2 expression is set by transcriptional regulators including TEAD1, BACH1, and PARP-1/Ku80 binding to a CA-repeat promoter element, by enhancer chromatin looping, and by epigenetic CpG methylation and EZH2-mediated repression [PMID:17669516, PMID:20090957, PMID:25549357, PMID:25662931, PMID:37311571, PMID:38169150, PMID:40321134]. Coding polymorphisms define the HPA-5 platelet alloantigen system (Glu505Lys) and the C807T variant that scales receptor surface density [PMID:7913826, PMID:10468872].","teleology":[{"year":1989,"claim":"Establishing the primary structure of the alpha2 subunit revealed a unique I-domain insert not present in other integrin alpha chains, immediately implicating a dedicated ligand-binding module.","evidence":"cDNA cloning with direct N-terminal protein sequencing and domain analysis","pmids":["2545729"],"confidence":"High","gaps":["Sequence alone did not prove which residues contact collagen","No structural model of the I-domain at this stage"]},{"year":1989,"claim":"It was unknown whether GPIa/IIa was a true functional collagen receptor; antibody blockade showed it directly mediates platelet adhesion and aggregation on collagen independently of plasma proteins.","evidence":"Monoclonal antibody (6F1) inhibition of platelet adhesion/aggregation and collagen-bead agglutination","pmids":["2546619"],"confidence":"High","gaps":["Did not localize the binding site within the subunit","Did not address signaling downstream of adhesion"]},{"year":1994,"claim":"The collagen-binding site was localized to the I-domain and specific residues, defining the molecular determinants of ligand recognition and showing the recombinant I-domain alone suffices for cation-independent collagen binding.","evidence":"Interspecies chimeras, site-directed mutagenesis (Asp-151, Asp-254, Thr-221), recombinant I-domain binding and antibody epitope mapping","pmids":["7511592","7523399"],"confidence":"High","gaps":["Reconciling cation-independence of isolated I-domain with cation-dependence of intact receptor","No co-crystal with collagen"]},{"year":1994,"claim":"The receptor's ligand breadth and physiological relevance were defined: it is a universal platelet collagen receptor across types I–VIII under static and flow conditions.","evidence":"Platelet adhesion assays across eight collagen types under stasis and shear with antibody (176D7) inhibition","pmids":["8118028"],"confidence":"High","gaps":["Did not resolve signaling consequences of engagement","Relative contribution versus other platelet collagen receptors not quantified"]},{"year":1994,"claim":"Coding polymorphisms were defined molecularly, linking ITGA2 sequence variation to the HPA-5 alloantigen system and laying groundwork for genotype–phenotype studies.","evidence":"RT-PCR/cDNA sequencing and PCR-RFLP genotyping of the bp1648 A→G (Glu505Lys) variant","pmids":["7913826","7916494"],"confidence":"High","gaps":["Functional consequence of the substitution on collagen binding not established","Clinical alloimmunization outcomes not addressed here"]},{"year":1999,"claim":"It was unclear whether common ITGA2 variants alter receptor abundance; flow cytometry tied the C807T and HPA-5 alleles to platelet surface receptor density.","evidence":"Flow cytometry of platelet GPIa/IIa with PCR genotyping in blood-donor cohorts","pmids":["10468872","10220262"],"confidence":"Medium","gaps":["Association studies do not establish the molecular mechanism of altered density","Functional adhesion consequences not directly measured"]},{"year":1993,"claim":"Ligand specificity beyond collagen was probed; alpha2beta1 was shown to bind thrombospondin at a distinct, divalent-cation-independent site.","evidence":"Saturable binding with purified GPIa/IIa, competition and antibody (6F1) inhibition","pmids":["8240284"],"confidence":"Medium","gaps":["Single biochemical study without cellular validation","Physiological role of TSP binding unresolved"]},{"year":2001,"claim":"The outside-in signaling machinery was defined: alpha2beta1 constitutively associates with Src/Lyn and, upon agonist (rhodocytin) engagement, transduces a tyrosine-phosphorylation cascade to Syk/PLCgamma2 and Ca2+ flux.","evidence":"Liposome reconstitution of recombinant receptor, immunoprecipitation, in vitro kinase assays and Western blotting","pmids":["11038351"],"confidence":"High","gaps":["Direct kinase–subunit interaction interface not mapped","Relevance to physiological collagen signaling versus venom agonist not fully resolved"]},{"year":2001,"claim":"The widely used DX5 antibody antigen was identified as CD49b/ITGA2, establishing the subunit as an NK-cell marker and its loss with IL-2-driven proliferation.","evidence":"Retroviral expression cloning with flow cytometry and antibody competition","pmids":["11466327"],"confidence":"High","gaps":["Functional role of CD49b on NK cells not defined here"]},{"year":2007,"claim":"Transcriptional and epigenetic control of ITGA2 abundance began to be defined, distinguishing CA-repeat/Sp1 promoter regulation and PARP-1/Ku80 binding from ITGA1 methylation.","evidence":"Bisulfite sequencing, promoter-luciferase reporters, demethylation treatment and transcriptome analysis","pmids":["17669516"],"confidence":"Medium","gaps":["Causality between factor binding and expression only correlative at this stage","Single lineage (megakaryocytic) context"]},{"year":2010,"claim":"The promoter regulatory logic was refined: PARP-1/Ku80 bind the longer (CA)12 allele with enhanced affinity, enabling ranking of ITGA2 haplotypes by transcriptional activity together with the C-52T Sp1 site.","evidence":"DNA affinity chromatography, ChIP and promoter-luciferase reporter assays","pmids":["20090957"],"confidence":"Medium","gaps":["In vivo relevance of haplotype ranking not established","Single experimental system"]},{"year":2013,"claim":"An in vivo adhesion function for ITGA2 in immunity was established: CD49b is required for memory CD4 T-cell precursor homing to bone marrow, where collagen II-expressing stroma provide ligand.","evidence":"CD49b-deficient mice, antibody blockade, adoptive transfer and confocal imaging","pmids":["23897120"],"confidence":"Medium","gaps":["Downstream signaling in homing not dissected","Single lab"]},{"year":2014,"claim":"EZH2 was shown to directly repress ITGA2, and de-repression activates ITGA2-dependent cofilin phosphorylation that constrains colorectal cancer migration—linking chromatin regulation to cytoskeletal control.","evidence":"ChIP, EZH2 inhibition (DZNep/GSK343), siRNA and phospho-cofilin/migration assays","pmids":["25549357"],"confidence":"Medium","gaps":["Direction of migratory effect appears context-dependent","Mechanism linking ITGA2 to cofilin not fully resolved"]},{"year":2015,"claim":"ITGA2 was shown to act as a pro-migratory/pro-stemness driver in epithelial cancers and inflammatory T cells, with promoter CpG methylation controlling its expression and IL-7R co-engagement amplifying its function.","evidence":"Bisulfite