Molecular mechanisms of transmitted endoplasmic reticulum stress mediating immune escape of gastric cancer via PVR overexpression in TAMs

Abstract

Gastric cancer (GC) is the fourth leading cause of cancer death worldwide. Due to the complex tumor microenvironment (TME), the efficacy of immunotherapy in GC has not met expectations. Malignant changes in the TME induce endoplasmic reticulum stress (ERS). ERS can be transmitted between tumor cells and tumor-associated macrophages (TAMs), promoting tumor immune escape, but the specific mechanism in GC remains unclear. We established a TAM model of transmitted ERS (TERS), and iTRAQ proteomic analysis identified overexpressed proteins. The overexpression of poliovirus receptor (PVR) was screened while flow cytometry and ELISA showed that PVR mediated the immunosuppressive function of TAMs by downregulating the proliferative activity and cytotoxicity of cocultured CD8+ T lymphocytes. With EMSA and dual-luciferase reporter assays, we confirmed that erythropoietin-producing hepatocellular receptor A2 (EphA2) affected PVR expression by increasing the transcriptional activity of activator protein-1 (AP-1). MFC cells were mixed with EphA2 knockdown or control RAW264.7 cells to establish subcutaneous tumor models with or without tunicamycin treatment in vivo. The vivo experiments revealed that ERS promoted subcutaneous xenograft growth, which was reversed by EphA2 knockdown. Clinically, GC patients with high expression of PVR and EphA2 tended to have an immunosuppressive TME, which were determined by immunohistochemical and immunofluorescence analyses. In conclusion, the transcriptional activity of AP-1 is upregulated in ERS-transmitted TAMs through EphA2 to increase PVR expression, which promotes immune escape in GC. Our study provides a new perspective on the role of ERS in tumor immunity.