Figure 4. Rapamycin-derived cells demonstrate checkpoint control and functional p53Waf1 signaling pathway. (A) Flow cytometry. Rapa-cells were left untreated (left panel) or treated with etoposide (ETO, middle panel) for 1 h (12.5 M), the right panel shows data for the serum-starved cells (48 h). (B) Western blotting. Cells were left untreated, treated with etoposide (ETO) for 1 h (12.5 M) or serum-starved for 48 h. Cell extracts were prepared after 1 h-ETO treatment for p53 (Ser15) staining or 12 h post-ETO treatment for p21Waf1 staining. 1, REF (Ctrl); 2, Rapa, passage 8 (untreated); 3, Rapa, passage 21 (untreated); 4, REF (Etoposide); 5, Rapa, passage 8 (Etoposide); 6, Rapa, passage 21 (Etoposide).