Role of TMS1/ASC in Breast Epithelial Anoikis and Migration Open Access

Patel, Pritty Jashvantlal (2011)

Permanent URL: https://etd.library.emory.edu/concern/etds/2801pg976?locale=en
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Abstract

Cellular detachment from the extracellular matrix (ECM) induces a form of apoptosis, referred to as "anoikis." Most cancer cells are resistant to anoikis and survive independently of ECM interactions. Previously, we identified a pro-apoptotic gene, TMS1 that is epigenetically silenced in breast cancers. Overexpression of TMS1 is sufficient to induce procaspase-8 cleavage in breast cells in the absence of death receptor-ligand interactions. Additionally, TMS1 aggregates to form ‘specks' in some apoptotic cells, although the function of this structure remains unclear. Here we established a role for TMS1 in anoikis and uncovered a nonapoptotic role for TMS1 in cell migration. We found that cellular detachment induces TMS1 expression. In addition, we showed that silencing TMS1 confers resistance to anoikis through a delay in procaspase-8 cleavage and accumulation of BimEL. ERK1/2 signaling negatively regulates BimEL accumulation during detachment. We found that silencing TMS1 resulted in persistent ERK1/2 signaling during anoikis. We conclude that loss of TMS1 promotes resistance to anoikis in part through misregulation of ERK1/2 signaling and suppression of BimEL accumulation. During the course of these studies a nonapoptotic role for procaspase-8 in adhesion and migration was elucidated by many groups. The next phase of our research was aimed towards deciphering a role for TMS1 upstream of procaspase-8 in anoikis. Thus, we next investigated a nonapoptotic role for TMS1 in these processes. We found that adhesion to fibronectin induced the redistribution of TMS1 to barrel-like structures. Silencing TMS1 delayed FAK and ERK1/2 signaling in response to integrin-fibronectin interactions. Phosphorylated FAK and centrosomal markers colocalized with TMS1 at barrel-like structures in a subset of cells. Through functional analyses, we further demonstrated a role for TMS1 in cell migration. These data suggest that an association of TMS1 with centrosomes results in the formation of a critical signaling center that may regulate migration. In conclusion, our data demonstrate distinct functions for TMS1 in anoikis and migration. Overall, results from these studies have increased our understanding of the intricate functions TMS1 exhibits in epithelial cells and has provided great insight into the consequences of aberrant methylation and silencing of TMS1 observed in many cancers.

Table of Contents

Table of Contents

Chapter 1: Introduction……………………………………………………………………1

Figures……………………………………………………………………………30

Chapter 2: Silencing of TMS1/ASC promotes resistance to anoikis in breast epithelial cells………………………………………………………………………………………41

Figures…………………………………………………………………………....55

Chapter 3: A nonapoptotic role for TMS1 in breast epithelial cell migration…………...64

Figures…………………………………………………………………………....86 Chapter 4: Discussion……………………………………………………………………96 Figures…………………………………………………………………………..121

Appendix: 3D Morphogenesis Assay…………………………………………………..128

Figures………………………………………………………………………..…138 References…………………………………………………………………………..…..141

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