Figure 6. R137Q is more sensitive to MMS and H₂O₂.

(a,b) Cells (1 × 10⁵ per well) were plated in triplicate in six-well plates. Cells were treated or untreated with different doses of MMS or H₂O₂ for 2 hours. After treatment, the cells were washed with PBS and cultured in a fresh media for 3 days. The number of viable cells in every well was determined following the trypsinization of the cells and counting with a cell counter (CountStar IC1000). The control growth ratio was calculated based on the treated/untreated cell numbers. The data represent the mean ± SD from triplicate wells. Three independent experiments were performed. (c) After treatment with MMS (1.5 mM) or H₂O₂ (0.8 mM), WT, WT/R137Q and R137Q MEFs were lysed to examine γH2AX protein level via Western blot. TUNEL assay results show that a stronger TUNEL-positive fluorescence signal was detected in R137Q MEFs after MMS (d) or H₂O₂ (e) treatment. Scale bar: 10 μm. Cells (3 × 10³) were analyzed, and the percentages of positive cells were calculated and plotted. Values are expressed as the mean ± SD of three independent experiments (d, **P < 0.01; e, ***P < 0.001, Student’s t-test).