{"gene":"AP2A1","run_date":"2026-06-09T22:02:43","timeline":{"discoveries":[{"year":2006,"finding":"AP2A1 (alpha-adaptin, component of clathrin-coated vesicles) physically associates with m-Numb in mouse testis germ cells, as demonstrated by co-immunoprecipitation, and the two proteins co-localize by confocal immunofluorescence microscopy of seminiferous tubules and isolated germ cells.","method":"Co-immunoprecipitation; confocal immunofluorescence microscopy","journal":"Reproduction (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — reciprocal co-IP and co-localization in two cell types, single lab","pmids":["17127749"],"is_preprint":false},{"year":2010,"finding":"AP2A1 is required for clathrin-mediated endocytosis (CME)-dependent entry of human enterovirus 71 (HEV71) into rhabdomyosarcoma cells; siRNA knockdown of AP2A1 significantly inhibited HEV71 infection in a dose-dependent manner, placing AP2A1 in the CME pathway essential for viral entry.","method":"siRNA knockdown; immunofluorescence co-localization; dominant-negative mutant expression; drug inhibition assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (siRNA, dominant-negative, pharmacological inhibition, co-localization) in a single study","pmids":["20956521"],"is_preprint":false},{"year":2016,"finding":"AP2A1 (along with AP2A2 and AP2B1) shows increased protein levels associated with the EGFR interactome in erlotinib-resistant non-small cell lung cancer cells (HCC4006rERLO0.5) compared to parental cells, identified by affinity purification coupled with mass spectrometry.","method":"Affinity purification-mass spectrometry (AP-MS)","journal":"European journal of pharmaceutical sciences","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single AP-MS experiment, no functional follow-up on AP2A1 specifically","pmids":["27112992"],"is_preprint":false},{"year":2017,"finding":"AP2A1 (alpha subunit of AP-2) is recruited to clathrin-mediated endocytosis sites concurrently with clathrin in Arabidopsis plant cells, as shown by TIRF microscopy using a departure assay; this temporal recruitment pattern differs from AP2M (mu subunit), which is not recruited in concert with clathrin.","method":"Total internal reflection fluorescence (TIRF) microscopy; automated departure assay","journal":"Frontiers in plant science","confidence":"Low","confidence_rationale":"Tier 3 / Weak — TIRF localization study in plant cells (potential ortholog context), single lab, no functional mutagenesis","pmids":["28484480"],"is_preprint":false},{"year":2016,"finding":"Ap2a1 is required for hematopoietic stem/progenitor cell (HSPC) specification and development; knockdown of Ap2a1 in zebrafish impaired HSPC development in vivo, validating it as a gene essential for the endothelial-to-hematopoietic transition identified in a genome-wide RNAi screen.","method":"Genome-wide RNAi screen (in vitro ESC differentiation); zebrafish in vivo knockdown validation","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal systems (in vitro screen + in vivo zebrafish), single lab","pmids":["27797851"],"is_preprint":false},{"year":2020,"finding":"AP2A1/2 complex mediates clathrin-dependent endocytosis of IGF-1 receptor (IGF1R) in human keratinocytes; concurrent shRNA knockdown of AP2A1/2 and FLOT1/2 reduced IGF1R association with clathrin, internalization, and downstream pathway activation (phospho-IGF1R, phospho-AKT, phospho-MAPK) by >50%. AP2A1/2-mediated endocytosis routes IGF1R to Rab11-positive slow recycling endosomes, distinguishing it from the Flot-1/Rab4 fast-recycling pathway.","method":"shRNA knockdown; confocal/TIRF/SIM microscopy; co-immunoprecipitation; Western blot (phosphorylation assays); Rab11 association assay","journal":"The Journal of investigative dermatology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, multiple imaging modalities, functional rescue assays, pathway activation quantification, and Rab11 sorting established with orthogonal methods in a single rigorous study","pmids":["32027876"],"is_preprint":false},{"year":2020,"finding":"AP2A1 and AP2B1 subunits of AP-2 complex are upregulated by full-length IL-33 (FLIL33) overexpression in human lung fibroblasts, and siRNA-mediated knockdown of AP2A1/AP2B1 blocked FLIL33-induced Smad3 phosphorylation, while AP-2 subunit overexpression induced Smad3 phosphorylation independently of FLIL33, placing AP2A1 as a required mediator of TGFBR-dependent Smad3 activation downstream of FLIL33.","method":"siRNA knockdown; Western blotting; overexpression experiments","journal":"Cellular immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function and gain-of-function experiments with defined signaling readout (Smad3 phosphorylation), single lab","pmids":["32977155"],"is_preprint":false},{"year":2020,"finding":"AP2A1 siRNA knockdown and pharmacological inhibition of clathrin-mediated endocytosis blocked HAdV-D37 (human adenovirus type 37) early gene expression in human corneal epithelial cells, establishing AP2A1 as required for this noncanonical clathrin-mediated viral entry pathway.","method":"siRNA knockdown; quantitative PCR; Western blot; chemical inhibitor assays","journal":"Investigative ophthalmology & visual science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with gene expression readout plus pharmacological inhibition, single lab","pmids":["32852546"],"is_preprint":false},{"year":2021,"finding":"AP2A1 (alpha-1 subunit of AP-2) associates with CLDN2 (claudin-2), clathrin, and LC3 upon starvation-induced autophagy in intestinal epithelial cells, as shown by co-immunoprecipitation; this interaction facilitates clathrin-mediated endocytosis of CLDN2 followed by lysosomal degradation, thereby reducing tight junction permeability.","method":"Co-immunoprecipitation; membrane fractionation; immunofluorescence; pharmacological inhibition","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with multiple partners, fractionation, and pharmacological inhibition in a single lab study","pmids":["34964704"],"is_preprint":false},{"year":2021,"finding":"AP2A1 is recruited by MYO1F as an adaptor to α-tubulin during Dectin-1-induced signaling in macrophages; MYO1F acts as a scaffold recruiting both AP2A1 and α-tubulin N-acetyltransferase 1 (ATAT1) to α-tubulin to promote its acetylation, which in turn controls membrane-to-cytoplasm trafficking of SYK and CARD9 required for antifungal innate immune signaling.","method":"Co-immunoprecipitation; knockdown (Myo1f-deficient mice); in vivo infection models; Western blot","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP in macrophages plus genetic knockout mouse model with functional immune readout, single lab","pmids":["34301894"],"is_preprint":false},{"year":2021,"finding":"AP2A1 colocalizes with tau pathology (neurofibrillary tangles) in Alzheimer's disease brains and is present