The microRNA cluster miR-214/miR-3120 prevents tumor cell switching from an epithelial to a mesenchymal-like phenotype and inhibits autophagy in gallbladder cancer

Tumor cells switch from an epithelial to a mesenchymal-like phenotype, which represents a key hallmark of human cancer metastasis, including gallbladder cancer (GBC). A large set of microRNAs (miRNAs/miRs) have been studied to elucidate their functions in initiating or inhibiting this phenotypic switching in GBC cells. In this paper, we attempted to identify the expression pattern of the miR-214/-3120 cluster and its mode of action in the context of GBC, with a specific focus being placed on their effects on EMT and autophagy in GBC cells. Human GBC cells GBC-SD were assayed for their migration, invasion, and autophagy using the Transwell chamber system, MDC staining, and transmission electron microscopy. The tumorigenicity and metastatic behavior of GBC-SD cells were tested in nude mice. The expression of EMT- and autophagy-specific markers (E-cadherin, N-cadherin, vimentin, ATG5, LC3II/LC3I, and Beclin1) was analyzed in cultured GBC-SD cells and in human GBC-SD xenografts. The E2F3 luciferase reporter activity in the presence of miR-214/-3120 was evaluated by a dual luciferase assay. The miR-214/-3120 was downregulated in GBC. Exogenous miR-214/-3120 inhibited the phenotypic switching of GBC cells from epithelial to mesenchymal, prevented autophagy, and suppressed the tumorigenicity and metastatic behavior of GBC-SD cells in vitro and in vivo. E2F3 was demonstrated to be the target gene of miR-214/-3120, and its knockdown in part mimicked the effect of miR-214/-3120 on the EMT, autophagy, tumorigenicity, and metastatic behavior of GBC-SD cells. These results demonstrated that the miR-214/-3120 cluster blocks the process of EMT and autophagy to limit GBC metastasis by repressing E2F3 expression.