Negative Regulators of Nrf2 in the Early Response to Oxidative Stress

Abstract

Uncontrolled levels of oxidative stress have been implicated in causing a variety of diseases, including neurodegenerative disorders and cancer. The complex signaling pathways that combat oxidative stress are clinically relevant targets for development of safe and effective methods for treatment of these ailments. Enhancement of these pathways in various disease states could decrease the levels of oxidative stress and improve the status of patients with different afflictions. The NF-E2 related factor 2 (Nrf2) signaling pathway could be a therapeutic target for preventing oxidative stress related diseases. Nrf2 is a basic leucine zipper transcription factor that binds antioxidant response elements (AREs) located in promoters of antioxidant genes. Nrf2 regulates expression and induction of cytoprotective genes in response to oxidative stress. Several negative regulators of Nrf2 have been elucidated and may be potential targets for therapies to enhance the protective abilities of Nrf2. They may also be manipulated to decrease the activity of Nrf2 in specific diseases where Nrf2 exhibits harmful effects. The main focus of this thesis is the regulation and cellular signaling of the negative regulators of Nrf2 including INrf2, Cul3, Rbx1, Bach1, and Fyn. The molecular mechanisms triggered in the early response of cells to oxidative stress are not well understood. The present studies demonstrate that within 0.5 hours of antioxidant or xenobiotic treatment, the negative regulators of Nrf2 export out of the nucleus allowing Nrf2 unimpeded movement to the ARE. Mutation of tyrosine residues in the negative regulators stymied nuclear export suggesting tyrosine phosphorylation controls nuclear export. Furthermore, mutant negative regulators interfered with the ability of Nrf2 to activate defensive genes. This study also found that Nrf2 is able to control the regulation of some of its other negative regulators including Cul3 and Rbx1. Thus, the pre-induction regulation of Nrf2 is controlled by the nuclear export of the negative regulators allowing for activation of defensive gene expression. In summation, the work done in this thesis provides insights into the mechanisms by which Nrf2 activity is tightly controlled during oxidative stress. Negative regulators of Nrf2 may be prime targets for preventing diseases caused by chronic oxidative stress.