id: Q8TD06 gene_symbol: AGR3 product_type: PROTEIN status: COMPLETE taxon: id: NCBITaxon:9606 label: Homo sapiens description: >- AGR3 encodes anterior gradient protein 3, a small secretory-pathway AGR/thioredoxin-like protein with an N-terminal signal peptide and C-terminal ER retrieval motif. AGR3 is enriched in ciliated airway epithelial cells and other epithelia, and loss-of-function evidence supports a role in calcium-dependent control of ciliary beat frequency and mucociliary clearance. AGR3 also has reported cancer-associated extracellular interactions with alpha-dystroglycan and LYPD3/C4.4a, but its precise molecular catalytic activity and physiological client proteins remain unresolved. existing_annotations: - term: id: GO:0005783 label: endoplasmic reticulum evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: is_active_in review: summary: >- ER localization is well supported for AGR3 by its signal peptide, QSEL retrieval motif, KDEL-receptor localization study, and airway epithelial cell localization evidence. action: ACCEPT reason: >- ER residence is the best-supported compartment for AGR3 and is consistent with both phylogenetic transfer and direct experimental localization evidence. additional_reference_ids: - PMID:18086916 - PMID:25751668 supported_by: - reference_id: PMID:18086916 supporting_text: >- Three of the 16 constructs, ERp18, Hag3, and GP7R, changed their localization from the ER to the Golgi when the putative ER-retention motif was not present reference_section_type: RESULTS - reference_id: PMID:25751668 supporting_text: >- Here we report that AGR3, unlike its closest homolog AGR2, is restricted to ciliated cells in the airway epithelium and is not induced by ER stress. reference_section_type: ABSTRACT - term: id: GO:0002162 label: dystroglycan binding evidence_type: IBA original_reference_id: GO_REF:0000033 qualifier: enables review: summary: >- AGR3 binding to alpha-dystroglycan was reported in yeast two-hybrid screens, but the evidence is cancer/extracellular-context interaction evidence rather than the main physiological airway/ER function of AGR3. action: KEEP_AS_NON_CORE reason: >- The term is specific enough to retain, and the IBA is consistent with the original AGR2/AGR3 two-hybrid evidence, but it should not be treated as the core function because the paper itself called for additional clinical-context validation. additional_reference_ids: - PMID:12592373 supported_by: - reference_id: PMID:12592373 supporting_text: >- Yeast two-hybrid cloning identified metastasis-associated GPI-anchored C4.4a protein and extracellular alpha-dystroglycan (DAG-1) as binding partners for both hAG-2 and hAG-3 reference_section_type: ABSTRACT - reference_id: PMID:12592373 supporting_text: >- Clearly, further analyses such as coimmunoprecipitation are required to confirm that these interactions occur in clinical cancers reference_section_type: RESULTS - term: id: GO:0002162 label: dystroglycan binding evidence_type: IEA original_reference_id: GO_REF:0000117 qualifier: enables review: summary: >- ARBA transfer of dystroglycan binding is consistent with direct AGR3/DAG1 yeast two-hybrid evidence, but it remains a non-core cancer/extracellular interaction. action: KEEP_AS_NON_CORE reason: >- Keep the specific binding term as non-core: the interaction is reported, but the strongest physiological evidence for AGR3 concerns ER-localized control of airway ciliary beat regulation. additional_reference_ids: - PMID:12592373 supported_by: - reference_id: PMID:12592373 supporting_text: >- Yeast two-hybrid cloning identified metastasis-associated GPI-anchored C4.4a protein and extracellular alpha-dystroglycan (DAG-1) as binding partners for both hAG-2 and hAG-3 reference_section_type: ABSTRACT - reference_id: PMID:12592373 supporting_text: >- Clearly, further analyses such as coimmunoprecipitation are required to confirm that these interactions occur in clinical cancers reference_section_type: RESULTS - term: id: GO:0005783 label: endoplasmic reticulum evidence_type: IEA original_reference_id: GO_REF:0000120 qualifier: located_in review: summary: >- Automated ER localization is consistent with experimental literature and the UniProt-recognized AGR3 ER retrieval motif. action: ACCEPT reason: >- ER is the principal supported cellular compartment for AGR3. additional_reference_ids: - PMID:18086916 - PMID:25751668 supported_by: - reference_id: PMID:18086916 supporting_text: >- Three of the 16 constructs, ERp18, Hag3, and GP7R, changed their localization from the ER to the Golgi when the putative