Date of Award

2025

Embargo Period

8-6-2030

Document Type

Thesis - MUSC Only

Degree Name

Master of Science (MS)

Department

Biomedical Sciences

Additional Department

Cell and Molecular Pharmacology and Experimental Therapeutics

College

College of Graduate Studies

First Advisor

Joe B. Blumer

Second Advisor

Scott T. Eblen

Third Advisor

Haizhen Wang

Fourth Advisor

Daniel Gioeli

Abstract

Ovarian cancer is the most lethal gynecological cancer and one of the leading causes of cancer-related deaths. In the United States, it is estimated that over 20,000 new cases and over 12,000 deaths will occur in 2025. The high mortality rate can be attributed to both acquired drug resistance and to the shedding of malignant cells and dissemination of multicellular aggregates known as spheroids into the peritoneal cavity to promote metastasis. Importantly, spheroids have been shown to promote chemoresistance due to their dormant characteristics. Most ovarian cancer research, however, has overlooked the study of spheroids despite the overwhelming clinical importance of spheroids in ovarian cancer metastases which has limited our understanding of ovarian cancer metastases. The study of metastatic ovarian cancer spheroids is necessary to determine new mechanisms that contribute to metastases that can improve the standard of care for ovarian cancer. We have previously shown that the E3 ubiquitin ligase UBR5 promotes cisplatin resistance in ovarian cancer in cells and xenografts. Proteomic screening revealed ATAD2 - an AAA+ ATPase transcriptional coactivator for c-Myc and a key driver in ovarian cancer cell proliferation - to be a direct substrate of UBR5. Indeed, UBR5, ATAD2, and c-Myc are located closely together on chromosome 8q, resulting in co-amplification. In this study, we hypothesize that UBR5 promotes proteasomal degradation of cell-proliferation drivers ATAD2 and c-Myc in ovarian vi cancer spheroids to facilitate dormancy. To elucidate this mechanism, we investigated the effects of ATAD2 knockout or UBR5 knockdown on spheroid morphology, proliferation, and gene and protein expression in traditional adherent culture conditions compared to a 3D suspension spheroid model by using imaging, cell viability assay, RT-qPCR, and immunoblotting. Knockout and inhibition of ATAD2 downregulated expression of UBR5 in traditional adherent culture conditions. Knockdown of UBR5 mediated spheroid morphology, increased proliferation, upregulated ATAD2 responsive gene expression, and upregulated ATAD2 and c-Myc protein expression. Together, these results demonstrate a novel role of UBR5 in promoting proteasomal degradation of ATAD2 and c-Myc in ovarian cancer spheroids to facilitate dormancy and suggest a novel gene regulatory mechanism that may contribute to chemoresistance in ovarian cancer.

Rights

Copyright is held by the author. All rights reserved.

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Available for download on Tuesday, August 06, 2030

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