Figure 4. Altering p21 protein levels changes the sensitivity of cells to ferroptosis. (A, B) HCT116 (A) or H1299 (B) cells were transfected with two different siRNAs (#1, #2) directed against p21 mRNA for 24 hours, and then treated with erastin or IKE as indicated for an additional 48 hours. As a control, cells were transfected with luciferase siRNA a (siCtrl/C). The right panels in A and B show the corresponding changes in p21 protein levels. (C) HCT-116 cells and HCT116 p21 (-/-) cells were treated with increasing doses of either erastin (left panel) or IKE (right panel) for 48 hours. (D) Left panel: Viability of HT-1080 cells that were transfected with the indicated plasmids expressing p21 variants or an empty vector and then treated with either DMSO or IKE for 48 hours. The panel on the right shows the corresponding immunoblot detecting p21 protein levels. The data in (A, B) represent the mean ± SE for two of three independent experiments, in (C) represent the mean ± SE for two out of four independent experiments, in (D) represent the mean ± SE for three independent experiments. The viability data have been normalized to the DMSO control in (A–C) and to their respective untreated control in (D).