A new phosphorylated form of Ku70 identified in resistant leukemic cells confers fast but unfaithful dna repair in cancer cell lines

// Julien Bouley 1, 7, * , Lina Saad 1, * , Romain Grall 1, * , Amelie Schellenbauer 1 , Denis Biard 2 , Vincent Paget 1 , Sandrine Morel-Altmeyer 1 , Olivier Guipaud 1, 8 , Christophe Chambon 3 , Bernard Salles 4 , Karim Maloum 5 , Hélène Merle-Béral 5, 6 , Sylvie Chevillard 1 , Jozo Delic 1 1 Laboratoire de Cancérologie Expérimentale, Institut de Radiobiologie Cellulaire et Moléculaire (IRCM), Commissariat à l’Energie Atomique et aux Energies Renouvelables (CEA), 92265 Fontenay aux Roses, France 2 Institut de Maladies Emergentes et des Thérapies Innovantes (iMETI), Service d’Étude des Prions et des Infections Atypiques (SEPIA), CEA, 92265 Fontenay aux Roses, France 3 Service de Spectrométrie de Masse, INRA Theix, 63122 St Genès Champanelle, France 4 UMR 1331 TOXALIM, INRA/INP/UPS, F-31027 Toulouse, France 5 Service d’Hématologie Biologique, Hôpital Pitié-Salpêtrière, 75000 Paris, France 6 Université Pierre et Marie Curie, Paris VI, INSERM, UMR-S 872, Programmed Cell Death and Physiopathology of Tumor Cells, Centre de Recherche des Cordeliers 75000 Paris, France 7 Laboratoire de Spectrométrie de Masse, Stallergens, 92160 Antony, France 8 Laboratoire de Radiopathologie et de Thérapies Expérimentales, Institut de Radioprotection et de Sureté Nucléaire (IRSN), 92265 Fontenay aux Roses, France * These authors have contributed equally to this work Correspondence to: Jozo Delic, e-mail: jozo.delic@cea.fr Keywords: phospho-Ku70, c-NHEJ, DNA repair kinetic, CLL, gamma-H2AX/ATM/DNA-PKcs Received: February 10, 2015 Accepted: August 03, 2015 Published: August 13, 2015 ABSTRACT Ku70-dependent canonical nonhomologous end-joining (c-NHEJ) DNA repair system is fundamental to the genome maintenance and B-cell lineage. c-NHEJ is upregulated and error-prone in incurable forms of chronic lymphocytic leukemia which also displays telomere dysfunction, multiple chromosomal aberrations and the resistance to DNA damage-induced apoptosis. We identify in these cells a novel DNA damage inducible form of phospho-Ku70. In vitro in different cancer cell lines, Ku70 phosphorylation occurs in a heterodimer Ku70/Ku80 complex within minutes of genotoxic stress, necessitating its interaction with DNA damage-induced kinase pS2056-DNA-PKcs and/or pS1981-ATM. The mutagenic effects of phospho-Ku70 are documented by a defective S/G2 checkpoint, accelerated disappearance of γ-H2AX foci and kinetics of DNA repair resulting in an increased level of genotoxic stress-induced chromosomal aberrations. Together, these data unveil an involvement of phospho-Ku70 in fast but inaccurate DNA repair; a new paradigm linked to both the deregulation of c-NHEJ and the resistance of malignant cells.