in the detergent-insoluble fraction of cognitively impaired but not control brains, in an isoform-specific manner (AP2A1 but not AP2A2 labels neurofibrillary tangles), as determined by immunohistochemistry and immunofluorescence with antibody specificity validated by immunoblot after plasmid transfection.","method":"Immunoblot (after plasmid transfection for antibody validation); immunohistochemistry; immunofluorescence; fractionation","journal":"Neuropathology and applied neurobiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — validated antibody specificity with transfection controls, histochemistry across multiple brain samples, single lab","pmids":["34820873"],"is_preprint":false},{"year":2023,"finding":"AP2A1 binds directly to the circRNA circEIF3I and interacts with SMAD3, forming a ternary complex (circEIF3I–SMAD3–AP2A1) that facilitates recruitment of SMAD3 to TGFβRI on early endosomes, thereby promoting SMAD3 phosphorylation and activation of MMPs in pancreatic cancer cells.","method":"Co-immunoprecipitation; MS2-RNA affinity purification; mass spectrometry; RNA immunoprecipitation; RNA pulldown; immunofluorescence; RNA-protein interaction simulation","journal":"Molecular cancer","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, RNA pulldown, IF), single lab, AP2A1 role defined within a ternary complex context","pmids":["37689715"],"is_preprint":false},{"year":2023,"finding":"AP2A1 expression in the orbitofrontal cortex predicts alcohol use disorder severity; prefrontal Ap2a1 expression significantly correlates with voluntary alcohol drinking in genetically diverse mice, and recombinant inbred strains inheriting the C57BL/6J Ap2a1 allele consumed more alcohol than those inheriting the DBA/2J allele, linking AP2A1 to synaptic/presynaptic endocytosis mechanisms governing drinking behavior.","method":"Proteomics; machine learning; reverse genetics (mouse strains); gene expression correlation","journal":"Molecular psychiatry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — genetic association via recombinant inbred strains and expression correlation, no direct mechanistic manipulation of AP2A1 in neurons","pmids":["37679472"],"is_preprint":false},{"year":2023,"finding":"Radiation-induced ROS accumulation triggers excessive autophagy in NK cells, leading to increased association of the NKG2D receptor with AP2A1, AP2M1, LC3, and lysosomes, resulting in NKG2D endocytosis and lysosomal degradation that impairs NK cell function; this was demonstrated by immunoprecipitation after radiation exposure.","method":"Immunoprecipitation; immunofluorescence; Western blot","journal":"Frontiers in immunology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP experiment with limited mechanistic follow-up on AP2A1 specifically, single lab","pmids":["38077388"],"is_preprint":false},{"year":2025,"finding":"AP2A1 is upregulated in replicatively senescent human fibroblasts along enlarged actin stress fibers; AP2A1 knockdown reversed senescence-associated phenotypes (rejuvenation), while overexpression in young cells accelerated senescence. AP2A1 co-localizes with integrin β1 and both move linearly along stress fibers, suggesting AP2A1 facilitates integrin β1 translocation to reinforce focal adhesion and anchorage in senescent cells.","method":"shRNA knockdown; overexpression; immunofluorescence co-localization; live-cell imaging; proteomics","journal":"Cellular signalling","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — bidirectional genetic manipulation (KD and OE) with defined cellular phenotype plus co-localization, single lab","pmids":["39848456"],"is_preprint":false},{"year":2025,"finding":"AP2A1 physically interacts with and activates Rab7 (promotes GTP-loading) in neurons, facilitating recruitment of retrograde axonal transport proteins DIC1 and RILP, enhancing retrograde autophagosome transport, restoring autophagic flux, reducing Aβ accumulation, and improving behavioral deficits in Alzheimer's disease models.","method":"Co-immunoprecipitation; Rab7 pulldown activation assay; molecular docking; live-cell imaging; immunofluorescence; transmission electron microscopy; Western blot; ELISA; behavioral tests (Morris water maze, open field, object recognition, Y-maze)","journal":"Alzheimer's research & therapy","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (Co-IP, GTPase activation assay, live-cell imaging, in vivo rescue), functional readouts in cells and transgenic mice, single lab with comprehensive validation","pmids":["40490761"],"is_preprint":false},{"year":2025,"finding":"Ap2a1 binding to membrane μ-opioid receptors (MORs) in paraventricular thalamus (PVT) neurons regulates MOR trafficking (externalization); reduced Ap2a1–MOR binding was associated with increased membrane MOR levels after fentanyl contextual memory retrieval, and conditional knockdown of MOR in PVT demonstrated MOR's contribution to fentanyl contextual memory through modulation of PVT neuronal activity.","method":"Co-immunoprecipitation; Western blotting; proteomics; conditional knockdown; chemogenetic manipulation; c-Fos immunofluorescence","journal":"Acta pharmacologica Sinica","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus conditional KD and chemogenetics in a single lab, functional behavioral readout","pmids":["41326807"],"is_preprint":false},{"year":2025,"finding":"FMRP associates with AP2A1 mRNA and represses its translation; loss of FMRP in fragile X syndrome models leads to increased steady-state AP2A1 protein levels, enhanced AP-2-dependent endocytosis (including AMPA receptor endocytosis), which is rescued by shRNA downregulation of AP2B1 to wild-type levels.","method":"Quantitative mass spectrometry; FMRP RNA binding assay; Western blot; endocytosis functional assay; shRNA rescue","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-protein association, quantitative proteomics, and functional rescue with shRNA, single lab","pmids":["40740492"],"is_preprint":false},{"year":2025,"finding":"DNAJC5 interacts with AP2A1 and strengthens AP2A1's interaction with EGFR, promoting EGFR endocytosis and recycling in lung adenocarcinoma cells; knockdown of AP2A1 attenuated DNAJC5-driven EGFR endocytosis and cell proliferation/migration.","method":"Co-immunoprecipitation; knockdown experiments; in vitro and in vivo proliferation/migration assays","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus KD with functional cellular readouts, single lab","pmids":["40374748"],"is_preprint":false},{"year":2026,"finding":"MDK (Midkine) activates the PI3K/AKT signaling pathway leading to increased AP2A1 expression, which in turn promotes epithelial-mesenchymal transition (EMT) in colorectal cancer cells; PI3K inhibitor LY294002 significantly reduces AP2A1 levels and inhibits MDK-induced malignant behaviors.","method":"Western