Figure 4.

p120^E4F-mediated growth arrest is pRB-dependent. (A) Rb^+/+ (Upper) or Rb^−/− (Lower) mouse fibroblasts were transfected with the pcDNA–p120^E4F plasmid. Twenty-four hours after transfection with the indicated plasmids, cells were assessed for BrdUrd uptake in their DNA (14 h in BrdUrd) as a marker of cell proliferation. Cells were fixed and labeled with 4′,6′-diamidino-2-phenylindole (DAPI) (blue). p120^E4F-expressing cells were identified by immunofluoresence by using anti-human E4F (E4F 88.2) (red) and monitored for BrdUrd incorporation by using an anti-BrdUrd-specific Ab (green). (B) Diagram showing the average of four independent experiments (200 cells counted per experiment) performed as reported in A. Average of similar experiments performed in p107/p130^−/− cells are also shown as indicated. As a control, Rb^−/− cells are also transfected with p34(RB).