Antagonism of miR-21 Reverses Epithelial-Mesenchymal Transition and Cancer Stem Cell Phenotype through AKT/ERK1/2 Inactivation by Targeting PTEN

Background: Accumulating evidence suggested that epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) characteristics, both of which contribute to tumor invasion and metastasis, are interrelated with miR-21. MiR-21 is one of the important microRNAs associated with tumor progression and metastasis, but the molecular mechanisms underlying EMT and CSC phenotype during miR-21 contributes to migration and invasion of breast cancer cells remain to be elucidated. Methodology/Principal Findings: In this study, MDA-MB-231/anti-miR-21 cells were established by transfected hsa-miR-21 antagomir into breast cancer MDA-MB-231 cells. EMT was evaluated by the changes of mesenchymal cell markers (N-cadherin, Vimentin, and alpha-SMA), epithelial cell marker (E-cadherin), as well as capacities of cell migration and invasion; CSC phenotype was measured using the changes of CSC surface markers (ALDH1 and CD44), and the capacity of sphereforming (mammospheres). We found that antagonism of miR-21 reversed EMT and CSC phenotype, accompanied with PTEN up-regulation and AKT/ERK1/2 inactivation. Interestingly, down-regulation of PTEN by siPTEN suppressed the effects of miR-21 antagomir on EMT and CSC phenotype, confirming that PTEN is a target of miR-21 in reversing EMT and CSC phenotype. The inhibitors of PI3K-AKT and ERK1/2 pathways, LY294002 and U0126, both significantly suppressed EMT and CSC phenotype, indicating that AKT and ERK1/2 pathways are required for miR-21 mediating EMT and CSC phenotype. Conclusions/Significance: In conclusion, our results demonstrated that antagonism of miR-21 reverses EMT and CSC phenotype through targeting PTEN, via inactivation of AKT and ERK1/2 pathways, and showed a novel mechanism of which might relieve the malignant biological behaviors of breast cancer.