ER-retention motif was not present reference_section_type: RESULTS - reference_id: PMID:25751668 supporting_text: >- Here we report that AGR3, unlike its closest homolog AGR2, is restricted to ciliated cells in the airway epithelium and is not induced by ER stress. reference_section_type: ABSTRACT - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:21516116 qualifier: enables review: summary: >- This Stitch-seq interactome annotation reports an AGR3 binary interaction but collapses it to generic protein binding, which is not informative for AGR3 functional curation. action: MARK_AS_OVER_ANNOTATED reason: >- Generic protein binding should not be retained as a meaningful AGR3 function, especially for high-throughput interactome rows without a mechanistic connection to AGR3 airway or ER biology. supported_by: - reference_id: PMID:21516116 supporting_text: >- We describe a massively parallel interactome-mapping pipeline, Stitch-seq, that combines PCR stitching with next-generation sequencing and used it to generate a new human interactome dataset. reference_section_type: ABSTRACT - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:25416956 qualifier: enables review: summary: >- The proteome-scale interactome map contributes several AGR3 binary interaction rows, but the resulting GO term protein binding is too broad to clarify AGR3 function. action: MARK_AS_OVER_ANNOTATED reason: >- The annotation should not be treated as core AGR3 biology because it is a broad high-throughput interaction label without a specific biochemical or pathway interpretation. supported_by: - reference_id: PMID:25416956 supporting_text: >- Here, we describe a systematic map of ?14,000 high-quality human binary protein-protein interactions. reference_section_type: ABSTRACT - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:32296183 qualifier: enables review: summary: >- HuRI reports many AGR3 binary interaction partners, but generic protein binding obscures rather than explains the protein's biological role. action: MARK_AS_OVER_ANNOTATED reason: >- This high-throughput interaction evidence is useful as candidate-interactor context but should not be propagated as a core or informative molecular function annotation. supported_by: - reference_id: PMID:32296183 supporting_text: >- Here we present a human 'all-by-all' reference interactome map of human binary protein interactions, or 'HuRI'. reference_section_type: ABSTRACT - term: id: GO:0005783 label: endoplasmic reticulum evidence_type: IDA original_reference_id: GO_REF:0000052 qualifier: located_in review: summary: >- Immunofluorescence-based ER localization is consistent with direct literature showing AGR3 as an ER-resident ciliated-airway protein. action: ACCEPT reason: >- The experimental cellular-component annotation matches the best-supported localization for AGR3. additional_reference_ids: - PMID:18086916 - PMID:25751668 supported_by: - reference_id: PMID:18086916 supporting_text: >- Three of the 16 constructs, ERp18, Hag3, and GP7R, changed their localization from the ER to the Golgi when the putative ER-retention motif was not present reference_section_type: RESULTS - reference_id: PMID:25751668 supporting_text: >- Here we report that AGR3, unlike its closest homolog AGR2, is restricted to ciliated cells in the airway epithelium and is not induced by ER stress. reference_section_type: ABSTRACT - term: id: GO:0005515 label: protein binding evidence_type: IPI original_reference_id: PMID:12592373 qualifier: enables review: summary: >- The protein-binding annotation from PMID:12592373 reflects specific yeast-two-hybrid interactions with C4.4a/LYPD3 and alpha-dystroglycan; dystroglycan binding is the more informative existing GO term. action: MODIFY reason: >- Protein binding is too generic. Replace it with the specific supported DAG1 interaction term, while noting that the LYPD3/C4.4a interaction does not currently have an equivalently specific GO binding term in this review. proposed_replacement_terms: - id: GO:0002162 label: dystroglycan binding supported_by: - reference_id: PMID:12592373 supporting_text: >- Yeast two-hybrid cloning identified metastasis-associated GPI-anchored C4.4a protein and extracellular alpha-dystroglycan (DAG-1) as binding partners for both hAG-2 and hAG-3 reference_section_type: ABSTRACT - reference_id: PMID:12592373 supporting_text: >- Clearly, further analyses such as coimmunoprecipitation are required to confirm that these interactions occur in clinical cancers reference_section_type: RESULTS - term: id: GO:0002162 label: dystroglycan binding