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Title: Regulation of COX-2 expression by the BCL-3:NF-KappaB homodimeric complex : implications for colorectal carcinogenesis
Author: Fallatah , Hafsah M.
ISNI:       0000 0004 5924 072X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Cyclooxygenase-2 (COX-2) is an enzyme that plays a key role in the synthesis of prostaglandin (PGE2). COX-2 has been widely investigated in cancer progression studies generally and in colorectal cancer (CRC) specifically, not only because it is regulated by various signalling pathways, but also because it is one of the main players in the inflammation/cancer link. The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-KB) is among the transcription factors that have been repOlied to regulate the transcriptional activity of the COX-2 gene. Constitutive activity of NF-KB clearly results in the over-expression observed of COX-2. Although there are two KB sites localised at the promoter region of COX-2, the definitive mechanism by which COX-2 is regulated by NF-KB needs more elucidation. Several modulators have been repOlied that control NF-KB activity in order to maintain the selectivity or specificity of responses to the trigger. B-cell lymphoma-3 (BCL-3) is an oncogene that is up-regulated by inflammatory cytokines, such as tumour necrosis factor-a (TNF-a) and interleukin-l ~ (IL-l ~). It functions as a co-activator protein that binds favourably to the homodimer' subunits of NF-KB, namely pSO/pSO or pS2/pS2. Those two dimers are found to have repressor roles in the regulation of NF-KB target genes. However, when they bind to BCL-3, their action switches to an activator role. Therefore, understanding the exact role ofBCL-3: NF-KB homodimers complex in the context ofCOX-2 regulation by NF-KB signalling is crucial. Initially, I investigated the expression of BCL-3 and COX-2 in a range of different adenoma and carcinoma cells. I chose HCA 7/P and HT29 cells to be included in subsequent studies. In studying the effect of BCL-3 suppression in the level of COX-2 protein and its activity, potential regulation of COX-2 and PGE2 by BCL-3 has been revealed. This regulation has also been observed after the treatment of cells with TNF-a. Interestingly, the mRNA level of COX-2 has also been regulated by BCL-3 suppression, especially at 48 hours of BCL-3 silencing. Dual-Luciferase assay results of COX-2 gene also support this finding. Transfecting the cells with mutant BCL-3 (which cannot bind the homodimer pSO/pSO) has shown no change to the promoter activity of COX-2 as compared with cells transfected with wild-type BCL-3 protein; this suggests an addition to requirement amount of pSO to regulate COX-2 by BCL-3. Results obtained from Chromatin Immunoprecipitation (ChIP) experiments emphasised the presence of both BCL-3 and pSO in the predicted KB site of the COX-2 promoter. In vivo, there was a marked increase of both BCL-3 and COX-2 expression in carcinoma tissue as compared to healthy normal tissue, indicating the important role they play in the progression from adenoma to carcinoma. Because BCL-3 has been shown to regulate the level of PGE2, it was important to investigate whether this had . any consequence on the role played by PGE2 in the proliferation and sternness of the adenoma cell RG/C2. It was also significant to study the effect of Nonsteroidal anti-inflammatory drugs (NSAIDs) on the function of BCL-3 in regards to the COX-2/PGE2 signalling pathway. Treating cells with aspirin results in a decrease in the protein level of BCL-3 and COX-2, which strengthens the notion of aspirin chemoprevention 's role in tumour regression. This study is proposing, for the first time, the potential use of BCL-3: COX-2/PGE2 as a therapeutic target of CRC prevention and treatment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available