sequencing, siRNA, migration assays (prostate) and flow/adhesion/in vivo blockade with pathway inhibition (Th17)","pmids":["25662931","26408663"],"confidence":"Medium","gaps":["Context-dependent pro- vs anti-migratory roles unreconciled","Direct signaling intermediates not all defined"]},{"year":2019,"claim":"Specific oncogenic signaling outputs were mapped: ITGA2 interacts with STAT3 to drive PD-L1, and ADAR1 p110 upregulates ITGA2 to enhance ECM adhesion and metastasis.","evidence":"Co-IP, RNA-seq and functional proliferation/invasion assays (pancreatic); lentiviral gain/loss and orthotopic xenografts (HCC)","pmids":["31818309","30798327"],"confidence":"Medium","gaps":["Co-IP without reciprocal/structural validation of ITGA2–STAT3 interaction","Direct versus indirect effects on PD-L1 not fully separated"]},{"year":2021,"claim":"ITGA2 was placed upstream of multiple signaling axes (FAK/AKT, RhoA-p38 MAPK, PI3K/AKT) governing invasion, apoptosis and mechanotransduction, with pharmacological rescue confirming pathway directionality.","evidence":"Antibody blockade (gastric), overexpression/knockdown with MK-2206 rescue (ESCC), and mechanical stretch with siRNA (nucleus pulposus)","pmids":["29743821","34113124","33815660"],"confidence":"Medium","gaps":["Tissue-specific differences in downstream wiring not unified","Single lab per context"]},{"year":2022,"claim":"A non-canonical nuclear role was uncovered: nuclear ITGA2 inhibits NHEJ by restraining DNA-PKcs recruitment to Ku70/80, modulating genome stability and radiosensitivity.","evidence":"Nuclear fractionation, NHEJ activity assay, DNA-PKcs/Ku70/80 immunoprecipitation and radiation sensitivity assays","pmids":["35998796"],"confidence":"Medium","gaps":["Mechanism of ITGA2 nuclear import unknown","Single lab; reciprocal validation of the repair interaction limited"]},{"year":2023,"claim":"Additional upstream transcriptional regulators were defined—BACH1 directly activates ITGA2 to drive FAK-RAC1-PAK migration, and macrophage-conditioned mesothelial cells upregulate ITGA2 via JNK/Akt to promote adhesion.","evidence":"ChIP and dual-luciferase reporter with downstream Western blot (lung); mRNA-seq, siRNA and pathway inhibitors with adhesion assay (ovarian)","pmids":["37311571","36766725"],"confidence":"Medium","gaps":["Network of overlapping transcriptional regulators not integrated","Single lab per study"]},{"year":2024,"claim":"TEAD1 was identified as a key transcriptional regulator of ITGA1/ITGA2, and combined loss triggers TGFbeta1/YAP1-driven EMT and tumorigenic conversion, revealing a tumor-suppressive facet of these integrins in benign epithelium.","evidence":"CRISPR-Cas9 deletion, co-expression analysis, EMT markers, TGFbeta1 ELISA and in vivo tumorigenicity","pmids":["38169150"],"confidence":"Medium","gaps":["Reconciliation of pro-tumor vs tumor-suppressor roles across tissues","Redundancy between ITGA1 and ITGA2 not separated"]},{"year":2025,"claim":"Enhancer-level control of ITGA2 was defined: a NONO-dependent enhancer-associated lncRNA loops the ITGA2 enhancer to its promoter and increases H3K27ac to drive expression and vascular smooth muscle proliferation/migration.","evidence":"CUT&Tag, promoter capture Hi-C, CRISPR knockout, CHIRP/RIP and carotid wire-injury model","pmids":["40321134"],"confidence":"Medium","gaps":["Generalizability beyond vascular smooth muscle unknown","Direct lncRNA–NONO–chromatin contact stoichiometry not resolved"]},{"year":null,"claim":"How the distinct adhesive, signaling, transcriptional-regulatory, and nuclear DNA-repair-modulating functions of ITGA2 are integrated—and what governs its nuclear versus membrane partitioning across cell types—remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No mechanism for ITGA2 nuclear import/trafficking","Context-dependent pro- versus anti-tumor activities not unified","No high-resolution structure of the intact alpha2beta1–collagen complex in the corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098631","term_label":"cell adhesion mediator activity","supporting_discovery_ids":[1,4,2,26]},{"term_id":"GO:0001618","term_label":"virus receptor activity","supporting_discovery_ids":[2]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[17,21]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[0,1,9]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[23]}],"pathway":[{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[1,4,10]},{"term_id":"R-HSA-1474244","term_label":"Extracellular matrix organization","supporting_discovery_ids":[1,4,26]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[10,20,24]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[11,16,19]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[23]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[14,15,25,27,32]}],"complexes":["integrin alpha2beta1 (GPIa/IIa, VLA-2)"],"partners":["ITGB1","SRC","LYN","STAT3","DNA-PKCS","KU70/80","NONO"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P17301","full_name":"Integrin alpha-2","aliases":["CD49 antigen-like family member B","Collagen receptor","Platelet membrane glycoprotein Ia","GPIa","VLA-2 subunit alpha"],"length_aa":1181,"mass_kda":129.3,"function":"Integrin alpha-2/beta-1 is a receptor for laminin, collagen, collagen C-propeptides, fibronectin and E-cadherin. It recognizes the proline-hydroxylated sequence G-F-P-G-E-R in collagen. It is responsible for adhesion of platelets and other cells to collagens, modulation of collagen and collagenase gene expression, force generation and organization of newly synthesized extracellular matrix (Microbial infection) Integrin ITGA2:ITGB1 acts as a receptor for Human rotavirus A (Microbial infection) Integrin ITGA2:ITGB1 acts as a receptor for Human echoviruses 1 and 8","subcellular_location":"Membrane","url":"https://www.uniprot.org/uniprotkb/P17301/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/ITGA2","classification":"Not Classified","n_dependent_lines":4,"n_total_lines":1208,"dependency_fraction":0.0033112582781456954},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/ITGA2","total_profiled":1310},"omim":[{"mim_id":"621267","title":"FETOMATERNAL ALLOIMMUNE THROMBOCYTOPENIA 3; FMAIT3","url":"https://www.omim.org/entry/621267"},{"mim_id":"621264","title":"FETOMATERNAL ALLOIMMUNE THROMBOCYTOPENIA 1; FMAIT1","url":"https://www.omim.org/entry/621264"},{"mim_id":"617569","title":"KINESIN FAMILY, MEMBER 15; KIF15","url":"https://www.omim.org/entry/617569"},{"mim_id":"614200","title":"BLEEDING DISORDER, PLATELET-TYPE, 9; BDPLT9","url":"https://www.omim.org/entry/614200"},{"mim_id":"612759","title":"SYNESTHESIA","url":"https://www.omim.org/entry/612759"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/ITGA2"},"hgnc":{"alias_symbol":["GPIa","VLAA2","HPA-5"],"prev_symbol":["CD49B"]},"alphafold":{"accession":"P17301","domains":[{"cath_id":"3.40.50.410","chopping":"174-367","consensus_level":"high","plddt":90.0159,"start":174,"end":367},{"cath_id":"2.60.40.1460","chopping":"654-784","consensus_level":"high","plddt":84.3218,"start":654,"end":784},{"cath_id":"2.60.40.1510","chopping":"800-935","consensus_level":"high","plddt":86.8921,"start":800,"end":935},{"cath_id":"2.60.40.1530","chopping":"940-1123","consensus_level":"high","plddt":86.3727,"start":940,"end":1123},{"cath_id":"1.20.5","chopping":"1132-1157","consensus_level":"medium","plddt":77.3923,"start":1132,"end":1157}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P17301","model_url":"https://alphafold.ebi.ac.uk/files/AF-P17301-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P17301-F1-predicted_aligned_error_v6.png","plddt_mean":85.