evidence_type: IDA original_reference_id: PMID:12592373 qualifier: enables review: summary: >- Direct yeast-two-hybrid evidence supports AGR3 binding to alpha-dystroglycan, but this is not AGR3's main supported physiological function. action: KEEP_AS_NON_CORE reason: >- Retain the specific molecular interaction as non-core because the best functional evidence instead points to ER-localized regulation of ciliary beat frequency in airway epithelium. supported_by: - reference_id: PMID:12592373 supporting_text: >- Yeast two-hybrid cloning identified metastasis-associated GPI-anchored C4.4a protein and extracellular alpha-dystroglycan (DAG-1) as binding partners for both hAG-2 and hAG-3 reference_section_type: ABSTRACT - reference_id: PMID:12592373 supporting_text: >- Clearly, further analyses such as coimmunoprecipitation are required to confirm that these interactions occur in clinical cancers reference_section_type: RESULTS - term: id: GO:0003351 label: epithelial cilium movement involved in extracellular fluid movement evidence_type: ISS original_reference_id: PMID:25751668 qualifier: involved_in review: summary: >- NEW annotation. Mouse Agr3 loss reduces airway ciliary beat frequency and mucociliary transport while preserving ciliary ultrastructure, supporting a conserved AGR3 role in epithelial motile-cilium function rather than ciliogenesis. action: NEW reason: >- This is the clearest biological-process annotation for AGR3's best-supported physiological role. It is proposed for human AGR3 by sequence/orthology-supported inference from the mouse knockout and airway epithelial evidence. supported_by: - reference_id: PMID:25751668 supporting_text: >- Mice lacking AGR3 are viable and develop ciliated cells with normal-appearing cilia. However, ciliary beat frequency was lower in airways from AGR3-deficient mice compared with control mice reference_section_type: ABSTRACT - reference_id: PMID:25751668 supporting_text: >- Decreased CBF was associated with impaired mucociliary clearance in AGR3-deficient airways. reference_section_type: ABSTRACT - term: id: GO:0019722 label: calcium-mediated signaling evidence_type: ISS original_reference_id: PMID:25751668 qualifier: involved_in review: summary: >- NEW annotation. AGR3 deficiency affects ciliary beat frequency in a calcium-dependent manner, supporting involvement in calcium-mediated control of airway ciliary function. action: NEW reason: >- This term captures the calcium-dependent mechanism reported for AGR3 more conservatively than asserting a specific calcium transporter, channel, or enzymatic activity. supported_by: - reference_id: PMID:25751668 supporting_text: >- AGR3 deficiency had no detectable effects on ciliary beat frequency (CBF) when airways were perfused with a calcium-free solution, suggesting that AGR3 is required for calcium-mediated regulation of ciliary function. reference_section_type: ABSTRACT references: - id: GO_REF:0000033 title: Annotation inferences using phylogenetic trees findings: [] - id: GO_REF:0000052 title: Gene Ontology annotation based on curation of immunofluorescence data findings: [] - id: GO_REF:0000117 title: Electronic Gene Ontology annotations created by ARBA machine learning models findings: [] - id: GO_REF:0000120 title: Combined Automated Annotation using Multiple IEA Methods findings: [] - id: PMID:12592373 title: hAG-2 and hAG-3, human homologues of genes involved in differentiation, are associated with oestrogen receptor-positive breast tumours and interact with metastasis gene C4.4a and dystroglycan. findings: - statement: AGR3 was reported to bind C4.4a/LYPD3 and alpha-dystroglycan in yeast two-hybrid screens. supporting_text: >- Yeast two-hybrid cloning identified metastasis-associated GPI-anchored C4.4a protein and extracellular alpha-dystroglycan (DAG-1) as binding partners for both hAG-2 and hAG-3 reference_section_type: ABSTRACT - id: PMID:18086916 title: A molecular specificity code for the three mammalian KDEL receptors. findings: - statement: AGR3/hAG-3 is ER localized and loses ER localization when its C-terminal retrieval motif is removed. supporting_text: >- Three of the 16 constructs, ERp18, Hag3, and GP7R, changed their localization from the ER to the Golgi when the putative ER-retention motif was not present reference_section_type: RESULTS - id: PMID:21516116 title: Next-generation sequencing to generate interactome datasets. findings: [] - id: PMID:25416956 title: A proteome-scale map of the human interactome network. findings: [] - id: PMID:25751668 title: The Endoplasmic Reticulum Resident