Tumor-Associated Macrophage-Derived Exosomes Promote the Progression of Gastric Cancer by Regulating the P38MAPK Signaling Pathway and the Immune Checkpoint PD-L1

Objective: To investigate the effects of M2 macrophage-derived exosomes (M2-Exos) on proliferation, migration, and apoptosis of gastric cancer cells in the tumor microenvironment and to further explore their possible molecular mechanism. Materials and Methods: M2 macrophages were induced from THP-1 cells and identified by qRT-PCR. Exosomes were extracted by ultracentrifugation and identified by transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and Western blot analysis. Fluorescence labeling was used to detect the internalization of exosomes in receptors. The proliferation, migration, and invasion of AGS and HGC27 cells were determined by EdU and MTS, wound healing and Transwell assay, and flow cytometry, respectively. Proteins in the related pathway of M2-Exos affecting the progression of gastric cancer were detected by Western blot analysis. Results: In this study, M2 macrophages and M2-Exos were successfully obtained. The purified M2-Exos were observed as small round vesicles with diameters of 50-90 nm and positive expression of CD63, CD9, and TSG101. Besides, M2-Exos can be effectively taken up and internalized by AGS and HGC27 cells. Cell behavior studies showed that M2-Exos promoted proliferation and migration and inhibited the apoptosis of AGS and HGC27. Further research illustrated that M2-Exos promoted the phosphorylation of P38 and high expression of programmed death ligand 1 (PD-L1). Conclusions: This study demonstrated that M2-Exos promoted proliferation and migration and inhibited the apoptosis of gastric cancer cells. Mechanically, M2-Exos may promote gastric cancer progression through the P38MAPK signaling pathway and achieve immune escape through elevating the expression of PD-L1.