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=ITGA2","jax_strain_url":"https://www.jax.org/strain/search?query=ITGA2"},"sequence":{"accession":"P17301","fasta_url":"https://rest.uniprot.org/uniprotkb/P17301.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P17301/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P17301"}},"corpus_meta":[{"pmid":"23624599","id":"PMC_23624599","title":"Coexpression 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The sequence contains three metal-binding domains (DXDXDGXXD), 20 cysteine residues, and a unique 191-amino acid I-domain insert (residues ~140-359) not found in other integrin alpha chains at the time, with homology to von Willebrand factor A1/A3 domains and cartilage matrix protein—regions associated with collagen binding.\",\n      \"method\": \"cDNA cloning, direct NH2-terminal protein sequencing, sequence analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — primary sequence determination by cDNA cloning confirmed by direct protein sequencing; foundational structural characterization replicated across subsequent studies\",\n      \"pmids\": [\"2545729\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"GPIa/IIa (integrin alpha2beta1, ITGA2/ITGB1) directly mediates platelet adhesion to collagen independently of plasma adhesive proteins. Monoclonal antibody 6F1 against GPIa/IIa blocked >95% of collagen-induced platelet adhesion in the absence of plasma and nearly completely inhibited collagen-induced platelet aggregation, establishing GPIa/IIa as a direct collagen receptor.\",\n      \"method\": \"Monoclonal antibody inhibition of platelet adhesion and aggregation assays; 6F1 affinity-purified GPIa/IIa complex; collagen-coated bead agglutination assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — antibody blockade with functional readout replicated across multiple assay systems and subsequently confirmed by many independent labs\",\n      \"pmids\": [\"2546619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The I-domain of ITGA2 (residues 140–359) contains the collagen-binding site of integrin alpha2beta1. Mutations of Asp-151 and Asp-254 block alpha2beta1 binding to collagen, while a small region (residues 173–259) within the I-domain is recognized by function-blocking anti-alpha2 monoclonal antibodies (6F1, RMAC11, 12F1, AA10) that block both collagen and echovirus 1 binding. Collagen and echovirus 1 binding sites are adjacent or overlapping within the I-domain.\",\n      \"method\": \"Interspecies (human/bovine) alpha2 chimeras, site-directed mutagenesis, antibody epitope mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — site-directed mutagenesis combined with chimera mapping in functional binding assays; independently confirmed by recombinant I-domain studies\",\n      \"pmids\": [\"7511592\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The recombinant I-domain of ITGA2 alpha2 subunit is sufficient for collagen binding, and this binding is divalent cation-independent (unlike full-length integrin binding). Thr-221 within the I-domain is a critical residue for collagen binding to both alpha2beta1 and the isolated I-domain fragment.\",\n      \"method\": \"Recombinant I-domain expression, collagen-binding assay, site-directed mutagenesis (Thr-221), divalent cation chelation experiments\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro binding with mutagenesis validation; identifies a specific residue for collagen contact\",\n      \"pmids\": [\"7523399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"GPIa/IIa (integrin alpha2beta1) is a major and universal platelet receptor mediating adhesion to collagen types I–VIII under both static conditions and flow. Monoclonal antibody 176D7 against GPIa (ITGA2) completely inhibited platelet adhesion to all collagen types tested under stasis and flow conditions.\",\n      \"method\": \"Platelet adhesion assays to multiple collagen types under static and flow conditions; monoclonal antibody inhibition studies\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic functional inhibition across eight collagen types and multiple shear rates; confirmed independently\",\n      \"pmids\": [\"8118028\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The HPA-5 alloantigen system on GPIa/IIa (ITGA2) is caused by an A→G polymorphism at base pair 1648 of the GPIa coding sequence, resulting in a Glu/Lys substitution at amino acid position 505 of the mature protein (HPA-5a = Glu505; HPA-5b = Lys505).\",\n      \"method\": \"RT-PCR, cDNA sequencing, allele-specific restriction enzyme analysis (Mnl I PCR-ASRA)\",\n      \"journal\": \"British journal of haematology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct sequencing of cDNA from genotyped individuals; confirmed by multiple independent laboratories\",\n      \"pmids\": [\"7913826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The Br (HPA-5) polymorphism of GPIa is encoded by a single base change at position 1648 on platelet GPIa mRNA, causing an amino acid substitution at position 505 of mature GPIa. This polymorphism is located within a 144 bp exon of the GPIa (ITGA2) gene flanked by two introns (~1.7 and ~1.9 kb).\",\n      \"method\": \"PCR of genomic DNA, RFLP analysis with MnlI endonuclease, correlation with serological MAIPA typing\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — genomic structure determined by PCR and confirmed by correlation with serological phenotyping\",\n      \"pmids\": [\"7916494\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"The recombinant alpha2 I-domain (residues D145–S334) fused to maltose-binding protein binds immobilized collagen type I in a concentration-dependent and Mg2+-dependent manner (inhibited by EDTA or Ca2+ but sustained in Mg2+), and the I-domain alone can inhibit platelet adhesion to collagen and collagen-induced platelet aggregation (IC50 ~0.7 µM for both), confirming the I-domain as the collagen-binding site of alpha2beta1.\",\n      \"method\": \"Recombinant I-domain expression and purification, ELISA binding assay, platelet adhesion inhibition assay, platelet aggregation inhibition assay\",\n      \"journal\": \"Thrombosis and haemostasis\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted recombinant protein with functional inhibition assays; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"9184414\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The C807T dimorphism (TTC/TTT in codon 224) of the GPIa (ITGA2) cDNA is associated with variation in GPIa/IIa receptor density on the platelet surface, with the 807T allele associated with higher GPIa/IIa surface density.