The Role of Alternative Splicing in the Phenotypic Plasticity of Colon and Ovarian Cancer Metastasis

Carcinomas arise from normal tissues along a multistep progression from precursor lesions to increasingly more invasive stages. Along this sequence of events, a stepwise accumulation of genetic alterations in specific tumor suppressors and oncogenes is regarded as the driving force in tumor initiation and progression towards malignancy. These alterations reflect well-defined cellular changes, the hallmarks of cancer, which provide growth advantage to the developing tumor cell and are thought to represent essential requirements for cancer onset and progression towards malignancy. However, with regard to the capacity to invade the tumor microenvironment and form distant metastases, phenotypic plasticity is possibly the most clinically relevant hallmark of cancer cells. It is now well-established that malignant cells and in particular those responsible for local dissemination and distant metastasis are endowed with plasticity, i.e. the capacity to undergo transient and reversible morphological and functional changes. In particular, epithelial to mesenchymal transition (EMT), i.e. the loss of epithelial identity and acquisition of a migratory and more mesenchymal phenotype, is regarded as the crucial event in invasion and dissemination. Of note, EMT endows cancer cells with stem-like features which underlie their phenotypic plasticity and capacity not only to acquire mesenchymal morphology at the invasive front of the primary tumor but also to reverse back to more epithelial states (MET, mesenchymal to epithelial transition) at the metastasis site. Epigenetic alterations at EMT-inducing transcription factors (EMT-TFs) underlie the transient nature of these cellular modifications.

Among the spectrum of epigenetic mechanisms that can underlie phenotypic plasticity in epithelial cancers, alternative splicing -as the result of differential expression of RNA binding proteins- can alter the function of key genes and underlie EMT/MET and other processes responsible for local dissemination and distant metastasis. Here, by taking advantage of the results obtained in the Dutch Digestive Foundation (MLDS) project FP 15-08 entitled “EpCAM^lo cancer stem cells: the culprit of liver metastasis in colon cancer?”, and by combining computational and experimental approaches on colon and ovarian cancer cell lines, we aim to elucidate the key alternative splicing events alterations that characterize the transition from the quasi-mesenchymal and highly metastatic EpCAM^lo cells into the more committed and epithelial EpCAM^hi cells.

This approach is expected to result in the identification of not only key therapeutic and diagnostic gene targets in colon and ovarian cancer but in the elucidation of the cellular and molecular mechanisms underlying metastasis. Follow-up experiments will include the use of in vitro (cell lines, organoids) and in vivo preclinical mouse models for the functional analysis of the alternative splicing targets.