Involvement of DNA-dependent protein kinase in regulation of stress-induced JNK activation

DNA-dependent protein kinase (DNA-PK) is composed of a 460-kDa catalytic su bunit and the regulatory subunits Ku70 and Ku80. The complex is activated o n DNA damage and plays an essential role in double-strand-break repair and V(D)J recombination. In addition, DNA-PK is involved in S-phase checkpoint arrest following irradiation, although its role in damage-induced checkpoin t arrest is not clear. In an effort to understand the role of DNA-PK in dam age signaling, human and mouse cells containing the DNA-PK catalytic subuni t (DNA-PKcs proficient) were compared with those lacking DNA-PKcs. for c-Ju n N-terminal kinase (JNK) activity that mediates physiologic responses to D NA damage. The DNA-PKcs-proficient cells showed much tighter regulation of JNK activity after DNA damage, while the level of JNK protein in both cell lines remained unchanged. The JNK proteins physically associated with DNA-P Kcs and Ku70/Ku80 heterodimer, and the interaction was significantly stimul ated after DNA damage. Various JNK isoforms not only contained a DNA-PK pho sphorylation consensus site (serine followed by glutamine) but also were ph osphorylated by DNA-PK in vitro. Together, our results suggest that DNA dam age induces physical interaction between DNA-PK and JNK, which may in turn negatively affect JNK activity through JNK phosphorylation by DNA-PK.