A role for Chk2 in DNA damage induced mitotic delays in human colorectal cancer cells.

Progression into mitosis in the presence of DNA damage leads to spindle checkpoint (SAC) dependent mitotic delays and cytokinesis failure. In Drosophila embryos, DNA damage does not delay mitotic entry but triggers Checkpoint kinase-2 (Chk2) kinase dependent delays in mitotic exit. It is unclear if damage associated mitotic delays in human cells result from kinase signaling or breaks in centromere DNA that disrupt kinetochore function and activate the SAC. We show that transgenic expression of Human Chk2 in a Drosophila chk2 mutant background restores damage induced mitotic delays during early embryogenesis. Parental HCT116 colorectal cancer cells that progress into mitosis following DNA damage, due to either G(2) checkpoint adaptation or G(2) checkpoint abrogation by caffeine or the Chk1 inhibitor UCN-01, delay in mitosis and show high rates of cytokinesis failure. Significantly, these mitotic responses are suppressed in HCT116 chk2 knockout cells, and the response is restored by transgenic expression of wild type Chk2. However, both parental and chk2(-/-)HCT116 cells arrested in G(2) for prolonged periods by DNA damage prior to release from the G(2) block do show significant mitotic delays. Chk2 thus appears to have a conserved function in control of mitotic progression following G(2)/M transition with DNA damage. However, prolonged G(2) arrest with DNA damage can trigger Chk2 independent mitotic delays that may be secondary to kinetochore disruption.