To identify the protein kinase involved in the DSB-induced phosphorylation of Ku70, we treated CLL cells (Figure 3A, 3B) and the HeLa DNA-PKcskd cell line [30] (Figure 3C, 3D) with NCS in the presence of wortmannin (WM), a PI3 kinase and PI3-like kinase inhibitor, or with NU7026, which at low concentrations inhibits DNA-PKcs but not ATM or ATR [31]. Here, ATM is linked to B-cell chronic lymphocytic leukemia.