Targeted deletion of alkylpurine-DNA-N-glycosylase in mice eliminates repair of 1,N-6-ethenoadenine and hypoxanthine but not of 3,N-4-ethenocytosine or 8-oxoguanine

It has previously been reported that 1,N-6-ethenoadenine (epsilon A), deaminated adenine (hypoxanthine, Hx), and 7,8-dihydro-8-oxoguanine (8-oxoG), but not 3,N-4-ethenocytosine (epsilon C), are released from DNA in vitro by the DNA repair enzyme alkylpurine-DNA-N-glycosylase (APNG), To assess the potential contribution of APNG to the repair of each of these mutagenic lesions in vivo, we have used cell-free extracts of tissues from APNG-null mutant mice and wild-type controls, The ability of these extracts to cleave defined oligomers containing a single modified base was determined, The results showed that both testes and liver cells of these knockout mice completely lacked activity toward oligonucleotides containing epsilon A and Hx, but retained wild-type levels of activity for epsilon C and 8-oxoG, These findings indicate that (i) the previously identified epsilon A-DNA glycosylase and Hx-DNA glycosylase activities are functions of APNG; (ii) the two structurally closely related mutagenic adducts epsilon A and epsilon C are repaired by separate gene products; and (iii) APNG does not contribute detectably to the repair of 8-oxoG.