FIGURE 2.

Reversible regulation of p53-induced genes. (A) HT29-tsp53 cells were incubated for 16 h at the permissive temperature (32°C) to increase the expression of p53-responsive transcripts. Cells were then returned for 6 h to the restrictive temperature (38°C) to monitor the attenuation of the p53 response. Unstable transcripts were expected to decrease rapidly, whereas stable mRNAs were expected to remain elevated at the restrictive temperature. Total RNA was collected and subjected to oligonucleotide microarray analysis. Twenty-nine known p53-induced transcripts were significantly induced following 16 h at 32°C. Seven transcripts retained at least 25% of their induced level, while the other 22 retained <25% of their induced levels (indicated stable and unstable, respectively). (B) HT29-tsp53 cells were treated as described in panel A. Two of the stable and seven of the unstable transcripts were selected for further study using qRT-PCR. Each value in panels A and B represents the mean (±SEM) response of the indicated transcript determined from a minimum of three independent experiments. (C) Residual expression determined by quantitative RT-PCR is plotted relative to residual expression determined by microarray for the nine transcripts presented in panel B.