Gene mutations in experimental models of carcinogenesis and their effects on responses to chemopreventive agents in the azoxymethane-treated rat model

Persistent Link:
http://hdl.handle.net/10150/282340
Title:
Gene mutations in experimental models of carcinogenesis and their effects on responses to chemopreventive agents in the azoxymethane-treated rat model
Author:
Wu, Hsiao-Chi David, 1967-
Issue Date:
1997
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The Ki-ras oncogene and the p53 tumor suppressor gene are mutated in a high percentage of human colon cancers. The mutation status of these two genes were assessed in colon adenocarcinomas obtained from azoxymethane (AOM)- and dimethylhydrazine (DMH)-treated rats, widely used experimental models of human colon carcinogenesis. The status of p53 mutations was examined using polymerase chain reaction (PCR) amplification of these sequences. In so doing, it was discovered that the rat p53 gene is structurally distinct from the human p53 gene, since it is missing one intron between exons 6 and 7. Further analysis using single stranded DNA conformational polymorphism (SSCP) analysis and direct DNA sequencing of the highly conserved regions of rat exons 5-7, highly mutated in human colon cancers, revealed no p53 mutations in any of these regions. Mutations at codon 12 of the Ki-ras gene were also characterized. Mutation frequency was approximately 60% which is close to the frequency of Ki-ras mutations found in human cancers. Since Ki-ras mutations have been shown to occur early in human colon carcinogenesis, while p53 mutations are thought to occur in late stage tumors, these data suggest this model may be a good for early, but not late, events of human colon carcinogenesis. It was also found that the non-steroidal anti-inflammatory drug (NSAID), sulindac sulfone, could reduce Ki-ras mutation frequency in this model. NSAIDs are agents being studied as a possible chemopreventive agent in both human colon cancers and the AOM model. Previous studies have found that the NSAIDs, sulindac and its sulfone metabolite, decrease the frequency of colon tumors in the AOM model. In this study, sulindac and sulindac sulfone specifically induced apoptosis in normal rat embryo cells (RECs) transfected with either an EJ-ras or activated myc and ras but not in non-transfected RECs. These data suggest that sulindac and sulindac sulfone may be reducing tumor frequency and Ki-ras frequency by inducing apoptosis in those cells with specific mutations that give them carcinogenic potential, possibly through non-prostaglandin dependent pathways.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Biology, Molecular.; Biology, Cell.; Health Sciences, Oncology.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Cancer Biology
Degree Grantor:
University of Arizona
Advisor:
Gerner, Eugene W.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleGene mutations in experimental models of carcinogenesis and their effects on responses to chemopreventive agents in the azoxymethane-treated rat modelen_US
dc.creatorWu, Hsiao-Chi David, 1967-en_US
dc.contributor.authorWu, Hsiao-Chi David, 1967-en_US
dc.date.issued1997en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe Ki-ras oncogene and the p53 tumor suppressor gene are mutated in a high percentage of human colon cancers. The mutation status of these two genes were assessed in colon adenocarcinomas obtained from azoxymethane (AOM)- and dimethylhydrazine (DMH)-treated rats, widely used experimental models of human colon carcinogenesis. The status of p53 mutations was examined using polymerase chain reaction (PCR) amplification of these sequences. In so doing, it was discovered that the rat p53 gene is structurally distinct from the human p53 gene, since it is missing one intron between exons 6 and 7. Further analysis using single stranded DNA conformational polymorphism (SSCP) analysis and direct DNA sequencing of the highly conserved regions of rat exons 5-7, highly mutated in human colon cancers, revealed no p53 mutations in any of these regions. Mutations at codon 12 of the Ki-ras gene were also characterized. Mutation frequency was approximately 60% which is close to the frequency of Ki-ras mutations found in human cancers. Since Ki-ras mutations have been shown to occur early in human colon carcinogenesis, while p53 mutations are thought to occur in late stage tumors, these data suggest this model may be a good for early, but not late, events of human colon carcinogenesis. It was also found that the non-steroidal anti-inflammatory drug (NSAID), sulindac sulfone, could reduce Ki-ras mutation frequency in this model. NSAIDs are agents being studied as a possible chemopreventive agent in both human colon cancers and the AOM model. Previous studies have found that the NSAIDs, sulindac and its sulfone metabolite, decrease the frequency of colon tumors in the AOM model. In this study, sulindac and sulindac sulfone specifically induced apoptosis in normal rat embryo cells (RECs) transfected with either an EJ-ras or activated myc and ras but not in non-transfected RECs. These data suggest that sulindac and sulindac sulfone may be reducing tumor frequency and Ki-ras frequency by inducing apoptosis in those cells with specific mutations that give them carcinogenic potential, possibly through non-prostaglandin dependent pathways.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBiology, Molecular.en_US
dc.subjectBiology, Cell.en_US
dc.subjectHealth Sciences, Oncology.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineCancer Biologyen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorGerner, Eugene W.en_US
dc.identifier.proquest9729514en_US
dc.identifier.bibrecord.b34819290en_US
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