miR-33a suppresses the nuclear translocation of β-catenin to enhance gemcitabine sensitivity in human pancreatic cancer cells.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers, partly due to its high level of drug resistance. β-Catenin is critical for drug resistance in pancreatic cancer, which occurs through multiple mechanisms. Here, we observed that miR-33a targeted the 3'UTR of β-catenin, inducing apoptosis and inhibiting the growth of human pancreatic cancer cells. Moreover, gemcitabine (GEM) treatment enhanced β-catenin expression by reducing miR-33a expression in a dose-dependent manner. GEM-resistant MiaPaCa-2(res) cells with a low level of miR-33a expression and high level of β-catenin expression adopted spindle-shaped morphologies, similar to their morphologies during the epithelial-to-mesenchymal transition (EMT), and their normal morphologies were restored by miR-33a overexpression. Furthermore, miR-33a downregulated β-catenin nuclear translocation, decreasing the transcription of survivin, cyclin D1, and MDR-1, and the protein expression of slug, vimentin, and N-cadherin, thereby mediating sensitization to GEM. Thus, miR-33a might function as a tumor suppressor to downregulate β-catenin expression, affecting cell growth, apoptosis, the EMT, and GEM resistance.