Protein AGR3. Required for Regulation of Ciliary Beat Frequency in the Airway. findings: - statement: AGR3 is required for calcium-mediated ciliary beat regulation and mucociliary clearance in airway epithelium. supporting_text: >- AGR3 deficiency had no detectable effects on ciliary beat frequency (CBF) when airways were perfused with a calcium-free solution, suggesting that AGR3 is required for calcium-mediated regulation of ciliary function. Decreased CBF was associated with impaired mucociliary clearance in AGR3-deficient airways. reference_section_type: ABSTRACT full_text_unavailable: true - id: PMID:26170690 title: Anterior gradient protein 3 is associated with less aggressive tumors and better outcome of breast cancer patients. findings: - statement: AGR3 is expressed in ciliated cells of the oviduct and in several cancer contexts. supporting_text: >- AGR3 expression was demonstrated in various cancers, including breast,7 prostate,21 ovary,19,20 and liver.18 reference_section_type: DISCUSSION - id: PMID:32296183 title: A reference map of the human binary protein interactome. findings: [] - id: file:human/AGR3/AGR3-deep-research-falcon.md title: Falcon deep research report for human AGR3. findings: - statement: AGR3 is not currently supported as a canonical protein disulfide isomerase despite its PDI-family/thioredoxin-like fold. supporting_text: >- Although structurally in the PDI/thioredoxin family, AGR3's **DCYQS** motif (lacking the second cysteine) supports the view that AGR3 is **not a canonical disulfide isomerase**; it likely mediates **selective protein interactions** or specialized redox behavior rather than generalized thiol-disulfide exchange core_functions: - description: >- AGR3 is an ER-retained AGR/thioredoxin-like protein in ciliated airway epithelial cells that is required for normal calcium-dependent regulation of ciliary beat frequency and mucociliary clearance. The molecular client or catalytic activity remains unresolved, and current evidence does not justify a canonical protein disulfide isomerase activity annotation. directly_involved_in: - id: GO:0003351 label: epithelial cilium movement involved in extracellular fluid movement - id: GO:0019722 label: calcium-mediated signaling locations: - id: GO:0005783 label: endoplasmic reticulum supported_by: - reference_id: PMID:25751668 supporting_text: >- AGR3 deficiency had no detectable effects on ciliary beat frequency (CBF) when airways were perfused with a calcium-free solution, suggesting that AGR3 is required for calcium-mediated regulation of ciliary function. Decreased CBF was associated with impaired mucociliary clearance in AGR3-deficient airways. reference_section_type: ABSTRACT - reference_id: file:human/AGR3/AGR3-deep-research-falcon.md supporting_text: >- AGR3 lacks the canonical PDI/thioredoxin CXXC or WCXXC motif; structure paper reports a DCYQS motif with solvent-exposed Cys71 in reduced state. Because the second catalytic cysteine is absent and an adjacent acidic residue likely raises cysteine pKa, AGR3 is inferred to have reduced/atypical thiol-disulfide exchange activity relative to classical PDIs proposed_new_terms: [] suggested_questions: - question: >- Does purified AGR3 have measurable protein disulfide isomerase or other redox/foldase activity, or should the PN PDI-family projection be treated as family context only? - question: >- Which ER client protein or calcium-handling pathway links AGR3 to airway epithelial ciliary beat regulation? - question: >- Is extracellular AGR3/Src signaling a physiological epithelial function, a cancer-specific state, or a consequence of altered ER retention/secretion? suggested_experiments: - description: >- Test purified AGR3, Cys71 mutants, and canonical PDI controls against standard disulfide isomerase/reductase substrates and candidate airway epithelial client proteins. experiment_type: biochemical activity assay - description: >- Rescue AGR3-deficient differentiated airway epithelial cultures with wild-type AGR3, QSEL-retention mutants, and Cys71 mutants while measuring ER localization, live-cell Ca2+ dynamics, ciliary beat frequency, and mucociliary transport. experiment_type: structure-function rescue - description: >- Use proximity labeling or crosslinking/coimmunoprecipitation in differentiated ciliated airway epithelium to identify AGR3-proximal ER proteins and distinguish physiological clients from high-throughput interactome candidates. experiment_type: client discovery tags: - proteostasis-network-review - pn-projection-reviewed - ciliary-function - er-localized