{"gene":"APPBP2","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2023,"finding":"CUL2-APPBP2 is the ubiquitin E3 ligase that determines PRDM16 protein stability by catalysing its polyubiquitination. Inhibition of CUL2-APPBP2 extended the half-life of PRDM16 protein and promoted beige adipocyte biogenesis. Adipocyte-specific deletion of CUL2-APPBP2 counteracted diet-induced obesity and metabolic dysfunction in mice.","method":"Biochemical ubiquitination assays, protein half-life measurement, adipocyte-specific CUL2-APPBP2 knockout mouse model with metabolic phenotyping","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (biochemical assays, KO mouse model, metabolic phenotyping) in a single rigorous study establishing E3 ligase-substrate relationship","pmids":["35978186"],"is_preprint":false},{"year":2023,"finding":"APPBP2 (as part of CRL2APPBP2) specifically recognizes R-x-x-G/C-degrons at or near the C-terminus of substrate proteins via a bipartite mechanism, where arginine and glycine occupy distinct pockets spaced by two residues. The binding pocket accommodates the motif placed at or up to three residues upstream of the C-terminus. CRL2APPBP2 assembles as a dimer and tetramer.","method":"Cryo-EM structure determination of active CRL2APPBP2 bound with different R-x-x-G/C-degrons, complemented by binding experiments and cell-based assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures with multiple degron complexes, binding experiments, and cell-based validation in a single rigorous study","pmids":["37844242"],"is_preprint":false},{"year":2023,"finding":"CRL2APPBP2 ubiquitin ligase targets TSPYL2 (a negative regulator of proliferation) for ubiquitin-proteasome-mediated degradation via APPBP2 as the substrate receptor. This degradation downregulates P21waf1/cip1 and delays senescence in human mesenchymal stem cells.","method":"CRISPR/Cas9-mediated CUL2 deletion, differentiation of hESCs into hMSCs, identification of TSPYL2 as substrate via APPBP2 substrate receptor, proteasome inhibition assays, senescence phenotype analysis","journal":"Science China. Life sciences","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR KO with defined cellular phenotype and substrate identification, single lab","pmids":["38170390"],"is_preprint":false},{"year":2023,"finding":"A multiplex CRISPR screening platform identified substrates and degron motifs for Cul2APPBP2, refining understanding of the C-degron pathways it targets and confirming its substrate specificity within the ubiquitin-proteasome system.","method":"Multiplex CRISPR screening (~100 screens in a single experiment) with site-saturation mutagenesis for degron identification","journal":"Nature cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — large-scale CRISPR screen with mutagenesis, but APPBP2-specific mechanistic detail is not fully described in the abstract","pmids":["37735597"],"is_preprint":false},{"year":2019,"finding":"APPBP2 physically interacts with PPM1D (as shown by co-immunoprecipitation) and promotes NSCLC cell proliferation, migration, and invasion. Silencing APPBP2 decreases PPM1D and SPOP expression, and overexpression of PPM1D or SPOP rescues the inhibitory effects of APPBP2 knockdown.","method":"Co-immunoprecipitation, shRNA knockdown, overexpression rescue experiments, cell proliferation and invasion assays, xenograft tumor growth","journal":"EBioMedicine","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single Co-IP plus functional rescue experiments, single lab, multiple cell-based methods","pmids":["31105033"],"is_preprint":false},{"year":2019,"finding":"PAT1/APPBP2 colocalizes with early endosomal markers (Rab5, Rab4, EEA1, Rabaptin-5) but not with Rab11 or Rab7. PAT1 expression regulates the number of EEA1 and Rab5 vesicles and the endocytosis/recycling of transferrin receptor. Overexpression of the APP binding domain of PAT1 is sufficient to compromise endocytosis.","method":"Colocalization by fluorescence microscopy, live imaging, transferrin uptake assay, domain overexpression","journal":"Cellular and molecular life sciences : CMLS","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization experiments with functional consequence (endocytosis assay), multiple orthogonal approaches, single lab","pmids":["31139847"],"is_preprint":false},{"year":2009,"finding":"SLY1 (mouse Y-linked spermatid protein) interacts with the microtubule-associated protein APPBP2, as demonstrated by yeast two-hybrid and co-immunoprecipitation studies.","method":"Yeast two-hybrid assay, co-immunoprecipitation","journal":"Biology of