Identifier

etd-04022007-085414

Degree

Doctor of Philosophy (PhD)

Department

Biomedical and Veterinary Medical Sciences - Comparative Biomedical Sciences

Document Type

Dissertation

Abstract

Cancer metastasis is a frequent manifestation of malignant melanoma progression. Successful invasion into distant organs by tumor cells must include attachment to microvessel endothelial cells, and degradation of extracellular matrix. Heparan sulfate proteoglycans are ubiquitous macromolecules associated with cell surface and extracellular matrix of a wide range of cells and tissues. Heparanase is an extracellular matrix degradative enzyme which degrades the heparan sulfate chains of heparan sulfate proteoglycans. To investigate effects of changes in heparanase gene expression in metastatic melanoma cells, we constructed adenoviral vectors containing the full-length human heparanase cDNA in both sense (Ad-S/hep) and anti-sense orientations (Ad-AS/hep). We demonstrated increased heparanase expression and activity in melanoma cell lines following Ad-S/hep infection by Western blot analyses and heparanase activity assay. Conversely, heparanase content was significantly inhibited following infection with Ad-AS/hep. Alteration of heparanase protein expression by these adenoviral constructs correlated with invasive cellular properties in vitro and in vivo. Unexpectedly, overexpression of heparanase inhibited brain tumor formation in vivo possibly by extensive remodeling of the extracellular matrix which in turn modifies growth factor signaling and activity. Finally, cell-surface heparan sulfate is also known to inhibit or promote tumorigenesis depending on size and composition. We proposed that heparanase generates bioactive heparan sulfate chains from the melanoma cell-surface that modify biological activities associated with vascular endothelial growth factor, a molecule essential for brain metastasis. Heparanase-degraded melanoma cell-surface heparan sulfate stimulated migration, but not proliferation of melanoma in vitro. It also enhanced angiogenesis in vivo, independent of vascular endothelial growth factor activity, an unexpected finding. Interestingly, melanoma cell-surface heparan sulfate did not have an observed effect on endothelioma migration in vitro. We also attempted to characterize the melanoma cell-surface heparan sulfate isolated by heparanase degradation by ion-pair high pressure liquid chromatography. This method proved to be not sensitive enough to detect nanogram quantities of HSGAG present in our samples.

Date

2007

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Gary E. Wise

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