Figure 4.

c-Abl kinase regulates irradiation-induced apoptosis by p53-dependent and -independent mechanisms. (A) MCF-7/E6 cells were transfected with 8 μg of pSR, c-Abl, or c-Abl(K-R) vector. Cells were harvested at 48 h and assessed for DNA content. Transfection efficiency as determined by cotransfection with pSV-β-gal vector was 40–45%. (B) (Left) MCF-7/pSR (lanes 1 and 2, counting from the left) and MCF-7/E6 (lanes 3 and 4) were irradiated with 5 Gy (lanes 2 and 4). Lysates prepared at 3 h were subjected to immunoblotting with anti-p53 (Ab-6; Oncogene Science) or anti-p21 (Ab-1; Oncogene Science). (Right) MCF-7/pSR (□), MCF-7/E6 (•), and MCF-7/E6/c-Abl(K-R) (▪) cells were irradiated with the indicated doses. Colony formation was assessed at 10 days. (C) p53^−/− MEFs (33) were transfected with 8 μg of pSR, c-Abl, or c-Abl(K-R) vector. Transfection efficiency as determined by cotransfection of pSV-β-gal vector was 15–20%. Cells were harvested at 48 h and assessed for DNA content. (D) p53^−/− MEFs stably tranfected with pSR vector or c-Abl(K-R) were treated with 10 Gy of ionizing radiation and collected at 120 h for assessment of DNA content. The results (mean ± SEM of three experiments) are expressed as the percentage of apoptotic cells with sub-G₁ DNA.