{"gene":"UBAC2","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2024,"finding":"UBAC2 functions as an ER-phagy (reticulophagy) receptor: its cytoplasmic domain contains a canonical LC3-interacting region (LIR) that binds autophagosomal GABARAP, enabling selective autophagic degradation of ER fragments.","method":"Identification of LIR motif in UBAC2, binding assay with GABARAP, ER-phagy functional assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — receptor identification with LIR motif characterization, GABARAP binding, and functional ER-phagy assays in a single focused study; confirmed in a companion commentary (PMID:39580148)","pmids":["39284914","39580148"],"is_preprint":false},{"year":2024,"finding":"MARK2 (microtubule affinity-regulating kinase 2) phosphorylates UBAC2 at serine 223, promoting UBAC2 dimerization; dimerized UBAC2 binds GABARAP more strongly, thereby facilitating ER-phagy progression.","method":"Kinase assay identifying MARK2 as the writer of pS223-UBAC2; phosphorylation-site mutagenesis; dimerization and GABARAP-binding assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — phosphorylation site mapped, writer kinase identified, mechanistic consequence (dimerization and enhanced GABARAP binding) demonstrated with site-specific mutants in one rigorous study","pmids":["39284914","39580148"],"is_preprint":false},{"year":2024,"finding":"UBAC2-mediated ER-phagy restrains inflammatory responses and reduces acute ulcerative colitis severity in mice; loss of UBAC2 ER-phagy activity leads to increased ER stress (UPR) and enhanced inflammation.","method":"UBAC2 knockdown/knockout in mouse models of colitis; measurement of inflammatory markers and UPR activation; in vivo rescue experiments","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — defined cellular/in vivo phenotype (inflammation, colitis) linked to UBAC2 ER-phagy function; single lab study","pmids":["39284914"],"is_preprint":false},{"year":2021,"finding":"UBAC2 (TM4) protein contains 4 transmembrane domains and one ubiquitin-binding domain and is subject to ubiquitin-proteasome-mediated degradation; PS-341 (proteasome inhibitor) stabilizes UBAC2 protein levels in vitro and in vivo.","method":"TM4/UBAC2 knockout mouse model; PS-341 treatment in vitro and in db/db mice; protein expression analysis","journal":"Nutrition & metabolism","confidence":"Medium","confidence_rationale":"Tier 2–3 / Weak — proteasome-dependent degradation demonstrated by PS-341 rescue in vivo and in vitro; single lab, limited mechanistic depth on the degradation machinery","pmids":["34074311"],"is_preprint":false},{"year":2021,"finding":"UBAC2 (TM4) negatively regulates the Nur77/IKKβ/NF-κB inflammatory signaling axis; TM4 knockout mice show enhanced NF-κB pathway activation under metabolic stress conditions.","method":"TM4 KO mouse metabolic phenotyping; measurement of Nur77, IKKβ, NF-κB expression in vivo and in vitro","journal":"Nutrition & metabolism","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic KO with defined pathway readout (NF-κB axis) in vivo; single lab, single study","pmids":["34074311"],"is_preprint":false},{"year":2011,"finding":"The SNP rs7999348 (A/G) within UBAC2 is a functional variant: individuals homozygous for the Behçet's disease-associated 'G' allele show increased mRNA expression of a UBAC2 transcript variant in peripheral blood mononuclear cells.","method":"Haplotype conditional analysis; real-time PCR measurement of UBAC2 transcript variant expression in PBMCs stratified by rs7999348 genotype","journal":"Arthritis and rheumatism","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — functional variant mapped by conditional haplotype analysis and expression quantification; replicated in additional cohorts from multiple labs","pmids":["21918955","22455605"],"is_preprint":false},{"year":2012,"finding":"The promoter polymorphism rs3825427 in UBAC2 reduces promoter activity: the risk T allele shows lower luciferase reporter activity and is associated with decreased UBAC2 transcript variant 1 expression in PBMCs and skin.","method":"Luciferase reporter assay; real-time PCR of UBAC2 expression in PBMCs and skin tissue stratified by genotype","journal":"Arthritis research & therapy","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — luciferase reporter assay plus expression quantification in primary tissues; single lab with two orthogonal methods","pmids":["22455605"],"is_preprint":false},{"year":2022,"finding":"Transcription