Aliquots of the protein extracts were subjected to the western
blot analysis (whole cell extracts in RIPA buffer) or separated by
SDS-PAGE (10% T; BioRad mini protean III cell; BioRad Laboratories
GmbH, München, Germany) for further in-gel digestion (nuclearenriched
extracts). Western blot analysis was performed using
following primary antibodies: phospho-specific (Ser139) and total
histone H2AX (Cell signaling Technology) and β-actin (BD Biosciences).
Secondary antibodies were obtained from Jackson ImmunoResearch
(West Grove, PA). Total and phosphorylated histone
H2AX levels were normalized to β-actin. Western blots were developed
using chemiluminescence detection and analyzed by
densitometry