The activity of the DNA-dependent protein kinase (DNA-PK) complex is determinant in the cellular response to nitrogen mustards

The DNA-dependent protein kinase plays a critical role in mammalian DNA dou ble strand break (DSB) repair and in specialized recombination, such as lym phoid V(D)J recombination. Its regulatory subunit Ku (dimer of the Ku70 and Ku80 protein) binds to DNA and recruits the kinase catalytic sub-unit, DNA -PKcs. We show here that three different strains deficient in either the Ku 80 (xrs-6) or DNA-PKcs (V-3, scid) component of DNA-PK are markedly sensiti ve (3.5- to 5-fold) to a group of DNA cross-linking agents, the nitrogen mu stards (NMs) (melphalan and mechlorethamine) as compared to their parental cell line. Importantly, the level of hypersensitivity to these drugs was cl ose to the level of hypersensitivity observed for radiomimetic agents that create DSBs in DNA (bleomycin and neocarzinostatin). In addition, sensitivi ty to NMs was restored to the parental level in the xrs-6 cell line stably transfected with the human Ku80 gene (xrs-6/Ku80), showing unequivocally th at DNA-PK is involved in this phenotype. These results indicate that a func tion of the whole DNA-PK protein complex is involved in the cellular respon se to NMs and suggest that the repair of DNA interstrand cross-links induce d in DNA by NMs involved a DNA-PK dependent pathway that shares common feat ures with DNA DSBs repair. (C) 2000 Societe francaise de biochimie et biolo gie moleculaire/Editions scientifiques et medicales Elsevier SAS.