factor CTCF positively regulates UBAC2 transcription; the rs3825427 C allele acts as an enhancer element that promotes CTCF binding to the UBAC2 promoter, increasing transcription. CTCF knockdown significantly reduces UBAC2 mRNA expression.","method":"Luciferase reporter assay with CTCF overexpression and mutation of rs3825427; siRNA knockdown of CTCF with measurement of UBAC2 mRNA levels","journal":"Environmental science and pollution research international","confidence":"Medium","confidence_rationale":"Tier 2–3 / Weak — luciferase reporter and siRNA knockdown experiments identify CTCF as a transcriptional activator; single lab, focused mechanistic follow-up on a specific SNP","pmids":["35020141"],"is_preprint":false}],"current_model":"UBAC2 is a multi-pass transmembrane ER protein that acts as a reticulophagy (ER-phagy) receptor via a cytoplasmic LIR motif that binds GABARAP; MARK2-mediated phosphorylation at serine 223 drives UBAC2 dimerization and enhanced GABARAP binding to promote selective ER degradation, thereby restraining ER stress-induced NF-κB inflammatory signaling, while its transcription is positively regulated by the CTCF transcription factor and its protein stability is controlled by the ubiquitin-proteasome system."},"narrative":{"mechanistic_narrative":"UBAC2 is a multi-pass transmembrane endoplasmic reticulum protein that serves as a selective ER-phagy (reticulophagy) receptor, coupling ER turnover to the control of inflammatory signaling [PMID:39284914, PMID:39580148]. Its cytoplasmic domain carries a canonical LC3-interacting region (LIR) that binds the autophagosomal protein GABARAP, enabling targeted autophagic degradation of ER fragments [PMID:39284914, PMID:39580148]. This receptor activity is switched on by phosphorylation: MARK2 phosphorylates UBAC2 at serine 223, driving UBAC2 dimerization, which strengthens GABARAP binding and advances ER-phagy [PMID:39284914, PMID:39580148]. Through this pathway UBAC2-mediated ER-phagy limits ER stress (UPR) and restrains inflammation, with loss of function increasing UPR activation and aggravating acute ulcerative colitis in mice [PMID:39284914]; consistent with an anti-inflammatory role, UBAC2 negatively regulates the Nur77/IKKβ/NF-κB axis [PMID:34074311]. UBAC2 protein levels are set by ubiquitin-proteasome-mediated degradation, as proteasome inhibition with PS-341 stabilizes the protein [PMID:34074311], while its transcription is positively driven by CTCF acting at a promoter polymorphism [PMID:35020141]. Genetic variants in UBAC2 that alter its transcript expression are associated with Behçet's disease [PMID:21918955, PMID:22455605].","teleology":[{"year":2011,"claim":"Established that UBAC2 is a disease-relevant locus whose expression is genetically tunable, raising the question of what UBAC2 does mechanistically.","evidence":"Haplotype conditional analysis and real-time PCR of a UBAC2 transcript variant in PBMCs stratified by rs7999348 genotype","pmids":["21918955","22455605"],"confidence":"Medium","gaps":["Does not define UBAC2 protein function","Causal link between transcript variant level and disease mechanism unresolved"]},{"year":2012,"claim":"Showed that a specific promoter polymorphism quantitatively controls UBAC2 transcription, pinpointing a cis-regulatory mechanism for the disease association.","evidence":"Luciferase reporter assay and real-time PCR of UBAC2 in PBMCs and skin stratified by rs3825427 genotype","pmids":["22455605"],"confidence":"Medium","gaps":["Trans-acting factor binding the promoter not identified","Does not connect transcript level to a cellular function"]},{"year":2021,"claim":"Defined the first functional handles on UBAC2 protein — that it is a 4-transmembrane, ubiquitin-binding protein turned over by the proteasome and that it suppresses an inflammatory signaling axis.","evidence":"TM4/UBAC2 knockout mouse, PS-341 proteasome inhibition in vitro and in db/db mice, and Nur77/IKKβ/NF-κB pathway readouts","pmids":["34074311"],"confidence":"Medium","gaps":["E3 ligase and degron driving proteasomal turnover not identified","Molecular mechanism linking UBAC2 to NF-κB suppression unresolved","Single lab"]},{"year":2022,"claim":"Identified the trans-acting regulator of UBAC2 transcription, showing CTCF binds the promoter polymorphism as an enhancer to activate expression.","evidence":"Luciferase reporter with CTCF overexpression and rs3825427 mutation, plus siRNA