Date of Award

Fall 2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Chemical and Biomolecular Engineering

First Advisor

Daniel A. Hammer

Abstract

Biochemical and mechanical cues of the extracellular matrix have been shown to play important roles in cell-matrix and cell-cell interactions. We have experimentally tested the combined influence of these cues on cell motility, cell-cell interaction and assembly and traction force profile in an in vitro breast cancer model. The behavior of non-tumorigenic mammary epithelial cells was observed on surfaces with varying ligand concentration and polyacrylamide gel rigidity. Our data shows that cell velocity is biphasic in both matrix rigidity and adhesiveness, which are inversely related. Traction force microscopy revealed that maximum migration velocity is reached at intermediate force of single cells.

Cell-cell adhesion becomes strongly favored on softer gels with elasticity ≤1250 Pascals. This result implies an existence of a compliance threshold that promotes cell-cell over cell-matrix adhesion. On softer gels of 400 Pa, stiffness similar to pre-malignant breast tissue in vivo, cells undergo multi-cellular assembly, division and re-arrangement into 3D spherical aggregates on 2D surface. The aggregates resemble the spherical acini found in vivo and are also formed with EpH4-J3B1 mouse mammary epithelial cells at same compliance.

We establish mechanical cross talk between cell-cell and cell-matrix adhesions. Our findings of mechanotransduction show cell pairs exhibit 'tug of war' competitive dynamics between cell-cell and cell-matrix traction forces. Deletion of E-cadherin binding site to β-catenin results in loss of cell-cell tension magnitude and loss of the cross talk.

We are first to show force dynamics of cell division and cytokinesis in adherent mammalian cells. In normal division intercellular force goes through a maximum. Inhibition of myosin II mediated contractility with blebbistatin completely inhibits cell cytokinesis on gel surfaces. However inhibition of Rho-associated kinase ROCK does not inhibit cytokinesis, only reduces the magnitude of the forces. Therefore myosin II mediated contractility is necessary for cytokinesis on physiologically relevant substrates.

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