FIG. 1.

p53 is stabilized and differentially phosphorylated in response to different stress signals. (A and B) Western blot analysis of p53 protein immunoprecipitated from MRC-5 (A) or RKO (B) cells harvested at the indicated time points after treatment with actinomycin D (ActD; 5 nM), CPT (2 μM), or DFX (500 or 250 μM, respectively). The blots were probed with phosphoserine 15- or phosphoserine 20-specific antibodies (α-phos-Ser15 or -20) or PAb1801 (α-p53) to detect total p53 levels. (B) Western blot analysis of p53 protein immunoprecipitated from RKO cells harvested at the indicated time points after treatment with actinomycin D (5 nM), CPT (2 μM), or DFX (250 μM). The blots were probed with phosphoserine 15- or phosphoserine 20-specific antibodies or PAb1801 to detect total p53 levels. (C and D) Western blot analysis of Ser15 and Ser20 phosphorylation of immunoprecipitated p53 protein from MCF-7 (C) or U2OS (D) cell harvested 24 h after treatment with actinomycin D (5 nM), CPT (2 μM), DFX (250 μM), or LLnL (10 μM). The blots were probed with antibodies as described for panel A. −, no treatment.