knockdown of CTCF with UBAC2 mRNA measurement","pmids":["35020141"],"confidence":"Medium","gaps":["Whether CTCF regulation operates in disease-relevant cell types in vivo unaddressed","Single lab, focused on one SNP"]},{"year":2024,"claim":"Resolved the core molecular function of UBAC2 as a LIR-containing ER-phagy receptor for GABARAP, and showed MARK2 phosphorylation at S223 acts as the activating switch via dimerization, linking ER turnover to restraint of ER-stress-driven inflammation.","evidence":"LIR motif identification with GABARAP binding assays, MARK2 kinase assay and S223 phospho-site mutagenesis with dimerization/binding readouts, and UBAC2 loss-of-function mouse colitis models with UPR and inflammation measurements","pmids":["39284914","39580148"],"confidence":"High","gaps":["Structural basis of S223-driven dimerization not solved","How dimerization mechanistically enhances GABARAP avidity not detailed","Relationship between ER-phagy receptor role and the earlier ubiquitin-binding/NF-κB functions not reconciled"]},{"year":null,"claim":"How the ubiquitin-binding domain of UBAC2 and its proteasomal turnover integrate with its ER-phagy receptor function and NF-κB suppression remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No identified E3 ligase or ubiquitin ligand for the ubiquitin-binding domain","Unclear whether ER-phagy and NF-κB regulation are the same or parallel pathways","No structural model of the full receptor"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[0]},{"term_id":"GO:0060089","term_label":"molecular transducer activity","supporting_discovery_ids":[1]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,2]}],"pathway":[{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[0,1,2]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[2,4]}],"complexes":[],"partners":["GABARAP","MARK2","CTCF"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NBM4","full_name":"Ubiquitin-associated domain-containing protein 2","aliases":["Phosphoglycerate dehydrogenase-like protein 1"],"length_aa":344,"mass_kda":39.0,"function":"Restricts trafficking of FAF2 from the endoplasmic reticulum to lipid droplets (PubMed:23297223). In association with LMBR1L and E3 ubiquitin-protein ligase AMFR, negatively regulates the canonical Wnt signaling pathway in the lymphocytes by promoting the ubiquitin-mediated degradation of CTNNB1 and Wnt receptors FZD6 and LRP6 (PubMed:31073040)","subcellular_location":"Endoplasmic reticulum membrane","url":"https://www.uniprot.org/uniprotkb/Q8NBM4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UBAC2","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"VCP","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/UBAC2","total_profiled":1310},"omim":[{"mim_id":"621399","title":"UBA DOMAIN-CONTAINING PROTEIN 2; UBAC2","url":"https://www.omim.org/entry/621399"},{"mim_id":"610007","title":"LIMB REGION 1 HOMOLOG-LIKE; LMBR1L","url":"https://www.omim.org/entry/610007"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/UBAC2"},"hgnc":{"alias_symbol":["FLJ30548","RP11-178C10.1"],"prev_symbol":["PHGDHL1"]},"alphafold":{"accession":"Q8NBM4","domains":[{"cath_id":"1.20.1540","chopping":"13-222","consensus_level":"high","plddt":80.2412,"start":13,"end":222},{"cath_id":"1.10.8","chopping":"304-344","consensus_level":"medium","plddt":73.4217,"start":304,"end":344}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NBM4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NBM4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NBM4-F1-predicted_aligned_error_v6.png","plddt_mean":72.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UBAC2","jax_strain_url":"https://www.jax.org/strain/search?query=UBAC2"},"sequence":{"accession":"Q8NBM4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NBM4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NBM4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NBM4"}},"corpus_meta":[{"pmid":"29313416","id":"PMC_29313416","title":"Dicot-specific ATG8-interacting ATI3 proteins interact with conserved UBAC2 proteins and play critical roles in plant stress responses.","date":"2018","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/29313416","citation_count":65,"is_preprint":false},{"pmid":"21918955","id":"PMC_21918955","title":"A putative functional variant within the UBAC2 gene is associated with increased risk of Behçet's disease.","date":"2011","source":"Arthritis and