Figure 4. Caspase-8 DEDs activate p53, p21 and trigger apoptosis or cell cycle arrest.

A. Bright field images of NB7 neuroblastoma cells expressing DED-GFP at passages 8 (early) and 30 (late) (scale bar = 10 µm). At earlier passages, a few multinucleated DED-expressing cells are detectable (yellow arrows). By passage 30, DED-GFP cells show high numbers of elongated or apoptotic cells. Late passage cells were stained with propidium iodide and assessed by flow cytometry to quantitate the sub-G1 apoptotic population at passage 30. B. Confocal microscopy confirmed the increase in nuclear expression of p21 and p53 (two markers of cell cycle arrest) and the cytoplasmic upregulation of the neuronal differentiation marker MAP2 in DED-GFP cells at passage 25 (scale bar = 10 µm). White arrows show nuclear accumulation of p21 and p53 (red channel).