Construction and Characterization of a Cell Line Deficient in Repair of Mitochondrial, but Not Nuclear, Oxidative DNA Damage

Oxidative base lesions, such as 8-oxoguanine, accumulate in nuclear and mitochondrial DNAs under oxidative stress, resulting in cell death. However, it is not known whether only oxidative lesion accumulated in mitochondrial DNA is involved in such cell death. By introducing human cDNA encoding a nuclear form of 8-oxoG DNA glycosylase (hOGG1-1a) into immortalized mouse embryo fibroblasts lacking Ogg1 gene, we established a cell line which selectively accumulates 8-oxoguanine in mitochondrial DNA under oxidative stress. Selective accumulation of 8-oxoguanine in mitochondrial DNA in this cell line causes degradation of mitochondrial DNA followed by ATP depletion, mitochondrial membrane permeability transition, and Ca²⁺ efflux, which in turn activates calpains to execute cell death. Knockdown of MUTYH which excises adenine opposite 8-oxoG in DNA prevents degradation of mitochondrial DNA and activation of calpain, thus suppressing the cell death induced by menadione.