Autophosphorylation of DNA-PKCS regulates its dynamics at DNA double-strand breaks

The DNA-dependent protein kinase catalytic subunit (DNA-PKCS) plays an important role during the repair of DNA double-strand breaks (DSBs). It is recruited to DNA ends in the early stages of the nonhomologous end-joining (NHEJ) process, which mediates DSB repair. To study DNA-PKCSrecruitment in vivo, we used a laser system to introduce DSBs in a specified region of the cell nucleus. We show that DNA-PKCSaccumulates at DSB sites in a Ku80-dependent manner, and that neither the kinase activity nor the phosphorylation status of DNA-PKCSinfluences its initial accumulation. However, impairment of both of these functions results in deficient DSB repair and the maintained presence of DNA-PKCSat unrepaired DSBs. The use of photobleaching techniques allowed us to determine that the kinase activity and phosphorylation status of DNA-PKCSinfluence the stability of its binding to DNA ends. We suggest a model in which DNA-PKCSphosphorylation/autophosphorylation facilitates NHEJ by destabilizing the interaction of DNA-PKCSwith the DNA ends.

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