Medicine (Austin & Northern Health) - Theses
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ItemInvestigating the role of the EHF transcription factor in the regulation of differentiation in colorectal cancer( 2017)Colorectal cancer is characterized by aberrant cell proliferation, resistance to apoptosis and loss of differentiation. While the pathways which drive cell proliferation and resistance to apoptosis in this disease are relatively well characterized, the mechanisms which underpin the loss of differentiation are not well understood. The central aim for this thesis was to identify novel transcription factors which mediate differentiation loss in colorectal cancer. Analysis of gene expression differences between moderately and undifferentiated colorectal cancers identified coordinate downregulation of multiple transcription factors in undifferentiated cell lines. This included the EHF transcription factor (Ets homologous factor) which was highly expressed in well to moderately differentiated colorectal cancer cell lines and downregulated in undifferentiated lines. EHF was also found to be highly expressed in the normal colonic epithelium. Loss of EHF expression also correlated with reduced expression of colonic epithelial differentiation markers in primary colorectal tumours. To assess the direct role of EHF in colorectal cancer cell differentiation, EHF expression was downregulated in moderately differentiated cell lines and stably reexpressed in undifferentiated cell lines. These experiments demonstrated that knockdown or re-expression of EHF alone was not sufficient to alter the differentiation status of colorectal cancer cell lines. Alternatively, EHF was found to play a key role in the suppression of migration and invasion of colorectal cancer cells. As multiple transcription factors are downregulated in undifferentiated colorectal cancers, we next determined whether EHF may impact differentiation status by working in combination with other transcription factors. To address this, systematic knockdown of EHF with other downregulated transcription factors in undifferentiated colorectal cancer cell lines was performed in moderately differentiated colorectal cancer cell lines. This analysis revealed that knockdown of EHF in combination with CDX1 significantly downregulates the expression of differentiation markers and disrupts the glandular architecture of moderately differentiated colorectal cancer cell lines. Conversely, the re-expression of EHF and CDX1 in undifferentiated colorectal cancer cells significantly induced differentiation marker expression and induced some features of gland formation. Furthermore, the re-induction of EHF and CDX1 significantly reduced cell proliferation and migration of colorectal cancer cell lines. These findings demonstrate that EHF in combination with CDX1 regulates the differentiation of colorectal cancer cells, and that the coordinate loss of these transcription factors contributes to the loss of differentiation in colorectal cancer.