rheumatism","url":"https://pubmed.ncbi.nlm.nih.gov/21918955","citation_count":36,"is_preprint":false},{"pmid":"22455605","id":"PMC_22455605","title":"Replication study confirms the association between UBAC2 and Behçet's disease in two independent Chinese sets of patients and controls.","date":"2012","source":"Arthritis research & therapy","url":"https://pubmed.ncbi.nlm.nih.gov/22455605","citation_count":33,"is_preprint":false},{"pmid":"28389674","id":"PMC_28389674","title":"Comprehensive analysis of the association between UBAC2 polymorphisms and Behçet's disease in a Japanese population.","date":"2017","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/28389674","citation_count":20,"is_preprint":false},{"pmid":"32913183","id":"PMC_32913183","title":"UBAC2 promotes bladder cancer proliferation through BCRC-3/miRNA-182-5p/p27 axis.","date":"2020","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/32913183","citation_count":16,"is_preprint":false},{"pmid":"39284914","id":"PMC_39284914","title":"ER-phagy restrains inflammatory responses through its receptor UBAC2.","date":"2024","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/39284914","citation_count":11,"is_preprint":false},{"pmid":"35020141","id":"PMC_35020141","title":"Association between UBAC2 gene polymorphism and the risk of noise-induced hearing loss: a cross-sectional study.","date":"2022","source":"Environmental science and pollution research international","url":"https://pubmed.ncbi.nlm.nih.gov/35020141","citation_count":6,"is_preprint":false},{"pmid":"34074311","id":"PMC_34074311","title":"PS-341 alleviates chronic low-grade inflammation and improves insulin sensitivity through the inhibition of TM4 (UBAC2) degradation.","date":"2021","source":"Nutrition & metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/34074311","citation_count":1,"is_preprint":false},{"pmid":"39580148","id":"PMC_39580148","title":"UBAC2 serves as a reticulophagy receptor to suppress inflammatory responses.","date":"2024","source":"Autophagy","url":"https://pubmed.ncbi.nlm.nih.gov/39580148","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7236,"output_tokens":1977,"usd":0.025681,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8904,"output_tokens":2251,"usd":0.050397,"stage2_stop_reason":"end_turn"},"total_usd":0.076078,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2024,\n      \"finding\": \"UBAC2 functions as an ER-phagy (reticulophagy) receptor: its cytoplasmic domain contains a canonical LC3-interacting region (LIR) that binds autophagosomal GABARAP, enabling selective autophagic degradation of ER fragments.\",\n      \"method\": \"Identification of LIR motif in UBAC2, binding assay with GABARAP, ER-phagy functional assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — receptor identification with LIR motif characterization, GABARAP binding, and functional ER-phagy assays in a single focused study; confirmed in a companion commentary (PMID:39580148)\",\n      \"pmids\": [\"39284914\", \"39580148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"MARK2 (microtubule affinity-regulating kinase 2) phosphorylates UBAC2 at serine 223, promoting UBAC2 dimerization; dimerized UBAC2 binds GABARAP more strongly, thereby facilitating ER-phagy progression.\",\n      \"method\": \"Kinase assay identifying MARK2 as the writer of pS223-UBAC2; phosphorylation-site mutagenesis; dimerization and GABARAP-binding assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — phosphorylation site mapped, writer kinase identified, mechanistic consequence (dimerization and enhanced GABARAP binding) demonstrated with site-specific mutants in one rigorous study\",\n      \"pmids\": [\"39284914\", \"39580148\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UBAC2-mediated ER-phagy restrains inflammatory responses and reduces acute ulcerative colitis severity in mice; loss of UBAC2 ER-phagy activity leads to increased ER stress (UPR) and enhanced inflammation.\",\n      \"method\": \"UBAC2 knockdown/knockout in mouse models of colitis; measurement of inflammatory markers and UPR activation; in vivo rescue experiments\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — defined cellular/in vivo phenotype (inflammation, colitis) linked to UBAC2 ER-phagy function; single lab study\",\n      \"pmids\": [\"39284914\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"UBAC2 (TM4) protein contains 4 transmembrane domains and one ubiquitin-binding domain and is subject to ubiquitin-proteasome-mediated degradation; PS-341 (proteasome inhibitor) stabilizes UBAC2 protein levels in vitro and in vivo.