Reduction of Werner Syndrome Protein Enhances G:C → A:T Transition by<i>O</i>⁶‑Methylguanine in Human Cells

<i>O</i>⁶-Methylguanine (<i>O</i>⁶-MeG) is a damaged base produced by methylating reagents. The Werner syndrome protein (WRN) is a cancer-related human DNA helicase. The effects of WRN reduction on <i>O</i>⁶-MeG-caused mutagenesis were assessed by an siRNA-mediated knockdown in human U2OS cells, using a shuttle plasmid with a single <i>O</i>⁶-MeG base in the <i>supF</i> gene. The plasmid DNA was replicated in the cells, isolated, and electroporated into an <i>Escherichia coli</i> indicator strain. The lowered amount of WRN increased the frequency of mutations induced by <i>O</i>⁶-MeG, mainly G:C → A:T substitution. The increased mutation rate suggested that the cancer-related WRN suppresses the G:C → A:T substitution by <i>O</i>⁶-MeG in human cells