Figure 4. DNA-damage response triggered by As₂O₃ occurred at telomeres.

A-D. As₂O₃-treated U87 cells were double stained with the indicated antibodies. Representative confocal images showing merged TRF1 (red) with ATR, 53BP1, γ-H₂AX or Mer11 (green) staining in untreated and As₂O₃-treated cells. Scale bar = 5 μm. E. TIF indexes, defined as foci of DNA-damage response factors that coincide with TRF1, were calculated as the percentage of TIF-positive cells among glioma cells treated with As₂O₃. Cells with four or more co-localization foci were scored as TIF-positive. The mean of three independent experiments was reported. Error bars indicate s.d. **P < 0.001, two-tailed Student's t-test. F. Average number of TIFs per nucleus in As₂O₃-treated glioma cells. The mean of three independent experiments with comparable results is shown. Error bars indicate ± s.d. **P < 0.005, two-tailed Student's t-test. G. Chip assays showed the effect of 4 μm As₂O₃ on binding of ATR, γ-H₂AX, 53BP1 or Mer11 to telomeres. Data depict triplicate ChIP experiments, each with technical triplicates of qRT-PCR; **P < 0.01 as compared to control.