reproduction","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP/Y2H identifying APPBP2 as a binding partner of SLY1, no further mechanistic characterization of APPBP2 function","pmids":["19176879"],"is_preprint":false},{"year":2014,"finding":"Appbp2 is a novel thyroid hormone (TH)-responsive gene in the fetal cerebral cortex, with thyroid hormone response elements confirmed in the Appbp2 gene.","method":"Gene expression microarray in fetal mouse cortex with TH manipulation, confirmation of TH response elements","journal":"Cerebral cortex (New York, N.Y. : 1991)","confidence":"Low","confidence_rationale":"Tier 3 / Weak — identification of TH-responsive transcriptional regulation via microarray and TH response element confirmation, but no downstream functional mechanism established for APPBP2 protein","pmids":["24436321"],"is_preprint":false}],"current_model":"APPBP2 is the substrate receptor of the CUL2-RING E3 ubiquitin ligase complex (CRL2APPBP2), which recognizes substrates bearing C-terminal R-x-x-G/C-degron motifs via a bipartite mechanism (structurally resolved by cryo-EM) and mediates their polyubiquitination and proteasomal degradation; established substrates include PRDM16 (regulating beige adipogenesis) and TSPYL2 (counteracting stem cell senescence), and APPBP2 also functions in early endocytosis and interacts with PPM1D to promote cancer cell proliferation and invasion."},"narrative":{"mechanistic_narrative":"APPBP2 is the substrate-recognition subunit of a CUL2-RING E3 ubiquitin ligase (CRL2APPBP2) that targets proteins bearing C-terminal R-x-x-G/C degron motifs for polyubiquitination and proteasomal degradation [PMID:35978186, PMID:37844242, PMID:37735597]. Cryo-EM of the active complex shows that APPBP2 engages the degron through a bipartite pocket in which the arginine and glycine occupy distinct subsites spaced by two residues, accommodating motifs at or within three residues of the C-terminus, and that the ligase assembles into dimeric and tetrameric forms [PMID:37844242]. Through this activity APPBP2 sets the abundance of specific substrates: it polyubiquitinates PRDM16, controlling its half-life and thereby beige adipocyte biogenesis and systemic metabolic homeostasis [PMID:35978186], and it degrades TSPYL2 to downregulate P21waf1/cip1 and delay senescence in human mesenchymal stem cells [PMID:38170390]. Independently of its E3 ligase role, APPBP2 localizes to early endosomes, where it regulates Rab5/EEA1 vesicle number and transferrin receptor endocytosis and recycling [PMID:31139847]. In non-small-cell lung cancer cells APPBP2 physically associates with PPM1D and supports proliferation, migration, and invasion, with PPM1D and SPOP acting downstream of its effects [PMID:31105033].","teleology":[{"year":2009,"claim":"An early interaction screen placed APPBP2 in a protein-binding context, identifying it as a microtubule-associated partner of the spermatid protein SLY1 before any enzymatic role was known.","evidence":"Yeast two-hybrid and co-immunoprecipitation","pmids":["19176879"],"confidence":"Low","gaps":["Single Y2H/Co-IP without reciprocal validation or functional consequence","No mechanistic role for APPBP2 established","Relevance of microtubule association to later E3 ligase function unresolved"]},{"year":2014,"claim":"Transcriptional profiling showed APPBP2 is a thyroid-hormone-responsive gene in fetal cortex, addressing how its expression is regulated but not what the protein does.","evidence":"Expression microarray with thyroid hormone manipulation and TH response element confirmation in fetal mouse cortex","pmids":["24436321"],"confidence":"Low","gaps":["No downstream protein function established","Physiological role of TH-induced APPBP2 in brain development unknown"]},{"year":2019,"claim":"Two studies expanded APPBP2 function beyond a binding partner: one assigned it an early-endocytic role, the other linked it to cancer cell proliferation through PPM1D.","evidence":"Endosomal marker colocalization, transferrin uptake and domain-overexpression assays; and co-immunoprecipitation with shRNA knockdown, rescue, and xenograft assays in NSCLC","pmids":["31139847","31105033"],"confidence":"Medium","gaps":["Endocytic role not mechanistically connected to E3 ligase activity","PPM1D interaction is a single Co-IP without reciprocal validation","Whether the PPM1D effect involves ubiquitin ligase activity is untested"]},{"year":2023,"claim":"APPBP2 was defined as a CUL2 substrate receptor and a physiological E3 ligase, with PRDM16 identified as a substrate whose degradation gates beige adipogenesis and metabolic health.","evidence":"Biochemical