Internucleosomal DNA fragmentation assay

The cells were dissolved in lysis buffer [10 mM Tris-HCl (pH 7.4), 150 mM NaCl, 5 mM Na-ethylenediaminetetraacetic acid (EDTA), 0.5% Triton X-100, and 0.1 mg/ml proteinase K] for 30 min at RT. DNA from the supernatant was extracted by chloroform/phenol/isoamyl alcohol (24/25/1, v/v/v), and was precipitated by ethanol. The extracted DNA was then transferred to 1.5% agarose gel containing 0.1 µg/ml ethidium bromide (EtBr), and electrophoresis was carried out at 70 V.