Figure 2. DNA damage or chromatin relaxation induces E2F1 and p19 through ATM/ATR-Chk1/Chk2 signaling.

A. HEK-293 cells, previously treated with 10 µM Ku-55933 or 5 mM caffeine for 1 h, were exposed to 40 J/m² UV or 50 ng/ml neocarzinostatin (left panel) or incubated with 100 µM chloroquine or 200 nM TSA or subjected to hypotonic medium (right panel). B. HEK-293 cells, previously treated with 10 µM Ku-55933 or 15 nM SB-218078 or 20 nM Chk2 inhibitor for 1 h, were exposed to 40 J/m² UV or 50 ng/ml neocarzinostatin (left panel) or incubated with 100 µM chloroquine or 200 nM TSA or subjected to hypotonic medium (right panel). In (A) and (B) after 4 h, cells were harvested and subjected to northern blot analysis using a ³²P-labelled probe specific for human p19 mRNA and reprobed for E2F1 and β-tubulin mRNA. C and D. ATM-deficient Seckel cells (C) or primary human fibroblasts C5RO (D), previously treated with 10 µM Ku-55933, were exposed to 40 J/m² UV or 50 ng/ml neocarzinostatin or incubated with 100 µM chloroquine or 200 nM TSA or subjected to hypotonic medium (50 mM NaCl). In (C) and (D) after 4 h, cells were harvested and subjected to northern blot analysis using a ³²P-labelled probe specific for human p19 mRNA and reprobed for β-tubulin mRNA. Each figure shows a representative autoradiograph of three independent experiments with similar results. Densitometric analysis of p19 and E2F1 are represented in the lower panels. Bars represent the mean ± S.D. of three experiments. Student’s t-test was used to compare treated and non-treated samples (* p<0.05, at least). None (N), β-tubulin (β-tub), caffeine (C), Ku-55933 (K), chloroquine (chlo), hypotonic medium (hypo), SB-218078 (SB), Chk2 inhibitor (2I).