The epigenetic landscape shapes smoking-induced mutagenesis by modulating DNA damage susceptibility and repair efficiency.

Lung cancer sequencing efforts have uncovered mutational signatures that are attributed to exposure to the cigarette smoke carcinogen benzo[a]pyrene. Benzo[a]pyrene metabolizes in cells to benzo[a]pyrene diol epoxide (BPDE) and reacts with guanine nucleotides to form bulky BPDE adducts. These DNA adducts block transcription and replication, compromising cell function and survival, and are repaired in human cells by the nucleotide excision repair pathway. Here, we applied high-resolution genomic assays to measure BPDE-induced damage formation and mutagenesis in human cells. We integrated the new damage and mutagenesis data with previous repair, DNA methylation, RNA expression, DNA replication, and chromatin component measurements in the same cell lines, along with lung cancer mutagenesis data. BPDE damage formation is significantly enhanced by DNA methylation and in accessible chromatin regions, including transcribed and early-replicating regions. Binding of transcription factors is associated primarily with reduced, but also enhanced damage formation, depending on the factor. While DNA methylation does not appear to influence repair efficiency, this repair was significantly elevated in accessible chromatin regions, which accumulated fewer mutations. Thus, when damage and repair drive mutagenesis in opposing directions, the final mutational patterns appear to be dictated by the efficiency of repair rather than the frequency of underlying damages.