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Title: Aspirin effects on the activation of c-Src-induced NF-κB-dependent apoptotic mechanisms in colorectal cancer
Author: Brady, Richard R. W.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2013
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Compelling evidence indicates that long-term aspirin or related non-steroidal anti-inflammatory drugs (NSAIDs) ingestion can protect against colorectal cancer (CRC). The predominant mechanism of action of NSAIDs is the induction of apoptosis and it has been shown that NSAIDs stimulate the NFkB pathway as a key component of this pro-apoptotic effect. Here, I demonstrate that aspirin activates the c-Src tyrosine kinase pathway in CRC cells. This activation occured in a time- and dose-dependent manner, preceding aspirin-mediated degradation of IkBcx, nuclear/nucleolar translocation of NFKB/ ReIA and the induction of apoptosis. Furthermore, inhibition of c-Src activity, by chemical inhibition or expression of a kinase-dead form of the protein, abrogated aspirin-mediated degradation of IkBcx, nuclear translocation of RelA and apoptosis, suggesting a causal link. Expression of constitutively active c-Src mimics aspirin-induced stimulation of the NF-kB pathway. These data established the role of c-Src activation in the NF-kB and apoptotic response to aspirin in CRC cells in vitro. However, difficulty exists in the translational relevance of experimental findings derived from cancer cell lines, therefore I developed and optimised an in-vitro organ culture (IVOC) of human ex-vivo colonic mucosa. This provides an experimental platform that recapitulates the complex molecular, cellular and architectural environment of the in-vivo human colonic mucosa. I demonstrated that following a period of degeneration, the tissue regained its original architecture and was repopulated with a cell population that was representative of the original tissue. Furthermore, I identified putative colonic stem cell (CSC) populations within the tissue and demonstrated that colonic tissue growth and differentiation can be modulated by Wnt signalling agonists and Notch signalling antagonists. Finally, I show aspirin-mediated c-Src activation, NF-kB signalling and apoptosis in this setting. These data provide compelling evidence that c-Src is an upstream mediator of aspirin effects on NF-kB signaling and apoptosis in CRC cells and have relevance to the development of future chemotherapeutic / chemopreventative agents. Furthermore, these data describe a model system providing a relevant and translational experimental platform of much utility to the future study of aspirin-induced effects, CSC regulation and dynamics in the human colonic mucosa, including further confirmation of the role of Wnt and Notch signalling pathways in cell proliferation and differentiation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (M.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available