ubiquitination assays, protein half-life measurement, and adipocyte-specific CUL2-APPBP2 knockout mice with metabolic phenotyping","pmids":["35978186"],"confidence":"High","gaps":["Degron in PRDM16 not yet defined in this study","Regulation of CRL2APPBP2 assembly/activity in adipocytes unknown"]},{"year":2023,"claim":"Structural and screening work established the molecular logic of substrate recognition, showing CRL2APPBP2 reads C-terminal R-x-x-G/C degrons via a bipartite pocket and identifying its substrate repertoire.","evidence":"Cryo-EM of CRL2APPBP2 bound to multiple degrons with binding and cell-based assays; and multiplex CRISPR screening with site-saturation mutagenesis","pmids":["37844242","37735597"],"confidence":"High","gaps":["Functional significance of dimer/tetramer assembly states unresolved","Full physiological substrate set not enumerated"]},{"year":2023,"claim":"A second physiological substrate, TSPYL2, was identified, connecting CRL2APPBP2 activity to P21-dependent control of stem cell senescence.","evidence":"CRISPR/Cas9 CUL2 deletion, hESC-to-hMSC differentiation, proteasome inhibition, and senescence phenotyping","pmids":["38170390"],"confidence":"Medium","gaps":["Direct degron in TSPYL2 not structurally mapped","Single-lab study without orthogonal substrate confirmation"]},{"year":null,"claim":"How APPBP2's endosomal/microtubule-associated roles relate mechanistically to its CRL2 E3 ligase activity, and whether its cancer-promoting PPM1D interaction reflects ubiquitin ligase function, remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No unifying model linking endocytic and E3 ligase functions","Substrate dependence of cancer phenotypes untested","Tissue-specific regulation of CRL2APPBP2 assembly unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,3]}],"localization":[{"term_id":"GO:0005768","term_label":"endosome","supporting_discovery_ids":[5]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,2]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[5]}],"complexes":["CRL2APPBP2 (CUL2-RING E3 ubiquitin ligase)"],"partners":["CUL2","PRDM16","TSPYL2","PPM1D","SLY1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q92624","full_name":"Amyloid protein-binding protein 2","aliases":["Amyloid beta precursor protein-binding protein 2","APP-BP2","Protein interacting with APP tail 1"],"length_aa":585,"mass_kda":66.9,"function":"Substrate-recognition component of a Cul2-RING (CRL2) E3 ubiquitin-protein ligase complex of the DesCEND (destruction via C-end degrons) pathway, which recognizes a C-degron located at the extreme C terminus of target proteins, leading to their ubiquitination and degradation (PubMed:29775578, PubMed:29779948, PubMed:37844242). The C-degron recognized by the DesCEND pathway is usually a motif of less than ten residues and can be present in full-length proteins, truncated proteins or proteolytically cleaved forms (PubMed:29775578, PubMed:29779948, PubMed:37844242). The CRL2(APPBP2) complex specifically recognizes proteins with a -Arg-Xaa-Xaa-Gly degron at the C-terminus, leading to their ubiquitination and degradation (PubMed:29775578, PubMed:29779948, PubMed:37844242). The CRL2(APPBP2) complex mediates ubiquitination and degradation of truncated SELENOV selenoproteins produced by failed UGA/Sec decoding, which end with a -Arg-Xaa-Xaa-Gly degron (PubMed:26138980, PubMed:37844242). The CRL2(APPBP2) complex negatively regulates beige adipocyte differentiation by mediating ubiquitination and degradation of PRDM16 (By similarity). May play a role in intracellular protein transport: may be involved in the translocation of APP along microtubules toward the cell surface (PubMed:9843960)","subcellular_location":"Nucleus; Cytoplasm, cytoskeleton; Membrane","url":"https://www.uniprot.org/uniprotkb/Q92624/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/APPBP2","classification":"Not Classified","n_dependent_lines":9,"n_total_lines":1208,"dependency_fraction":0.0074503311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/APPBP2","total_profiled":1310},"omim":[{"mim_id":"605324","title":"AMYLOID BETA PRECURSOR PROTEIN-BINDING PROTEIN 2; APPBP2","url":"https://www.omim.org/entry/605324"},{"mim_id":"605100","title":"PROTEIN PHOSPHATASE, MAGNESIUM/MANGANESE-DEPENDENT, 