\",\n      \"method\": \"Flow cytometry for platelet GPIa/IIa levels; PCR genotyping of C807T polymorphism\",\n      \"journal\": \"British journal of haematology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single genotype–phenotype association study; replicated in other studies linking C807T to receptor density\",\n      \"pmids\": [\"10468872\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Both the 807C/T and HPA-5 polymorphisms of GPIa (ITGA2) independently correlate with GPIa/IIa molecule number on the platelet surface, with 807T and HPA-5b alleles associated with increased receptor density. The two polymorphisms are genetically linked (HPA-5b linked to ~15.8% of 807C alleles).\",\n      \"method\": \"Flow cytometry for platelet GPIa/IIa levels; PCR-RFLP genotyping; 159 blood donors\",\n      \"journal\": \"Transfusion\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — quantitative flow cytometry phenotype-genotype correlation; single study but consistent with prior data\",\n      \"pmids\": [\"10220262\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Rhodocytin from Calloselasma rhodostoma venom directly binds to GPIa/IIa (integrin alpha2beta1, ITGA2) independently of divalent cations, induces platelet aggregation, and activates GPIa/IIa-associated Src and Lyn kinases. Src constitutively associates with GPIa/IIa and its activity transiently increases after rhodocytin stimulation, leading to Cas tyrosine phosphorylation; downstream signals include Syk and PLCγ2 phosphorylation and Ca2+ mobilization.\",\n      \"method\": \"Anti-GPIa mAb blockade, rhodocytin-coupled bead binding assay, liposome-reconstitution with recombinant GPIa/IIa, GPIa immunoprecipitation, in vitro kinase assay, Western blotting, cytochalasin D inhibition\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted direct binding to recombinant GPIa/IIa, in vitro kinase assays, immunoprecipitation; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"11038351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"DX5 monoclonal antibody recognizes CD49b (ITGA2, alpha2 integrin, VLA-2), as identified by retrovirus-mediated expression cloning from an NK cell cDNA library. Binding of DX5 to NK cells and CD49b transfectants is blocked by other anti-CD49b mAbs. CD49b expression on NK cells is progressively lost upon IL-2-driven proliferation.\",\n      \"method\": \"Retrovirus-mediated expression cloning; transfection and flow cytometry; antibody competition assays\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — expression cloning with functional antibody competition confirmation; establishes molecular identity of DX5 antigen as CD49b\",\n      \"pmids\": [\"11466327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"EMS16, a C-type lectin-like protein from Echis multisquamatus venom, is a potent and selective inhibitor of GPIa/IIa (integrin alpha2beta1). Its crystal structure at 1.9 Å resolution reveals a heterodimer with domain swapping of the central loop and a unique positively charged electrostatic patch on the concave surface that may interact with the I-domain of GPIa/IIa.\",\n      \"method\": \"X-ray crystallography at 1.9 Å resolution; structural analysis\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure determined at high resolution; single study but rigorous structural method\",\n      \"pmids\": [\"14580195\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"GPIa/IIa (integrin alpha2beta1, ITGA2) specifically binds thrombospondin (TSP) in an ion-independent manner (Kd = 0.69 µM), whereas GPIIb/IIIa binding to TSP is divalent cation-dependent. Anti-GPIa/IIa antibody 6F1 inhibits GPIa/IIa binding to TSP; GPIa/IIa and GPIIb/IIIa bind to distinct sites on TSP.\",\n      \"method\": \"Saturable binding assay with purified GPIa/IIa and GPIIb/IIIa; competition experiments; antibody inhibition; ion dependence experiments\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct biochemical binding assay with purified proteins, single study\",\n      \"pmids\": [\"8240284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The ITGA2 promoter is regulated by transcription factors including Sp1 (at SNP C-52T binding site). PARP-1 and Ku80/70 bind specifically and with enhanced affinity to the longer (CA)12 repeat allele in the 5'-regulatory region of ITGA2, coinciding with enhanced alpha2beta1 expression. A CpG-rich ITGA1 promoter region is selectively methylated in megakaryocytic cells, but ITGA2 promoter methylation does not change during megakaryocyte differentiation—indicating distinct epigenetic regulation for ITGA1 vs. ITGA2.\",\n      \"method\": \"Bisulfite genomic sequencing, promoter-luciferase reporter assay, transcriptome analysis, 5-aza-2'-deoxycytidine treatment\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (bisulfite sequencing, reporter assays, pharmacological demethylation); single lab\",\n      \"pmids\": [\"17669516\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PARP-1 and Ku80/70 bind specifically and with enhanced affinity to the longer (CA)12 repeat allele in the 5'-regulatory region of ITGA2 (beginning at -605). This enhanced binding correlates with increased ITGA2/alpha2beta1 expression. Together with SNP C-52T (Sp1 binding site), four ITGA2 haplotypes can be ranked for transcriptional activity: (CA)12/-52C > (CA)11/-52C > (CA)11/-52T > (CA)10/-52T.\",\n      \"method\": \"DNA affinity chromatography, chromatin immunoprecipitation (ChIP), promoter-luciferase reporter assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — DNA affinity chromatography and ChIP with functional reporter assays; single lab\",\n      \"pmids\": [\"20090957\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"CD49b (ITGA2) is required for migration of memory CD4 T-cell precursors from blood into the bone marrow sinusoidal endothelium. CD49b-deficient or CD49b-blocked memory CD4 T-cell precursors fail to home to the bone marrow. In the marrow, memory CD4 T cells contact stromal cells expressing collagen II (a ligand for CD49b).\",\n      \"method\": \"CD49b-deficient mice, antibody blockade, adoptive transfer, in vivo migration assays, confocal imaging of stromal cell interactions\",\n      \"journal\": \"Immunology and cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout combined with antibody blockade and adoptive transfer; single lab\",\n      \"pmids\": [\"23897120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"EZH2 epigenetically regulates ITGA2 expression (via chromatin immunoprecipitation-confirmed direct targeting), and de-repression of ITGA2 following EZH2 inhibition (genetic or pharmacological with DZNep and GSK343) activates ITGA2 signaling to increase cofilin phosphorylation at Ser3, thereby reducing colorectal cancer cell migration.