DEFECTIVE-DNA CROSS-LINK REMOVAL IN CHINESE-HAMSTER CELL MUTANTS HYPERSENSITIVE TO BIFUNCTIONAL ALKYLATING-AGENTS

  • 1 January 1985
    • journal article
    • research article
    • Vol. 45  (4) , 1737-1743
Abstract
DNA repair-deficient mutants from 5 genetic complementation groups isolated previously from Chinese hamster cells were assayed for survival after exposure to the bifunctional alkylating agents mitomycin C or diepoxybutane. Groups 1, 3 and 5 exhibited 1.6- to 3-fold hypersensitivity compared to the wild-type cells; Groups 2 and 4 exhibited extraordinary hypersensitivity (30- to 90-fold). Mutants from Groups 1 and 2 were exposed to 22 other bifunctional alkylating agents in a rapid assay that compared cytotoxicity of the mutants to the wild-type parental strain, AA8. With all but 2 of the compounds, the Group 2 mutant (UV4) was 15- to 60-fold more sensitive than AA8 or the Group 1 mutant (UV5). UV4 showed only 6-fold hypersensitivity to quinacrine mustard. Alkaline elution measurements showed that this compound produced few DNA interstrand cross-links but numerous strand breaks that were revealed by proteinase treatment. The extreme hypersensitivity of mutants from Groups 2 and 4 appeared specific for compounds the main cytotoxic lesions of which were DNA crosslinks. Mutant UV5 was only 1- to 4-fold hypersensitive to all the compounds. Repair kinetics of DNA interstrand crosslink production and removal was measured by alkaline elution for AA8 and mutants UV4 and UV5 after exposure to diepoxybutane. Although the initial number of crosslinks was similar for the 3 cell lines, during 24-h incubation, the efficiency of removal of crosslinks was lowest in UV4 and intermediate in UV5. Apparently, the different levels of sensitivity of the 5 complementation groups to bifunctional alkylation damage are specifically related to different efficiencies of DNA crosslink removal. The phenotype of hypersensitivity to both UV radiation and crosslink damage exhibited by the mutants in Groups 2 and 4 appears to differ from those of the known human DNA repair syndromes.