1D; PPM1D","url":"https://www.omim.org/entry/605100"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/APPBP2"},"hgnc":{"alias_symbol":["KIAA0228","Hs.84084","PAT1"],"prev_symbol":[]},"alphafold":{"accession":"Q92624","domains":[{"cath_id":"1.25.40.10","chopping":"204-301","consensus_level":"medium","plddt":95.9132,"start":204,"end":301},{"cath_id":"1.25.40.10","chopping":"423-547","consensus_level":"medium","plddt":95.7618,"start":423,"end":547},{"cath_id":"1.25.40","chopping":"303-419","consensus_level":"medium","plddt":95.8912,"start":303,"end":419}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92624","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q92624-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q92624-F1-predicted_aligned_error_v6.png","plddt_mean":93.38},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=APPBP2","jax_strain_url":"https://www.jax.org/strain/search?query=APPBP2"},"sequence":{"accession":"Q92624","fasta_url":"https://rest.uniprot.org/uniprotkb/Q92624.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q92624/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q92624"}},"corpus_meta":[{"pmid":"12702577","id":"PMC_12702577","title":"PPM1D is a potential target for 17q gain in neuroblastoma.","date":"2003","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/12702577","citation_count":203,"is_preprint":false},{"pmid":"17234809","id":"PMC_17234809","title":"An infectious retrovirus susceptible to an IFN antiviral pathway from human prostate tumors.","date":"2007","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/17234809","citation_count":175,"is_preprint":false},{"pmid":"16400626","id":"PMC_16400626","title":"Comprehensive genomic analysis of desmoplastic medulloblastomas: identification of novel amplified genes and separate evaluation of the different histological components.","date":"2006","source":"The Journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/16400626","citation_count":105,"is_preprint":false},{"pmid":"35978186","id":"PMC_35978186","title":"Post-translational control of beige fat biogenesis by PRDM16 stabilization.","date":"2022","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/35978186","citation_count":97,"is_preprint":false},{"pmid":"21159603","id":"PMC_21159603","title":"Genome-wide mRNA and microRNA profiling of the NCI 60 cell-line screen and comparison of FdUMP[10] with fluorouracil, floxuridine, and topoisomerase 1 poisons.","date":"2010","source":"Molecular cancer therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/21159603","citation_count":74,"is_preprint":false},{"pmid":"19176879","id":"PMC_19176879","title":"The multi-copy mouse gene Sycp3-like Y-linked (Sly) encodes an abundant spermatid protein that interacts with a histone acetyltransferase and an acrosomal protein.","date":"2009","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/19176879","citation_count":55,"is_preprint":false},{"pmid":"37735597","id":"PMC_37735597","title":"Defining E3 ligase-substrate relationships through multiplex CRISPR screening.","date":"2023","source":"Nature cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/37735597","citation_count":53,"is_preprint":false},{"pmid":"23260012","id":"PMC_23260012","title":"Structural analysis of the genome of breast cancer cell line ZR-75-30 identifies twelve expressed fusion genes.","date":"2012","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/23260012","citation_count":40,"is_preprint":false},{"pmid":"31893575","id":"PMC_31893575","title":"FOLFOX treatment response prediction in metastatic or recurrent colorectal cancer patients via machine learning algorithms.","date":"2020","source":"Cancer medicine","url":"https://pubmed.ncbi.nlm.nih.gov/31893575","citation_count":32,"is_preprint":false},{"pmid":"36880288","id":"PMC_36880288","title":"MicroRNA-128 suppresses tau phosphorylation and reduces amyloid-beta accumulation by inhibiting the expression of GSK3β, APPBP2, and mTOR in Alzheimer's disease.","date":"2023","source":"CNS neuroscience & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/36880288","citation_count":27,"is_preprint":false},{"pmid":"24436321","id":"PMC_24436321","title":"Transient Maternal Hypothyroxinemia Potentiates the Transcriptional Response to Exogenous Thyroid Hormone in the Fetal Cerebral Cortex Before the Onset of Fetal Thyroid Function: A Messenger and MicroRNA Profiling Study.","date":"2014","source":"Cerebral cortex (New York, N.Y. : 1991)","url":"https://pubmed.ncbi.nlm.nih.gov/24436321","citation_count":22,"is_preprint":false},{"pmid":"38170390","id":"PMC_38170390","title":"CRL2APPBP2-mediated TSPYL2 degradation counteracts human mesenchymal stem cell senescence.","date":"2023","source":"Science China. Life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38170390","citation_count":18,"is_preprint":false},{"pmid":"37844242","id":"PMC_37844242","title":"Molecular basis for C-degron