Date of Award

Spring 5-22-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Science

First Advisor

Valerie Odero-Marah, Ph.D.

Second Advisor

Cimona Hinton, Ph.D.

Third Advisor

Manu O. Platt, Ph.D.

Abstract

Prostate and breast cancer are the leading causes of cancer-related death in men and women, respectively, and metastasis is the primary factor underlying the high mortality rates.1 Snail transcription factor is an important molecule that drives prostate and breast cancer metastasis through the process of epithelial mesenchymal transition (EMT). Proteolytic enzymes that promote invasion and metastasis such as the lysosomal cysteine protease cathepsin L (Cat L) have been shown to degrade E-cadherin, promoting the epithelial mesenchymal transition (EMT).2 It has also been shown that silencing Cat L can inhibit transforming growth factor-beta (TGF-β)-mediated EMT by suppressing Snail transcription factor.3 Several recent studies have highlighted an additional unexpected localization and site of action for Cat L within the nucleus in breast, colon and prostate cancer.4 Natural products have been shown to be efficacious in prevention and possible treatment of cancer.5 Specifically, we have been studying Muscadine Grape Skin Extract (MSKE) as a possible candidate to inhibit Snail signaling. MSKE has previously been shown to promote prostate cancer apoptosis.6 We hypothesized that Snail promotes nuclear localization of Cat L, which promotes EMT associated with increased migration and invasion, and that antagonizing Snail-Cat L signaling would lead to mesenchymal epithelial transition (MET). We showed for the first time that MSKE promotes apoptosis through induction of endoplasmic reticulum stress response and autophagy. Additionally, MSKE could inhibit Snail-mediated EMT via scavenging reactive oxygen species. Moreover, Snail could promote nuclear localization of Cat L, which then promoted cleavage of CDP/Cux, increased Snail transcription and decreased E-cadherin transcription by direct promoter binding of cleaved CDP/Cux, leading to EMT associated with increased migration and invasion. Interestingly, Z-FY-CHO, a small molecule specific inhibitor of Cat L, as well as MSKE could antagonize this signaling by promoting nuclear to cytoplasmic re-localization of Cat L. Therefore, we have dissected novel mechanisms of action of Snail and how it can be antagonized by MSKE natural product.