| Topic | Key findings | Evidence type | Primary source (first author, journal) | Publication date (month year) | URL | Notes/limitations |
|---|---|---|---|---|---|---|
| Identity | Human AGR3 corresponds to UniProt Q8TD06 / PDIA18, an AGR-family, PDI-like protein encoded on chromosome 7p21.1; reported as a 166-aa protein of ~19.2 kDa (pqac-00000000, pqac-00000005) | Review synthesis of gene/protein annotation; primary experimental background | Boisteau, *Oncogene*; Bonser, *Am J Respir Cell Mol Biol* | Sep 2022; Oct 2015 | https://doi.org/10.1038/s41388-022-02452-1 ; https://doi.org/10.1165/rcmb.2014-0318oc | Annotation-level facts; not itself a direct functional assay |
| Domains / family | AGR3 is a small, single-domain PDI-family protein with a thioredoxin-like fold; it carries an N-terminal signal peptide for secretory-pathway entry and a noncanonical ER-retention motif QSEL (pqac-00000008, pqac-00000000) | Crystal structure; review | Nguyen, *Acta Crystallogr F Struct Biol Commun*; Boisteau, *Oncogene* | Jun 2018; Sep 2022 | https://doi.org/10.1107/S2053230X18009093 ; https://doi.org/10.1038/s41388-022-02452-1 | Signal peptide/retention motif support localization but do not identify client proteins |
| Active-site motif / catalytic implication | 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 (pqac-00000008, pqac-00000009, pqac-00000011, pqac-00000007) | Crystal structure; comparative structural inference | Nguyen, *Acta Crystallogr F Struct Biol Commun* | Jun 2018 | https://doi.org/10.1107/S2053230X18009093 | Catalytic activity is inferred structurally; no direct AGR3 enzymatic rate/substrate assay in provided snippets |
| Structural features / oligomerization | AGR3 adopts a thioredoxin fold with four β-strands and four α-helices, a bent helix 2, and cis-Pro117 near the DCYQS motif. Two molecules appear in the asymmetric unit, but biochemical/PISA analysis found no evidence for a stable dimer in solution; AGR3 lacks an AGR2-like inter-subunit salt-bridge component (pqac-00000009, pqac-00000011) | X-ray crystal structure | Nguyen, *Acta Crystallogr F Struct Biol Commun* | Jun 2018 | https://doi.org/10.1107/S2053230X18009093 | Structural study does not establish physiological oligomer state in cells |
| Subcellular localization | AGR3 is ER luminal/ER resident in ciliated airway cells. In human airway epithelium, 99.5% of AGR3 signal colocalized with ER markers GRP78/GRP94, and 97.7% of AGR3 staining was spatially distinct from AGR2. Review evidence also notes membrane and extracellular detection in some cancer contexts (pqac-00000003, pqac-00000000) | Immunostaining / colocalization; review synthesis | Bonser, *Am J Respir Cell Mol Biol*; Boisteau, *Oncogene* | Oct 2015; Sep 2022 | https://doi.org/10.1165/rcmb.2014-0318oc ; https://doi.org/10.1038/s41388-022-02452-1 | Membrane/extracellular localization in cancer is less mechanistically resolved than ER localization |
| Expression pattern | AGR3 is enriched in ciliated airway epithelial cells and increases strongly with epithelial differentiation; AGR3 mRNA rose by ~1000-fold from day 7 to day 21 in differentiated airway epithelial cultures. It is not induced by ER stress; tunicamycin increased AGR2 mRNA 13-fold but not AGR3 (pqac-00000002, pqac-00000003, pqac-00000005, pqac-00000004) | Differentiation time course; ER-stress perturbation | Bonser, *Am J Respir Cell Mol Biol*; Boisteau, *Oncogene* | Oct 2015; Sep 2022 | https://doi.org/10.1165/rcmb.2014-0318oc ; https://doi.org/10.1038/s41388-022-02452-1 | Expression data do not by themselves reveal molecular clients |
| Airway / ciliary function | Agr3-/- mice were viable and had morphologically normal cilia, but tracheal ciliary beat frequency (CBF) was reduced by ~20% at baseline; with ATP stimulation CBF was ~35% lower than controls. Mucociliary particle transport speed was reduced by 35%, supporting a role in mucociliary clearance rather than ciliogenesis (pqac-00000002, pqac-00000005) | Mouse knockout; ex vivo tracheal physiology | Bonser, *Am J Respir Cell Mol Biol* | Oct 2015 | https://doi.org/10.1165/rcmb.2014-0318oc | Evidence is strong for airway physiology, but does not identify direct AGR3 molecular substrate(s) |
