Phenotypic plasticity and partial EMT underlie local invasion and distant metastasis in colon cancer

Phenotypic plasticity represents the most relevant hallmark of the metastasizing carcinoma cell as it bestows it with the capacity of altering its own cellular identity when exposed to different environments along the invasion-metastasis cascade. However, the study of the mechanisms underlying phenotypic plasticity is hindered by the rarity of these events within primary lesions and by the lack of experimental study models. Here, we identified a subpopulation of colon cancer cells endowed with phenotypic plasticity: CD44hi/EpCAMlo cells are highly motile, invasive, chemoresistant, and metastatic both in vitro and in vivo. Bulk and single-cell RNAseq analysis indicated that they encompass a broad spectrum of degrees of EMT activation, together with stem/progenitor-like feature, enhanced Wnt/β-catenin signaling, and a high correlation with the CMS4 subtype, accounting for ∼25% of colon cancer cases with poor prognosis. Enhanced Wnt and the downstream upregulation of EMT transcription factors such as ZEB1 represent key events in eliciting phenotypic plasticity to cancer cells along the invasive front of primary colon carcinomas. Of note, different combinations of distinct sets of epithelial and mesenchymal genes define alternative transcriptional trajectories through which state transitions arise. Hybrid E/M stages are predicted to represent the origin of these differentiation routes through biologically-distinct cellular states and as such to underlie the phenotypic plasticity of colon cancer cells.