Figure 3.
p53 is necessary for nucleolar stress-induced cytoprotection. (a) Verification of the p53-deficient status of Bop1Δ-inducible cell lines D411/C5 and D411/B1. To upregulate p53 protein levels, cells were treated for 6 h with 10 μM 9-aminoacridine (9AA), a strong activator of p5377. Representative immunoblots of p53 and p21 levels are shown in comparison with the parental D411 cell line; β-actin was used as a loading control. Full-size immunoblot images are shown in Supplementary Figure S7. (b) p53-deficient cells are sensitive to CPT and MTX regardless of the induction of Bop1Δ. D411 and its p53-null derivatives were stained with crystal violet after treatment with CPT for 24 h or MTX for 48 h as detailed in Fig. 1c. (c) Bop1Δ induction has little to no effect on the dose response to CPT and MTX in the p53-deficient cell lines. The assay was performed as in Fig. 2. (d) Representative DNA profiles of the D411/C5 cells show that S-phase accumulation caused by 0.4 μM CPT is not affected by Bop1Δ expression on the p53-null background. Cell cycle analysis was performed as in Fig. 1d.