Acetylation of Abl on K921 is required for transcription-independent apoptosis triggered by DNA strand breaks. (a) Abl+ 3T3 cells expressing WT or K921R Abl mutant were pre-treated with 100 μg/ml of CHX or vehicle for 1 h and then exposed to 10 μΜ bleomycin (Blm) for 1 h. Cells were collected 48 h later, stained with Annexin V/PI and analyzed by flow cytometry. (b) Percent AnnexinV/PI-positive and cell population shown in panel A is graphed. Mean value obtained from three independent experiments with SD is given. *P < 0.01; **P < 0.05. (c) Lysates of mock and Blm-treated cells (10 μM; 1 h), shown in panel A, were adjusted for equal protein content and immunoblotted against PARP (top panel), caspase-3 (middle panel) or tubulin antibody (bottom panel).