Access Type

Open Access Thesis

Date of Award

January 2013

Degree Type

Thesis

Degree Name

M.S.

Department

Biological Sciences

First Advisor

Karen A. Beningo

Abstract

Metastasis is a multistep process driven by various biochemical and mechanical factors, which eventually leads to formation of secondary tumors. The tumor mass is surrounded by basement membrane (BM) and stroma made of various extracellular matrix (ECM) proteins. During metastasis tumor cells disseminate from the primary tumor, breach the BM, invade the stroma, travel through blood and lymph and colonize tissues distant from the primary tumor. Formation of secondary tumors by metastasis is a leading cause of death in cancer patients. Even though plenty of research has been focused on biochemical factors affecting metastasis, information on role of mechanical factors in this process is very limited. Using our previously developed in vitro mechano-invasion assay, we had observed enhanced cellular invasion in response to tugging forces in the stroma during cancer cell invasion. In vivo, such tugging forces would be produced by contractile cells within the stroma as they migrate and remodel the matrix fibers. In addition, we found this mechanically enhanced invasion by cancer cells to be dependent on the presence of fibronectin in the extracellular matrix. The objective of our study is to understand the mechanotransduction pathway leading to enhanced invasion. We hypothesized that in response to mechanical forces in the stroma, tumor cells will show an altered expression of genes involved in mechanosensing. We performed expression profiling of several genes related to cell migration, adhesion and tumor metastasis by real-time PCR analysis. Six genes were confirmed to be differentially expressed between mechanically stimulated and non-stimulated conditions. Surprisingly, one of the genes found to be significantly down-regulated in the mechanically stimulated invasion culture is a fibronectin specific integrin subunit, integrin β3. Over-expression of this gene resulted in a significant decrease in enhanced invasion, supporting its role in sensing the mechanical stimulus. Furthermore, down-regulation of integrin β3 resulted in decrease in amounts of inactive form of cofilin (Ser3 phospho-cofilin).

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