Abstract
Cisplatin (DDP) resistance is one of the main causes of treatment failure in patients with colon cancer (CC). Autophagy is a key mechanism of resistance to chemotherapy. Since autophagy-related 7 (ATG7) has been reported to be involved in the regulation of autophagy and DDP resistance for lung and esophageal cancer, the present study aimed to explore the functions of microRNA (miR)-4486 in the autophagy-mediated DDP resistance of CC. The expression level of miR-4486 in HCT116, DDP-resistant HCT116 cells (HCT116/DDP), SW480 and DDP-resistant SW480 cells (SW480/DDP) was quantified by reverse transcription-quantitative PCR. Western blotting was utilized to analyze the expression of ATG7, autophagy-related proteins Beclin 1 and LC3-I/II, as well as apoptosis-related proteins Bcl-2, Bax and cleaved-caspase 3 in HCT116/DDP and SW480/DDP cells. The half maximal inhibitory concentration of DDP on all cell lines and the cell viability of HCT116/DDP and SW480/DDP cells were measured using Cell Counting Kit 8 assay. Luciferase assay was used to examine the potential targets of miR-4486 and ATG7. The effects of upregulating mimic miR-4486 expression on the apoptosis and autophagy of HCT116/DDP and SW480/DDP cells were determined by flow cytometry and electron microscopy, respectively. It was found that miR-4486 expression was significantly decreased in HCT116/DDP and SW480/DDP cells compared with that in HCT116 and SW480 cells. Overexpression of miR-4486 could increase the sensitivity of HCT116/DDP and SW480/DDP cells to DDP by reducing cell viability, promoting apoptosis and inhibiting autophagy through downregulating Beclin 1 expression and the LC3-II/LC3-I ratio. Additionally, ATG7 was identified to be a target gene of miR-4486, where ATG7 overexpression could partially reverse the effects of miR-4486 on cell viability and apoptosis by promoting the formation of autophagosomes. In conclusion, the present results demonstrated that miR-4486 could reverse DDP resistance in HCT116/DDP and SW480/DDP cells by targeting ATG7 to inhibit autophagy.