Purpose: We investigated the role of tumor-associated macrophages (TAMs) on the epithelial to mesenchymal transition (EMT) of colorectal cancer cells and determined the potential mechanism involved in the metastatic process.
Materials and methods: In this study, flow cytometry was used to detect the expression of target proteins. We used transwell assay to evaluate the migration of cancer cells under specific conditions. Using real-time polymerase chain reaction, we examined the expressions of cytokines and EMT-related markers in mRNA level. Animal assay was performed for analysis in vivo and hematoxylin and eosin was used to visualize the effect of TAMs on tumor metastasis. We also used immunohistochemistry and Western blotting to detect the expression of target proteins.
Results: Here, we observed enrichment of TAMs in colorectal tumor tissues, resulting in high metastasis in clinical therapy. Moreover, those TAMs could facilitate the EMT progression of colorectal cancer cells, which is induced by the transforming growth factor-β (TGF-β) derived from TAMs, leading to the invasion and migration of cancer cells.
Conclusion: Our results demonstrated that TAMs contributed the EMT progression through a TGF-β/Smad2,3-4/Snail signaling pathway, and disrupting this pathway with TGF-β receptor inhibitor could suppress metastasis, readjusting our focus to the connection of TAMs and cancer metastasis.
Keywords: Colorectal neoplasms; Epithelial to mesenchymal transition; Transforming growth factor β; Tumor associated macrophages.