Action-at-a-Distance Mutagenesis Induced by Oxidized Guanine in Werner Syndrome Protein-Reduced Human Cells

8-Oxo-7,8-dihydroguanine (G^O, 8-hydroxyguanine) in DNA is one of the most important oxidatively damaged bases and causes G:C → T:A substitution mutations. The Werner syndrome protein (WRN) is a cancer-related RecQ DNA helicase and plays many roles in DNA replication and repair. To examine the relationships between G^O-induced mutations and WRN, shuttle plasmid DNA containing a G^O:C pair in the <i>supF</i> gene was transfected into human U2OS cells, in which WRN was knocked down. The plasmid DNA replicated in the knockdown cells was introduced into an <i>Escherichia coli</i> indicator strain. The knockdown of WRN increased the mutant frequency of the G^O-plasmid DNA. Unexpectedly, however, the WRN knockdown only slightly enhanced the targeted G:C → T:A mutation. Instead, base-substitution mutations at various positions were more frequently detected, with statistical significance. The results obtained in this study suggested that the reduction of the cancer-related WRN induced action-at-a-distance mutagenesis by the G^O:C pair in human cells. In addition, the WRN knockdown decreased the G^O:A-induced A:T → C:G mutations, suggesting that WRN may enhance the mutations caused by G^O in the nucleotide pool