blotting; PI3K inhibitor treatment; overexpression/knockdown; in vitro and in vivo functional assays","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological pathway inhibition with AP2A1 protein level readout plus functional assays, single lab","pmids":["42073635"],"is_preprint":false}],"current_model":"AP2A1 (αA-adaptin, the alpha-1 subunit of the AP-2 clathrin adaptor complex) functions as a core component of clathrin-mediated endocytosis (CME), directly mediating internalization of diverse cargo including IGF-1 receptor, μ-opioid receptors, claudin-2, and EGFR; beyond classical CME, AP2A1 acts as a scaffold recruited by MYO1F to promote α-tubulin acetylation for antifungal immune signaling, interacts with and activates the GTPase Rab7 to drive retrograde axonal autophagosome transport relevant to Alzheimer's disease, is subject to translational repression by FMRP (loss of which increases AP2A1 and enhances endocytosis in fragile X syndrome), colocalizes with integrin β1 along actin stress fibers to reinforce cell anchorage during senescence, and mediates Smad3 phosphorylation downstream of full-length IL-33 through a TGF-β receptor-dependent but TGF-β-independent pathway."},"narrative":{"mechanistic_narrative":"AP2A1 is the alpha-1 subunit of the AP-2 clathrin adaptor complex and serves as a core component of clathrin-mediated endocytosis (CME), recruited to endocytic sites concurrently with clathrin to drive cargo internalization [PMID:28484480, PMID:32027876]. It mediates clathrin-dependent uptake of diverse transmembrane cargo: it routes the IGF-1 receptor to Rab11-positive slow-recycling endosomes in keratinocytes, controlling downstream AKT and MAPK signaling [PMID:32027876]; it internalizes claudin-2 for lysosomal degradation during starvation-induced autophagy to tighten junctional permeability [PMID:34964704]; and it cooperates with DNAJC5 to promote EGFR endocytosis and recycling [PMID:40374748]. As an adaptor it also governs receptor trafficking in neurons, regulating μ-opioid receptor externalization in thalamic neurons [PMID:41326807] and acting downstream of FMRP-mediated translational repression, where loss of FMRP raises AP2A1 levels and enhances AP-2-dependent AMPA receptor endocytosis [PMID:40740492]. Beyond classical CME, AP2A1 functions as a scaffold recruited by MYO1F together with ATAT1 to promote α-tubulin acetylation, controlling SYK/CARD9 trafficking in antifungal innate immune signaling [PMID:34301894]; it physically interacts with and GTP-loads Rab7 to recruit DIC1 and RILP, enhancing retrograde axonal autophagosome transport and clearing Aβ in Alzheimer's disease models [PMID:40490761]; it acts as a required mediator of Smad3 phosphorylation downstream of full-length IL-33 and within a circEIF3I–SMAD3–AP2A1 complex that delivers SMAD3 to TGFβRI on endosomes [PMID:32977155, PMID:37689715]; and it accumulates along actin stress fibers in senescent fibroblasts, co-localizing with integrin β1 to reinforce cell anchorage [PMID:39848456]. AP2A1 is required for hematopoietic stem/progenitor cell specification in vivo [PMID:27797851] and accumulates in the detergent-insoluble fraction of Alzheimer's disease brains, isoform-specifically labeling neurofibrillary tangles [PMID:34820873].","teleology":[{"year":2006,"claim":"Established an early physical partner for AP2A1, placing the adaptin in a defined protein-protein context in germ cells before its endocytic roles were dissected.","evidence":"Reciprocal co-immunoprecipitation and confocal co-localization with m-Numb in mouse testis germ cells","pmids":["17127749"],"confidence":"Medium","gaps":["No functional consequence of the Numb interaction tested","Cargo or pathway specificity not defined"]},{"year":2010,"claim":"Demonstrated functional requirement for AP2A1 in CME by showing it is needed for clathrin-dependent viral entry, moving beyond association to loss-of-function dependence.","evidence":"siRNA knockdown, dominant-negative expression, and pharmacological inhibition of HEV71 entry in rhabdomyosarcoma cells","pmids":["20956521"],"confidence":"Medium","gaps":["Direct cargo-AP2A1 contact not mapped","Whether AP2A1 acts in canonical AP-2 complex versus independently not resolved"]},{"year":2016,"claim":"Connected AP2A1 to a developmental program, establishing an organismal requirement distinct from cell-autonomous endocytosis assays.","evidence":"Genome-wide RNAi screen with zebrafish in vivo knockdown of Ap2a1 impairing HSPC development","pmids":["27797851"],"confidence":"Medium","gaps":["Endocytic cargo driving the HSPC phenotype unidentified","Tissue-specific mechanism not dissected"]},{"year":2020,"claim":"Provided the most rigorous mechanistic anchor: AP2A1 sorts a specific receptor (IGF1R) into a defined recycling route and controls its downstream signaling output.","evidence":"shRNA knockdown, reciprocal Co-IP, multimodal imaging, phospho-pathway and Rab11 sorting assays in human keratinocytes","pmids":["32027876"],"confidence":"High","gaps":["Direct sorting motif on IGF1R recognized by AP2A1 not mapped","Generalizability of Rab11 routing to other cargo unknown"]},{"year":2020,"claim":"Extended AP2A1 from a structural endocytic role into a signaling mediator, showing it is required for Smad3 phosphorylation downstream of full-length IL-33 via a TGFBR-dependent pathway.","evidence":"siRNA loss-of-function and overexpression gain-of-function with Smad3 phosphorylation readout in lung fibroblasts; parallel AP2A1 requirement for adenoviral entry","pmids":["32977155","32852546"],"confidence":"Medium","gaps":["Direct AP2A1-TGFBR or AP2A1-Smad3 contact not established in this work","How an adaptor mediates Smad3 activation mechanistically unclear"]},{"year":2021,"claim":"Revealed a moonlighting scaffold function: AP2A1 is recruited by MYO1F to promote α-tubulin acetylation, linking it to cytoskeletal modification and innate immune signaling rather than membrane internalization.","evidence":"Co-IP in macrophages plus Myo1f-knockout mice and antifungal infection models","pmids":["34301894"],"confidence":"Medium","gaps":["Whether AP2A1's adaptor surface or AP-2 complex is involved not resolved","Direct AP2A1-tubulin contact not mapped"]},{"year":2021,"claim":"Linked AP2A1 to autophagy-coupled cargo degradation and to disease pathology, showing it bridges claudin-2/clathrin/LC3 for lysosomal turnover and isoform-specifically marks neurofibrillary tangles.","evidence":"Co-IP, fractionation and inhibitor assays for CLDN2 in intestinal epithelium; validated immunohistochemistry/fractionation in Alzheimer's disease brains","pmids":["34964704","34820873"],"confidence":"Medium","gaps":["Causal role of AP2A1 in tangle formation versus association unknown","Mechanism coupling CME to LC3/lysosomal route not detailed"]},{"year":2023,"claim":"Placed AP2A1 