Phosphorylated E2F4 is able to induce cell cycle reentry and apoptosis in DCRNs. (A) Luciferase activity, normalized to β-galactosidase, in extracts from DCRNs transfected with c-Myc-luciferase, β-galactosidase, and either a constitutively active form of E2F4 (E2F4-CA) or the pcDNA6 plasmid (control) and maintained for 16 h in the presence of the p38MAPK-selective inhibitor SB203580 or vehicle. (B and C) BrdU incorporation (30-min pulse) (B) and proportion of apoptotic nuclei (C) in DCRNs transfected with either E2F4-CA or the pcDNA6 plasmid (control), and maintained for 16 h in the presence of the p38MAPK-selective inhibitor SB203580 or vehicle. (D) Luciferase activity, normalized to β-galactosidase, in extracts from DCRNs transfected with c-Myc-luciferase and β-galactosidase and either wild-type E2F4 (E2F4-WT) or the pcDNA6 plasmid (control) and maintained for 16 h in the presence of either NGF or vehicle. (E and F) BrdU incorporation (30-min pulse) (E) and proportion of apoptotic nuclei (F) in DCRNs transfected with either wild-type E2F4 (E2F4-WT) or the pcDNA6 plasmid (control) and maintained for 16 h in the presence of either NGF or vehicle. (G) Luciferase activity, normalized to β-galactosidase, in extracts from DCRNs transfected with c-Myc-luciferase and β-galactosidase and either a dominant-negative form of E2F4 (E2F4-DN) or the pcDNA6 plasmid (control) and maintained for 16 h in the presence of either NGF or vehicle. (H and I) BrdU incorporation (30-min pulse) (H) and proportion of apoptotic nuclei (I) in DCRNs transfected with either a dominant-negative form of E2F4 (E2F4-DN) or the pcDNA6 plasmid (control), and maintained for 16 h in the presence of either NGF or vehicle. *, P < 0.05; **, P < 0.001; ***, P < 0.005 (Student t test; n = 3).