Defense Date

2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biochemistry

First Advisor

Swati Palit Deb

Abstract

Deregulation of genome duplication is a common theme in cancer cells. Although multitude of pathways has been discovered and implicated in the ability of oncogenes or loss of function tumor suppressors to induce oncogenesis, most of the pathways ultimately converge in deregulated genome duplication or uncoupling of DNA replication and segregation in cancer cells. It is important to determine how known oncogenes deregulate genome duplication, and if prevention of deregulated genome duplication could be a feasible target to thwart uncontrolled proliferation of cancer cells. Conventional paradigm ascribes the cell proliferative function of the human oncoprotein mouse double minute2 (MDM2) primarily to its ability to degrade p53. Here we demonstrate that in the absence of p53, MDM2 induces replication stress eliciting an early S-phase checkpoint response to inhibit further firing of DNA replication origins. Our data uncovers a novel pathway, defended by the intra-S-phase checkpoint, by which MDM2 induces unscheduled origin firing and accelerates S-phase entry of cells in the absence of p53. To identify cell proliferative events consequent to MDM2 overexpression in noncancerous lung, transgenic mice expressing human MDM2 in either lung Club or alveolar cells after doxycycline (Dox) treatment were generated. Dox-induced MDM2 expression considerably increased the frequency of DNA replicating Club or alveolar cells after naphthalene or radiation-induced lung injury, and clonal expansion of lung progenitor cells accelerating restoration of the lost epithelial layer.

Gain of function (GOF) p53 mutations, observed frequently in most intractable human cancers, establish dependency for tumor maintenance and progression. We show that GOF p53 increases DNA replication origin firing, stabilizes replication forks, and promotes micronuclei formation, thus facilitating the proliferation of cells with genomic abnormalities. Following genome-wide analyses utilizing ChIP-Seq and RNA-Seq, GOF p53-induced origin firing, micronuclei formation and fork protection were traced to the ability of GOF p53 to transactivate Cyclin A and Chk1. Highlighting the therapeutic potential of Chk1’s role in GOF p53 dependency, experiments in cell culture and mouse xenografts demonstrated that inhibition of Chk1 selectively blocked proliferation of cells and tumors expressing GOF p53. Our data suggest the exciting possibility that checkpoint inhibitors could efficiently and selectively target cancers expressing GOF p53 alleles.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

5-8-2018

Available for download on Sunday, May 07, 2023

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