| NF-kappaB is a pleiotropic transcription factor, which is instrumental in regulating diverse cellular processes such as inflammation and cell survival. Enhanced NF-kappaB activity, due either to prolonged NF-kappaB activation upon exposure to cellular stress or misregulation of NF-kappaB, can lead to many neurodegenerative diseases as well as cancer. Thus, in this study, biological and biochemical approaches were used to characterize how NF-kappaB regulates the cellular stress response and how NF-kappaB 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-kappaB. Chapter 2 characterizes the mechanism of NF-kappaB's cell death promoting function in response to oxidative stress and shows that NF-kappaB signaling actually promotes cell death. Furthermore, we suggest that NF-kappaB 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-kappaB inhibitor molecule IkappaBgamma. We clearly show that the 20S proteasome is able to degrade IkappaBgamma in an ubiquitin independent manner. Preliminary LC-MS/MS data suggests that the 20S proteasome, which displays enhanced activity towards IkappaBgamma, 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 PA28alphabeta bound 20S proteasome is responsible for the ubiquitin independent degradation of another NF-kappaB inhibitor molecule, free IkappaBalpha. All together, this work delineates how NF-kappaB signaling can mediate cell death in response to oxidative stress, how oxidative stress can potentially increase the ubiquitin independent degradation of IkappaBgamma by enhancing the proteolytic activity of the 20S proteasome, and how PA28alphabeta bound 20S proteasome is responsible for the ubiquitin independent degradation of free IkappaBalpha. |
