FOXM1 upregulation, promotes immune escape in gastric cancer through activation of Notch signaling pathway.

Abstract

Forkhead box M1 (FOXM1) exhibits elevated level in various tumors and is linked with tumor immune escape. The role of FOXM1 in gastric cancer (GC) progression and immune escape remains poorly understood. FOXM1 and programmed death-ligand 1 (PD-L1) levels were determined through qRT-PCR and Western blot. Co-immunoprecipitation confirmed the interaction between FOXM1 and PD-L1. The malignant biological properties of GC cells were assessed by MTT, EdU staining, scratch-wound assay, transwell and flow cytometry. CD8 + T cells were separated and co-cultured with GC cells, and the proliferation and apoptosis of CD8 + T cells were detected through CFSE staining, flow cytometry and LDH kit. CD8 + T cytokine contents were measured using ELISA kits. Western blot detected CD8 + T cell activation markers and Notch signaling pathway-related proteins levels. A nude mouse subcutaneous graft tumor model was constructed, Ki-67 positivity and CD8 + T cell infiltration were detected by immunohistochemistry and flow cytometry. FOXM1 and PD-L1 were highly expressed in GC. Overexpression of FOXM1 increased migrating and infiltrating cell counts and GC cell viability, and declined the killing impact of CD8 + T cells. After knockdown of FOXM1, all of the above indicators were significantly reversed. After co-cultured with GC cells overexpressing FOXM1, CD8 + T cells exhibited a declined in CFSE positivity percentage, cytotoxicity, cytokines and activation markers levels, and an increase in apoptosis. FOXM1 up-regulated PD-L1 expression by activating the Notch signaling pathway, and both silencing PD-L1 and Notch inhibitor attenuated the impact of overexpression of FOXM1. Knockdown of FOXM1 reduced Ki67 positivity in GC tumors and promoted CD8 + T cell infiltration. FOXM1 up-regulates PD-L1 level by activating Notch signaling pathway, thus hinders CD8 + T cell activation and promotes immune escape in GC cells. This study provides a theoretical basis for the development of GC-targeted therapeutic targets as well as immunotherapy, which is beneficial to the clinical diagnosis and treatment of GC.