Strand-specific processing of 8-oxoguanine by the human mismatch repair pathway: inefficient removal of 8-oxoguanine paired with adenine or cytosine.
Genomic DNA and its precursors are susceptible to oxidation during aerobic cellular metabolism, and at least five distinct repair activities target a single common lesion, 7,8-dihydro-8-oxoguanine (8-oxoG). The human mismatch repair (MMR) pathway, which has been implicated in an apoptotic response to covalent DNA damage, is likely to encounter 8-oxoG in both the parental and daughter strand during replication. Here, we show that lesions containing 8-oxoG paired with adenine or cytosine, which are most likely to arise during replication, are not efficiently processed by the mismatch repair system. Lesions containing 8-oxoG paired with thymine or guanine, which are unlikely to arise, are excised in an MSH2/MSH6-dependent manner as effectively as the corresponding mismatches when placed in a context that reflects the daughter strand during replication. Using a newly developed assay based on methylation sensitivity, we characterized strand-excision events opposite 8-oxoG situated to reflect placement in the parental strand. Lesions that efficiently trigger strand excision and resynthesis (8-oxoG paired with thymine or guanine) result in adenine or cytosine insertion opposite 8-oxoG. These latter pairings are poor substrates for further action by mismatch repair, but precursors for alternative pathways with non-mutagenic outcomes. We suggest that the lesions most likely to be encountered by the human mismatch repair pathway during replication, 8-oxoG.A or 8-oxoG.C, are likely to escape processing in either strand by this system. Taken together, these data suggest that the human mismatch repair pathway is not a major contributor to removal of misincorporated 8-oxoG, nor is it likely to trigger repeated attempts at lesion processing.
Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Erik D
ED
Larson
Keith
K
Iams
James T
JT
Drummond
D000225:Adenine / Q000378:metabolism*; D020137:Base Pair Mismatch; D001483:Base Sequence; D045744:Cell Line, Tumor; D003596:Cytosine / Q000378:metabolism*; D004249:DNA Damage; D004260:DNA Repair; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008957:Models, Genetic
C024829:8-hydroxyguanine; D006147:Guanine; D003596:Cytosine; D000225:Adenine