| Calcium-linked mechanism | The CBF defect in Agr3-/- airways disappeared in calcium-free solution, and intracellular Ca2+ in cultured tracheal epithelial cells was lower in Agr3-/- vs wild type (139.7 ± 98.2 nM vs 362.1 ± 55.0 nM; n=6; p<0.001), implicating AGR3 in calcium-dependent regulation of ciliary activity (pqac-00000002, pqac-00000005) | Mouse knockout; calcium imaging | Bonser, *Am J Respir Cell Mol Biol* | Oct 2015 | https://doi.org/10.1165/rcmb.2014-0318oc | Mechanistic link to specific calcium-handling proteins remains unresolved in provided evidence |
| Cancer association (intracellular/expression) | AGR3 was first identified in breast tumor membranes; review evidence states expression correlates with estrogen receptor status, correlates with AGR2, and is reported to promote migration/metastasis. AGR3 has also been detected at the cell membrane and extracellularly in cancer contexts (pqac-00000000) | Review synthesis drawing on earlier primary literature | Boisteau, *Oncogene* | Sep 2022 | https://doi.org/10.1038/s41388-022-02452-1 | Broad cancer statements are summarized from prior literature; quantitative tumor-outcome estimates are not given in the snippet |
| Extracellular AGR3 secretion | ER-positive breast cancer cell lines MCF-7 and T-47D secrete AGR3; conditioned media contained extracellular AGR3 at nanomolar concentrations. Serum eAGR3 was reported significantly elevated in breast cancer patients versus healthy controls (pqac-00000017, pqac-00000015) | Cell culture secretion assays; patient serum measurement | Obacz, *Oncology Letters* | Sep 2019 | https://doi.org/10.3892/ol.2019.10849 | Provided snippets do not include absolute serum concentrations or fold change |
| Extracellular AGR3 function in cancer | Recombinant eAGR3 promoted breast-cancer-cell migration and increased resistance to detachment/adhesion-related phenotypes. Functional assays used 5 ng/ml eAGR3 commonly, with testing across 0.5–50 ng/ml; migration was measured in wound-healing assays and adhesion in detachment assays (pqac-00000016, pqac-00000017, pqac-00000018) | Recombinant-protein treatment in breast cancer cell culture | Obacz, *Oncology Letters* | Sep 2019 | https://doi.org/10.3892/ol.2019.10849 | Exact effect sizes are not present in the provided snippets |
| Src signaling downstream of eAGR3 | eAGR3 increased tyrosine phosphorylation and c-Src phosphorylation. Dasatinib blocked c-Src phosphorylation and significantly reduced migration of control and eAGR3-stimulated cells; genetic interference with kinase-dead Src (K298R) abolished the migratory response to eAGR3. Dasatinib did not fully abolish migration, implying additional pathways may contribute (pqac-00000016, pqac-00000015, pqac-00000018) | Pharmacologic inhibition and dominant-negative Src in cell culture | Obacz, *Oncology Letters* | Sep 2019 | https://doi.org/10.3892/ol.2019.10849 | Strong evidence for Src involvement in vitro, but receptor(s) for eAGR3 and in vivo relevance remain unresolved |
| Known gaps | Across the provided evidence, no definitive AGR3-specific enzymatic substrate, direct folding client, or biochemical turnover measurement is established. Review and structure sources suggest possible roles in secretory/transmembrane protein biogenesis and possible mucin interaction by family analogy, but direct AGR3 client validation is lacking in the cited snippets (pqac-00000008, pqac-00000004, pqac-00000000) | Cross-source synthesis | Nguyen, *Acta Crystallogr F Struct Biol Commun*; Boisteau, *Oncogene* | Jun 2018; Sep 2022 | https://doi.org/10.1107/S2053230X18009093 ; https://doi.org/10.1038/s41388-022-02452-1 | Important limitation for functional annotation: much of AGR3 biochemistry remains inferential rather than directly measured |


*Table: This table summarizes the key experimentally supported properties and functions of human AGR3 (UniProt Q8TD06) from the provided evidence only. It highlights what is well supported—especially ER localization, ciliary function, and extracellular cancer signaling—and where important mechanistic gaps remain.*