miR-190 suppresses breast cancer metastasis by regulation of TGF-β-induced epithelial-mesenchymal transition

Background: Breast cancer is the most common cancer among women worldwide and metastasis is the leading cause of death among patients with breast cancer. The transforming growth factor-beta (TGF-beta) pathway plays critical roles during breast cancer epithelial-mesenchymal transition (EMT) and metastasis. SMAD2, a positive regulator of TGF-beta signaling, promotes breast cancer metastasis through induction of EMT. Methods: The expression of miR-190 and SMAD2 in breast cancer tissues, adjacent normal breast tissues and cell lines were determined by RT-qPCR. The protein expression levels and localization were analyzed by western blotting and immunofluorescence. ChIP and dual-luciferase report assays were used to validate the regulation of ZEB1-miR-190-SMAD2 axis. The effect of miR-190 on breast cancer progression was investigated both in vitro and in vivo. Results: miR-190 down-regulation is required for TGF-beta-induced EMT. miR-190 suppresses breast cancer metastasis both in vitro and in vivo by targeting SMAD2. miR-190 expression is down-regulated and inversely correlates with SMAD2 in breast cancer samples, and its expression level was associated with outcome in patients with breast cancer. Furthermore, miR-190 is transcriptionally regulated by ZEB1. Conclusions: Our data uncover the ZEB1-miR-190-SMAD2 axis and provide a mechanism to explain the TGF-beta network in breast cancer metastasis.