Date of Award

Winter 4-30-2013

Thesis Access

Open Access Honors Thesis

Thesis Location

Honors College Thesis

Degree Name

B.S.

Department

Biological Sciences

Faculty Advisor

Q. Ping Dou

Abstract

As the occurrence of breast cancer increases around the world, the need for new therapeutic medicine becomes more vital to sustain the population. In order to accomplish this, specific mechanisms need to be understood to gain a perspective on the overall process of breast cancer development. One mechanism that is being researched is SUMOylation. The SUMOylation reaction uses small ubiquitin-like modifier (SUMO) proteins, which act as a type of post-translational modification that is necessary in order to preserve protein homeostasis and regulate cellular processes including apoptosis, cell proliferation, and response to stress. The SUMOs attach to a target protein through a SUMO E3 ligase and the modified protein then gains different cellular functions. An example of the SUMO-mediated protein degradation involves Arkadia, a SUMO-targeted ubiquitin ligase, which stimulates the degradation of the Ski protein, which is associated with tumor growth and development.

Breast Cancer Associated Gene 2 or BCA2 is identified as an E3 ligase in the ubiquitin proteasome system. It has been found that BCA2 is co-expressed with the estrogen receptor (ER) in ER-positive breast cancer cells. ER is crucial in the regulation of cell cycle progression and growth of breast cancer epithelial cells. Previous studies have shown that the BCA2 gene is regulated by the ER and BCA2 protein interacts with UBC9 and E2 ligase in the SUMOylation pathway. The regulation of BCA2 could prove critical since it could mediate the ubiquitination and possible SUMOylation of target proteins. While BCA2 as an Ubiquitin E3 ligase has been well established, its role in SUMOylation is unknown. The aim of this thesis is to identify BCA2’s involvement in SUMOylation. To achieve this, I performed bioinformatics analysis of the BCA2 protein sequence and found that out of the 6 lysines (Ks) in the sequence, K32 is the possible lysine important for SUMO attachment. I also tested the SUMOylation of BCA2 in an in vitro assay by using SUMO-specific proteins. The results have revealed an association between SUMO 2/3 and BCA2. Plasmids containing SUMO 1 and 2/3 were then purified from Top10 bacterial cultures and were transfected into HEK293 cells for immunoprecipitation experiments. Preliminary data from these experiments reveal a possible interaction of BCA2 with SUMO2/3. The involvement of BCA2 in both ubiquitination and SUMOylation pathways as an E3 ligase makes it a novel target for therapeutic intervention for the prevention and treatment of breast cancer patients.

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