miR-409-3p sensitizes colon cancer cells to oxaliplatin by inhibiting Beclin-1-mediated autophagy

The chemoresistance of colon cancer cells limits the efficacy of chemotherapy. miR-409-3p has been shown to be downregulated in various types of cancer. In the present study, we examined the role of miR-409-3p in colon cancer as well as the effects of miR-409-3p on the sensitivity of colon cancer cells to oxaliplatin. The expression of miR-409 was significantly downregulated in the human colon cancer cell lines compared with the normal colon epithelial cells. Importantly, the miR-409-3p expression levels were lower in human colon cancer patient samples than in normal colon tissues. Moreover, we observed a negative correlation between the miR-409-3p levels and resistance to oxaliplatin: the oxaliplatin-resistant colon cancer cells exhibited significantly downregulated miR-409-3p levels, but higher autophagic activity than the oxaliplatin- sensitive cells. Using bioinformatics analysis, we predicted that miR-409-3p miRNA binds to the key autophagy gene encoding Beclin-1. Our findings indicated that the overexpression of miR-409-3p inhibited Beclin-1 expression and autophagic activity by binding to the 3'-untranslated region of Beclin-1 mRNA. In addition, the overexpression of miR-409-3p enhanced the chemosensitivity of the oxaliplatin-sensitive and oxaliplatin-resistant colon cancer cells. The restoration of Beclin-1 abrogated these effects of miR-409-3p. In a xenograft model using nude mice, we examined the effects of miR-409-3p on tumor growth during chemotherapy. miR-409-3p overexpression sensitized the tumor to chemotherapy, while inhibiting chemotherapy-induced autophagy in a manner dependent on Beclin-1. The findings of our study suggest that miR-409-3p is capable of enhancing the chemosensitivity of colon cancer cells by inhibiting Beclin-1-mediated autophagy.