Epigenetics in regulation of oesophageal cancer stromal myofibroblasts

Giger, OT
(2017) Epigenetics in regulation of oesophageal cancer stromal myofibroblasts. PhD thesis, University of Liverpool.

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Cancer is the 2nd most common cause of death in our society and is associated with high morbidity and costs. The word ‘cancer’ amalgamates the complex interplay between cells which have acquired genetic alterations leading to uncontrolled proliferation, i.e. the malignant cells, and genetically ‘normal’ host cells, i.e. stromal cells, vascular cells and inflammatory cells which all acquire modified biological phenotypes in the presence of malignant cells. This community of cells and their secreted proteins defines the tumour microenvironment. Stromal cells in the tumour microenvironment display characteristic biological changes which promote cancer growth. Little is known on the underlying regulatory mechanisms defining this phenotype. Epigenetics describes inheritable changes not encoded by the nucleic acid sequence. Epigenetic regulation has been described to occur in stromal cells in the tumour microenvironment, but little is known about its role on myofibroblasts. In this work I describe how oesophageal cancer derived stromal cells, i.e. cancer associated myofibroblasts (CAMs) accelerate tumour growth in vivo. I observed that CAMs not only affect the local tumour microenvironment but might also accelerate tumour growth at a distant site. I also show how myofibroblasts play an important role in early tumour niche formation in xenograft models and describe their disappearance and replacement by murine stromal cells during tumour progression. Oesophageal CAMs were shown to be epigenetically distinct from matched adjacent tissue myofibroblasts (ATMs). They exhibited a global DNA hypo- methylation compared to ATMs. We identified distinct DNA methylation signatures between oesophageal cancer CAMs and ATMs with the use of the Illumina 450k bead chip methylation array. The methylation array data showed altered methylation signatures of genes implicated Wnt/β-catenin signalling pathway. The transcription factor paired like homeodomain (PITX) 2 and the regulatory protein secreted frizzled like protein (SFRP) 2 both showed altered methylation signatures and expression patterns between oesophageal cancer CAMs and ATMs. I found that upregulation of SFRP2 in myofibroblasts induces angiogenesis and I hypothesise that epigenetic modification regulates myofibroblasts-derived SFRP2 expression which may play an important role in tumour neovascularisation. Based on these findings I conclude that ATMs and CAMs are epigenetically distinct and altered protein expression is at least partially regulated by altered DNA methylation. This work also presents a model for epigenetic modification of tumour stroma cells: exposure of myofibroblasts to the DNA methyl transferase inhibitor 5’Aza-3’deoxycytosine (DAC) lead to a mild decrease of global DNA methylation and induced persistent biological changes in myofibroblasts. These epigenetically modified myofibroblasts induced an accelerated xenograft growth when injected together with oesophageal cancer cells. Based on these experiments I conclude that DAC epigenetically modifies myofibroblasts which induces an activation of normally silenced genes leading to a biologically more active cell.

Item Type: Thesis (PhD)
Divisions: Faculty of Health and Life Sciences > Faculty of Health and Life Sciences
Depositing User: Symplectic Admin
Date Deposited: 12 Sep 2017 09:59
Last Modified: 19 Jan 2023 07:03
DOI: 10.17638/03007985
URI: https://livrepository.liverpool.ac.uk/id/eprint/3007985