Novel functions of N-acetyltransferase 10 (NAT10) in DNA repair and replication with potential implications for premature ageing syndromes
Hutchinson-Gilford Progeria Syndrome (HGPS) is an invariably fatal disease with a range of diverse symptoms that are normally associated with those of advanced age. In recent decades, clinicians and scientists together have made great progress in deriving the mechanisms of disease initiation and progression. Nonetheless, the discovery of a cure remains elusive. Inhibition of the acetyltransferase activity of the N-acetyltransferase 10 (NAT10) protein has been shown to have profoundly positive effects on both cellular and mouse models of premature ageing; however, the pathways it is involved in remained largely unexplored. This project set out to identify, characterise and derive mechanistic detail surrounding the functions of NAT10 to better determine its cellular function and potential candidacy as a drug target in HGPS. To this aim, I set out to investigate both the interactome and acetylome of NAT10. While the latter approach was unsuccessful, my interactome studies were able to identify several hits of potential interest that had not been previously identified in the literature. This project focussed particularly on a putative interaction of NAT10 with the complex of three proteins: MRE11, RAD50 and NBS1/NBN (MRN complex). This complex plays an important role in the sensing and repair of DNA double-strand breaks (DSBs), highly genotoxic lesions that can result in unrestrained cellular lethality or genomic instability. During this project, I showed that NAT10 also plays a role in the repair of DSBs. Specifically, I observed that NAT10 localises to DSBs, dependent on the activity of the protein PARP1, and promotes repair by one of the main DSB repair pathways, homologous recombination, most probably by allowing the initial MRE11-mediated resection step to occur. Supporting this repair-promoting role, I also showed that depleting NAT10 leads to increased cellular sensitivity to a range of genotoxic agents. In searching for direct NAT10 acetyltransferase substrates, I showed that NAT10 does not acetylate MRN components. Instead, I observed that NAT10 acetylates PARP1, corroborating recently published findings from others. Among other roles, PARP1 is known to modify the chromatin state around DSBs. As I showed that NAT10 depletion prevents chromatin decompaction after DNA damage induction, my hypothesis is that NAT10-mediated acetylation of PARP1 is involved in chromatin decompaction to allow DNA repair. This is currently under investigation in the lab. While investigating homologous recombination, I observed that NAT10 depletion leads to an accumulation of cells in S-phase of the cell cycle. This was likely due to increased replication stress in these cells, as I observed global replication fork slowing and increased chromosomal abnormalities after NAT10 depletion. I also showed that NAT10 interacts with the replication fork component PCNA. Finally, I attempted to connect these novel pathways to HGPS, but it is still unclear how or whether inhibiting these specific functions of NAT10 might be beneficial for HGPS.