Molecular mechanisms of ionizing radiation carcinogenesis in mouse skin

Persistent Link:
http://hdl.handle.net/10150/282881
Title:
Molecular mechanisms of ionizing radiation carcinogenesis in mouse skin
Author:
Gupta, Ashok Kumar
Issue Date:
1999
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:
Ionizing radiation is a physical agent that is tumorigenic in all exposed tissues. These radiation-induced secondary neoplasms tend to be more aggressive and carry a poor prognosis. Our knowledge of the molecular mechanisms of ionizing radiation carcinogenesis is not as advanced as compared to chemical carcinogenesis. We have used repeated exposure to low LET radiation in the mouse skin model to study the molecular mechanisms of ionizing radiation as a complete carcinogen and as a tumor progression agent. Shaved backs of CD-1 mice were treated with fractionated doses of beta-irradiation in a complete carcinogenesis experiment. A total of 27 carcinomas and sarcomas were seen. Cell lines were established from four sarcomas and one squamous cell carcinoma. Biochemical studies revealed that three sarcoma cell lines were derived from rhabdomyosarcornas. All four sarcoma cell lines had a p53 null phenotype. We screened cDNA expression libraries from three cell lines for dominant transforming activities. GAPDH was isolated as a candidate transforming gene in the squamous cell carcinoma cell line. Using a papilloma producing mouse keratinocyte cell line, we have shown that repeated doses of ionizing radiation are equally effective as a tumor progression agent when compared to N-methyl N'-nitro-N-nitrosoguanidine (MNNG). In this model, elevated reactive oxygen species levels were seen in both radiation and MNNG progressed cells. Elevated transcription factor transactivation as well as constitutive activation of Erk-1/2 and p38 MAP kinase activities were found to be potential mediators of the reactive oxygen species mediated mitogenic signaling in the progressed phenotype. Analyses of the anti-oxidant defense mechanisms showed that attenuation of catalase activity was a potentially important mechanism for the establishment of the pro-oxidant state. Forced re-expression of catalase in the malignant variants resulted in a reduction in transcription factor transactivation. Taken together, the results from experiments presented in this dissertation suggest that inactivation of gene products that maintain genomic stability, such as p53, may be an important step during neoplastic transformation with fractionated doses of ionizing radiation. Altered expression patterns of genes related to cell metabolism and oxidative stress can be functionally involved during the later stages of ionizing radiation-induced malignant transformation.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Biology, Genetics.; Biology, Cell.; Health Sciences, Oncology.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Cancer Biology
Degree Grantor:
University of Arizona
Advisor:
Bowden, G. Tim

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleMolecular mechanisms of ionizing radiation carcinogenesis in mouse skinen_US
dc.creatorGupta, Ashok Kumaren_US
dc.contributor.authorGupta, Ashok Kumaren_US
dc.date.issued1999en_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.abstractIonizing radiation is a physical agent that is tumorigenic in all exposed tissues. These radiation-induced secondary neoplasms tend to be more aggressive and carry a poor prognosis. Our knowledge of the molecular mechanisms of ionizing radiation carcinogenesis is not as advanced as compared to chemical carcinogenesis. We have used repeated exposure to low LET radiation in the mouse skin model to study the molecular mechanisms of ionizing radiation as a complete carcinogen and as a tumor progression agent. Shaved backs of CD-1 mice were treated with fractionated doses of beta-irradiation in a complete carcinogenesis experiment. A total of 27 carcinomas and sarcomas were seen. Cell lines were established from four sarcomas and one squamous cell carcinoma. Biochemical studies revealed that three sarcoma cell lines were derived from rhabdomyosarcornas. All four sarcoma cell lines had a p53 null phenotype. We screened cDNA expression libraries from three cell lines for dominant transforming activities. GAPDH was isolated as a candidate transforming gene in the squamous cell carcinoma cell line. Using a papilloma producing mouse keratinocyte cell line, we have shown that repeated doses of ionizing radiation are equally effective as a tumor progression agent when compared to N-methyl N'-nitro-N-nitrosoguanidine (MNNG). In this model, elevated reactive oxygen species levels were seen in both radiation and MNNG progressed cells. Elevated transcription factor transactivation as well as constitutive activation of Erk-1/2 and p38 MAP kinase activities were found to be potential mediators of the reactive oxygen species mediated mitogenic signaling in the progressed phenotype. Analyses of the anti-oxidant defense mechanisms showed that attenuation of catalase activity was a potentially important mechanism for the establishment of the pro-oxidant state. Forced re-expression of catalase in the malignant variants resulted in a reduction in transcription factor transactivation. Taken together, the results from experiments presented in this dissertation suggest that inactivation of gene products that maintain genomic stability, such as p53, may be an important step during neoplastic transformation with fractionated doses of ionizing radiation. Altered expression patterns of genes related to cell metabolism and oxidative stress can be functionally involved during the later stages of ionizing radiation-induced malignant transformation.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBiology, Genetics.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.advisorBowden, G. Timen_US
dc.identifier.proquest9923184en_US
dc.identifier.bibrecord.b39472140en_US
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