Centrosomes stain positive for CHK2 in human colon cancer cells deficient in CHK2. (A) There is no expression of CHK2 in HCT116 CHK2−/− cells. HCT116 WT and HCT116 CHK2 knockout cells were subjected to Western blotting with anti-CHK2 antibody. (B) We did not detect differences in the staining between WT and CHK2 knockout cells. Exponentially growing HCT116 WT and CHK2−/− cells were fixed and immunostained with antibodies against the N-terminal portion of CHK2 (H-300) or the Thr68-phosphorylated form (P-Thr 68) (green). Cells were costained for γ-tubulin (red) and counterstained with DAPI (blue).