DEFINING NOVEL ROLES OF E3 LIGASES IN DNA REPLICATION AND DNA DAMAGE RESPONSE IN CANCER

ABSTRACTDeepika Jayaprakash: Defining novel roles of E3 ligases in DNA replication and DNA damage response in cancer(Under the direction of Cyrus Vaziri) Ubiquitination is a post-translational modification process that labels target protein substrates with ubiquitin linkages for specific downstream fates. Ubiquitination has a widespread impact on almost all cellular processes in humans including DNA damage response and repair pathways. E3 ligases are essential components of ubiquitination system since they catalyze the last step of the reaction which is transferring ubiquitin from E2 conjugase to the substrate. Furthermore, E3 ligases are known to be mutated/amplified in various cancers, with implications on prognosis of the disease. Additionally, due to their high substrate specificity and efficiency, E3 ligases are promising potential candidates for therapeutic targeting in cancers. Although well-studied in the context of various biological processes, E3 ligases are understudied in genome maintenance pathways, particularly with respect to mechanisms of deployment. However, it is important to uncover E3 ligase mediated molecular underpinnings in both health and disease to be able to achieve better therapeutic strategies in cancers. Therefore, my dissertation focuses on identifying non-canonical roles of E3 ligases in genome maintenance and contribution to chemotherapy tolerance. Chapter 2 in my dissertation elucidates the mechanism of RNF168 recruitment to replication site and the ensuing function thereof. In chapter 3, with the help of sgCRISPR screen, we identify and define mechanisms of two E3 ligases, RNF25 and PIAS1, in promoting tolerance to WEE1 inhibition in PDAC cell lines. Thus, the findings of my thesis unravel new roles of known E3 ligases in genome maintenance and the underlying mechanisms in cancers.