\",\n      \"method\": \"siRNA knockdown, pharmacological EZH2 inhibition (DZNep, GSK343), chromatin immunoprecipitation, western blotting for phospho-cofilin, cell migration assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-confirmed epigenetic regulation with pharmacological and genetic perturbation and functional migration readout; single lab\",\n      \"pmids\": [\"25549357\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ITGA2 promoter CpG island methylation inversely regulates ITGA2 expression in prostate cancer: highly methylated in non-invasive LNCaP cells (low expression) and hypomethylated in highly metastatic PC3 and 22Rv1 cells (high expression). siRNA knockdown of ITGA2 reduces prostate cancer cell migration.\",\n      \"method\": \"Bisulfite sequencing of ITGA2 promoter CpG island, qPCR, siRNA knockdown, cell migration scratch assay\",\n      \"journal\": \"The Prostate\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bisulfite sequencing correlated with expression and confirmed functionally by siRNA knockdown; single lab\",\n      \"pmids\": [\"25662931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Human Th17 cells co-express IL-7R and the collagen-binding integrin alpha2beta1 (CD49b/ITGA2). IL-7 increases Th17 adhesion to collagen via alpha2beta1. Co-engagement of IL-7R and alpha2beta1 cooperatively enhances IL-17 production and osteoclastogenic function via JAK/PI3K/AKT and MAPK/ERK pathways. Blockade of alpha2beta1 with a neutralizing mAb inhibited IL-7-induced bone loss in vivo.\",\n      \"method\": \"Flow cytometry, adhesion assays to collagen, neutralizing antibody blockade in vivo, ELISA for IL-17, osteoclast differentiation assay, signaling pathway inhibition\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays in vitro and in vivo; single lab with functional antibody blockade\",\n      \"pmids\": [\"26408663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ITGA2 interacts with STAT3 (demonstrated by co-immunoprecipitation) and upregulates STAT3 phosphorylation, which transcriptionally increases PD-L1 expression in pancreatic cancer cells. ITGA2 overexpression promotes cancer cell proliferation and invasion; ITGA2 knockdown inhibits these processes.\",\n      \"method\": \"Co-immunoprecipitation, Western blot, RT-qPCR, RNA-seq, MTS assay, colony formation assay, transwell assay, immunohistochemistry\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP establishes protein-protein interaction; multiple functional assays; single lab\",\n      \"pmids\": [\"31818309\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Blockade of ITGA2 with a specific antibody induces apoptosis in ITGA2-overexpressing gastric cancer cells by upregulating RhoA-p38 MAPK signaling and promoting expression of Bim, Apaf-1, and Caspase-9. At lower doses, anti-ITGA2 antibody inhibits gastric cancer cell migration by downregulating N-WASP, PAK, and LIMK, thereby impairing actin organization.\",\n      \"method\": \"Anti-ITGA2 antibody treatment, Western blot, flow cytometry apoptosis assay, cell migration assay\",\n      \"journal\": \"Biological procedures online\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — antibody-mediated functional blockade with pathway-level Western blot validation; single lab\",\n      \"pmids\": [\"29743821\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cyclic mechanical stretch promotes proliferation and inhibits apoptosis of nucleus pulposus cells via the ITGA2/PI3K/AKT signaling pathway. Downregulation of ITGA2 by RNA interference abrogates stretch-induced PI3K/AKT activation and blocks stretch-induced COL2A1 expression and cell proliferation.\",\n      \"method\": \"Cyclic tensile stress application, microarray gene expression analysis, Western blot, RNA interference (siRNA), MTT assay, flow cytometry\",\n      \"journal\": \"Oxidative medicine and cellular longevity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA interference validates pathway dependency; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"33815660\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ITGA2 localizes to the nucleus in pancreatic cancer cells and inhibits the non-homologous end joining (NHEJ) DNA repair pathway by restraining recruitment of DNA-PKcs to the Ku70/80 heterodimer during DNA damage response, thereby sensitizing cells to radiotherapy.\",\n      \"method\": \"Nuclear fractionation, TCGA data analysis (genome stability parameters), NHEJ activity assay, DNA-PKcs/Ku70/80 immunoprecipitation, radiation sensitivity assays\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct biochemical demonstration of impaired DNA-PKcs recruitment to Ku70/80 with functional radiation sensitivity readout; single lab\",\n      \"pmids\": [\"35998796\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"ITGA2 overexpression promotes esophageal squamous cell carcinoma cell invasion and migration via FAK/AKT pathway activation and EMT induction. Treatment with AKT inhibitor MK-2206 rescues the ESCC progression caused by ITGA2 overexpression, placing ITGA2 upstream of FAK/AKT in this context.\",\n      \"method\": \"siRNA knockdown, overexpression, Western blot, Transwell assay, wound healing assay, xenograft tumor model, AKT inhibitor (MK-2206) rescue experiment\",\n      \"journal\": \"OncoTargets and therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological rescue places ITGA2 upstream of FAK/AKT; multiple functional assays; single lab\",\n      \"pmids\": [\"34113124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"BACH1 transcription factor directly binds the upstream promoter region of ITGA2 (confirmed by ChIP and dual-luciferase reporter assay) to transcriptionally activate ITGA2 expression, and the BACH1-ITGA2 axis promotes lung adenocarcinoma cell migration and invasion by activating the FAK-RAC1-PAK signaling pathway and regulating cytoskeletal organization.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), dual-luciferase reporter assay, RNA sequencing, Western blot, cell adhesion assay, migration/invasion assays\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct promoter binding confirmed by ChIP and luciferase reporter; downstream signaling validated by Western blot; single lab\",\n      \"pmids\": [\"37311571\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Elevated ITGA2 expression in intrahepatic cholangiocarcinoma cells promotes clonogenic growth induced by collagen type I. ITGA2 depletion or integrin alpha2beta1-selective inhibitor treatment abolishes robust iCCA cell interaction with collagen type I and blocks collagen type I-induced colony growth (3–6 fold enhancement).