DNA-PK phosphorylation mediated regulation of NHEJ repair process of DNA double strand break

抄録

In mammals, the most deleterious double strand breaks are repaired by non-homologous end joining (NHEJ) repair pathway. This pathway includes Ku70/86, DNA-PKcs, Artemis, XRCC4, DNA Ligase IV and recently discovered Cernunnos/XLF. In this process DNA-PK is considered an important or crucial enzyme; it phosphorylates many of DNA repair proteins. But, phosphorylation mediated regulation of NHEJ process remains to be clarified. In the present study an attempt has been made to investigate or identify new DNA-PK phosphorylation targets and their possible biological significance in the process of NHEJ repair. We have identified four phosphorylation sites in XRCC4 and two phosphorylation sites in XLF in vitro. By the use of phosphorylation specific antibodies, we have also observed that these phosphorylation sites in XRCC4 are found to be phosphorylated in living cells in response to ionizing radiation. Out of 4, three phosphorylation sites in the XRCC4 are also biologically important in the process of DNA repair, as their mutation into alanine lead to elevated radiosensitivity with deficient DNA repair capability. From the findings of present study we can concluded that XRCC4 phosphorylation in the non homologous end joining repair pathway is an important event in the DSB repair. To analyze the biological importance of XLF phosphorylation further studies are currently under progress. In this study as we have also identified a new threonine phosphorylation site in XRCC4 so, now we are seeking to find out possible interaction with phospho-threonine and FHA domain containing proteins. Supported by Grant-in-Aid for Scientific Research from JSPS and MEXT, Japan.