Unravelling key regulators of cell fate changes during epithelial-mesenchymal transition

Abstract

Tumour metastasis is considered as a significant challenge to patient survival, meanwhile epithelial to mesenchymal transition (EMT) as a key driver of tumour aggressiveness. Understanding the mechanisms underlying EMT regulation is crucial for developing effective strategies to prevent further cancer cell metastasis. While many transcription factors and histone regulators have been identified as promoters of EMT, the understanding of regulators that can prevent mesenchymal transition and maintain epithelial cell identity is limited. In our study, we aimed to uncover novel transcription factors involved in EMT regulation using chromatin profiling through ATAC-seq (Assay for Transposase-Accessible Chromatin sequencing). Through this approach, we identified a previously uncharacterized transcription factor – PITX1 (Paired Like Homeodomain 1) which displayed a unique pattern of activity during the global reduction of chromatin accessibility induced by TGF-β in human mammary epithelial cells. We also investigated the expression and activity level of PITX1 across various cancers. We further found that PITX1 showed significantly higher activity and expression in both epithelial carcinoma cells and EMT - low breast cancer patients (Figure 3.5). Furthermore, we conducted in vitro experiments to confirm the role of PITX1 in maintaining epithelial cell identity and preventing mesenchymal-like transitions. Our results demonstrated that the depletion of PITX1 enhanced the expression levels of specific genes involved in promoting EMT, supporting its function in preserving epithelial identity. Our analysis revealed a decline in promoter site accessibility during EMT progression. Notably, PITX1 exhibits higher expression in epithelial breast cancer cells, with its knockdown leading to increased mesenchymal gene expression and chromatin decompaction. The impact of PITX1 on EMT and the tumour microenvironment underscores its significance in cancer biology. By unravelling the mechanisms through which PITX1 and other similar regulators preserve epithelial characteristics, we can develop targeted therapies aimed at preventing metastasis by maintaining epithelial cell identity.

Thesis is embargoed until 31st December 2025.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Vijay Tiwari (Supervisor) & Selinda Orr (Supervisor)