\",\n      \"method\": \"ITGA2 siRNA depletion, integrin alpha2beta1-selective inhibitor, cell adhesion assay, colony formation assay in 4 iCCA cell lines vs. non-cancerous cholangiocyte line\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic and pharmacological inhibition with functional colony growth readout; four cell lines compared; single lab\",\n      \"pmids\": [\"36575207\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Loss of both ITGA1 and ITGA2 (via genomic deletion or TEAD1 loss) activates epithelial-to-mesenchymal transition in benign prostate epithelial cells via enhanced secretion and autocrine activation of TGFβ1 and nuclear targeting of YAP1, converting cells to tumorigenic in vivo. TEAD1 is identified as a key transcriptional regulator of ITGA1 and ITGA2 expression.\",\n      \"method\": \"Genomic deletion (CRISPR-Cas9), in vitro invasion assays, in vivo tumorigenicity assay, genome-wide co-expression analysis, EMT marker Western blot, TGFβ1 ELISA\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR-mediated loss-of-function with in vitro and in vivo functional readout; mechanistic pathway placement via TGFβ1/YAP1; single lab\",\n      \"pmids\": [\"38169150\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"ITGA2 promotes breast cancer stemness and metastasis downstream of miR-206 (direct miR-206 target). ITGA2 knockdown suppresses mammosphere formation, pluripotency marker expression, cell cycling (G1 arrest), migration, and invasion, and reduces lung metastasis. ITGA2 overexpression reverses miR-206-induced G1 arrest. RNA-seq reveals ITGA2 regulates CCND1 (cell cycle) and ACLY (lipid metabolism) as downstream targets.\",\n      \"method\": \"siRNA knockdown, miRNA overexpression/inhibition, RNA sequencing, mammosphere formation assay, flow cytometry cell cycle analysis, Transwell migration/invasion, lung metastasis in vivo model\",\n      \"journal\": \"Genes & diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic rescue experiments with RNA-seq for downstream target identification; multiple functional assays; single lab\",\n      \"pmids\": [\"34179312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"ADAR1 p110 enhances adhesion of hepatocellular carcinoma cells to extracellular matrix by upregulating ITGA2 at both mRNA and protein levels. ADAR1 p110 overexpression promotes HCC metastasis in an orthotopic xenograft mouse model, and positive correlation between ADAR1 and ITGA2 was confirmed in patient HCC specimens.\",\n      \"method\": \"Lentivirus-mediated ADAR1 overexpression/knockdown, in vitro cell adhesion assay, Western blot, RT-PCR, orthotopic xenograft mouse model, IHC of patient samples\",\n      \"journal\": \"Medical science monitor\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — lentiviral gain/loss-of-function with functional adhesion assay and in vivo validation; single lab\",\n      \"pmids\": [\"30798327\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"miR-99a-3p suppresses PTC metastasis by targeting GRP94; GRP94 overexpression reverses miR-99a-3p inhibition of metastasis. The miR-99a-3p/GRP94 axis exerts its effect by inhibiting the expression and cytoplasmic relocation of ITGA2, implicating ITGA2 localization (cytoplasmic vs. membrane) as functionally important for metastasis.\",\n      \"method\": \"miRNA overexpression/inhibition, siRNA knockdown, subcellular fractionation/localization, EMT markers, invasion assay, in vivo xenograft model\",\n      \"journal\": \"Acta biochimica et biophysica Sinica\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — indirect evidence for ITGA2 localization; single lab, no direct imaging of ITGA2 trafficking mechanism\",\n      \"pmids\": [\"34687203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"In ovarian cancer metastasis, macrophage-stimulated mesothelial cells upregulate ITGA2 expression via JNK and Akt signaling pathways; knockdown of ITGA2 in macrophage-conditioned mesothelial cells significantly reduces ovarian cancer cell adhesion to mesothelial cells.\",\n      \"method\": \"mRNA sequencing, siRNA knockdown, signaling pathway inhibition (JNK, Akt inhibitors), cell adhesion assay\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with functional adhesion readout; pathway inhibitors identify upstream regulators; single lab\",\n      \"pmids\": [\"36766725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LncRNA-ITGA2 is an enhancer-associated lncRNA that, in a NONO-dependent manner, mediates chromatin looping interactions between the ITGA2 enhancer and ITGA2 promoter, increases H3K27 acetylation at both the enhancer and promoter, and thereby upregulates ITGA2 expression to promote vascular smooth muscle cell proliferation and migration.\",\n      \"method\": \"CUT&Tag, promoter capture Hi-C, microarray, CRISPR-Cas9 knockout of lncRNA-ITGA2 and NONO, RNA sequencing, chromatin immunoprecipitation sequencing (ChIP-seq), CHIRP, RIP, carotid artery wire injury mouse model\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiomics approach with CRISPR knockout validation and in vivo model; mechanistic regulation of ITGA2 expression established; single lab\",\n      \"pmids\": [\"40321134\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"ITGA2 encodes the alpha2 subunit of integrin alpha2beta1 (GPIa/IIa, VLA-2, CD49b), which functions as a direct collagen receptor via its I-domain (residues ~140–359), with Thr-221, Asp-151, and Asp-254 being critical for collagen binding; the receptor mediates platelet adhesion to collagen types I–VIII under static and flow conditions, constitutively associates with Src/Lyn kinases to transduce activation signals upon ligand engagement, binds thrombospondin independently of divalent cations, regulates cancer cell migration, invasion, and stemness through FAK/AKT, RhoA-p38 MAPK, STAT3-PD-L1, and PI3K/AKT pathways, and in the nucleus inhibits NHEJ DNA repair by blocking DNA-PKcs recruitment to Ku70/80; its expression is regulated transcriptionally by TEAD1, BACH1, HOXD3, and PARP-1/Ku80 binding to a CA-repeat promoter element, and epigenetically by CpG methylation and EZH2-mediated histone modification.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"ITGA2 encodes the alpha2 subunit of integrin alpha2beta1 (GPIa/IIa, VLA-2, CD49b), a heterodimeric cell-surface receptor whose principal function is direct, high-affinity binding to collagen and related matrix ligands to mediate cell adhesion, signaling, and motility [#0, #1, #4]. The collagen-binding activity resides in a unique 191-residue I-domain insert (~residues 140\\u2013359) homologous to von Willebrand factor A domains; the recombinant I-domain alone is sufficient for collagen binding, with Asp-151, Asp-254 and Thr-221 critical for ligand contact, and this isolated-domain binding is divalent-cation-independent in contrast to the Mg2+-dependence of the intact receptor [#0, #2, #3, #7]. On platelets, alpha2beta1 is the major universal receptor for collagen types I\\u2013VIII under both static and flow conditions and additionally binds thrombospondin at a distinct, ion-independent site [#1, #4, #13]. Ligand engagement triggers outside-in signaling through a constitutively associated Src/Lyn module, leading to Cas, Syk