within a circRNA-scaffolded signaling complex, defining how it recruits SMAD3 to endosomal TGFβRI to drive oncogenic signaling.","evidence":"Co-IP, MS2-RNA affinity purification, RNA pulldown and IF establishing the circEIF3I-SMAD3-AP2A1 ternary complex in pancreatic cancer","pmids":["37689715"],"confidence":"Medium","gaps":["Direct AP2A1-SMAD3 binding interface not mapped","Generality beyond pancreatic cancer untested"]},{"year":2025,"claim":"Defined a direct biochemical activity beyond adaptor function: AP2A1 binds and GTP-loads Rab7 to recruit retrograde transport machinery and restore autophagic flux.","evidence":"Co-IP, Rab7 GTPase activation assay, live imaging, and in vivo rescue in Alzheimer's disease mouse models","pmids":["40490761"],"confidence":"High","gaps":["Mechanism by which AP2A1 catalyzes or promotes Rab7 GTP-loading unresolved","Relationship to its CME role in the same neurons unclear"]},{"year":2025,"claim":"Showed AP2A1 dosage is set by FMRP translational control and that it governs neuronal receptor endocytosis, connecting it to fragile X syndrome and synaptic cargo trafficking.","evidence":"FMRP RNA-binding, quantitative proteomics, endocytosis assays and shRNA rescue; plus Co-IP/chemogenetics for μ-opioid receptor trafficking in PVT neurons","pmids":["40740492","41326807"],"confidence":"Medium","gaps":["Direct FMRP-AP2A1 mRNA binding site not mapped","Whether AP2A1 directly binds receptor sorting motifs in neurons untested"]},{"year":2025,"claim":"Implicated AP2A1 in cellular senescence through a cytoskeletal/adhesion role, showing bidirectional control of senescence phenotypes via integrin β1 translocation.","evidence":"shRNA knockdown, overexpression, co-localization and live-cell imaging along actin stress fibers in senescent fibroblasts","pmids":["39848456"],"confidence":"Medium","gaps":["Molecular basis of AP2A1 movement along stress fibers unknown","Direct AP2A1-integrin β1 contact not established"]},{"year":2025,"claim":"Tied AP2A1 expression to oncogenic EGFR trafficking and EMT, positioning it downstream of growth-factor signaling pathways in cancer.","evidence":"DNAJC5-AP2A1 Co-IP and knockdown affecting EGFR endocytosis; MDK/PI3K-AKT regulation of AP2A1 in colorectal cancer with functional assays","pmids":["40374748","42073635"],"confidence":"Medium","gaps":["Whether AP2A1 directly binds EGFR sorting signals not mapped","Causal contribution of AP2A1 to EMT versus correlation incompletely separated"]},{"year":null,"claim":"How AP2A1's canonical AP-2 adaptor function mechanistically relates to its non-endocytic activities (Rab7 GTP-loading, tubulin acetylation scaffolding, SMAD3 recruitment, integrin translocation) and which depend on the intact AP-2 complex remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model distinguishing adaptor versus moonlighting surfaces","Direct cargo-recognition motifs not mapped for most substrates","Whether functions are AP-2-complex-dependent or AP2A1-autonomous untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[5,8,3,18]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[15,9]}],"localization":[{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[5,8,16]},{"term_id":"GO:0031410","term_label":"cytoplasmic vesicle","supporting_discovery_ids":[5,8,11]},{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[11,5]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[14,9]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[5,8,18,3]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[8,15,13]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,6,11]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[9,13]}],"complexes":["AP-2 clathrin adaptor complex","circEIF3I-SMAD3-AP2A1 complex"],"partners":["AP2B1","CLDN2","IGF1R","EGFR","RAB7","SMAD3","DNAJC5","MYO1F"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O95782","full_name":"AP-2 complex subunit alpha-1","aliases":["100 kDa coated vesicle protein A","Adaptor protein complex AP-2 subunit alpha-1","Adaptor-related protein complex 2 subunit alpha-1","Alpha-adaptin A","Alpha1-adaptin","Clathrin assembly protein complex 2 alpha-A large chain","Plasma membrane adaptor HA2/AP2 adaptin alpha A subunit"],"length_aa":977,"mass_kda":107.5,"function":"Component of the adaptor protein complex 2 (AP-2). Adaptor protein complexes function in protein transport via transport vesicles in different membrane traffic pathways. Adaptor protein complexes are vesicle coat components and appear to be involved in cargo selection and vesicle formation. AP-2 is involved in clathrin-dependent endocytosis in which cargo proteins are incorporated into vesicles surrounded by clathrin (clathrin-coated vesicles, CCVs) which are destined for fusion with the early endosome. The clathrin lattice serves as a mechanical scaffold but is itself unable to bind directly to membrane components. Clathrin-associated adaptor protein (AP) complexes which can bind directly to both the clathrin lattice and to the lipid and protein components of membranes are considered to be the major clathrin adaptors contributing the CCV formation. AP-2 also serves as a cargo receptor to selectively sort the membrane proteins involved in receptor-mediated endocytosis. AP-2 seems to play a role in the recycling of synaptic vesicle membranes from the presynaptic surface. AP-2 recognizes Y-X-X-[FILMV] (Y-X-X-Phi) and [ED]-X-X-X-L-[LI] endocytosis signal motifs within the cytosolic tails of transmembrane cargo molecules. AP-2 may also play a role in maintaining normal post-endocytic trafficking through the ARF6-regulated, non-clathrin pathway. During long-term potentiation in hippocampal neurons, AP-2 is responsible for the endocytosis of ADAM10 (PubMed:23676497). The AP-2 alpha subunit binds polyphosphoinositide-containing lipids, positioning AP-2 on the membrane. The AP-2 alpha subunit acts via its C-terminal appendage domain as a scaffolding platform for endocytic accessory proteins. The AP-2 alpha and AP-2 sigma subunits are thought to contribute to the recognition of the [ED]-X-X-X-L-[LI] motif (By similarity)","subcellular_location":"Cell membrane; Membrane, coated pit","url":"https://www.uniprot.org/uniprotkb/O95782/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/AP2A1","classification":"Not Classified","n_dependent_lines":36,"n_total_lines":1208,"dependency_fraction":0.029801324503311258},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"AP2B1","stoichiometry":10.0},{"gene":"AP2S1","stoichiometry":4.0},{"gene":"CLTA","stoichiometry":0.2},{"gene":"CLTB","stoichiometry":0.2},{"gene":"EPS15","stoichiometry":0.2},{"gene":"NECAP1","stoichiometry":0.2},{"gene":"NECAP2","stoichiometry":0.2},{"gene":"RALBP1","stoichiometry":0.2},{"gene":"SF3B1","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/AP2A1","total_profiled":1310},"omim":[{"mim_id":"616826","title":"EPS15-LIKE