Figure 4.

E1A facilitates Cyt c release. (A) After drug treatment, Cyt c is released in transformed but not normal cells. IMR90 (top panels), IMR90-E1A (middle panels), and IMR90-E1A/casp9DN (bottom panels) cells were incubated with (“treated”) or without (“not treated”) 50 μM etoposide for 24 hours. The release of Cyt c was visualized by immunofluorescence. White arrows indicate cells with released Cyt c. The chromatin structure was visualized by staining with 4′,6-diamidino-2-phenylindole. The white star indicates a mitotic cell. (B) After etoposide treatment, the rate of apoptosis in IMR90-E1A cells is similar to the increase in the number of IMR90-E1A-casp9DN cells with released Cyt c. (C) Caspase-8 processing is not required for Cyt c release. Cells were treated as in Fig. 3; caspase-8 processing was assessed by immunoblotting. The two species of caspase-8 precursor revealed are probably previously reported isoforms (21).