Biology and Biomedical Sciences: Molecular Cell Biology
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
Proper regulation of cell death is critical for tissue development and homeostasis, with deregulation implicated in many illnesses. Cell death is morphologically categorised as apoptosis, autophagy, and necrosis, with apoptosis being the best studied. BCL-2 family members are critical apoptosis regulators. Death signals induce upstream "activator" BH3-only molecules to activate the essential mitochondrion apoptosis effectors BAX and BAK to execute death. Yet, combined loss of Bax and Bak causes developmental and homeostatic defects in restricted tissues, indicating the existence of additional death program(s). By using Bax-/-Bak-/- double- knockout (DKO) mouse embryonic fibroblasts (MEFs) to study non-apoptotic death, we discovered DNA double strand breaks (DSBs) activate a genetic program that upregulates reactive oxygen species (ROS) and the lysosomal protease cathepsin to execute a form of "programmed necrotic death" (PND). This refutes the long-held view that necrosis is a passive reponse to unmanageable physico-chemical stress.
However, the PND execution pathways triggered by death signals and the determinants of death versus long-term survival are unclear. Here, I demonstrated a critical role for the transcription factor DeltaNp63alpha in determining long-term survival in the face of oxidative stress, a central necrotic mediator. DeltaNp63alpha protected DKO MEFs against PND and enhanced long-term survival via a novel ability to control intracellular redox homeostasis by regulating glutathione metabolism. DeltaNp63alpha overexpression protected from oxidative stress induced by oxidants, DNA damage, and anoikis, while deficiency of DeltaNp63alpha increased oxidative stress and sensitized to oxidant-induced death. I further found that long-term survival of anchorage-dependent cells following loss of matrix attachment was enhanced by combined inhibition of apoptosis and oxidative stress by BCL-2 and DeltaNp63alpha, respectively. Furthermore, I showed that in DKO MEFs, DSBs triggered an ATM-mediated DNA damage response that increased ROS production by upregulating the activity of complex III of the electron transport chain. My work concluded a key role for oxidative stress in the loss of long-term survival triggered by intrinsic death signals and revealed an important role for DeltaNp63alpha in regulating redox homeostasis. These findings laid the groundwork for future studies on programmed necrotic death initiated by intrinsic death signals.
Wang, Gary Xiaoshi, "Molecular Mechanisms of Programmed Necrotic Death Initiated by Intrinsic Death Signals" (2014). All Theses and Dissertations (ETDs). 1267.