\",\n      \"method\": \"TM4/UBAC2 knockout mouse model; PS-341 treatment in vitro and in db/db mice; protein expression analysis\",\n      \"journal\": \"Nutrition & metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Weak — proteasome-dependent degradation demonstrated by PS-341 rescue in vivo and in vitro; single lab, limited mechanistic depth on the degradation machinery\",\n      \"pmids\": [\"34074311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"UBAC2 (TM4) negatively regulates the Nur77/IKKβ/NF-κB inflammatory signaling axis; TM4 knockout mice show enhanced NF-κB pathway activation under metabolic stress conditions.\",\n      \"method\": \"TM4 KO mouse metabolic phenotyping; measurement of Nur77, IKKβ, NF-κB expression in vivo and in vitro\",\n      \"journal\": \"Nutrition & metabolism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic KO with defined pathway readout (NF-κB axis) in vivo; single lab, single study\",\n      \"pmids\": [\"34074311\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The SNP rs7999348 (A/G) within UBAC2 is a functional variant: individuals homozygous for the Behçet's disease-associated 'G' allele show increased mRNA expression of a UBAC2 transcript variant in peripheral blood mononuclear cells.\",\n      \"method\": \"Haplotype conditional analysis; real-time PCR measurement of UBAC2 transcript variant expression in PBMCs stratified by rs7999348 genotype\",\n      \"journal\": \"Arthritis and rheumatism\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — functional variant mapped by conditional haplotype analysis and expression quantification; replicated in additional cohorts from multiple labs\",\n      \"pmids\": [\"21918955\", \"22455605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The promoter polymorphism rs3825427 in UBAC2 reduces promoter activity: the risk T allele shows lower luciferase reporter activity and is associated with decreased UBAC2 transcript variant 1 expression in PBMCs and skin.\",\n      \"method\": \"Luciferase reporter assay; real-time PCR of UBAC2 expression in PBMCs and skin tissue stratified by genotype\",\n      \"journal\": \"Arthritis research & therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — luciferase reporter assay plus expression quantification in primary tissues; single lab with two orthogonal methods\",\n      \"pmids\": [\"22455605\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Transcription factor CTCF positively regulates UBAC2 transcription; the rs3825427 C allele acts as an enhancer element that promotes CTCF binding to the UBAC2 promoter, increasing transcription. CTCF knockdown significantly reduces UBAC2 mRNA expression.\",\n      \"method\": \"Luciferase reporter assay with CTCF overexpression and mutation of rs3825427; siRNA knockdown of CTCF with measurement of UBAC2 mRNA levels\",\n      \"journal\": \"Environmental science and pollution research international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Weak — luciferase reporter and siRNA knockdown experiments identify CTCF as a transcriptional activator; single lab, focused mechanistic follow-up on a specific SNP\",\n      \"pmids\": [\"35020141\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UBAC2 is a multi-pass transmembrane ER protein that acts as a reticulophagy (ER-phagy) receptor via a cytoplasmic LIR motif that binds GABARAP; MARK2-mediated phosphorylation at serine 223 drives UBAC2 dimerization and enhanced GABARAP binding to promote selective ER degradation, thereby restraining ER stress-induced NF-κB inflammatory signaling, while its transcription is positively regulated by the CTCF transcription factor and its protein stability is controlled by the ubiquitin-proteasome system.