Cellular Repair of DNA-DNA Cross-Links Induced by 1,2,3,4-Diepoxybutane.

Xenobiotic-induced interstrand DNA-DNA cross-links (ICL) interfere with transcription and replication and can be converted to toxic DNA double strand breaks. In this work, we investigated cellular responses to 1,4--(guan-7-yl)-2,3-butanediol (-N7G-BD) cross-links induced by 1,2,3,4-diepoxybutane (DEB). High pressure liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ESI⁺-MS/MS) assays were used to quantify the formation and repair of -N7G-BD cross-links in wild-type Chinese hamster lung fibroblasts (V79) and the corresponding isogenic clones V-H1 and V-H4, deficient in the and genes, respectively. Both V-H1 and V-H4 cells exhibited enhanced sensitivity to DEB-induced cell death and elevated -N7G-BD cross-links. However, relatively modest increases of -N7G-BD adduct levels in V-H4 clones did not correlate with their hypersensitivity to DEB. Further, -N7G-BD levels were not elevated in DEB-treated human clones with defects in the or genes. Comet assays and γ-H2AX focus analyses conducted with hamster cells revealed that ICL removal was associated with chromosomal double strand break formation, and that these breaks persisted in V-H4 cells as compared to control cells. Our findings suggest that ICL repair in cells with defects in the Fanconi anemia repair pathway is associated with aberrant re-joining of repair-induced double strand breaks, potentially resulting in lethal chromosome rearrangements.