and PLCgamma2 phosphorylation and Ca2+ mobilization, as revealed by the snake-venom agonist rhodocytin [#10]. Beyond platelets, ITGA2 drives leukocyte trafficking and inflammatory function\\u2014homing of memory CD4 T-cell precursors to bone marrow and IL-7-cooperative Th17 osteoclastogenesis\\u2014and in epithelial and cancer cells it controls adhesion, migration, invasion, EMT and stemness through FAK/AKT, RhoA-p38 MAPK, STAT3\\u2013PD-L1 and PI3K/AKT signaling [#16, #19, #20, #21, #24, #28]. A non-canonical nuclear pool of ITGA2 inhibits non-homologous end-joining by restraining DNA-PKcs recruitment to the Ku70/80 heterodimer, sensitizing cells to radiotherapy [#23]. ITGA2 expression is set by transcriptional regulators including TEAD1, BACH1, and PARP-1/Ku80 binding to a CA-repeat promoter element, by enhancer chromatin looping, and by epigenetic CpG methylation and EZH2-mediated repression [#14, #15, #17, #18, #25, #27, #32]. Coding polymorphisms define the HPA-5 platelet alloantigen system (Glu505Lys) and the C807T variant that scales receptor surface density [#5, #8].\",\n  \"teleology\": [\n    {\n      \"year\": 1989,\n      \"claim\": \"Establishing the primary structure of the alpha2 subunit revealed a unique I-domain insert not present in other integrin alpha chains, immediately implicating a dedicated ligand-binding module.\",\n      \"evidence\": \"cDNA cloning with direct N-terminal protein sequencing and domain analysis\",\n      \"pmids\": [\"2545729\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Sequence alone did not prove which residues contact collagen\", \"No structural model of the I-domain at this stage\"]\n    },\n    {\n      \"year\": 1989,\n      \"claim\": \"It was unknown whether GPIa/IIa was a true functional collagen receptor; antibody blockade showed it directly mediates platelet adhesion and aggregation on collagen independently of plasma proteins.\",\n      \"evidence\": \"Monoclonal antibody (6F1) inhibition of platelet adhesion/aggregation and collagen-bead agglutination\",\n      \"pmids\": [\"2546619\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not localize the binding site within the subunit\", \"Did not address signaling downstream of adhesion\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"The collagen-binding site was localized to the I-domain and specific residues, defining the molecular determinants of ligand recognition and showing the recombinant I-domain alone suffices for cation-independent collagen binding.\",\n      \"evidence\": \"Interspecies chimeras, site-directed mutagenesis (Asp-151, Asp-254, Thr-221), recombinant I-domain binding and antibody epitope mapping\",\n      \"pmids\": [\"7511592\", \"7523399\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Reconciling cation-independence of isolated I-domain with cation-dependence of intact receptor\", \"No co-crystal with collagen\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"The receptor's ligand breadth and physiological relevance were defined: it is a universal platelet collagen receptor across types I\\u2013VIII under static and flow conditions.\",\n      \"evidence\": \"Platelet adhesion assays across eight collagen types under stasis and shear with antibody (176D7) inhibition\",\n      \"pmids\": [\"8118028\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve signaling consequences of engagement\", \"Relative contribution versus other platelet collagen receptors not quantified\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Coding polymorphisms were defined molecularly, linking ITGA2 sequence variation to the HPA-5 alloantigen system and laying groundwork for genotype\\u2013phenotype studies.\",\n      \"evidence\": \"RT-PCR/cDNA sequencing and PCR-RFLP genotyping of the bp1648 A\\u2192G (Glu505Lys) variant\",\n      \"pmids\": [\"7913826\", \"7916494\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of the substitution on collagen binding not established\", \"Clinical alloimmunization outcomes not addressed here\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"It was unclear whether common ITGA2 variants alter receptor abundance; flow cytometry tied the C807T and HPA-5 alleles to platelet surface receptor density.\",\n      \"evidence\": \"Flow cytometry of platelet GPIa/IIa with PCR genotyping in blood-donor cohorts\",\n      \"pmids\": [\"10468872\", \"10220262\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Association studies do not establish the molecular mechanism of altered density\", \"Functional adhesion consequences not directly measured\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Ligand specificity beyond collagen was probed; alpha2beta1 was shown to bind thrombospondin at a distinct, divalent-cation-independent site.\",\n      \"evidence\": \"Saturable binding with purified GPIa/IIa, competition and antibody (6F1) inhibition\",\n      \"pmids\": [\"8240284\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single biochemical study without cellular validation\", \"Physiological role of TSP binding unresolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The outside-in signaling machinery was defined: alpha2beta1 constitutively associates with Src/Lyn and, upon agonist (rhodocytin) engagement, transduces a tyrosine-phosphorylation cascade to Syk/PLCgamma2 and Ca2+ flux.\",\n      \"evidence\": \"Liposome reconstitution of recombinant receptor, immunoprecipitation, in vitro kinase assays and Western blotting\",\n      \"pmids\": [\"11038351\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct kinase\\u2013subunit interaction interface not mapped\", \"Relevance to physiological collagen signaling versus venom agonist not fully resolved\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"The widely used DX5 antibody antigen was identified as CD49b/ITGA2, establishing the subunit as an NK-cell marker and its loss with IL-2-driven proliferation.\",\n      \"evidence\": \"Retroviral expression cloning with flow cytometry and antibody competition\",\n      \"pmids\": [\"11466327\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional role of CD49b on NK cells not defined here\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Transcriptional and epigenetic control of ITGA2 abundance began to be defined, distinguishing CA-repeat/Sp1 promoter regulation and PARP-1/Ku80 binding from ITGA1 methylation.\",\n      \"evidence\": \"Bisulfite sequencing, promoter-luciferase reporters, demethylation treatment and transcriptome analysis\",\n      \"pmids\": [\"17669516\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causality between factor binding and expression only correlative at this stage\", \"Single lineage (megakaryocytic) context\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"The promoter regulatory logic was refined: PARP-1/Ku80 bind the longer (CA)12 allele with enhanced affinity, enabling ranking of ITGA2 haplotypes by transcriptional activity together with the C-52T Sp1 site.