Defense Date

2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biochemistry

First Advisor

Swati Deb

Abstract

Overexpression of oncoprotein MDM2 and mutations of tumor suppressor p53 are frequently observed in human cancers. The NFκB pathway is one of the deregulated pathways in oncogenesis. The overall goal of the project was to study the regulation of NFκB pathway by MDM2 in lung cancer. Our first effort was to determine the frequency of MDM2 overexpression in human lung tumor samples and to identify co-occurring abnormal gene expression by studying the levels of MDM2 and members of NFκB pathway with respect to p53 status. Higher than normal levels of MDM2 were found in approximately 30% of the cancer samples harboring wild-type (WT) and mutant p53. Expression of NFκB2, a mutant p53 inducible gene showed significant statistical correlation with MDM2 in cancer samples that harbored WT p53. A downstream target gene of NFκB2, Bcl2, showed a significant correlation to MDM2 levels, independent of p53 status. Lung cancer samples harboring mutant p53 exhibited elevated levels of NFκB2 though not statistically significant. Our next step was to corroborate findings from lung tumor samples with data from lung cancer cell line harboring WT p53-H460. Consistent with lung tumor samples, ectopic overexpression of MDM2 in H460, showed elevated expression of NFκB2 and Bcl2 with promoter upregulation of NFB2. Silencing of MDM2 proportionally downregulated NFκB2 and Bcl2 in H460 cells. Domain analysis of MDM2 suggested that increase in the NFκB2 promoter activity was not confined to the p53 binding domain of MDM2 suggesting their interaction via p53-dependent and p53-independent mechanisms. A functional cell growth assay showed retarded cell proliferation with downregulation of MDM2. Data from human lung tumor samples and lung cancer cell line suggest that overexpression of MDM2 mediates NFB2 upregulation to confer growth advantage, thus favoring oncogenesis.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

December 2008

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