Role of Nuclear Structure-Function Relationships in Epithelial to Mesenchymal Transitions

Abstract

Epithelial to mesenchymal transition (EMT) is a process essential for morphogenesis during embryonic development. The process of EMT is reactivated in epithelial tumors and is implicated in cancer progression and metastasis. EMT is associated with large-scale cellular and transcriptomic changes. However, how EMT impinges on nuclear structure and function remains unclear. Here we examined the role of two inducers of EMT - (a) TGF-β1 and (b) Twist1 and their impact on genome organization and function in cancer cell lines. We investigated the effect of TGF-β induced EMT by studying the spatial localization of chromosome territories, gene loci and its correlation with gene expression in human lung adenocarcinoma cells (A549). We also examined the regulatory role of components of the nuclear envelope and nuclear landmarks in EMT. Furthermore, we investigated the role of global genome organizers Lamins and CTCF in TGF-β1 induced EMT. Interestingly, while the loss of CTCF did not alter EMT, CTCF knockdown significantly deregulated TGF-β1 induced gene expression changes. In an independent study, we also examined the consequences of overexpressing Twist1 in colorectal cancer cells. Twist1 overexpression was accompanied by an increase in chromosomal instability (CIN). We uncovered the mechanistic involvement of Twist1 in the deregulation of factors that regulate the cell cycle. Twist1 overexpression was accompanied by copy number alterations and an increase in DNA Double Strand Breaks (DSBs). In addition, analyses of gene expression profiles of patient derived datasets from The Cancer Genome Atlas (TCGA) revealed a positive correlation between Twist1 and EMT associated genes across cancers, whereas the correlation of TWIST1 with CIN or DNA DSB repair genes is cancer subtype specific. Interestingly, Twist1 overexpression also downmodulates levels of nuclear lamins, likely to alter spatiotemporal organization of the genome. Taken together, these studies reveal an overarching impact of EMT on genome organization and function, potentially contributing to an increase in aggressive sub- populations of cancer cells.