Pathology - Theses
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ItemDissecting the role of laminin and Stat3 in colorectal cancer( 2018)Colorectal cancer (CRC) represents the 3rd most common causes of cancer-related death in the world, with increasing number of cases diagnosed every year in Australia. CRC is known to be associated with chronic inflammation, which induces responses in the tumour microenvironment (TME) including remodelling of the extracellular matrix (ECM) and aberrant activation of the key signalling effector Stat3. ECM remodelling is a crucial cellular event during tumour invasion and an essential step towards metastatic progression and/or tumour recurrence metastatic sites. Laminins are among the key ECM proteins that have been shown to regulate tumour invasion, and this study examined whether this could involve a role for laminins in the regulation of cancer stem cells (CSCs). CSCs represent a rare tumour cell subpopulation with enhanced self-renewal properties and a demonstrated role in tumour initiation and progression and therapy resistance. Here, we characterized the role of laminin-521 (LN-521), one of the laminin isoforms with a known function in maintaining normal stem cells, in the regulation of colorectal CSCs in vitro. Our results show that LN-521 promotes CSC self-renewal and invasion abilities and activates downstream signalling including Stat3. We identify the integrin isoforms mediating this effect, and provide results to suggest that LN-521 may contribute to poor survival of CRC patients, supporting its potential use of LN-521 as a prognostic marker for CRC. The impact of aberrant activation of Stat3 on primary tumour initiation and growth is well-described, but the consequences of it on the behaviour of metastatic CRC remain poorly understood. We therefore investigated the functions of Stat3 in metastatic tumours and their TME. This was performed by silencing Stat3 within tumour cells and/or within mice recipients in an orthotopic mouse allograft model of liver metastasis, the most prevalent type of CRC metastasis in patients. Our data indicate that Stat3 knockdown correlates with prolonged survival, reduced metastatic size, and decreased expression of genes implicated in tumour progression, which supports Stat3 being a potential therapeutic target for treating metastatic CRC.
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ItemInvestigating the role of hypoxia in tumour progression in breast cancer( 2015)Metastasis is a major cause of morbidity and mortality in breast cancer patients. The molecular processes and mediators that underpin this process have yet to be completely delineated. Hypoxia, the state of reduced oxygen conditions, occurs frequently in solid tumours and is a factor of poor prognosis for patient outcome. The upregulation of HIF-1α, the main mediator of the hypoxic response pathway, has been implicated in several different facets of tumour progression, including tumour growth, angiogenesis, therapy resistance and metastasis. Hypoxia has been shown to induce Epithelial-to-Mesenchymal Transition (EMT), a highly conserved developmental program that facilitates tumour cell dissemination. It is thought that EMT is co-opted by epithelial tumour cells in order to acquire a degree of plasticity, allowing them to undergo a number of genetic, biochemical and morphological changes to adopt a mesenchymal phenotype. This results in the loss of polarity, and the gain of migratory and invasive capabilities. EMT is regulated by a core cassette of transcription factors, including Snail, Slug, Twist, Zeb1 and Zeb2. Zeb1 is the most proximal transcription factor, however, how hypoxia modulates Zeb1 expression is not known. This study demonstrates that Siah, a family of E3 ubiquitin ligases and a master regulator of HIF-1α protein expression, binds to and targets Zeb1 for proteasomal degradation. Loss of Siah2 is sufficient to cause spontaneous EMT in tumour cells derived from the PyMT murine model of breast cancer. On the other hand, EMT induction led to the decrease in Siah protein expression. This work is the first to describe a post-translational mechanism of regulation of Zeb1 and further defines the relationship between hypoxia and EMT. There are, in fact, two forms of hypoxia in a growing tumour, chronic hypoxia and intermittent hypoxia. Chronic hypoxia describes the long-term limitations on oxygen diffusion caused by abnormal tumour vasculature. While intermittent hypoxia refers to the fluctuations of oxygen tension in a tumour, caused by the aberrant and temporary closing and reopening of tumour-supplying blood vessels. The consequences of these two different types of hypoxia in breast cancer have not yet been well characterised. Using the orthotopic, syngeneic PyMT murine model of breast cancer, it was found that intermittent hypoxia-treated cells gave rise to a greater number of larger lung metastases in vivo. This was facilitated by an enhanced ability for anchorage-independent growth, increased clonogenicity, the induction of a pro-tumourigenic gene expression and secretory profile, and the increase in tumour-initiating capacity through the gain of cancer stem cell properties. RNA sequencing of hypoxia-treated cells found distinct gene expression patterns between treatment groups. While, pathway analysis revealed a marked enrichment of immune-related pathways and a downregulation of DNA replication and cell cycle pathways, by both chronic and intermittent hypoxia. Interestingly, chronic hypoxia also upregulated extracellular matrix degradation pathways, in spite of the lack of an overt EMT in cells. These results unveil novel mechanisms and pathways involved in hypoxia-mediated metastasis while highlighting the extensive effects of hypoxia signalling in cancer. Taken together, this work demonstrates the complexity of hypoxia signalling in tumour progression. Not only does it endow tumour cells with an aggressive, tumour-initiating phenotype, but it also contributes to the priming of the tumour microenvironment to be pro-inflammatory and immunosuppressive and ultimately, tumour-promoting.