RESUMEN
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'-OH and dephosphorylates 3'-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 PNKP-Ser 114 and Ser 126-are 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.
Asunto(s)
Proteínas de Ciclo Celular/metabolismo , Roturas del ADN de Doble Cadena , Enzimas Reparadoras del ADN/metabolismo , Reparación del ADN/fisiología , Proteínas de Unión al ADN/metabolismo , Proteínas Serina-Treonina Quinasas/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Animales , Proteínas de la Ataxia Telangiectasia Mutada , Citotoxinas/farmacología , Roturas del ADN de Doble Cadena/efectos de los fármacos , Enzimas Reparadoras del ADN/genética , Células HEK293 , Humanos , Ratones , Fosforilación/efectos de los fármacos , Cinostatina/farmacologíaRESUMEN
The cellular response to DNA double-strand breaks (DSBs) is mobilized by the protein kinase ATM, which phosphorylates key players in the DNA damage response (DDR) network. A major question is how ATM controls DSB repair. Optimal repair requires chromatin relaxation at damaged sites. Chromatin reorganization is coupled to dynamic alterations in histone posttranslational modifications. Here, we show that in human cells, DSBs induce monoubiquitylation of histone H2B, a modification that is associated in undamaged cells with transcription elongation. We find that this process relies on recruitment to DSB sites and ATM-dependent phosphorylation of the responsible E3 ubiquitin ligase: the RNF20-RNF40 heterodimer. H2B monoubiquitylation is required for timely recruitment of players in the two major DSB repair pathways-nonhomologous end-joining and homologous recombination repair-and optimal repair via both pathways. Our data and previous data suggest a two-stage model for chromatin decondensation that facilitates DSB repair.