Stem cell-like properties and epithelial plasticity arise as stable traits after transient Twist1-activation .

  During Epithelial-Mesenchymal Transition (EMT), apical-basal polarized epithelial cells are converted to front-to-back polarized mesenchymal cells that only form loose cell-cell adhesions. These phenotypic changes are accompanied by acquisition of increased motility and invasiveness. EMT programs are orchestrated by pleiotropic transcription factors (TFs), such as Twist1 and effect morphogenetic steps during embryogenesis, including mesoderm formation and neural crest migration. EMTs have also been implicated in the acquisition of aggressive traits by carcinoma cells, including the ability to complete several steps of the metastatic cascade as well as propagation of the tumor by single cells, a defining trait of tumor-initiating or cancer stem cells. However, the molecular links between the expression of EMT-TFs, the process of EMT and acquisition of stem cell-like properties remain obscure. Using inducible Twist1 expressed in human mammary epithelial cells, we show that this EMT-TF primes a subset of CD24high cells for stem cell-like properties (assessed by Mammosphere (MS) formation) which only emerge and stably persist following Twist1 deactivation. However, complete EMT does not appear to be required for Twist1 to prime epithelial cells for MS forming ability. In addition, we show that after Twist1 deactivation cells do not return to their original cell state, evidenced by acquisition of invasive growth behavior in a 3D environment and a distinct gene expression profile. Within the differentially expressed genes, we identified the orphan receptor tyrosine kinase ROS1 as a potential drug target that is directly regulated by Twist1. In summary, our results suggest that transient Twist1 activation suffices to drive tumor progression of CD24high breast epithelial cells by permanently altering their cell state (Schmidt et al., Cell Reports, Vol. 10 Iss. 2, January 2015)