Date of Award
Doctor of Philosophy (PhD)
Protein quality control is essential for cellular homeostasis. The Ubiquitin-Proteasome System (UPS) is responsible for the regulated breakdown of intracellular proteins. All proteins are not degraded at the same rate in the cell. For instance, global protein turnover rates in mammals change with an average time between 1-2 days. On the other hand, a handful of proteins such as myelin exhibits limited turnover for months or even years. The UPS recycles most of the short-lived proteins in a time range from minutes to days depending on their localization and post-translational modifications. The post-translational modification, poly-ADPribosylation has an estimated half-life of only 1-6 min. My thesis research aimed to reveal how the substrates of Tankyrase are degraded rapidly. Using Drosophila melanogaster, I described the role of Iduna E3 ubiquitin ligase in the regulation of Axin and Tankyrase proteolysis. I found that Iduna controls the proliferation of stem cells in the Drosophila midgut. Using a MS-based approach, I identified lysine 598 as an ADP-ribose acceptor site in Drosophila Tankyrase and showed that TnksK598A adult flies live significantly shorter than control flies. TnksK598A adult flies also reduce their flight, climbing abilities, global protein poly-ADP-ribosylation, and the activation of JNK signaling with age. Furthermore, I demonstrated that the ubcD1 ubiquitin-conjugating enzyme enhances the ubiquitin ligase activity of Iduna. Finally, I proposed a model by which poly-ADP-ribosylation brings together Tankyrase, target proteins, E2 ubiquitin-conjugating enzymes, E3 ubiquitin ligases and 26S proteasomes to accelerate the breakdown of target proteins. My work addresses the general question of how proteins can be rapidly turned over, focusing on the role of Tankyrase-mediated poly-ADP-ribosylation. This work provides novel mechanistic insights into the regulation of protein quality control. Ultimately, these results may be useful to guide the development of new therapies.
Gultekin, Yetis, "Regulation of Protein Degradation by ADP-Ribosylation" (2019). Student Theses and Dissertations. 527.