Figure 8.

Chk1, Chk2, E2F1, and p73 play a role in p53-independent apoptosis of H1299 cells. (A) Asynchronously growing H1299-shU6 and H1299-shE2F1 cells were treated with the indicated doses of VP16 or camptothecin for 72 h and scored for viability by trypan blue exclusion assay. Data represent three independent experiments. (B, left panel) Saos2-132E cells were exposed or not to 2 ng/mL doxycyline for 24 h before the addition of 10 μM VP16 or 300 nM CPT for 72 h. Cells were then collected and processed for FACS analysis. (Right panels) Extracts were blotted for E2F1 and actin to assure mutant E2F1 induction. (C, left panel) H1299 cells were transfected with Luc, Chk1, Chk2, or p73 siRNAs as in Figure 2 and then treated with 60 μM VP16 for 48 h followed by trypan blue exclusion assay. Data represent five independent experiments. (Right panels) Western blotting of extracts from H1299 cells treated as on the left.