Quantifying DNA Damage Response via 53BP1 Kinetics

IR-induced 53BP1 kinetics were determined as previously outlined with modifications (19 (link)). Cells were grown on coverslips one day before the experiment and on the day of the experiment, cells were exposed to 1Gy of γ-rays. At different time points after IR (see figure), cells were washed twice with ice cold 1× PBS and fixed with 4% paraformaldehyde (in 1× PBS) for 20 min at RT, washed 5 times with 1× PBS, and incubated in 0.5% Triton X-100 on ice for 10 min. Cells were washed 5 times with 1× PBS and incubated in blocking solution (5% goat serum (Jackson Immuno Research) in 1× PBS) overnight. The blocking solution was then replaced with the 53BP1 (SC-22760, Santa Cruz) primary antibody diluted in 5% goat serum in 1x PBS and the cells were incubated for 2 h. Cells were then washed 5 times with wash buffer (1% BSA in 1× PBS). Cells were incubated with the Alexa Fluor 488 (1:1000) (Molecular Probes) secondary antibody in 1% BSA, 2.5% goat serum in 1× PBS for 1 h in the dark, followed by five washes. After the last wash, cells were mounted in VectaShield mounting medium containing DAPI. The images were acquired using a Zeiss Axio Imager fluorescence microscope utilizing a 63× oil objective. ≥100 cells were analyzed for each time point.