Date of Award

2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Cell & Molecular Biology

First Advisor

Anil K. Rustgi

Second Advisor

Ben Z. Stanger

Abstract

Esophageal cancer is one of the deadliest cancers in the U.S and worldwide. Esophageal cancer is characterized by two subtypes: esophageal adenocarcinoma (EAC) and esophageal squamous cell carcinoma (ESCC). One of the major risk factors for the development of EAC is Barrett's esophagus (BE). BE is defined as incomplete intestinal metaplasia characterized by the presence of columnar and goblet cells in the formerly stratified squamous epithelium of the esophagus. Currently, the cell of origin for human BE has yet to identified. Using an innovative 3D organotypic culture system, we explored the role of inhibition of Notch signaling promotion of transdifferentiation of esophageal epithelial cells to BE. Our RNA microarray and tissue microarray (TMA) data support the premise that loss of Notch signaling is involved in BE. Inhibition of Notch signaling by dominant-negative-Mastermind-like (dnMAML), in concert with MYC and CDX1 overexpression, promoted transdifferentiation of esophageal epithelial cells towards BE as demonstrated by increased expression of columnar keratins and glandular mucins with decreased expression of squamous keratins. Our data show KLF4 and HATH1, as downstream effectors of the inhibition of Notch signaling, are involved in the initiation of BE. We investigated whether these findings translated into a genetically engineered mouse model. We addressed this by engineering transgenic mice to conditionally overexpress MYC specifically in the esophageal epithelium with the EBV-L2 (L2) promoter. We used a Tet-ON system to conditionally express MYC. To achieve this we created two new transgenic mice: TetOp-Myc and L2-rtTA;TetOp-CreERT2. We bred L2-rTta; TetOp-Myc mice with K14-Cdx2 and TetOp-dnMAML mice, in order to replicate our in vivo studies. These studies are ongoing. Invasion is a theme common to BE/EAC and ESCC. As a separate consideration, we investigated the mechanisms underlying invasion in ESCC. Using esophageal epithelial cells transformed by overexpression of EGFR and p53R175H, we found a novel link between p53R175H and c-Met, a receptor tyrosine kinase. These transformed cells show increased expression of the c-Met receptor mediated by p53R175H overexpression. We show inhibition of c-Met expression in the transformed cells (EPC-hTERT-EGFR-p53R175H) diminishes invasion. Our data suggest a new avenue of therapeutics for ESCC through the use of c-Met inhibitors.

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