Fig. 7. Effect of PML depletion on cell cycle progression in the presence of DNA damage caused by etoposide. GM-847 cells were transfected with control siRNAs (GL2) or PML-specific siRNAs, and at 24 hours following transfection the culture medium was supplemented with 10 µM BrdU. At 48 hours post-transfection the BrdU-containing medium was removed and cells were incubated for another 24 hours in medium containing the indicated concentrations of etoposide. (A) Quantitative determination of cells containing ssDNA foci within PML-NBs. For each sample, more than 500 immunofluorescence labeled cells were evaluated. Bars represent the average of two independent experiments ± s.d. (B) Western blot analysis of soluble cell extracts using an antibody specific for histone H3 phosphorylated on Ser10. The MCM2 protein is used as loading control. (C) Analysis of To-Pro-3-stained cells by laser scanning cytometry.