PROTEIN 1; EPS15L1","url":"https://www.omim.org/entry/616826"},{"mim_id":"614888","title":"ALPHA- AND GAMMA-ADAPTIN-BINDING PROTEIN; AAGAB","url":"https://www.omim.org/entry/614888"},{"mim_id":"614825","title":"RALBP1-ASSOCIATED EPS DOMAIN-CONTAINING PROTEIN 1; REPS1","url":"https://www.omim.org/entry/614825"},{"mim_id":"612453","title":"MULTIPLE EPIDERMAL GROWTH FACTOR-LIKE DOMAINS 10; MEGF10","url":"https://www.omim.org/entry/612453"},{"mim_id":"611624","title":"NECAP ENDOCYTOSIS-ASSOCIATED PROTEIN 2; NECAP2","url":"https://www.omim.org/entry/611624"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Vesicles","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/AP2A1"},"hgnc":{"alias_symbol":[],"prev_symbol":["CLAPA1","ADTAA"]},"alphafold":{"accession":"O95782","domains":[{"cath_id":"1.25.40","chopping":"185-320","consensus_level":"medium","plddt":93.4994,"start":185,"end":320},{"cath_id":"1.25.10.10","chopping":"378-598","consensus_level":"medium","plddt":91.8071,"start":378,"end":598},{"cath_id":"2.60.40.1230","chopping":"737-858","consensus_level":"high","plddt":91.2439,"start":737,"end":858},{"cath_id":"3.30.310.10","chopping":"861-974","consensus_level":"high","plddt":90.2518,"start":861,"end":974}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95782","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95782-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95782-F1-predicted_aligned_error_v6.png","plddt_mean":83.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=AP2A1","jax_strain_url":"https://www.jax.org/strain/search?query=AP2A1"},"sequence":{"accession":"O95782","fasta_url":"https://rest.uniprot.org/uniprotkb/O95782.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95782/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95782"}},"corpus_meta":[{"pmid":"25427136","id":"PMC_25427136","title":"Inhibition 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microscopy\",\n      \"journal\": \"Reproduction (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — reciprocal co-IP and co-localization in two cell types, single lab\",\n      \"pmids\": [\"17127749\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"AP2A1 is required for clathrin-mediated endocytosis (CME)-dependent entry of human enterovirus 71 (HEV71) into rhabdomyosarcoma cells; siRNA knockdown of AP2A1 significantly inhibited HEV71 infection in a dose-dependent manner, placing AP2A1 in the CME pathway essential for viral entry.\",\n      \"method\": \"siRNA knockdown; immunofluorescence co-localization; dominant-negative mutant expression; drug inhibition assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (siRNA, dominant-negative, pharmacological inhibition, co-localization) in a single study\",\n      \"pmids\": [\"20956521\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"AP2A1 (along with AP2A2 and AP2B1) shows increased protein levels associated with the EGFR interactome in erlotinib-resistant non-small cell lung cancer cells (HCC4006rERLO0.5) compared to parental cells, identified by affinity purification coupled with mass spectrometry.\",\n      \"method\": \"Affinity purification-mass spectrometry (AP-MS)\",\n      \"journal\": \"European journal of pharmaceutical sciences\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single AP-MS experiment, no functional follow-up on AP2A1 specifically\",\n      \"pmids\": [\"27112992\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"AP2A1 (alpha subunit of AP-2) is recruited to clathrin-mediated endocytosis sites concurrently with clathrin in Arabidopsis plant cells, as shown by TIRF microscopy using a departure assay; this temporal recruitment pattern differs from AP2M (mu subunit), which is not recruited in concert with clathrin.\",\n      \"method\": \"Total internal reflection fluorescence (TIRF) microscopy; automated departure assay\",\n      \"journal\": \"Frontiers in plant science\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — TIRF localization study in plant cells (potential ortholog context), single lab, no functional mutagenesis\",\n      \"pmids\": [\"28484480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Ap2a1 is required for hematopoietic stem/progenitor cell (HSPC) specification and development; knockdown of Ap2a1 in zebrafish impaired HSPC development in vivo, validating it as a gene essential for the endothelial-to-hematopoietic transition identified in a genome-wide RNAi screen.\",\n      \"method\": \"Genome-wide RNAi screen (in vitro ESC differentiation); zebrafish in vivo knockdown validation\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal systems (in vitro screen + in vivo zebrafish), single lab\",\n      \"pmids\": [\"27797851\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"AP2A1/2 complex mediates clathrin-dependent endocytosis of IGF-1 receptor (IGF1R) in human keratinocytes; concurrent shRNA knockdown of AP2A1/2 and FLOT1/2 reduced IGF1R association with clathrin, internalization, and downstream pathway activation (phospho-IGF1R, phospho-AKT, phospho-MAPK) by >50%. AP2A1/2-mediated endocytosis routes IGF1R to Rab11-positive slow recycling endosomes, distinguishing it from the Flot-1/Rab4 fast-recycling pathway.\",\n      \"method\": \"shRNA knockdown; confocal/TIRF/SIM microscopy; co-immunoprecipitation; Western blot (phosphorylation assays); Rab11 association assay\",\n      \"journal\": \"The Journal of investigative dermatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, multiple imaging modalities, functional rescue assays, pathway activation quantification, and Rab11 sorting established with orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"32027876\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"AP2A1 and AP2B1 subunits of AP-2 complex are upregulated by full-length IL-33 (FLIL33) overexpression in human lung fibroblasts, and siRNA-mediated knockdown of AP2A1/AP2B1 blocked FLIL33-induced Smad3 phosphorylation, while AP-2 subunit overexpression induced Smad3 phosphorylation independently of FLIL33, placing AP2A1 as a required mediator of TGFBR-dependent Smad3 activation downstream of FLIL33.\",\n      \"method\": \"siRNA knockdown; Western blotting; overexpression experiments\",\n      \"journal\": \"Cellular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function and gain-of-function experiments with defined signaling readout (Smad3 phosphorylation), single lab\",\n      \"pmids\": [\"32977155\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"AP2A1 siRNA knockdown and pharmacological inhibition of clathrin-mediated endocytosis blocked HAdV-D37 (human adenovirus type 37) early gene expression in human corneal epithelial cells, establishing AP2A1 as required for this noncanonical clathrin-mediated viral entry pathway.