Formation of DNA-protein Cross-links Mediated by C1'-oxidized Abasic Lesion in Mouse Embryonic Fibroblast Cell-free Extracts

Oxidized abasic residues arise as a major class of DNA damage by a variety of agents involving free radical attack and oxidation of deoxyribose sugar components. 2-deoxyribonolactone (dL) is a C1'-oxidized abasic lesion implicated in DNA strand scission, mutagenesis, and covalent DNA-protein cross-link (DPC). We show here that mammalian cell-free extract give rise to stable DPC formation that is specifically mediated by dL residue. When a duplex DNA containing dL at the site-specific position was incubated with cell-free extracts of Po ${\beta}-proficient$ and -deficient mouse embryonic fibroblast cells, the formation of major dL-mediated DPC was dependent on the presence of DNA polymerase (Pol) ${\beta}$. Formation of dL-specific DPC was also observed with histones and FEN1 nuclease, although the reactivity in forming dL-mediated DPC was significantly higher with Pol ${\beta}$ than with histones or FEN1. DNA repair assay with a defined DPC revealed that the dL lesion once cross-linked with Pol ${\beta}$ was resistant to nucleotide excision repair activity of cell-free extract. Analysis of nucleotide excision repair utilizing a model DNA substrate containing a (6-4) photoproduct suggested that excision process for DPC was inhibited because of DNA single-strand incision at 5' of the lesion. Consequently DPC mediated by dL lesion may not be readily repaired by DNA excision repair pathway but instead function as unusual DNA damage causing a prolonged DNA strand break and trapping of the major base excision repair enzyme.