Investigating the role of cyclin-dependent kinases in the regulation of DNA repair by non-homologous end-joining (360G-Wellcome-206834_Z_17_Z)

DNA double-strand breaks (DSBs) are highly toxic lesions that can drive genome instability and cancer. In human cells, most DSBs are repaired by the non-homologous end joining (NHEJ) pathway, except when they occur during DNA replication or mitosis when NHEJ is toxic and can generate chromosomal translocations. NHEJ must therefore be tightly regulated to maintain genome stability. However, little is understood about how the core NHEJ repair machinery is regulated. PAXX is the last core NHEJ factor to be identified, and may be a substrate for cyclin-dependent kinases (CDKs). A highly conserved residue in PAXX, S148, matches the consensus for phosphorylation by CDK1/2, and preliminary data indicate that it is indeed phosphorylated by these kinases. The aim of my project is to generate human cell lines expressing PAXX-S148 mutants that either prevent or mimic phosphorylation (Ser > Ala or Ser > Glu) on this site and investigate how expression of these PAXX variants impacts on DSB repair. Key goal 1: produce human cell lines expressing wild-type or mutant fluorescent PAXX variants and examine their DSB repair capacity and sensitivity to ionising radiation Key goal 2: investigate when CDK-dependent phosphorylation of PAXX occurs during the cell cycle