\",\n      \"method\": \"siRNA knockdown; quantitative PCR; Western blot; chemical inhibitor assays\",\n      \"journal\": \"Investigative ophthalmology & visual science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with gene expression readout plus pharmacological inhibition, single lab\",\n      \"pmids\": [\"32852546\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"AP2A1 (alpha-1 subunit of AP-2) associates with CLDN2 (claudin-2), clathrin, and LC3 upon starvation-induced autophagy in intestinal epithelial cells, as shown by co-immunoprecipitation; this interaction facilitates clathrin-mediated endocytosis of CLDN2 followed by lysosomal degradation, thereby reducing tight junction permeability.\",\n      \"method\": \"Co-immunoprecipitation; membrane fractionation; immunofluorescence; pharmacological inhibition\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with multiple partners, fractionation, and pharmacological inhibition in a single lab study\",\n      \"pmids\": [\"34964704\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"AP2A1 is recruited by MYO1F as an adaptor to α-tubulin during Dectin-1-induced signaling in macrophages; MYO1F acts as a scaffold recruiting both AP2A1 and α-tubulin N-acetyltransferase 1 (ATAT1) to α-tubulin to promote its acetylation, which in turn controls membrane-to-cytoplasm trafficking of SYK and CARD9 required for antifungal innate immune signaling.\",\n      \"method\": \"Co-immunoprecipitation; knockdown (Myo1f-deficient mice); in vivo infection models; Western blot\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP in macrophages plus genetic knockout mouse model with functional immune readout, single lab\",\n      \"pmids\": [\"34301894\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"AP2A1 colocalizes with tau pathology (neurofibrillary tangles) in Alzheimer's disease brains and is present in the detergent-insoluble fraction of cognitively impaired but not control brains, in an isoform-specific manner (AP2A1 but not AP2A2 labels neurofibrillary tangles), as determined by immunohistochemistry and immunofluorescence with antibody specificity validated by immunoblot after plasmid transfection.\",\n      \"method\": \"Immunoblot (after plasmid transfection for antibody validation); immunohistochemistry; immunofluorescence; fractionation\",\n      \"journal\": \"Neuropathology and applied neurobiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — validated antibody specificity with transfection controls, histochemistry across multiple brain samples, single lab\",\n      \"pmids\": [\"34820873\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"AP2A1 binds directly to the circRNA circEIF3I and interacts with SMAD3, forming a ternary complex (circEIF3I–SMAD3–AP2A1) that facilitates recruitment of SMAD3 to TGFβRI on early endosomes, thereby promoting SMAD3 phosphorylation and activation of MMPs in pancreatic cancer cells.\",\n      \"method\": \"Co-immunoprecipitation; MS2-RNA affinity purification; mass spectrometry; RNA immunoprecipitation; RNA pulldown; immunofluorescence; RNA-protein interaction simulation\",\n      \"journal\": \"Molecular cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, RNA pulldown, IF), single lab, AP2A1 role defined within a ternary complex context\",\n      \"pmids\": [\"37689715\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"AP2A1 expression in the orbitofrontal cortex predicts alcohol use disorder severity; prefrontal Ap2a1 expression significantly correlates with voluntary alcohol drinking in genetically diverse mice, and recombinant inbred strains inheriting the C57BL/6J Ap2a1 allele consumed more alcohol than those inheriting the DBA/2J allele, linking AP2A1 to synaptic/presynaptic endocytosis mechanisms governing drinking behavior.\",\n      \"method\": \"Proteomics; machine learning; reverse genetics (mouse strains); gene expression correlation\",\n      \"journal\": \"Molecular psychiatry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — genetic association via recombinant inbred strains and expression correlation, no direct mechanistic manipulation of AP2A1 in neurons\",\n      \"pmids\": [\"37679472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Radiation-induced ROS accumulation triggers excessive autophagy in NK cells, leading to increased association of the NKG2D receptor with AP2A1, AP2M1, LC3, and lysosomes, resulting in NKG2D endocytosis and lysosomal degradation that impairs NK cell function; this was demonstrated by immunoprecipitation after radiation exposure.\",\n      \"method\": \"Immunoprecipitation; immunofluorescence; Western blot\",\n      \"journal\": \"Frontiers in immunology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP experiment with limited mechanistic follow-up on AP2A1 specifically, single lab\",\n      \"pmids\": [\"38077388\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"AP2A1 is upregulated in replicatively senescent human fibroblasts along enlarged actin stress fibers; AP2A1 knockdown reversed senescence-associated phenotypes (rejuvenation), while overexpression in young cells accelerated senescence. AP2A1 co-localizes with integrin β1 and both move linearly along stress fibers, suggesting AP2A1 facilitates integrin β1 translocation to reinforce focal adhesion and anchorage in senescent cells.\",\n      \"method\": \"shRNA knockdown; overexpression; immunofluorescence co-localization; live-cell imaging; proteomics\",\n      \"journal\": \"Cellular signalling\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — bidirectional genetic manipulation (KD and OE) with defined cellular phenotype plus co-localization, single lab\",\n      \"pmids\": [\"39848456\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"AP2A1 physically interacts with and activates Rab7 (promotes GTP-loading) in neurons, facilitating recruitment of retrograde axonal transport proteins DIC1 and RILP, enhancing retrograde autophagosome transport, restoring autophagic flux, reducing Aβ accumulation, and improving behavioral deficits in Alzheimer's disease models.\",\n      \"method\": \"Co-immunoprecipitation; Rab7 pulldown activation assay; molecular docking; live-cell imaging; immunofluorescence; transmission electron microscopy; Western blot; ELISA; behavioral tests (Morris water maze, open field, object recognition, Y-maze)\",\n      \"journal\": \"Alzheimer's research & therapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (Co-IP, GTPase activation assay, live-cell imaging, in vivo rescue), functional readouts in cells and transgenic mice, single lab with comprehensive validation\",\n      \"pmids\": [\"40490761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Ap2a1 binding to membrane μ-opioid receptors (MORs) in paraventricular thalamus (PVT) neurons regulates MOR trafficking (externalization); reduced Ap2a1–MOR binding was associated with increased membrane MOR levels after fentanyl contextual memory retrieval, and conditional knockdown of MOR in PVT demonstrated MOR's contribution to fentanyl contextual memory through modulation of PVT neuronal activity.