Date of Award

January 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Sciences

First Advisor

Jane R. Dunlevy

Abstract

Bladder cancer, the most common urinary tract malignancy, has environmental toxicant exposure as one of its biggest risk factors. This lab examines potential biomarkers employing an in vitro model of urothelial carcinoma using a normal bladder cell line and its malignantly transformed cells transformed counterpart, transformed by exposure to long term, low doses of cadmium (Cd2+). Initial microarray analysis determined that Secreted Protein Acidic and Rich in Cysteine (SPARC) was the most repressed gene across all transformed cell lines compared to its normal counterpart (Garrett et al., 2014, Larson et al., 2010).

SPARC, an extracellular matrix glycoprotein, functions by regulating cell-matrix interactions. It has both oncogene and tumor suppressor actions depending upon the cancer with its role in bladder carcinoma remaining unclear. Previous lab results identified three key findings regarding the role of SPARC: 1) SPARC was significantly repressed following short term, low dose cadmium exposure; 2) SPARC is expressed at moderate levels in the normal transitional epithelium, however, in urothelial carcinomas, SPARC expression is drastically repressed; and 3) when SPARC was transfected into Cd2+ transformed cells with expression being ‘forced’ via a CMV promoter, heterotransplant tumors again had very little, if any, SPARC expression (Larson et al., 2010; Slusser et al., 2016).

The current study is based on 3 overarching hypotheses: 1) SPARC plays a critical role in urothelial cell proliferation, migration, attachment, and spreading; 2) Cadmium transformation significantly decreases SPARC expression by silencing the promoter early in the malignant transformation process; and 3) that in urothelial tumors generated from Cd2+-transformed cell lines, SPARC is prohibitive to tumor initiation.

The results of this study advance the understanding of SPARC in transformed cells by showing that SPARC promotes cell spreading which may be inhibitory to tumor initiation, necessitating its repression; preferential transcription factor binding of SOX5 compared to Sp1/Sp3 contributing to SPARC repression; and that in serial heterotransplant tumors, repression of human tumor SPARC continues along with an increase in mouse stromal SPARC. Overall, the conclusion from this research is that SPARC acts as a tumor suppressor in the UROtsa model system requiring repression for malignant transformation and tumor initiation.

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