The role of telomeric proteins in regulating the metazoan DNA damage response

Abstract

Both telomere regulation and the repair of DNA damage are essential processes for maintaining genomic stability in eukaryotes. Distinctions between these processes have become harder to make as we further our understanding of their governing pathways and the overlap of proteins involved. The CST complex was originally discovered in budding yeast, it is the capping complex that ensures telomeric deoxyribonucleic acid (DNA) is appropriately replicated and protected. In 2009 the CST complex was identified in humans, but the role of the human CST complex has been found to extend beyond the telomere. Here I report that whilst loss of the CTC1-STN1-TEN1 (CST) complex component CTC1 in human cells does result in telomere mis-regulation, it also induces a rapid compromise to genomic stability unrelated to its telomeric function. My data suggest CTC1 ∆ human cells are failing to correctly repair DNA damage. I also show that STN1 , another CST complex component, can significantly compromise genomic stability when overexpressed. This instability may be due to the fact that a high level of STN1 appears capable of suppressing homology-directed repair (HDR) whilst promoting non-homologous end joining (NHEJ). Human STN1 mRNA, like the budding yeast homologue, appears to be degraded by nonsense-mediated decay (NMD), perhaps as a mechanism for NMD and the stress response to regulate repair pathways via STN1. Finally, I report that the recently proposed critical role for the nuclease/helicase Dna2 at the telomeres of budding yeast appears to be conserved in the nematode C. elegans. The overlap in proteins that regulate the telomere and those that play an active role in the repair of DNA damage continues to grow. The human CST complex was originally characterised as a regulator of the telomere but appears to also play a significant role in the DNA damage response. Telomere regulation and DNA damage repair play key roles in both the ageing processes and cancer development, and the data presented in this thesis link STN1 regulation and NMD to these processes.