Human DNA polymerase iota protects cells against oxidative stress

Human DNA polymerase iota (polι) is a unique member of the Y-family of specialised polymerases that displays a 5′deoxyribose phosphate (dRP) lyase activity. Although polι is well conserved in higher eukaryotes, its role in mammalian cells remains unclear. To investigate the biological importance of polι in human cells, we generated fibroblasts stably downregulating polι (MRC5-polι^KD) and examined their response to several types of DNA-damaging agents. We show that cell lines downregulating polι exhibit hypersensitivity to DNA damage induced by hydrogen peroxide (H₂O₂) or menadione but not to ethylmethane sulphonate (EMS), UVC or UVA. Interestingly, extracts from cells downregulating polι show reduced base excision repair (BER) activity. In addition, polι binds to chromatin after treatment of cells with H ₂O₂ and interacts with the BER factor XRCC1. Finally, green fluorescent protein-tagged polι accumulates at the sites of oxidative DNA damage in living cells. This recruitment is partially mediated by its dRP lyase domain and ubiquitin-binding domains. These data reveal a novel role of human polι in protecting cells from oxidative damage.