Alternative splicing downstream of EMT enhances phenotypic plasticity and malignant behavior in colon cancer

Abstract

Phenotypic plasticity allows carcinoma cells to transiently acquire the quasi mesenchymal features necessary to detach from the primary mass and proceed along the invasion-metastasis cascade. A broad spectrum of epigenetic mechanisms is likely to cause the epithelial to mesenchymal (EMT) and mesenchymal to epithelial (MET) transitions necessary to allow local dissemination and distant metastasis. Here, we report on the role played by alternative splicing (AS) in eliciting phenotypic plasticity in colon cancer. By taking advantage of the identification of a subpopulation of quasi-mesenchymal and highly metastatic EpCAMlo colon cancer cells, we here show that the differential expression of ESRP1 and other RNA-binding proteins (RBPs) downstream of the EMT master regulator ZEB1, alters the AS pattern of a broad spectrum of targets including CD44 and NUMB, thus resulting in the generation of specific isoforms functionally associated with increased invasion and metastasis. Additional functional and validation studies indicate that both the newly identified RBPs and the CD44s and NUMB2/4 splicing isoforms promote local invasion and distant metastasis and are associated with poor survival. The systematic elucidation of the spectrum of EMT-related RBPs and AS targets in colon cancer and in other malignancies, apart from the insights in the mechanisms underlying phenotypic plasticity, will lead to the identification of novel and tumor-specific therapeutic targets.