Title: Characterization of mammalian sirtuin regulators, targets, and complexes
Description: Yeast Sir2 is the founding member of a class of NAD + -dependent deacetylases commonly referred to as sirtuins. Sir2 plays a central role in regulating heterochromatic silencing at the rDNA, mating-type loci, and telomeres primarily by deacetylating histones and altering chromatin accessibility. Subsequent to its discovery as an epigenetic modulator, it was found that Sir2 is required for lifespan extension by caloric restriction, a diet known to induce longevity in various organisms. The closest mammalian homolog of Sir2, SIRT1, is an important regulator of metabolism, cell survival, DNA repair, and longevity. This dissertation focuses on understanding the role of mammalian sirtuins and the sirtuin activating compound resveratrol in cellular processes. In Chapter 2, I investigated the role of resveratrol in regulating autophagy, a process by which cells undergo self-directed catabolism to maintain bioenergetic requirements during nutrient limitation. My work showed that resveratrol suppressed autophagy induced by nutrient-withdrawal independently of SIRT1. In addition, S6K1 is inhibited by resveratrol and is required for full induction of mammalian autophagy. In Chapter 3, I examined binding partners for SIRT1, and discovered the polarity protein Par-3 could bind either SIRT1 or SIRT2.

My work showed that Par-3 is acetylated in cells on four specific lysine residues and that SIRT2 can deacetylate Par-3 in vitro and in vivo . Combined with work from the Milbrandt lab, my work led to the discovery that SIRT2 regulates myelination by deacetylating Par-3. In Chapter 4, I performed a more systematic proteomic analysis of SIRT1 to discover novel complexes and biological functions. Amongst the high confidence interactors determined by this method, I confirmed an interaction of SIRT1 with the deubiquitylating enzyme USP22. My work showed that this interaction absolutely required the ZnF-UBP domain of USP22 and was disrupted by the catalytic inactivating H363Y SIRT1 mutant. In addition, I mapped three unique USP22 acetylation sites and determined their effects on catalytic activity and complex formation. Finally, I discovered novel transcriptional targets co-regulated by USP22 and SIRT1, and speculate that these may be interesting avenues for research in the context of SIRT1 biology.