In this study, we demonstrate that constitutive activation of Raf-1 oncogenic signaling induces stabilization and accumulation of Aurora-A mitotic kinase that ultimately drives the transition from an epithelial to a highly invasive mesenchymal phenotype in estrogen receptor positive (ER+) breast cancer cells. The transition from an epithelial- to a mesenchymal-like phenotype was characterized by reduced expression of ER, HER-2/Neu overexpression and loss of CD24 su-rface receptor (CD24 -/low). Importantly, expression of key epithelial-to-mesenchymal transition (EMT) markers and upregulation of the stemness gene SOX2 was linked to acquisition of stem cell-like properties such as the ability to form mammospheres in vitro and tumor self-renewal in vivo. Moreover, aberrant Aurora-A kinase activity induced phosphorylation and nuclear translocation of SMAD5, indicating a novel interplay between Aurora-A and SMAD5 signaling pathways in the development of EMT, stemness and ultimately tumor progression. Importantly, pharmacological and molecular inhibition of Aurora-A kinase activity restored a CD24 + epithelial phenotype that was coupled to ER expression, downregulation of HER-2/Neu, inhibition of EMT and impaired self-renewal ability, resulting in the suppression of distant metastases. Taken together, our findings show for the first time the causal role of Aurora-A kinase in the activation of EMT pathway responsible for the development of distant metastases in ER+ breast cancer cells. Moreover, this study has important translational implications because it highlights the mitotic kinase Aurora-A as a novel promising therapeutic target to selectively eliminate highly invasive cancer cells and improve the disease-free and overall survival of ER+ breast cancer patients resistant to conventional endocrine therapy.
- Breast Cancer