Table 1.

CHK1 downregulation correlates with p53 transcriptional activity and not with its N-terminal phosphorylationa

InducerPhosphorylation at S15Phosphorylation at S20CHK1 downregulationp53 dependencep21 induction
Daunorubicin+ ND+ + +
Actinomycin D a + + +
γ-Irradiation + +b,c + + +
PALA ND + + +
Hydroxyurea + +d NA
Aphidiolin + ND NA
CPT + +a + +
DFX +a +
  • a HCT116 (p53+/+) and (p53−/−) cells were treated with different agents as described in the text. Cell lysates were analyzed by Western blotting for levels of p53, phosphorylation at S15, CHK1, and p21. Whether CHK1 downregulation requires p53 is indicated in the p53 dependence column. The efficient accumulation of p21 in p53+/+ cells is indicated in the p21 induction column. Note that no p53-independent induction of p21 was observed after any treatment. The superscript letters in the phosphorylation at S20 column refer to the sources of the information: a, Ashcroft et al. (4); b, Shieh et al. (60); c, Chehab et al. (18); d, Gottifredi and Prives (29a); ND, not determined; NA, not applicable.