Cancer cells adapt to high levels of oxidative stress in order to survive and proliferate, making the transcription factors involved in antioxidant defence regulation targets of interest. The transcription factor NF E2 Related Factor 2 (NRF-2) regulates cellular defence genes including those encoding intracellular redox-balancing proteins such as enzymes involved in glutathione metabolism. Glutathione in particular is an important intracellular antioxidant molecule. NRF-2 binds to the Antioxidant Response Element (ARE) in the promoter of its target genes. Under basal conditions, Kelch-like ECH-associated protein 1 (KEAP1) acts as an inhibitor that targets NRF-2 for ubiquitination. During oxidative stress, NRF-2 dissociates from KEAP1 and enters the nucleus to bind to the ARE sequence. It is hypothesized that the elevated Reactive Oxygen Species may be depleting the glutathione levels within the cancer cell. System xc- is a cystine/glutamate antiporter that exports glutamate while importing cystine to synthesize glutathione. In response to oxidative stress, the cells increase system xc- activity in order to provide cystine for glutathione synthesis. There is evidence that expression of xCT, the specific subunit of system xc-,is regulated by NRF-2. However this has not yet been demonstrated in human breast cancer cells, which is the focus of this project. Basal expression of NRF-2, KEAP1 and xCT was characterized in three breast cancer cell lines (MDA-MB-231, MCF-7 and T47D) and compared to two non-cancer cell lines (184B5 and MCF10A). Basal protein levels of NRF-2 and KEAP1 showed no differences between cell lines. Basal protein levels of xCT were increased in MCF10A cells than T47D cells. MCF-7 cells were treated with hydrogen peroxide (H2O2) resulting in NRF-2 protein accumulation in the nucleus. With H2O2 treatment, xCT mRNA levels increased in MCF-7 cells. Additionally, transient overexpression of NRF-2 increased extracellular glutamate levels in MCF-7 cells. These data support a model that under oxidative stress, NRF-2 is localized to the nucleus and transcriptionally upregulates xCT. This is the first study in which the regulation of xCT has been linked to oxidative stress via NRF-2 in human breast cancer cells. / Thesis / Master of Science (MSc)