Access Type

Open Access Dissertation

Date of Award

January 2010

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Cancer Biology

First Advisor

Marc D. Basson

Abstract

ABSTRACT

MOLECULAR MECHANISMS OF PRESSURE-STIMULATED CANCER CELL SIGNALING

by

CHRISTINA DOWNEY

June 2010

Advisor: Dr. Marc Basson, MD, PhD

Major: Cancer Biology

Degree: Doctor of Philosophy

Increased extracellular pressure stimulates cancer cell adhesion by a mechanism that is dependent upon beta-1-integrin activation, an intact cytoskeleton, and FAK and Src activation. By a different mechanism, increased extracellular pressure modulates cancer cell proliferation in a manner that is regulated by protein kinase C, but not Src or an intact cytoskeleton. Previous studies from our laboratory have shown that paxillin is a necessary mediator in the pathway by which pressure stimulates adhesion; however, it had not been determined whether paxillin acts simply as a scaffold, or participates in diverse signaling events. I therefore hypothesized that paxillin phosphorylation mediates pressure stimulated adhesion and further asked whether the independent pathway by which pressure induces proliferation is modulated by NF-kB. Finally, I postulated that increased pressures of the circulation activate cancer cells to increase adhesion, proliferation and overall tumor burden in vivo. My data illustrate that paxillin phosphorylation at tyrosines 31 and 118 is necessary for pressure stimulated adhesion, but tyrosine 81 phosphorylation is not. The phosphorylation events at tyrosine 31 and 118 form a docking site for the adaptor molecule Crk, which has a binding site for the highly phosphorylated molecule Cas. Each member of the paxillin/Crk/Cas complex is necessary for pressure stimulated adhesion. Furthermore, this complex promotes the activation of the small GTPase, Rac1.

Next, I evaluated whether Rac1 was necessary for pressure induced proliferation, and found that it is not. However, it was found that this pathway is dependent upon NF-kB activation. Increased extracellular pressure increases NF-kB activation in colon, breast and prostate cancer cells. This increase is abolished in the presence of NF-kB inhibitors. Further studies showed that increased pressure activates protein kinase C alpha/beta increases IKK and IkB phosphorylation, cyclin D1 expression and increased S-phase fractions. Immunohistochemical staining for NF-kB, IkB and cyclin D1 increased in the high pressure center of human tumors and decreased toward the periphery.

Finally, I determined that increased pressures of the circulation activate cancer cells in vivo by phosphorylation of beta-1-integrin, FAK and Src. Pre-treatment with pressure prior to systemic injection did not increase metastasis. However, in a local metastasis model, increased tumor burden and decreased long term survival occurred when cells were pre-treated with pressure. These increases were abolished when cells were pre-treated with FAK or Akt inhibitors prior to injection.

In summary, my data suggests pressure activation of malignant cells promotes tumor development and impairs tumor free survival. Preoperative inhibition of paxillin, NF-kB, or other interventions aimed at blocking pressure-induced integrin activation may abolish this effect.

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