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dc.contributor.authorSansom, Owen Jamesen
dc.date.accessioned2018-01-31T11:24:32Z
dc.date.available2018-01-31T11:24:32Z
dc.date.issued2002en
dc.identifier.urihttp://hdl.handle.net/1842/26919
dc.description.abstracten
dc.description.abstractColorectal cancer is one of the most predominant cancers in the Western World. By the age of 70, 1 in 2 people will have a colon tumour. The genetic analysis of both spontaneous and hereditary forms of this disease have greatly added to our understanding of colorectal cancer, with mutations in a range of genes now strongly linked to neoplasia. In recent years, several different transgenic models of colorectal cancer have been generated. Key amongst these are strains mutant for the Ape (.Adenamatous Polyposis Coli) gene and strains mutant for different members of the mismatch repair (MMR) gene family, the majority of which show predisposition to intestinal neoplasia. In this thesis, these transgenic models are used in an attempt to systematically characterise the nature of the genetic control over a series of end points. These include the apoptotic response of enterocytes to cytotoxic agents; the effect of genotype upon clonogenic survival and mutation and ultimately the effect of genoytype upon the development of intestinal neoplasia.en
dc.description.abstractPreviously analyses of enterocyte apoptosis had established roles for p53 and Msh2 following DNA damage of methylation type. This prompted an analysis in mice deficient for two other members of the MMR family, Mlhl and Pms2. Mlhl and Pms2 deficient mice were seen to have a significantly reduced apoptotic response to temozolomide, confirming again an association between the MMR family and apoptosis. However, both Mlhl'" and Pms2~/~ mice were found to possess a normal apoptotic response to high levels of the alkylating agent NMNU, even though they are deficient for functional MMR. This unexpected finding dissociates normal mismatch repair from MMR dependent apoptosis and raises fundamental questions about the nature of the death signal following damage of methylation type.en
dc.description.abstractPerturbations to the normal apoptotic response would be predicted to impact upon longer term survival as determined through the microcolony assay. Therefore clonogenic survival was examined using this approach in Msh2 and p53 null mice. Despite being necessary for apoptosis for all cytotoxic agents studied, loss ofp53 only led to an increased in survival following cisplatin treatment and not following NMNU or Nitrogen Mustard treatment.en
dc.description.abstractThe above data was obtained from morphologically normal tissue. Therefore this analysis was extended to the apoptotic response within intestinal lesions. This displayed that there was both lesion type dependent differences and genotype dependent differences in the apoptotic response. As there were high basal levels of apoptosis in the smallest lesions whilst virtually no apoptosis in adenomas, this highlighted that loss of this apoptotic programme may be crucial to tumour progression.en
dc.description.abstractThe interaction between Msh2 and p53 in tumourigenesis was also investigated. Both homozygosity and hemizygosity for p53 were found to dramatically accelerate tumourigenesis on a mismatch (Msh2) deficient background. Significantly, the levels of micro-satellite instability (MSI) were highest in tumours which were additionally heterozygous for p53. EMSA, Western and immunohistochemisty analysis of these tumours indicated retention of p53 function in at least a proportion of these tumours. Similar data were obtained from primary cultures, with again increased microsatellite instability and retained p53 functionality in cultures derived from p53 heterozygotes. Taken together, this data shows that hemizygosity for p53 increases microsatellite instability and that, at least in a percentage of tumours, complete loss of p53 is not a required event. These findings have particular relevance to our understanding of cross talk between p53 and MMR deficiency in human colorectal disease.en`
dc.description.abstractThe battery of in vivo analyses used throughout this thesis were applied to a new candidate tumour suppressor, Mbd4. Mbd4 deficient mice have no overt phenotype, but fail to mediate normal apoptosis following a wide variety of DNA damage. Following cisplatin treatment, Mbd4 treatment confers increased clonogenic survival Surprisingly, Mbd4 mice are not characterised by an in increase in either spontaneous or induced mutation rate, but when crossed to ApcMm mice they accelerate tumour development. These studies demonstrate that Mbd4 is a central mediator of the response to DNA damage and that it functions as an intestinal tumour suppressor in the mouse.en
dc.description.abstractFinally the ability of aspirin to suppress intestinal neoplasia in murine models of colorectal cancer was examined. Numerous epidemological and animals studies have shown that Non-Steroidal Anti-Inflamatory Drugs (NSAIDS) are associated with 5 lower risks of colorectal cancer. However studies using aspirin in the ApcMm/+ mouse have yielded contrasting results. Here it is shown that aspirin does not reduce tumourigenesis when ApcMl + mice are put on diet containing aspirin post weaning. However when parents were put on aspirin, a significant suppression of tumourigenesis was observed in the min offspring. In fact there was incomplete penetrance of the ApcMm/+ phenotype (40%). To test whether in utero administration of aspirin could also suppress murine models of HNPCC, Msh2 deficient and (ApcMm/+, Msh2~/~) deficient mice were examined. In both cases a significant attenuation of tumourigenesis was observed. Taken together this raises the exciting prospect of prophylactic treatment of FAP and HNPCC patients and highlight the power of using transgenic models to investigate intestinal neoplasia.en
dc.publisherThe University of Edinburghen
dc.relation.ispartofAnnexe Thesis Digitisation Project 2017 Block 15en
dc.relation.isreferencedbyen
dc.titleGenetic control of apoptosis and tumourigenesis in murine models of intestinal neoplasiaen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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