Fluctuating environment causes neoplastic transition and epithelial-mesenchymal plasticity in human cells.

How environmental selective pressures contribute to the emergence of a neoplastic tumorigenic state, remains incompletely understood. Here we show that the immortalized non-tumorigenic breast epithelial cell line (MCF10A) develops neoplastic clones under fluctuating conditions in-vitro that mimic the harsh tumor microenvironment. Long-term evolutionary experiments and genomic landscape analyses of the clones identified ROS as the dominant clonal mutational signature that facilitates the acquisition of oncogenic driver mutations and the onset of the Warburg phenotype. Single cell multi-omics and brightfield microscopy further elucidate that each clone adopts two plastic phenotypic states, epithelial-like and mesenchymal-like, the transition between which is epigenetically mediated by de novo expression of Grainyhead-like Transcription Factor 2 (GRHL2), following environmental cues from soluble factors and cell adhesion. Additional in-vitro experiments indicate the role of this plasticity in metastasis. Analysis of 70 human breast cancer cell lines and 2 independent breast cancer patient cohorts confirmed the generality of this mechanism and its epigenetic regulation in patients. Thus, this study elucidates fundamental evolutionary mechanisms behind tumorigenesis and identifies GRHL2 as a potential therapeutic target against epithelial-mesenchymal plasticity and metastatic spread in breast cancer.