Promutagenicity of 8-Chloroguanine, A Major Inflammation-Induced Halogenated DNA Lesion.

Chronic inflammation is closely associated with cancer development. One possible mechanism for inflammation-induced carcinogenesis is DNA damage caused by reactive halogen species, such as hypochlorous acid, which is released by myeloperoxidase to kill pathogens. Hypochlorous acid can attack genomic DNA to produce 8-chloro-2'-deoxyguanosine (ClG) as a major lesion. It has been postulated that ClG promotes mutagenic replication using its conformer; yet, the structural basis for ClG-induced mutagenesis is unknown. We obtained crystal structures and kinetics data for nucleotide incorporation past a templating ClG using human DNA polymerase β (polβ) as a model enzyme for high-fidelity DNA polymerases. The structures showed that ClG formed base pairs with incoming dCTP and dGTP using its and conformers, respectively. Kinetic studies showed that polβ incorporated dGTP only 15-fold less efficiently than dCTP, suggesting that replication across ClG is promutagenic. Two hydrogen bonds between -ClG and -dGTP and a water-mediated hydrogen bond appeared to facilitate mutagenic replication opposite the major halogenated guanine lesion. These results suggest that ClG in DNA promotes G to C transversion mutations by forming Hoogsteen base pairing between -ClG and -G during DNA synthesis.