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The role of heat shock factor-1 in the pathogenesis of human lung, breast and gastric cancers
thesisposted on 31.01.2017, 00:36 by Lang, Benjamin James
Abstract Chronic disruptions to the integrity of cellular proteins is an inherent property of cancer cells. Pathways that act to maintain protein functionality such as the Heat Shock Response (HSR) pathway support tumour cell viability by maintaining a tolerable level of protein functionality. Forms of protein-damaging (proteotoxic) stress have been recently linked to the induction of tumourigenic properties through induction of Epithelial-Mesenchymal Transition (EMT), a developmental process re-activated in cancers that promotes tumour cell dissemination and enhanced survival properties. The current study investigates a role for the master regulating factor of the HSR, Heat Shock Factor-1 (HSF1), in the induction of EMT and thereby aims to investigate a mechanism that links proteotoxic stress with the formation of advanced cancer phenotypes. To achieve this, in vitro human lung and breast cancer cell lines are utilised to examine the impact of HSF1 activity upon EMT phenotypes. In support of proteotoxic stress being a tumourigenic factor, heat stress is identified as a novel form of proteotoxic stress that induces an EMT phenotype. Subsequently, this study identifies KNK437 and triptolide, agents previously shown to have HSR inhibitory activity, to have anti-EMT action. By knockdown of HSF1 with expression of shRNAmir, both of these effects, however, are shown to occur independently to modulation of HSF1 action. Over-expression of HSF1 in A549 cells was not seen to alter the epithelial phenotype exhibited by this cell model. Additionally, knockdown of HSF1 in mesenchymal-type triple negative breast cancer (TNBC) cell lines BT549, Hs578T, MDA-MB-231 and MDA-MB-435 did not alter the properties of these models classically associated with an EMT phenotype. Together, these findings indicate HSF1 is not a universal driver of EMT. Knockdown of HSF1 in these models, however, is shown to reduce anchorage-dependent clonogenecity and enhance sensitivity to 17AAG, indicating that HSF1 modulates the survival properties of these advanced cancer cell lines. This highlights HSF1 to have therapeutic potential for the treatment of TNBC, a cancer type that currently has limited treatment options. Currently, the therapeutic inhibition of HSF1 is challenged by a lack of known potent inhibitory molecules. To address this, the current study investigates the mechanisms by which Helicobacter pylori mediates repression of the host HSR upon acute infection of human gastric cells in vitro. This study is the first to comprehensively demonstrate the H.pylori factor, cagA, to be essential for the downmodulation of host HSP protein expression. Whilst cagA expression within human cells is also shown to not be independently sufficient for this effect, future studies that identify the basis for which cagA mediates host HSP repression may reveal novel mechanisms for the inhibition of the human HSR. In summary, the findings within this study further highlight xiv proteotoxic stress as a tumourigenic factor. HSF1 is not found to be a universal driver of EMT phenotypes, however, HSF1 remains integral for the survival response of advanced cancer types to proteotoxic stress. This may provide an efficacious strategy for the treatment of therapy-resistant cancer subtypes.