Fig. 2. Activation of ATM and ATR in HGPS and RD cells. (A) CPT treatment was done by incubating the cells with 4 µM camptothecin for 1 hour. Cells with or without treatment were fixed with cold methanol (–20°C) followed by immunofluorescence microscopy with ATM antibody staining. Blue, DAPI; red, ATM. (B) UV treatment was performed by irradiating the cells with 20 J/m² UV. Two hours after the treatment, the cells with or without treatment were fixed and stained with ATR antibody for immunofluorescence microscopy. Blue, DAPI; red, ATR. (C) HeLa cells grown on coverslips were transfected with the plasmid for expressing progerin (LA50) or empty parent vector. Twenty-four hours after transfection, the cells were irradiated with 20 J/m² UV or mock treated. After additional 2-hour culture, the cells were processed for immunofluorescence microscopy. Blue, DAPI; green or red, ATR. Photomicrographs were taken at 63x magnification. Bar, 50 µm.