Abstract
DNA double strand breaks (DSBs) are induced by expose to ionizing radiation. The ends of DSB are processed by nuclease, such as Mre11, which is also involved in regulation of cell cycle checkpoints and repair of DSB. Here, we investigated the inhibitory effect on nuclease activity in responses to DSB. It is known that IR induces the foci formation of histone H2AX, and thereby recruitment of NBS1/MRE11/RAD50 complex to damaged sites. However, inhibition of nuclease activity altered the foci formation of phospho-H2AX(gamma-H2AX), and results in failure of NBS1, MDC1, phospho-ATM foci formation. In contrast, western blot analysis revealed phosphorylation of these proteins at a normal revel, suggesting that this disturbance of foci formation is not due to repression of ATM-dependent phosphorylation. Moreover, this nuclease activity are involved in IR-induced cell death. Although Ku70-/- mouse cells show hyper-sensitivity to IR, the inhibition of nuclease alleviated the IR-induced cell death. Since DSB repair is mainly regulated by two pathways; NHEJ(non homologous end joining) and HR(homologous recombination), we are investigating HR ability in Ku70-/- cells using DR-GFP assay.