recognition by CRL2APPBP2 ubiquitin ligase.","date":"2023","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/37844242","citation_count":14,"is_preprint":false},{"pmid":"30210606","id":"PMC_30210606","title":"Analyzing the disease module associated with osteosarcoma via a network- and pathway-based approach.","date":"2018","source":"Experimental and therapeutic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30210606","citation_count":13,"is_preprint":false},{"pmid":"34861803","id":"PMC_34861803","title":"Circ_SETD3 regulates gefitinib sensitivity and tumor progression by miR-873-5p-dependent regulation of APPBP2 in non-small cell lung cancer.","date":"2021","source":"Journal of chemotherapy (Florence, Italy)","url":"https://pubmed.ncbi.nlm.nih.gov/34861803","citation_count":9,"is_preprint":false},{"pmid":"35191420","id":"PMC_35191420","title":"circBIRC6 contributes to the development of non-small cell lung cancer via regulating microRNA-217/amyloid beta precursor protein binding protein 2 axis.","date":"2022","source":"Chinese medical journal","url":"https://pubmed.ncbi.nlm.nih.gov/35191420","citation_count":8,"is_preprint":false},{"pmid":"31105033","id":"PMC_31105033","title":"APPBP2 enhances non-small cell lung cancer proliferation and invasiveness through regulating PPM1D and SPOP.","date":"2019","source":"EBioMedicine","url":"https://pubmed.ncbi.nlm.nih.gov/31105033","citation_count":7,"is_preprint":false},{"pmid":"31139847","id":"PMC_31139847","title":"Protein interacting with Amyloid Precursor Protein tail-1 (PAT1) is involved in early endocytosis.","date":"2019","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/31139847","citation_count":6,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":12129,"output_tokens":2077,"usd":0.033771,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8987,"output_tokens":2496,"usd":0.053667,"stage2_stop_reason":"end_turn"},"total_usd":0.087438,"stage1_batch_id":"msgbatch_0179Z2pxRYBsXi2xADneafRw","stage2_batch_id":"msgbatch_01LaY9ZaVdgjWArcZo9eqQE5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2023,\n      \"finding\": \"CUL2-APPBP2 is the ubiquitin E3 ligase that determines PRDM16 protein stability by catalysing its polyubiquitination. Inhibition of CUL2-APPBP2 extended the half-life of PRDM16 protein and promoted beige adipocyte biogenesis. Adipocyte-specific deletion of CUL2-APPBP2 counteracted diet-induced obesity and metabolic dysfunction in mice.\",\n      \"method\": \"Biochemical ubiquitination assays, protein half-life measurement, adipocyte-specific CUL2-APPBP2 knockout mouse model with metabolic phenotyping\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (biochemical assays, KO mouse model, metabolic phenotyping) in a single rigorous study establishing E3 ligase-substrate relationship\",\n      \"pmids\": [\"35978186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"APPBP2 (as part of CRL2APPBP2) specifically recognizes R-x-x-G/C-degrons at or near the C-terminus of substrate proteins via a bipartite mechanism, where arginine and glycine occupy distinct pockets spaced by two residues. The binding pocket accommodates the motif placed at or up to three residues upstream of the C-terminus. CRL2APPBP2 assembles as a dimer and tetramer.\",\n      \"method\": \"Cryo-EM structure determination of active CRL2APPBP2 bound with different R-x-x-G/C-degrons, complemented by binding experiments and cell-based assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures with multiple degron complexes, binding experiments, and cell-based validation in a single rigorous study\",\n      \"pmids\": [\"37844242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CRL2APPBP2 ubiquitin ligase targets TSPYL2 (a negative regulator of proliferation) for ubiquitin-proteasome-mediated degradation via APPBP2 as the substrate receptor. This degradation downregulates P21waf1/cip1 and delays senescence in human mesenchymal stem cells.\",\n      \"method\": \"CRISPR/Cas9-mediated CUL2 deletion, differentiation of hESCs into hMSCs, identification of TSPYL2 as substrate via APPBP2 substrate receptor, proteasome inhibition assays, senescence phenotype analysis\",\n      \"journal\": \"Science China. Life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR KO with defined cellular phenotype and substrate identification, single lab\",\n      \"pmids\": [\"38170390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A multiplex CRISPR screening platform identified substrates and degron motifs for Cul2APPBP2, refining understanding of the C-degron pathways it targets and confirming its substrate specificity within the ubiquitin-proteasome system.