UV SENSITIVITY AND IMPAIRED NUCLEOTIDE EXCISION-REPAIR IN DNA-DEPENDENT PROTEIN-KINASE MUTANT-CELLS

DNA-dependent protein kinase (DNA-PK), a member of the phosphatidyl-in ositol (PI)3-kinase family, is involved in the repair of DNA double-st rand breaks, Its regulatory subunit, Ku, binds to DNA and recruits the kinase catalytic subunit (DNA-PKCS), We show here a new role of DNA-P K in the modulation of the process of nucleotide excision repair (NER) in vivo since, as compared with their respective parental cell lines, DNA-PK mutants (scid, V-3 and xrs 6 cells) exhibit sensitivity to UV- C irradiation (2.0- to 2.5-fold) and cisplatin (similar to 3- to 4-fol d) associated with a decreased activity (40-55%) of unscheduled DNA sy nthesis after UV-C irradiation, Moreover, we observed that wortmannin sensitized parental cells in vivo when combined with either cisplatin or UV-C light, but had no effect on the DNA-PKCS deficient scid cells, Despite a lower repair synthesis activity (similar to 2-fold) measure d in vitro with nuclear cell extracts from DNA-PK mutants, a direct in volvement of DNA-PK in the NER reaction in vitro has not been observed , This study establishes a regulatory function of DNA-PK in the NER pr ocess in vivo but rules out a physical role of the complex in the repa ir machinery at the site of the DNA lesion.