Figure 2. CHEK1 is not required for decatenation G₂ checkpoint function.

Diploid fibroblast lines were electroporated with non-targeting control (NTC) siRNA or siRNA directed towards CHEK1. A. Cells were harvested for immunoblot analysis of CHEK1 protein levels at 48 h after electroporation when protein depletion was maximal. Control and CHEK1-depleted cells were treated with 1.5 Gy IR or 6 J/m² UVC 30 min before cell harvest to test for ATM-dependent phosphorylation of CHEK2 and ATR-dependent phosphorylation of CHEK1. B. NTC-treated and CHEK1-depleted NHDFs were subjected to the mitotic index reduction assay as described in Figure 1B. (+sd, n=3). Depletion of CHEK1 also appeared to attenuate the ICRF-193-induced inhibition of the mitotic compartment emptying. C. NTC-treated and CHEK1-depleted NHF1hTERT cells were subjected to the mitotic entry assay described in Figure 1C. Similar to the ATR-depleted fibroblasts, 4 μM ICRF-193 blocked the accumulation of mitotic cells in the CHEK1-depleted fibroblasts, suggesting that CHEK1 is not required for decatenation G₂ checkpoint function. Results are representative of three independent experiments.