The cellular response to double-strand breaks (DSBs) in DNA is a complex signalling network, mobilized by the nuclear protein kinase ataxia- telangiectasia mutated (ATM), which phosphorylates many factors in the various branches of this network. A main question is how ATM regulates DSB repair. Here, we identify the DNA repair enzyme polynucleotide kinase/phosphatase (PNKP) as an ATM target. PNKP phosphorylates 5-2-OH and dephosphorylates 3-2-phosphate DNA ends that are formed at DSB termini caused by DNA-damaging agents, thereby regenerating legitimate ends for further processing. We establish that the ATM phosphorylation targets on human PNKPSer 114 and Ser 126are crucial for cellular survival following DSB induction and for effective DSB repair, being essential for damage-induced enhancement of the activity of PNKP and its proper accumulation at the sites of DNA damage. These findings show a direct functional link between ATM and the DSB-repair machinery.
- DNA damage response
- double strand break repair
- polynucleotide kinase/phosphatase
- protein phosphorylation