miR-665 inhibits epithelial-to-mesenchymal transition in bladder cancer via the SMAD3/SNAIL axis

Emerging research indicates that miRNAs can regulate cancer progression by influencing molecular pathways. Here, we studied miR-665, part of the DLK1-DIO3 miRNA cluster, which is downregulated by upstream methylation in bladder cancer. MiR-665 overexpression significantly downregulated the expression of SMAD3, phospho-SMAD3, and SNAIL, reversed epithelial–mesenchymal transition progression, and inhibited the migration of bladder cancer cells. To predict potential targets of miR-665, we used online databases and subsequently determined that miR-665 binds directly to the 3ʹ untranslated region of SMAD3. Moreover, silencing of SMAD3 with small interfering RNAs phenocopied the effect of miR-665 overexpression, and overexpression of SMAD3 restored miR-665-overexpression-induced metastasis. This study revealed the role of the miR-665/SMAD3/SNAIL axis in bladder cancer, as well as the potential of miR-665 as a promising therapeutic target.