UC San Diego

NF-[kappa]B is a pleiotropic transcription factor, which is instrumental in regulating diverse cellular processes such as inflammation and cell survival. Enhanced NF- [kappa]B activity, due either to prolonged NF-[kappa]B activation upon exposure to cellular stress or misregulation of NF-[kappa]B, can lead to many neurodegenerative diseases as well as cancer. Thus, in this study, biological and biochemical approaches were used to characterize how NF-[kappa]B regulates the cellular stress response and how NF-[kappa]B activity itself is regulated. Chapter 1 introduces oxidative stress, which is the specific cellular stress used in this study, and reviews how oxidative stress affects all cellular components, including the proteasome and NF-[kappa]B. Chapter 2 characterizes the mechanism of NF-[kappa]B's cell death promoting function in response to oxidative stress and shows that NF-[kappa]B signaling actually promotes cell death. Furthermore, we suggest that NF- [kappa]B promotes cell death through the repression of pro -survival genes and induction of pro-death genes. Chapter 3 focuses on whether oxidized 20S proteasome enhances the ubiquitin independent degradation of NF-[kappa]B inhibitor molecule I[kappa]B[gamma]. We clearly show that the 20S proteasome is able to degrade I[kappa]B[gamma] in an ubiquitin independent manner. Preliminary LC-MS/MS data suggests that the 20S proteasome, which displays enhanced activity towards I[kappa]B[gamma], can undergo cysteic acid modification. We suggest that mild oxidative stress can enhance proteasome activity, while severe oxidative stress impairs proteasomal activity. Chapter 4 provides strong evidence suggesting that PA28[alpha][beta] bound 20S proteasome is responsible for the ubiquitin independent degradation of another NF-[kappa]B inhibitor molecule, free I[kappa]B[alpha]. All together, this work delineates how NF-[kappa]B signaling can mediate cell death in response to oxidative stress, how oxidative stress can potentially increase the ubiquitin independent degradation of I[kappa]B[gamma] by enhancing the proteolytic activity of the 20S proteasome, and how PA28[alpha][beta] bound 20S proteasome is responsible for the ubiquitin independent degradation of free I[kappa]B[alpha]