FIG. 1.
DNA damage-induced p53 downregulates CHK1 protein levels. (A) HCT116 colorectal cancer cells (p53+/+) and its derivative p53−/− cells were treated with daunorubicin (0.22 μM) and harvested at the indicated times after treatment. Cell lysates were then subjected to Western blot analysis with antibodies specific for p53, CHK1, CHK2, and p21 as described in the text. Actin levels were probed as a loading control. (B) Densitrometric analysis of CHK1 and CHK2 protein levels after treatment of HCT116 (p53+/+) and its derivative (p53−/−) with daunorubicin. The data represent the reduction with respect to the value obtained in three independent experiments for the untreated controls (taken as 1). All samples were normalized to their respective actin levels. (C) Cells were treated as described for panel A, and at the indicated times (hours [hs]) were subjected to cell cycle analysis as described in the text.