\",\n      \"method\": \"Multiplex CRISPR screening (~100 screens in a single experiment) with site-saturation mutagenesis for degron identification\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — large-scale CRISPR screen with mutagenesis, but APPBP2-specific mechanistic detail is not fully described in the abstract\",\n      \"pmids\": [\"37735597\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"APPBP2 physically interacts with PPM1D (as shown by co-immunoprecipitation) and promotes NSCLC cell proliferation, migration, and invasion. Silencing APPBP2 decreases PPM1D and SPOP expression, and overexpression of PPM1D or SPOP rescues the inhibitory effects of APPBP2 knockdown.\",\n      \"method\": \"Co-immunoprecipitation, shRNA knockdown, overexpression rescue experiments, cell proliferation and invasion assays, xenograft tumor growth\",\n      \"journal\": \"EBioMedicine\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single Co-IP plus functional rescue experiments, single lab, multiple cell-based methods\",\n      \"pmids\": [\"31105033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PAT1/APPBP2 colocalizes with early endosomal markers (Rab5, Rab4, EEA1, Rabaptin-5) but not with Rab11 or Rab7. PAT1 expression regulates the number of EEA1 and Rab5 vesicles and the endocytosis/recycling of transferrin receptor. Overexpression of the APP binding domain of PAT1 is sufficient to compromise endocytosis.\",\n      \"method\": \"Colocalization by fluorescence microscopy, live imaging, transferrin uptake assay, domain overexpression\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization experiments with functional consequence (endocytosis assay), multiple orthogonal approaches, single lab\",\n      \"pmids\": [\"31139847\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"SLY1 (mouse Y-linked spermatid protein) interacts with the microtubule-associated protein APPBP2, as demonstrated by yeast two-hybrid and co-immunoprecipitation studies.\",\n      \"method\": \"Yeast two-hybrid assay, co-immunoprecipitation\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP/Y2H identifying APPBP2 as a binding partner of SLY1, no further mechanistic characterization of APPBP2 function\",\n      \"pmids\": [\"19176879\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Appbp2 is a novel thyroid hormone (TH)-responsive gene in the fetal cerebral cortex, with thyroid hormone response elements confirmed in the Appbp2 gene.\",\n      \"method\": \"Gene expression microarray in fetal mouse cortex with TH manipulation, confirmation of TH response elements\",\n      \"journal\": \"Cerebral cortex (New York, N.Y. : 1991)\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — identification of TH-responsive transcriptional regulation via microarray and TH response element confirmation, but no downstream functional mechanism established for APPBP2 protein\",\n      \"pmids\": [\"24436321\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"APPBP2 is the substrate receptor of the CUL2-RING E3 ubiquitin ligase complex (CRL2APPBP2), which recognizes substrates bearing C-terminal R-x-x-G/C-degron motifs via a bipartite mechanism (structurally resolved by cryo-EM) and mediates their polyubiquitination and proteasomal degradation; established substrates include PRDM16 (regulating beige adipogenesis) and TSPYL2 (counteracting stem cell senescence), and APPBP2 also functions in early endocytosis and interacts with PPM1D to promote cancer cell proliferation and invasion.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"APPBP2 is the substrate-recognition subunit of a CUL2-RING E3 ubiquitin ligase (CRL2APPBP2) that targets proteins bearing C-terminal R-x-x-G/C degron motifs for polyubiquitination and proteasomal degradation [#0, #1, #3]. Cryo-EM of the active complex shows that APPBP2 engages the degron through a bipartite pocket in which the arginine and glycine occupy distinct subsites spaced by two residues, accommodating motifs at or within three residues of the C-terminus, and that the ligase assembles into dimeric and tetrameric forms [#1]. Through this activity APPBP2 sets the abundance of specific substrates: it polyubiquitinates PRDM16, controlling its half-life and thereby beige adipocyte biogenesis and systemic metabolic homeostasis [#0], and it degrades TSPYL2 to downregulate P21waf1/cip1 and delay senescence in human mesenchymal stem cells [#2]. Independently of its E3 ligase role, APPBP2 localizes to early endosomes, where it regulates Rab5/EEA1 vesicle number and transferrin receptor endocytosis and recycling [#5]. In non-small-cell lung cancer cells APPBP2 physically associates with PPM1D and supports proliferation, migration, and invasion, with PPM1D and SPOP acting downstream of its effects [#4].