\",\n      \"method\": \"Co-immunoprecipitation; Western blotting; proteomics; conditional knockdown; chemogenetic manipulation; c-Fos immunofluorescence\",\n      \"journal\": \"Acta pharmacologica Sinica\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus conditional KD and chemogenetics in a single lab, functional behavioral readout\",\n      \"pmids\": [\"41326807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"FMRP associates with AP2A1 mRNA and represses its translation; loss of FMRP in fragile X syndrome models leads to increased steady-state AP2A1 protein levels, enhanced AP-2-dependent endocytosis (including AMPA receptor endocytosis), which is rescued by shRNA downregulation of AP2B1 to wild-type levels.\",\n      \"method\": \"Quantitative mass spectrometry; FMRP RNA binding assay; Western blot; endocytosis functional assay; shRNA rescue\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-protein association, quantitative proteomics, and functional rescue with shRNA, single lab\",\n      \"pmids\": [\"40740492\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"DNAJC5 interacts with AP2A1 and strengthens AP2A1's interaction with EGFR, promoting EGFR endocytosis and recycling in lung adenocarcinoma cells; knockdown of AP2A1 attenuated DNAJC5-driven EGFR endocytosis and cell proliferation/migration.\",\n      \"method\": \"Co-immunoprecipitation; knockdown experiments; in vitro and in vivo proliferation/migration assays\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus KD with functional cellular readouts, single lab\",\n      \"pmids\": [\"40374748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"MDK (Midkine) activates the PI3K/AKT signaling pathway leading to increased AP2A1 expression, which in turn promotes epithelial-mesenchymal transition (EMT) in colorectal cancer cells; PI3K inhibitor LY294002 significantly reduces AP2A1 levels and inhibits MDK-induced malignant behaviors.\",\n      \"method\": \"Western blotting; PI3K inhibitor treatment; overexpression/knockdown; in vitro and in vivo functional assays\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological pathway inhibition with AP2A1 protein level readout plus functional assays, single lab\",\n      \"pmids\": [\"42073635\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"AP2A1 (αA-adaptin, the alpha-1 subunit of the AP-2 clathrin adaptor complex) functions as a core component of clathrin-mediated endocytosis (CME), directly mediating internalization of diverse cargo including IGF-1 receptor, μ-opioid receptors, claudin-2, and EGFR; beyond classical CME, AP2A1 acts as a scaffold recruited by MYO1F to promote α-tubulin acetylation for antifungal immune signaling, interacts with and activates the GTPase Rab7 to drive retrograde axonal autophagosome transport relevant to Alzheimer's disease, is subject to translational repression by FMRP (loss of which increases AP2A1 and enhances endocytosis in fragile X syndrome), colocalizes with integrin β1 along actin stress fibers to reinforce cell anchorage during senescence, and mediates Smad3 phosphorylation downstream of full-length IL-33 through a TGF-β receptor-dependent but TGF-β-independent pathway.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"AP2A1 is the alpha-1 subunit of the AP-2 clathrin adaptor complex and serves as a core component of clathrin-mediated endocytosis (CME), recruited to endocytic sites concurrently with clathrin to drive cargo internalization [#3, #5]. It mediates clathrin-dependent uptake of diverse transmembrane cargo: it routes the IGF-1 receptor to Rab11-positive slow-recycling endosomes in keratinocytes, controlling downstream AKT and MAPK signaling [#5]; it internalizes claudin-2 for lysosomal degradation during starvation-induced autophagy to tighten junctional permeability [#8]; and it cooperates with DNAJC5 to promote EGFR endocytosis and recycling [#18]. As an adaptor it also governs receptor trafficking in neurons, regulating μ-opioid receptor externalization in thalamic neurons [#16] and acting downstream of FMRP-mediated translational repression, where loss of FMRP raises AP2A1 levels and enhances AP-2-dependent AMPA receptor endocytosis [#17]. Beyond classical CME, AP2A1 functions as a scaffold recruited by MYO1F together with ATAT1 to promote α-tubulin acetylation, controlling SYK/CARD9 trafficking in antifungal innate immune signaling [#9]; it physically interacts with and GTP-loads Rab7 to recruit DIC1 and RILP, enhancing retrograde axonal autophagosome transport and clearing Aβ in Alzheimer's disease models [#15]; it acts as a required mediator of Smad3 phosphorylation downstream of full-length IL-33 and within a circEIF3I–SMAD3–AP2A1 complex that delivers SMAD3 to TGFβRI on endosomes [#6, #11]; and it accumulates along actin stress fibers in senescent fibroblasts, co-localizing with integrin β1 to reinforce cell anchorage [#14]. AP2A1 is required for hematopoietic stem/progenitor cell specification in vivo [#4] and accumulates in the detergent-insoluble fraction of Alzheimer's disease brains, isoform-specifically labeling neurofibrillary tangles [#10].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Established an early physical partner for AP2A1, placing the adaptin in a defined protein-protein context in germ cells before its endocytic roles were dissected.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation and confocal co-localization with m-Numb in mouse testis germ cells\",\n      \"pmids\": [\"17127749\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence of the Numb interaction tested\", \"Cargo or pathway specificity not defined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated functional requirement for AP2A1 in CME by showing it is needed for clathrin-dependent viral entry, moving beyond association to loss-of-function dependence.\",\n      \"evidence\": \"siRNA knockdown, dominant-negative expression, and pharmacological inhibition of HEV71 entry in rhabdomyosarcoma cells\",\n      \"pmids\": [\"20956521\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct cargo-AP2A1 contact not mapped\", \"Whether AP2A1 acts in canonical AP-2 complex versus independently not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Connected AP2A1 to a developmental program, establishing an organismal requirement distinct from cell-autonomous endocytosis assays.