Inhibition of AGR2 triggers secretion of GRP78 and sensitizes gastroesophageal junction adenocarcinoma cells to ER Stress

The endoplasmic reticulum (ER) chaperone Anterior Gradient 2 (AGR2) is overexpressed in various adenocarcinomas, promoting tumor progression and chemoresistance. However, its exact role in modulating the Unfolded Protein Response (UPR) and remodeling the cancer cell secretome under proteotoxic stress remains poorly understood. Using shRNA-mediated silencing of AGR2 combined with high-throughput LC-MS/MS proteomic analysis in OE19 gastroesophageal junction adenocarcinoma cells, we profiled the global changes in protein secretion under basal and tunicamycin-induced ER stress conditions. Proteomic screening identified 75 differentially secreted proteins, with AGR2 depletion triggering a widespread up-secretion phenotype. Bioinformatic analysis revealed enrichment in pathways related to glycolysis, antigen processing and presentation, and extracellular matrix components. Notably, the ER-resident chaperone GRP78 was identified as a critical hub protein within the secretome. AGR2 knockdown downregulated intracellular GRP78 expression, and compromised UPR activation. Under ER stress, the absence of AGR2 triggered a massive secretion of GRP78 in the extracellular space, which correlated with a significantly increased sensitivity to tunicamycin-induced cell death. These findings identify AGR2 as a key regulator of GRP78 proteostasis and ER retention. By controlling the balance between intracellular retention and extracellular release of GRP78, AGR2 supports adaptive ER stress response and may contribute to tumor cell survival in gastroesophageal junction adenocarcinoma.