Sensitization of Gastric Cancer Cells to 5-FU by MicroRNA-204 Through Targeting the TGFBR2-Mediated Epithelial to Mesenchymal Transition

Background/Aims: Gastric cancer (GC) is the most common gastrointestinal malignancy, causing cancer-related deaths in East Asia. MicroRNAs (miRNAs) are small non-coding RNAs aberrantly expressed in human tumors. In this study, we aim to investigate the roles of miR-204 in the epithelial to mesenchymal transition (EMT)-associated chemosensitivity. Methods: The expression of miR-204 was detected in clinical tumor samples and GC cell lines by real time PCR. Tumor cell's growth, invasion, and migration were measured by MTT assay, wound healing assay, and transwell invasion assay, respectively. Western blot method was used to detect the protein levels of indicated genes. Luciferase reporter assay was performed to validate the target gene of miR-204. The in vivo role of miR-204 was measured using a xenograft mouse model of GC. Results: By comparing the expressions of miR-204 in human gastric tumors and their adjacent normal tissues, it was disclosed that miR-204 was significantly downregulated in gastric tumors. Moreover, miR-204 was downregulated in multiple GC cell lines compared with normal gastric epithelial cells. Overexpression of miR204 suppressed GC cells' proliferation, invasion, and migration. It is noteworthy that 5-FU treatments induced miR-204 expression and suppressed TGF-beta pathway. By establishment of 5-FU resistant GC cell line, it was revealed that miR-204 was significantly downregulated in 5-FU resistant GC cells, representing mesenchymal features with downregulation of epithelial marker, while mesenchymal markers were upregulated. We identified TGFBR2 as a direct target of miR-204 by Western blot method and luciferase assay in GC cells and tumor samples as well. In addition, overexpression of miR-204 sensitized GC cells to 5-FU in vitro. Xenograft experiments demonstrated that the combination of miR-204 and 5-FU efficiently inhibited tumor growth and improved survival rate of mice as well. Eventually, we illustrated the restoration of TGFBR2 in miR-204 overexpression GC cells, which recovered resistance to 5-FU treatments compared with miR-204 overexpression GC cells. Conclusion: This study describes a miRNA-based therapeutic strategy against 5-FU resistance in GC, contributing to the development of anti-chemoresistance therapeutic agents. (C) 2018 The Author(s) Published by S. Karger AG, Basel