Semester

Fall

Date of Graduation

2012

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Microbiology, Immunology, and Cell Biology

Committee Chair

Steven Frisch

Committee Co-Chair

Alexey Ivanov

Committee Member

Elena Pugacheva

Committee Member

John Michael Ruppert

Committee Member

Michael Schaller

Committee Member

Peter Stoilov

Abstract

The epithelial to mesenchymal transition (EMT) is a process that is essential for normal embryonic development as well as the healing of damaged adult tissues. In the context of cancer, oncogenic EMT induces enhanced invasion, survival and tumorigenicity which can promote disease progression and recurrence after therapy. Many factors that induce EMT during development and in culture are known and these include the transcription factors Twist, Snail1/2, ZEB1/2 and goosecoid. Transforming growth factor beta can induce EMT both in the contexts of wound healing and cancer, but some cell types are resistant to this stimulus. Furthermore, knowledge of factors which stabilize the epithelial phenotype is limited but include the bone morphogenic protein family of ligands, the epithelial splicing regulatory proteins, and the mir200 micro-RNAs. However, transcription factors which suppress EMT remain surprisingly elusive. In pursuit of identifying such a factor we searched EMT microarrays for transcription factors which were downregulated and that had been previously known to regulate the EMT related process of wound healing. Grainy-head-like-2 (GRHL2) met these criteria so we tested its role in regulating EMT. We found that GRHL2 induced mesenchymal to epithelial transition (MET) and antagonized Twist induced EMT. Also, knockdown of GRHL2 made mammary epithelial cells permissive to TGF-beta induced EMT. GRHL2 knockdown in the presence of activated HRAS induced EMT which was dependent on autocrine TGF-beta. The effect of GRHL2 was depended on direct repression of the ZEB1 promoter where it antagonized homeo-protein mediated transactivation. GRHL2 acted as a tumor suppressor as it enhanced anoikis, suppressed anchorage independent growth and invasion, and prevented tumor formation in xenograft assays. Wnt and TGF-beta were shown to down regulate GRHL2 by up-regulating ZEB1 which directly repressed its promoter. This body of work has identified GRHL2 as novel suppressor of EMT and tumorigenicity, which engages in a reciprocal repression loop with the EMT inducing oncogene ZEB1.

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