Chk1 antibody

For immunocytochemistry (ICC), cells incubated on coverslips were fixed by 10% neutral buffered formalin (Biosesang, Seongnam, Korea). After then, the cell was permeabilized and incubated with anti-phospho-histone H2A.X (Ser139) antibody (Merck Millipore, Darmstadt, Germany) or anti-Rad51 antibody (Abcam, Cambridge, UK) at 4 °C overnight. For IF, paraffin sections of xenograft tumors were used. The slides were incubated with the Chk1 antibody (Abcam) or anti-phospho-histone H2A.X (Ser139) antibody (Merck Millipore) at 4 °C overnight. For immunostaining microscopy, images were visualized by confocal laser scanning microscope (LSM 700, Carl Zeiss, Oberkochen, Germany), and each image was captured with identical exposure settings. For immunohistochemistry, staining with cleaved caspase-3 antibody (Cell Signaling Technology, Beverly, MA, USA) was performed using Vectastatin ABC kit (Vector Laboratories, Burlingame, CA, USA) according to the manufacturer’s instruction. Staining was visualized by NovaRED substrate (Vector Laboratories), and counterstaining was performed with hematoxylin.

Mouse p53 clone DO-1 (used at 1/200 dilution for immunoblotting) was purchased from Santa Cruz Biotechnology, Dallas, TX, USA; antibodies against phospho-p53 S15 (used at 1/500 dilution for immunoblotting), CHK2 phospho-CHK2 T68 (used at 1/500 dilution for immunoblotting), pATM/ATR substrate (used at 1/200 dilution for immunoblotting and 1/100 for immunofluorescence) and phospho-ATM S1981 (used at 1/1000 dilution for immunoblotting) were from Cell Signalling Technology, Danvers, MA, USA. Antibodies against Cip1/WAF-1/p21 were from Upstate, Lancaster, NY, USA (used at 1/100 dilution for immunoblotting), ATM (used at 1/1000 dilution for immunoblotting) and rabbit RAD51 antibodies (used at 1/200 dilution for immunofluorescence) were from Calbiochem, San Diego, CA, USA, Ki-67 from Dako, Santa Clara, CA, USA, and CHK1 antibody were from Abcam, Cambridge, UK.