Figure 6. Ezh2 knockdown decreases DSB repair efficiency and increases cellular sensitivity to IR. (A) U2OS cells stably expressing Ezh2-shRNA, and U2OS cells stably expressing Ezh2-shRNA reconstituted with shRNA-resistant GFP-Ezh2 construct were exposed to 40 Gy ionizing radiation. Cells were harvested immediately to determine total damage and after 5 hrs to determine the DNA damage remaining. Total DNA damage immediately after IR is referred to as 100% DNA damage. (B) U2OS cells transfected with control shRNA, two different Ezh2- shRNAs, or Ezh2-shRNA reconstituted with shRNA -esistant GFP-Ezh2 construct were plated at low density. Cells were then exposed to 0, 2, 4, or 6 Gy and left to recover for 2 wk. The cells were then fixed and stained and colonies were counted. Each colony represents a surviving cell, and the percent survival is plotted for each dose of IR.