\",\n  \"teleology\": [\n    {\n      \"year\": 2009,\n      \"claim\": \"An early interaction screen placed APPBP2 in a protein-binding context, identifying it as a microtubule-associated partner of the spermatid protein SLY1 before any enzymatic role was known.\",\n      \"evidence\": \"Yeast two-hybrid and co-immunoprecipitation\",\n      \"pmids\": [\"19176879\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Single Y2H/Co-IP without reciprocal validation or functional consequence\", \"No mechanistic role for APPBP2 established\", \"Relevance of microtubule association to later E3 ligase function unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Transcriptional profiling showed APPBP2 is a thyroid-hormone-responsive gene in fetal cortex, addressing how its expression is regulated but not what the protein does.\",\n      \"evidence\": \"Expression microarray with thyroid hormone manipulation and TH response element confirmation in fetal mouse cortex\",\n      \"pmids\": [\"24436321\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No downstream protein function established\", \"Physiological role of TH-induced APPBP2 in brain development unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Two studies expanded APPBP2 function beyond a binding partner: one assigned it an early-endocytic role, the other linked it to cancer cell proliferation through PPM1D.\",\n      \"evidence\": \"Endosomal marker colocalization, transferrin uptake and domain-overexpression assays; and co-immunoprecipitation with shRNA knockdown, rescue, and xenograft assays in NSCLC\",\n      \"pmids\": [\"31139847\", \"31105033\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endocytic role not mechanistically connected to E3 ligase activity\", \"PPM1D interaction is a single Co-IP without reciprocal validation\", \"Whether the PPM1D effect involves ubiquitin ligase activity is untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"APPBP2 was defined as a CUL2 substrate receptor and a physiological E3 ligase, with PRDM16 identified as a substrate whose degradation gates beige adipogenesis and metabolic health.\",\n      \"evidence\": \"Biochemical ubiquitination assays, protein half-life measurement, and adipocyte-specific CUL2-APPBP2 knockout mice with metabolic phenotyping\",\n      \"pmids\": [\"35978186\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degron in PRDM16 not yet defined in this study\", \"Regulation of CRL2APPBP2 assembly/activity in adipocytes unknown\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Structural and screening work established the molecular logic of substrate recognition, showing CRL2APPBP2 reads C-terminal R-x-x-G/C degrons via a bipartite pocket and identifying its substrate repertoire.\",\n      \"evidence\": \"Cryo-EM of CRL2APPBP2 bound to multiple degrons with binding and cell-based assays; and multiplex CRISPR screening with site-saturation mutagenesis\",\n      \"pmids\": [\"37844242\", \"37735597\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional significance of dimer/tetramer assembly states unresolved\", \"Full physiological substrate set not enumerated\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"A second physiological substrate, TSPYL2, was identified, connecting CRL2APPBP2 activity to P21-dependent control of stem cell senescence.\",\n      \"evidence\": \"CRISPR/Cas9 CUL2 deletion, hESC-to-hMSC differentiation, proteasome inhibition, and senescence phenotyping\",\n      \"pmids\": [\"38170390\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct degron in TSPYL2 not structurally mapped\", \"Single-lab study without orthogonal substrate confirmation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How APPBP2's endosomal/microtubule-associated roles relate mechanistically to its CRL2 E3 ligase activity, and whether its cancer-promoting PPM1D interaction reflects ubiquitin ligase function, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No unifying model linking endocytic and E3 ligase functions\", \"Substrate dependence of cancer phenotypes untested\", \"Tissue-specific regulation of CRL2APPBP2 assembly unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\"CRL2APPBP2 (CUL2-RING E3 ubiquitin ligase)\"],\n    \"partners\": [\"CUL2\", \"PRDM16\", \"TSPYL2\", \"PPM1D\", \"SLY1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}