The disorganized polarization of tumor-associated macrophages (TAMs) exerts a critical effect on tumor progression. MicroRNAs (miRNAs) in extracellular vesicles (EVs) secreted from cancer cells may contribute to this process. However, the relationship between TAMs and EVs-miRNAs-mediated regulation in esophageal squamous cell carcinoma (ESCC) remains unclear. In the present study, immunoaffinity magnetic beads combined with antiepithelial cell adhesion molecules (EpCAM) were used to isolate and identify EVs-miR-21-5p from the plasma of ESCC patients. An in vitro coculture system was designed to evaluate the effect of esophageal cancer cells with miR-21-5p overexpression on macrophage polarization. We found that phorbol myristate acetate-induced THP-1 macrophages took up EVs-miR-21-5p from EC109 or EC9706 cells and were transformed into M2 macrophages. This, in turn, contributed to the excessive migration and invasion of esophageal cancer cells. The mechanism underlying these changes may involve activation of M2 macrophages by upregulated ESCC-derived EVs-miR-21-5p through the PTEN/AKT/STAT6 pathway. This may result in esophageal cancer cell epithelial-mesenchymal transition (EMT) via TGF-β/Smad2 signaling. Our results indicate positive feedback between M2 macrophage polarization and EMT of esophageal cancer cells in the tumor microenvironment via shuttling of miR-21-5p in tumor-derived EVs.
Keywords: EVs-miR-21-5p; epithelial-mesenchymal transition; esophageal squamous cell carcinoma (ESCC); macrophage polarization.