Protection of BJAB cells against anti-Fas antibody–induced apoptosis by K1 expression. (A) Transfected BJAB cells after treatment with a buffer or 50 ng/mL anti-Fas antibody CH-11 for 24 hours and staining with DAPI. Morphologic features of apoptosis were less frequent in BJABK1 cells than in BJABK1m and BJABXS cells. Representative photomicrographs are shown. Original magnification, × 400. Images are visualized and captured as described in Figure 1D. (B) BJABK1 cells showed less-fragmented DNA than did BJABK1m and BJABXS cells after induction of apoptosis with CH-11. Cells were incubated with 50 ng/mL CH-11 for 24 hours. Genomic DNA was then isolated and analyzed by electrophoresis on an agarose gel stained with ethidium bromide. Similar results were obtained in 2 independent experiments. (C) Transfected BJAB cells were treated with 50 ng/mL for 12 or 24 hours, stained with propidium iodide, and analyzed by flow cytometry. The number of cells containing subdiploid DNA is indicated by the curve under the horizontal bar at the left side of each panel. (D) Transfected BJAB cells were treated with an antibody buffer or 50 ng/mL CH-11 for 2 or 4 hours; cells were labeled with propidium iodide (PI) plus annexin V–FITC and analyzed by flow cytometry. Antibody-treated BJABK1 cells had lower apoptosis rates than did antibody-treated BJABK1m and BJABXS cells. Similar results were obtained in 2 independent experiments.