Ku70 and phospho-S2056-DNA-PKcs localize at dysfunctional telomeres in CLL-R cells. (A) Ku70 protein levels at telomeric chromatin in CLL cells. ChIP assays were carried out on 5 CLL-R and 8 CLL-S samples. To exclude nonspecific binding between beads and crosslinked chromatin, a ChIP assay was performed in the absence of any antibody (No Ab). Input represents the total DNA used in each assay. (B) Quantification of the telomeric signals expressed as a percentage of the total telomeric DNA. Bars represent the mean percentage ± SD. (C) Alu probe control analysis. The quantification of the telomeric signal is expressed as described for the telomeric probe. (D) Double immunostaining of γ-H2AX and of phospho-S2056-DNA-PKcs in CLL cells after 2 Gy and 10 Gy irradiations was used as a nuclear labeling control for DNA DSBs. (E) Double immunostaining of phospho-S2056-DNA-PKcs and TRF2. Colocalizations are indicated by arrows. (F) Comparisons of phospho-DNA-PKcs-positive cells between CLL-S and CLL-R samples. Bars represent the mean percentage ± SD. The Mann-Whitney U test was used to assess statistical significance: ***P < .001