\",\n      \"evidence\": \"Genome-wide RNAi screen with zebrafish in vivo knockdown of Ap2a1 impairing HSPC development\",\n      \"pmids\": [\"27797851\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endocytic cargo driving the HSPC phenotype unidentified\", \"Tissue-specific mechanism not dissected\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Provided the most rigorous mechanistic anchor: AP2A1 sorts a specific receptor (IGF1R) into a defined recycling route and controls its downstream signaling output.\",\n      \"evidence\": \"shRNA knockdown, reciprocal Co-IP, multimodal imaging, phospho-pathway and Rab11 sorting assays in human keratinocytes\",\n      \"pmids\": [\"32027876\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct sorting motif on IGF1R recognized by AP2A1 not mapped\", \"Generalizability of Rab11 routing to other cargo unknown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended AP2A1 from a structural endocytic role into a signaling mediator, showing it is required for Smad3 phosphorylation downstream of full-length IL-33 via a TGFBR-dependent pathway.\",\n      \"evidence\": \"siRNA loss-of-function and overexpression gain-of-function with Smad3 phosphorylation readout in lung fibroblasts; parallel AP2A1 requirement for adenoviral entry\",\n      \"pmids\": [\"32977155\", \"32852546\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct AP2A1-TGFBR or AP2A1-Smad3 contact not established in this work\", \"How an adaptor mediates Smad3 activation mechanistically unclear\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Revealed a moonlighting scaffold function: AP2A1 is recruited by MYO1F to promote α-tubulin acetylation, linking it to cytoskeletal modification and innate immune signaling rather than membrane internalization.\",\n      \"evidence\": \"Co-IP in macrophages plus Myo1f-knockout mice and antifungal infection models\",\n      \"pmids\": [\"34301894\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether AP2A1's adaptor surface or AP-2 complex is involved not resolved\", \"Direct AP2A1-tubulin contact not mapped\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Linked AP2A1 to autophagy-coupled cargo degradation and to disease pathology, showing it bridges claudin-2/clathrin/LC3 for lysosomal turnover and isoform-specifically marks neurofibrillary tangles.\",\n      \"evidence\": \"Co-IP, fractionation and inhibitor assays for CLDN2 in intestinal epithelium; validated immunohistochemistry/fractionation in Alzheimer's disease brains\",\n      \"pmids\": [\"34964704\", \"34820873\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Causal role of AP2A1 in tangle formation versus association unknown\", \"Mechanism coupling CME to LC3/lysosomal route not detailed\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Placed AP2A1 within a circRNA-scaffolded signaling complex, defining how it recruits SMAD3 to endosomal TGFβRI to drive oncogenic signaling.\",\n      \"evidence\": \"Co-IP, MS2-RNA affinity purification, RNA pulldown and IF establishing the circEIF3I-SMAD3-AP2A1 ternary complex in pancreatic cancer\",\n      \"pmids\": [\"37689715\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct AP2A1-SMAD3 binding interface not mapped\", \"Generality beyond pancreatic cancer untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Defined a direct biochemical activity beyond adaptor function: AP2A1 binds and GTP-loads Rab7 to recruit retrograde transport machinery and restore autophagic flux.\",\n      \"evidence\": \"Co-IP, Rab7 GTPase activation assay, live imaging, and in vivo rescue in Alzheimer's disease mouse models\",\n      \"pmids\": [\"40490761\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which AP2A1 catalyzes or promotes Rab7 GTP-loading unresolved\", \"Relationship to its CME role in the same neurons unclear\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed AP2A1 dosage is set by FMRP translational control and that it governs neuronal receptor endocytosis, connecting it to fragile X syndrome and synaptic cargo trafficking.\",\n      \"evidence\": \"FMRP RNA-binding, quantitative proteomics, endocytosis assays and shRNA rescue; plus Co-IP/chemogenetics for μ-opioid receptor trafficking in PVT neurons\",\n      \"pmids\": [\"40740492\", \"41326807\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct FMRP-AP2A1 mRNA binding site not mapped\", \"Whether AP2A1 directly binds receptor sorting motifs in neurons untested\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Implicated AP2A1 in cellular senescence through a cytoskeletal/adhesion role, showing bidirectional control of senescence phenotypes via integrin β1 translocation.\",\n      \"evidence\": \"shRNA knockdown, overexpression, co-localization and live-cell imaging along actin stress fibers in senescent fibroblasts\",\n      \"pmids\": [\"39848456\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of AP2A1 movement along stress fibers unknown\", \"Direct AP2A1-integrin β1 contact not established\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Tied AP2A1 expression to oncogenic EGFR trafficking and EMT, positioning it downstream of growth-factor signaling pathways in cancer.\",\n      \"evidence\": \"DNAJC5-AP2A1 Co-IP and knockdown affecting EGFR endocytosis; MDK/PI3K-AKT regulation of AP2A1 in colorectal cancer with functional assays\",\n      \"pmids\": [\"40374748\", \"42073635\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether AP2A1 directly binds EGFR sorting signals not mapped\", \"Causal contribution of AP2A1 to EMT versus correlation incompletely separated\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How AP2A1's canonical AP-2 adaptor function mechanistically relates to its non-endocytic activities (Rab7 GTP-loading, tubulin acetylation scaffolding, SMAD3 recruitment, integrin translocation) and which depend on the intact AP-2 complex remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model distinguishing adaptor versus moonlighting surfaces\", \"Direct cargo-recognition motifs not mapped for most substrates\", \"Whether functions are AP-2-complex-dependent or AP2A1-autonomous untested\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [5, 8, 3, 18]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [15, 9]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [5, 8, 16]},\n      {\"term_id\": \"GO:0031410\", \"supporting_discovery_ids\": [5, 8, 11]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [11, 5]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [14, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [5, 8, 18, 3]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [8, 15, 13]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 6, 11]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [9, 13]}\n    ],\n    \"complexes\": [\"AP-2 clathrin adaptor complex\", \"circEIF3I-SMAD3-AP2A1 complex\"],\n    \"partners\": [\"AP2B1\", \"CLDN2\", \"IGF1R\", \"EGFR\", \"RAB7\", \"SMAD3\", \"DNAJC5\", \"MYO1F\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}