Il ruolo dei condensates nel modulare la risposta del danno al DNA: focus su APE1

Proper maintenance of genome stability is a struggle that cells need to face to afford life. Insurrection of genome instability, caused by both endogenous and environmental sources, is at the basis of several diseases’ development and progression, including aging, neurodegenerative diseases, and cancer. To provide proper genome stability, cells have evolved an intricate network, subdivided into interconnecting pathways, of proteins dedicated to DNA repair. Evolution has provided us with different proteins playing very similar roles, almost in a redundant manner, but this is not the case for APE1, the major enzyme possessing endonuclease activity within the base excision repair (BER) pathway. Besides its role as a key BER factor for DNA repair, APE1 has been discovered to play roles also in transcription, redox balance, RNA processing, and RNA quality control. Considering that APE1 alterations have been reported in several pathologies, including cancer, it is essential to understand how cells are able to finely tune all of those, apparently un-related, activities. In recent years, also thanks to the improvement of technologies such as informatic tools and more powerful imaging instruments, the scientific community discovered the existence and functionality of microscopic subcellular compartments not enclosed within membranes, now known as condensates. The fascinating reality of condensates is that they allow for “selective” interaction of biomolecules based on their physicochemical properties, enhancing the occurrence of biochemical reactions. Alteration of condensates is now being associated with pathology development and progression and there is a new, emerging, field of science dedicated to linking the alteration of condensates with diseases: condensatopathy. Thanks to their peculiar physicochemical properties, condensates have been shown to selectively capture and concentrate small molecules within them, opening a new frontier for therapeutical purposes. The main aim of my project was to generate a cellular model that would have allowed us to study, in the most physiological condition possible, APE1 ability to undergo phase separation both in vitro and in vivo. I dedicated most of my PhD to the generation and characterization of an endogenously tagged APE1 cell line that would have allowed me to investigate APE1 trafficking within the cellular environment upon different genotoxic stimuli. The newly generated cellular model allowed us to link APE1 nucleolar enrichment with active rRNA transcription, probably due to the formation of G-quadruplex structures within the rRNA sequences. Additionally, considering the growing importance of RNA binding protein (RBP) in DNA damage repair, I started to investigate the possible interaction between APE1 and FUS, a very well-known RBP with DNA repair activities associated with diseases progression.