\",\n      \"evidence\": \"DNA affinity chromatography, ChIP and promoter-luciferase reporter assays\",\n      \"pmids\": [\"20090957\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of haplotype ranking not established\", \"Single experimental system\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"An in vivo adhesion function for ITGA2 in immunity was established: CD49b is required for memory CD4 T-cell precursor homing to bone marrow, where collagen II-expressing stroma provide ligand.\",\n      \"evidence\": \"CD49b-deficient mice, antibody blockade, adoptive transfer and confocal imaging\",\n      \"pmids\": [\"23897120\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream signaling in homing not dissected\", \"Single lab\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"EZH2 was shown to directly repress ITGA2, and de-repression activates ITGA2-dependent cofilin phosphorylation that constrains colorectal cancer migration\\u2014linking chromatin regulation to cytoskeletal control.\",\n      \"evidence\": \"ChIP, EZH2 inhibition (DZNep/GSK343), siRNA and phospho-cofilin/migration assays\",\n      \"pmids\": [\"25549357\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direction of migratory effect appears context-dependent\", \"Mechanism linking ITGA2 to cofilin not fully resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"ITGA2 was shown to act as a pro-migratory/pro-stemness driver in epithelial cancers and inflammatory T cells, with promoter CpG methylation controlling its expression and IL-7R co-engagement amplifying its function.\",\n      \"evidence\": \"Bisulfite sequencing, siRNA, migration assays (prostate) and flow/adhesion/in vivo blockade with pathway inhibition (Th17)\",\n      \"pmids\": [\"25662931\", \"26408663\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Context-dependent pro- vs anti-migratory roles unreconciled\", \"Direct signaling intermediates not all defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Specific oncogenic signaling outputs were mapped: ITGA2 interacts with STAT3 to drive PD-L1, and ADAR1 p110 upregulates ITGA2 to enhance ECM adhesion and metastasis.\",\n      \"evidence\": \"Co-IP, RNA-seq and functional proliferation/invasion assays (pancreatic); lentiviral gain/loss and orthotopic xenografts (HCC)\",\n      \"pmids\": [\"31818309\", \"30798327\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Co-IP without reciprocal/structural validation of ITGA2\\u2013STAT3 interaction\", \"Direct versus indirect effects on PD-L1 not fully separated\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"ITGA2 was placed upstream of multiple signaling axes (FAK/AKT, RhoA-p38 MAPK, PI3K/AKT) governing invasion, apoptosis and mechanotransduction, with pharmacological rescue confirming pathway directionality.\",\n      \"evidence\": \"Antibody blockade (gastric), overexpression/knockdown with MK-2206 rescue (ESCC), and mechanical stretch with siRNA (nucleus pulposus)\",\n      \"pmids\": [\"29743821\", \"34113124\", \"33815660\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue-specific differences in downstream wiring not unified\", \"Single lab per context\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"A non-canonical nuclear role was uncovered: nuclear ITGA2 inhibits NHEJ by restraining DNA-PKcs recruitment to Ku70/80, modulating genome stability and radiosensitivity.\",\n      \"evidence\": \"Nuclear fractionation, NHEJ activity assay, DNA-PKcs/Ku70/80 immunoprecipitation and radiation sensitivity assays\",\n      \"pmids\": [\"35998796\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of ITGA2 nuclear import unknown\", \"Single lab; reciprocal validation of the repair interaction limited\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Additional upstream transcriptional regulators were defined\\u2014BACH1 directly activates ITGA2 to drive FAK-RAC1-PAK migration, and macrophage-conditioned mesothelial cells upregulate ITGA2 via JNK/Akt to promote adhesion.\",\n      \"evidence\": \"ChIP and dual-luciferase reporter with downstream Western blot (lung); mRNA-seq, siRNA and pathway inhibitors with adhesion assay (ovarian)\",\n      \"pmids\": [\"37311571\", \"36766725\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Network of overlapping transcriptional regulators not integrated\", \"Single lab per study\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"TEAD1 was identified as a key transcriptional regulator of ITGA1/ITGA2, and combined loss triggers TGFbeta1/YAP1-driven EMT and tumorigenic conversion, revealing a tumor-suppressive facet of these integrins in benign epithelium.\",\n      \"evidence\": \"CRISPR-Cas9 deletion, co-expression analysis, EMT markers, TGFbeta1 ELISA and in vivo tumorigenicity\",\n      \"pmids\": [\"38169150\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation of pro-tumor vs tumor-suppressor roles across tissues\", \"Redundancy between ITGA1 and ITGA2 not separated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Enhancer-level control of ITGA2 was defined: a NONO-dependent enhancer-associated lncRNA loops the ITGA2 enhancer to its promoter and increases H3K27ac to drive expression and vascular smooth muscle proliferation/migration.\",\n      \"evidence\": \"CUT&Tag, promoter capture Hi-C, CRISPR knockout, CHIRP/RIP and carotid wire-injury model\",\n      \"pmids\": [\"40321134\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generalizability beyond vascular smooth muscle unknown\", \"Direct lncRNA\\u2013NONO\\u2013chromatin contact stoichiometry not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the distinct adhesive, signaling, transcriptional-regulatory, and nuclear DNA-repair-modulating functions of ITGA2 are integrated\\u2014and what governs its nuclear versus membrane partitioning across cell types\\u2014remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mechanism for ITGA2 nuclear import/trafficking\", \"Context-dependent pro- versus anti-tumor activities not unified\", \"No high-resolution structure of the intact alpha2beta1\\u2013collagen complex in the corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098631\", \"supporting_discovery_ids\": [1, 4, 2, 26]},\n      {\"term_id\": \"GO:0001618\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [17, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 1, 9]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [1, 4, 10]},\n      {\"term_id\": \"R-HSA-1474244\", \"supporting_discovery_ids\": [1, 4, 26]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [10, 20, 24]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [11, 16, 19]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [23]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [14, 15, 25, 27, 32]}\n    ],\n    \"complexes\": [\"integrin alpha2beta1 (GPIa/IIa, VLA-2)\"],\n    \"partners\": [\"ITGB1\", \"SRC\", \"LYN\", \"STAT3\", \"DNA-PKcs\", \"Ku70/80\", \"NONO\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}