Figure 1.

GFP-IBD reporter reveals IRIF formation and kinetics. A, shRNA knockdown of the upstream DNA damage response protein ATM, MDC1 or RNF8 abrogates GFP-IBD reporter relocalization to IRIF. shRNA knockdown of endogenous 53BP1 increases foci numbers at 3 and 24 h. Scale bar, 10 μm. B, Formation and resolution of GFP-IBD foci in response to IR depend on time and dose. Scale bar, 10 μm. C, Mean number of GFP-IBD foci per cell ± SD (n > 50) at increasing IR doses evaluated at 3 h (solid circles) and 24 h (solid squares). D, Clonogenic survival of MCF7^Tet-On GFP-IBD cells treated with increasing doses of IR (means ± SD, n = 3). Clonogenicity is modeled as distinct regimes of lower lethality from 0 to 6 Gy (% survival = 330 × e^{−0.89 x (dose in Gy)}, R² = 0.958) and higher lethality from 6 to 12 Gy (% survival = 20.0 × e^{−1.99 x (dose in Gy)}, R² = 0.999). Clonogenic efficiency of untreated MCF7^Tet-On GFP-IBD cells represents 100% control.