FIG. 6.
ATR is dispensable for DSB-induced cyclin D1 loss. (A and B) ATR deletion does not alter cyclin D1 degradation following DNA damage. ATRflox/− CET fibroblasts were treated with 4-OH tamoxifen (TAM) for 24 h, followed by incubation at 37°C for 12 h to allow sufficient ATR depletion. Cells were then irradiated (A) or treated with 2 mM HU (B) as indicated, and the cyclin D1 levels were assessed by immunoblotting. Significant ATR deletion was obtained by TAM treatment. (C) siRNA-mediated attenuation of ATR expression does not inhibit cyclin D1 phosphorylation or degradation. U20S cells were transfected with ATR-specific siRNA and irradiated as indicated 60 h after siRNA delivery. Cyclin D1 phosphorylation and total cyclin D1 and the efficiency of ATR knockdown were assessed by immunoblotting.