Access Type

Open Access Dissertation

Date of Award

1-1-2011

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Pharmacology

First Advisor

Sandra A. Rempel

Second Advisor

Stanley R. Terlecky

Abstract

THE ROLE OF THE SPARC ACIDIC DOMAIN AND EGF-LIKE MODULE IN GLIOMA MIGRATION, INVASION, AND SIGNALING

HEATHER M. MCCLUNG

Advisor: Sandra A. Rempel, Ph.D.

Major: Pharmacology

Degree: Doctor of Philosophy

We have previously shown that Secreted Protein Acidic and Rich in Cysteine (SPARC) is upregulated in all astrocytoma grades and increases tumor cell migration and invasion. It is thought that different domains within the protein may regulate SPARC functions, suggesting domain-specific targeting to inhibit invasion. To enhance our understanding of SPARC-mediated invasion, we first confirm, at the protein level, our previous cDNA array results, that SPARC increases expression of the matrix metalloproteases (MMPs) MT1-MMP and MMP-2. We also demonstrate that SPARC increases MMP-2 activation and the secretion and processing of galectin-3, a known target of MMPs. To investigate the roles of specific domains, we used a SPARC-GFP fusion protein and deletion mutant constructs of SPARC-GFP with deletions of either the Acidic Domain or EGF-like Module. We confirm our previous findings that SPARC-GFP increases migration and activation of p38 MAPK and HSP27 signaling compared to GFP control cells. Deletion of the Acidic Domain increases cell adhesion and reduces SPARC-induced migration and p38 MAPK/HSP27 signaling. The EGF-like Module Deletion mutant decreases SPARC-induces migration and dramatically decreases the expression and phosphorylation of HSP27. The extent to which the deletions reduce migration was dependent upon the presence of extracellular matrix. Preliminary data also suggest that the deletions affect invasion and MMP-2 activation. In conclusion, both regions of interest regulate SPARC-induced migration and signaling though the p38 MAPK/HSP27 signaling pathway. Importantly, their impact on migration is influenced by the presence or absence of extracellular matrix. This and future studies of the deletion mutants will provide valuable insight into new strategies that effectively target invasion in SPARC-expressing tumors.