MicroRNA-33b Suppresses Epithelial-Mesenchymal Transition Repressing the MYC-EZH2 Pathway in HER2+ Breast Carcinoma

Front Oncol. 2020 Sep 10;10:1661. doi: 10.3389/fonc.2020.01661. eCollection 2020.


Downregulation of miR-33b has been documented in many types of cancers and is being involved in proliferation, migration, and epithelial-mesenchymal transition (EMT). Furthermore, the enhancer of zeste homolog 2-gene (EZH2) is a master regulator of controlling the stem cell differentiation and the cell proliferation processes. We aim to evaluate the implication of miR-33b in the EMT pathway in HER2+ breast cancer (BC) and to analyze the role of EZH2 in this process as well as the interaction between them. miR-33b is downregulated in HER2+ BC cells vs healthy controls, where EZH2 has an opposite expression in vitro and in patients' samples. The upregulation of miR-33b suppressed proliferation, induced apoptosis, reduced invasion, migration and regulated EMT by an increase of E-cadherin and a decrease of ß-catenin and vimentin. The silencing of EZH2 mimicked the impact of miR-33b overexpression. Furthermore, the inhibition of miR-33b induces cell proliferation, invasion, migration, EMT, and EZH2 expression in non-tumorigenic cells. Importantly, the Kaplan-Meier analysis showed a significant association between high miR-33b expression and better overall survival. These results suggest miR-33b as a suppressive miRNA that could inhibit tumor metastasis and invasion in HER2+ BC partly by impeding EMT through the repression of the MYC-EZH2 loop.

Keywords: EMT; EZH2; HER2+; MYC; breast cancer; miRNA-33b.