Investigating The Roles Of Tap63 And Tap73 In Cutaneous Squamous Cell Carcinoma And Lung Adenocarcinoma

Author

Andrew J. Davis, The University of Texas M D Anderson Cancer Center UTHealth Graduate School of Biomedical SciencesFollow

Date of Graduation

8-2018

Document Type

Dissertation (PhD)

Program Affiliation

Genes and Development

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Elsa R. Flores, Ph.D.

Committee Member

Nancy A. Jenkins, Ph.D.

Committee Member

Rebecca Berdeaux, Ph.D.

Committee Member

Lei Li, Ph.D.

Committee Member

Kenneth Y. Tsai, M.D., Ph.D.

Abstract

TP63 and TP73 (which encode p63 and p73, respectively) are highly conserved transcription factors with important roles in development and tissue homeostasis. Similar to their homolog, p53, both p63 and p73 have been shown to mediate tumor suppression in multiple tissue types. Interestingly, however, both genes are expressed as multiple isoforms, which appear to have different and, in many cases, antagonistic functions. Through the use of isoform-specific null alleles of p63 and p73 our lab and others have shown that the full-length N-terminal isoforms of p63 and p73 (referred to as TAp63 and TAp73, respectively) exhibit distinct functions in development, metabolism and tumor suppression. My thesis research focuses on understanding the conserved functions of TAp63 and TAp73 in tumorigenesis. To do so, I have utilized multiple model systems to investigate the contributions of TAp63 and TAp73 in the development and progression of cutaneous squamous cell carcinoma (cuSCC) and lung adenocarcinoma (LUAC). I have found that TAp63-null (TAp63-/-) mice exhibit increased susceptibility to UVR-induced cuSCC. To identify TAp63-regulated transcriptional programs relevant to the pathophysiology cuSCC, we performed RNA sequencing of cuSCC and normal tissues from wild-type (WT) and TAp63-/- mice. My data revealed significant perturbations in global miRNA and mRNA expression in TAp63-deficient tumors, which resembled similar transcriptional changes in human cuSCC, including the downregulation of miR-30c-2* and miR-497. Proteomic profiling of cuSCC cell lines and subsequent validation experiments led to the discovery of novel direct targets of miR-497 and miR-30c-2*. The most relevant of these proteins exhibited pro-oncogenic functions, including roles in cell cycle and mitotic progression. My data establishes TAp63 as an essential regulator of miRNA expression during skin carcinogenesis and reveals a previously undescribed network of miRNAs and mRNAs, which include viable, yet previously unexplored targets for therapeutic intervention. Along with TAp63-mediated tumor suppression in the skin, I have also developed a novel TAp73 conditional knockout mouse, which includes a conditional fluorescent reporter (TAp73fltd) that allows us to follow the deletion event at the cellular level. Using this model we have found that the loss of TAp73 accelerates the initiation and progression of oncogenic Krasdriven LUAC. Our data suggests that TAp73 may be necessary for anti-tumor immune responses. In addition, we have found that the loss of TAp73 promotes migration and invasion in human LUAC cell lines. These studies suggest that TAp73 can suppress tumor development and progression through both cell-autonomous and non-cell-autonomous mechanisms. Together, the studies described in this dissertation provide insights into the genetic and epigenetic mechanisms that contribute to cuSCC and LUAC development, which may, in turn, inform future biomarker and drug discovery studies.

Keywords

cancer biology, skin cancer, lung cancer, microRNAs, genetically-engineered mouse models, p53 family