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UBAC2 is a multi-pass transmembrane endoplasmic reticulum protein that serves as a selective ER-phagy (reticulophagy) receptor, coupling ER turnover to the control of inflammatory signaling [#0, #2]. Its cytoplasmic domain carries a canonical LC3-interacting region (LIR) that binds the autophagosomal protein GABARAP, enabling targeted autophagic degradation of ER fragments [#0]. This receptor activity is switched on by phosphorylation: MARK2 phosphorylates UBAC2 at serine 223, driving UBAC2 dimerization, which strengthens GABARAP binding and advances ER-phagy [#1]. Through this pathway UBAC2-mediated ER-phagy limits ER stress (UPR) and restrains inflammation, with loss of function increasing UPR activation and aggravating acute ulcerative colitis in mice [#2]; consistent with an anti-inflammatory role, UBAC2 negatively regulates the Nur77/IKKβ/NF-κB axis [#4]. UBAC2 protein levels are set by ubiquitin-proteasome-mediated degradation, as proteasome inhibition with PS-341 stabilizes the protein [#3], while its transcription is positively driven by CTCF acting at a promoter polymorphism [#7]. Genetic variants in UBAC2 that alter its transcript expression are associated with Behçet's disease [#5, #6].\",\n  \"teleology\": [\n    {\n      \"year\": 2011,\n      \"claim\": \"Established that UBAC2 is a disease-relevant locus whose expression is genetically tunable, raising the question of what UBAC2 does mechanistically.\",\n      \"evidence\": \"Haplotype conditional analysis and real-time PCR of a UBAC2 transcript variant in PBMCs stratified by rs7999348 genotype\",\n      \"pmids\": [\"21918955\", \"22455605\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Does not define UBAC2 protein function\", \"Causal link between transcript variant level and disease mechanism unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed that a specific promoter polymorphism quantitatively controls UBAC2 transcription, pinpointing a cis-regulatory mechanism for the disease association.\",\n      \"evidence\": \"Luciferase reporter assay and real-time PCR of UBAC2 in PBMCs and skin stratified by rs3825427 genotype\",\n      \"pmids\": [\"22455605\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Trans-acting factor binding the promoter not identified\", \"Does not connect transcript level to a cellular function\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the first functional handles on UBAC2 protein — that it is a 4-transmembrane, ubiquitin-binding protein turned over by the proteasome and that it suppresses an inflammatory signaling axis.\",\n      \"evidence\": \"TM4/UBAC2 knockout mouse, PS-341 proteasome inhibition in vitro and in db/db mice, and Nur77/IKKβ/NF-κB pathway readouts\",\n      \"pmids\": [\"34074311\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"E3 ligase and degron driving proteasomal turnover not identified\", \"Molecular mechanism linking UBAC2 to NF-κB suppression unresolved\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified the trans-acting regulator of UBAC2 transcription, showing CTCF binds the promoter polymorphism as an enhancer to activate expression.\",\n      \"evidence\": \"Luciferase reporter with CTCF overexpression and rs3825427 mutation, plus siRNA knockdown of CTCF with UBAC2 mRNA measurement\",\n      \"pmids\": [\"35020141\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether CTCF regulation operates in disease-relevant cell types in vivo unaddressed\", \"Single lab, focused on one SNP\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved the core molecular function of UBAC2 as a LIR-containing ER-phagy receptor for GABARAP, and showed MARK2 phosphorylation at S223 acts as the activating switch via dimerization, linking ER turnover to restraint of ER-stress-driven inflammation.\",\n      \"evidence\": \"LIR motif identification with GABARAP binding assays, MARK2 kinase assay and S223 phospho-site mutagenesis with dimerization/binding readouts, and UBAC2 loss-of-function mouse colitis models with UPR and inflammation measurements\",\n      \"pmids\": [\"39284914\", \"39580148\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of S223-driven dimerization not solved\", \"How dimerization mechanistically enhances GABARAP avidity not detailed\", \"Relationship between ER-phagy receptor role and the earlier ubiquitin-binding/NF-κB functions not reconciled\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the ubiquitin-binding domain of UBAC2 and its proteasomal turnover integrate with its ER-phagy receptor function and NF-κB suppression remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No identified E3 ligase or ubiquitin ligand for the ubiquitin-binding domain\", \"Unclear whether ER-phagy and NF-κB regulation are the same or parallel pathways\", \"No structural model of the full receptor\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 2]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"GABARAP\", \"MARK2\", \"CTCF\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}