Expression of xCT and activity of system xc? are regulated by {NRF2} in human breast cancer cells in response to oxidative stress

摘要

Cancer cells adapt to high levels of oxidative stress in order to survive and proliferate by activating key transcription factors. One such master regulator, the redox sensitive transcription factor {NF} {E2} Related Factor 2 (NRF2), controls the expression of cellular defense genes including those encoding intracellular redox-balancing proteins involved in glutathione (GSH) synthesis. Under basal conditions, Kelch-like ECH-associated protein 1 (KEAP1) targets {NRF2} for ubiquitination. In response to oxidative stress, {NRF2} dissociates from KEAP1, entering the nucleus and binding to the antioxidant response element (ARE) in the promoter of its target genes. Elevated reactive oxygen species (ROS) production may deplete {GSH} levels within cancer cells. System xc?, an antiporter that exports glutamate while importing cystine to be converted into cysteine for {GSH} synthesis, is upregulated in cancer cells in response to oxidative stress. Here, we provided evidence that the expression of xCT, the light chain subunit of system xc?, is regulated by {NRF2} in representative human breast cancer cells. Hydrogen peroxide (H2O2) treatment increased nuclear translocation of NRF2, also increasing levels of xCT mRNA and protein and extracellular glutamate release. Overexpression of {NRF2} up-regulated the activity of the xCT promoter, which contains a proximal ARE. In contrast, overexpression of {KEAP1} repressed promoter activity and decreased xCT protein levels, while siRNA knockdown of {KEAP1} up-regulated xCT protein levels and transporter activity. These results demonstrate the importance of the KEAP1/NRF2 pathway in balancing oxidative stress in breast cancer cells through system xc?. We have previously shown that xCT is upregulated in various cancer cell lines under oxidative stress. In the current investigation, we focused on MCF-7 cells as a model for mechanistic studies.