ORCID

0000-0003-1569-2452

Date of Award

4-26-2024

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Molecular Cell Biology)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

The majority of ovarian cancer patients have metastatic disease throughout the peritoneal cavity at the time of diagnosis, at which point the five-year survival is only around 30%. However, no effective therapy exists to prevent or treat ovarian cancer metastasis. To implant into the peritoneal cavity, ovarian cancer cells must attach to the mesothelial cell layer-a monolayer of cells that surrounds all organs of the peritoneal cavity- clear the mesothelial cell layer and invade into the underlying stroma, which hosts fibroblasts and extracellular matrix (ECM). The tumor microenvironment (TME) plays an important role in supporting metastasis and thus is a crucial area of study for potential targets to treat or prevent metastasis. Our investigations begin by testing the hypothesis that stromal cell discoidin domain receptor 2 (DDR2) promotes ovarian cancer metastasis. DDR2 is a receptor tyrosine kinase whose ligand is collagen, which is the most abundant ECM protein in the ovarian TME. We find that high stromal cell DDR2 expression correlates with poor overall survival of ovarian cancer patients. Using global Ddr2 knockout mice we demonstrate that stromal cell DDR2 promotes ovarian cancer in a syngeneic ovarian cancer mouse model. In cell-based assays we find fibroblast expression of DDR2 promotes tumor cell invasion via the secreted collagen remodeling protein LOXL2. We propose a mechanism by which DDR2 is required in fibroblasts in order to meet the energetic demands and increased protein production necessary to create a pro-metastatic ECM. We then explore DDR2 expression in mesothelial cells finding DDR2 expression promotes tumor cell attachment, clearance, and contributes to stabilizing a pro- metastatic mesenchymal state in mesothelial cells. We also find that DDR2 can have these effects even without stimulation by collagen, and thus begin to explore ligand-independent effects of DDR2. This will be an important area to further study so inhibitors that target all DDR2 functions can be developed. To understand whether mesothelial cell DDR2 expression promotes ovarian cancer metastasis we made, validated, and utilized a mesothelial cell specific Ddr2 knockout mouse model. Although we were unable to demonstrate significant differences in ovarian cancer tumor burden between wild type and knockout, this mouse model will be instrumental to answering future questions surrounding the contribution of mesothelial cells to ovarian cancer metastasis. We also investigated the role of tumor cell secreted factors’ ability to influence mesothelial cells during metastasis concluding that mesothelial cells exposed to tumor cell secreted factors demonstrate increased clearance. The mesothelial cells undergo transcriptional and translational changes after exposure to condition media, with enrichment of epithelial-to- mesenchymal associated genes. Future directions include identifying if tumor cell secreted factors promote attachment to the mesothelial cell layer using a microfluidic device that we have optimized to address this question, identifying specific secreted factor(s) that result in functional changes in mesothelial cells and exploring pathways in mesothelial cells that have a functional response after exposure to tumor cell secreted factors. Overall, we enhance our understanding of how the tumor microenvironment is influencing ovarian cancer metastasis, identifying DDR2 as a potential target, and developed tools to better address future questions on tumor-stroma interactions in ovarian cancer.

Language

English (en)

Chair and Committee

Gregory Longmore

Committee Members

Katherine Fuh

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