All ETDs from UAB

Advisory Committee Chair

Candece Gladson

Advisory Committee Members

Michael Brenner

Kevin Roth

Harald Sontheimer

Anne Theibert

Document Type

Dissertation

Date of Award

2009

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

The recombinant fifth kringle domain of plasminogen (rK5) has been shown to induce apoptosis of dermal microvessel endothelial cells (MvEC), and this pro-apoptotic effect required rK5 binding to cell surface glucose-regulated protein 78 (GRP78). GRP78 is a member of the heat shock protein family and under certain conditions is expressed on the cell surface. I am interested in identifying new anti-angiogenic therapy for glioblastoma tumors. The efficacy of certain anti-angiogenic therapy can be improved when combined with radiation, and radiation is a standard therapy for glioblastoma tumors; therefore, I investigated the pro-apoptotic effect of rK5 combined with radiation on primary human brain MvEC. I found that treatment of brain MvEC with rK5 induced apoptosis in a dose- and time-dependent manner, and that prior irradiation significantly sensitized (500-fold) the cells to the pro-apoptotic effect of rK5. In both the unirradiated and irradiated MvEC, the rK5-induced apoptosis required the expression of GRP78 and the low density lipoprotein receptor-related protein 1 (LRP1), a scavenger receptor. This was determined by blocking studies with an antibody directed toward GRP78 and with a competitive inhibitor of ligand binding to LRP1, as well as by downregulation studies with small interfering RNA. Also, I found p38 MAP kinase to be a necessary downstream effector of rK5-induced apoptosis, in contrast to Erk and JNK. These data suggest that irradiation sensitizes brain MvEC to rK5-induced apoptosis and that this signal requires LRP1 internalization of GRP78 and the activation of p38 MAP iii kinase. The physiologic relevance of these findings are supported by my observation that expression of GRP78 protein is upregulated on the brain MvEC in glioblastoma tumor biopsies as compared to the normal brain, suggesting a potential tumor-specific effect of rK5. In addition, in an orthotopic intracerebral xenograft mouse model of malignant glioma, I found that treatment with rK5 significantly decreased tumor volume. Taken together, these in vitro and in vivo data potentially present an important new therapeutic role for rK5 in the treatment of malignant gliomas.

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