PTBP3-Mediated Regulation of ZEB1 mRNA Stability Promotes Epithelial-Mesenchymal Transition in Breast Cancer

The RNA polypyrimidine tract-binding protein PTBP3 is a little studied paralog of PTBP1, which has oncogenic properties. In this study, we demonstrate that PTBP3 induces epithelial-mesenchymal transition (EMT) in breast tumor cells and promotes their invasive growth and metastasis. Elevated expression of PTBP3 associated significantly with lymph node metastasis, advanced histology grade, TNM stage, and poor 5-year overall survival of patients. In human mammary epithelial cells, PTBP3 overexpression was sufficient to induce EMT and to enhance cell migration, invasion, and cancer stem-like cell properties. PTBP3 regulated expression of the EMT regulatory transcription factor ZEB1 by binding the 3'UTR of its mRNA, thereby preventing its degradation. Conversely, ZEB1 ablation blocked the ability of PTBP3 to induce EMT. Overall, our findings define PTBP3 as a regulator of EMT that acts by governing expression of ZEB1, and they establish an oncogenic function of PTBP3, suggesting its candidacy as a theranostic target. (C) 2017 AACR.