TP53 and neoplasm: Fig. 3B summarizes the percentage of living, early and late apoptotic, and A−/PI+ cells. To get an indication about underlying pathways Western blot analysis of silenced and myriocin-treated cells was performed. Results of these experiments (Fig. 3C) revealed upregulation of p53 and p21 in silenced (and to a lower extent in myriocin-treated) cells, indicating a pro-apoptotic role of these tumor suppressors when de novo SL synthesis is inhibited. Statistical evaluation of p53 and p21 band intensities is shown in Fig. 3D and E.