Δ122p53 is defective for p53 functions. Splenocytes were treated with 1 μg/mL amsacrine, and RNA was isolated after 5 hours; p53 transcriptional profiling was carried out by microarray. (A) Comparison of the average fluorescence of 125 p53 target gene transcripts25 from p53+/+ mice with and without amsacrine was performed by plotting transcript levels from amsacrine-treated p53+/+ cells (y-axis) against untreated p53+/+ cells (x-axis). Transcripts above the line indicate up-regulation by wild-type p53; transcripts below the line, down-regulation; and transcripts on the line, the same or not regulated by this stress. (B) Comparison of the average fluorescence of the 125 p53 target gene transcripts from Δ122p53 mice; amsacrine-treated Δ122p53 cells (y-axis) are plotted against untreated Δ122p53 cells (x-axis). (C) Selected p53 target genes were validated by quantitative RT-PCR. Treated and untreated splenocytes from each of the genotypes were analyzed. Untreated samples were assigned a value of 1.0. **P < .001. ***P < .0001. (D) Thymocytes from p53+/+, p53−/−, p53mΔpro (mice homozygous for a deletion in the p53 proline domain), and Δ122p53 mice were irradiated with 4 Gy γ-radiation and harvested after 6 hours; apoptosis was assayed by staining for annexin V and propidium iodide. *P < .05. (E) Mice were treated with 2 Gy γ-radiation and 24 hours later pulsed with BrdU to label cells in S phase. Bone marrow was harvested, and the proportion of BrdU positive cells was determined by flow cytometry. **P < .01. ***P < .001. All experiments were performed using cells from 3 mice per genotype.
