Title

Molecular dissection of a multi-stage murine colon cancer model

Date of Completion

January 2004

Keywords

Biology, Animal Physiology|Health Sciences, Pathology|Biology, Veterinary Science|Health Sciences, Oncology

Degree

Ph.D.

Abstract

Dosing with azoxymethane (AOM) induces preneoplastic lesions called aberrant crypt foci (ACF) within both susceptible (A/J) and resistant (AKR/J) mouse colons. However, only the ACF within susceptible animals progress to tumor. Because there were no differences in the initiation of preneoplastic ACF in A/J and AKR/J strains; we hypothesized that the differential susceptibility phenotype was the outcome of disparate responses to hyperproliferative stimuli. Considering the importance of oncogene checkpoint function of the p19 ARF-p53 pathway, its status was studied in AOM-induced mouse colon tumors. Our results demonstrate that the transactivation-function of p53 protein can be overcome without p53 mutations and this could be due to aberrant post-translational modification. Because earlier work had demonstrated that differential susceptibility is likely to be a function of the histomorphologic feature of the ACF, we evaluated ACF by immunohistochemistry (IHC) and microarray-analysis to find biomarkers that would help distinguish ACF from the tumor-prone A/J and tumor-resistant AKR/J mice. Discrimination of ACF by IHC was not successful despite detection of high levels of the evaluated protein within ACF. However, global expression profiling of ACF from high-risk A/J and low-risk AKR/J mice did demonstrate that ACF with distinct tumorigenic potential have unique distinguishing molecular signatures. Additionally, using a microarray approach, we found no differences in the expression of genes that are regulated by p53, thereby indicating that there was no differential activation of the p19ARF-p53 pathway in ACF from both strains at early stages of carcinogenesis. However, we did find accumulation of nuclear, sequence-normal p53 within ACF from both strains, the significance of which is uncertain. Susceptibility to AOM was then evaluated within a panel of progenitor mouse strains that are commonly used for the construction of gene knockout/transgenic animals. Increasing use of the AOM-murine model for studying genetics and pathogenesis of colon cancer warranted this study. This study would also serve as a guide for future studies involving the manipulation of genes discovered by the microarray approach. Thus, differential susceptibility model of colon cancer provides a useful experimental system that may help in the identification of genes or pathways that confer differential susceptibility to colon cancer. ^