title: The presence of two distinct 8-oxoguanine repair enzymes in human cells: their potential complementary roles in preventing mutation.
abstract: 8-Oxoguanine (8-oxoG), induced by reactive oxygen species (ROS) and ionizing radiation, is arguably the most important mutagenic lesion in DNA. This oxidized base, because of its mispairing with A, induces GC-->TA transversion mutations often observed spontaneously in tumor cells. The human cDNA encoding the repair enzyme 8-oxoG-DNA glycosylase (OGG-1) has recently been cloned, however, its activity was never detected in cells. Here we show that the apparent lack of this activity could be due to the presence of an 8-oxoG-specific DNA binding protein. Moreover, we demonstrate the presence of two antigenically distinct OGG activities with an identical reaction mechanism in human cell (HeLa) extracts. The 38 kDa OGG-1, identical to the cloned enzyme, cleaves 8-oxoG when paired with cytosine, thymine and guanine but not adenine in DNA. In contrast, the newly discovered 36 kDa OGG-2 prefers 8-oxoG paired with G and A. We propose that OGG-1 and OGG-2 have distinct antimutagenic functions in vivo . OGG-1 prevents mutation by removing 8-oxoG formed in DNA in situ and paired with C, while OGG-2 removes 8-oxoG that is incorporated opposite A in DNA from ROS-induced 8-oxodGTP. We predict that OGG-2 specifically removes such 8-oxoG residues only from the nascent strand, possibly by utilizing the same mechanism as the DNA mismatch repair pathway.
authors.affiliation: Sealy Center for Molecular Science and Department of Human Biological Chemistry and Genetics,University of Texas Medical Branch, Galveston, TX 77555.
authors.forename: T K
authors.initials: TK
authors.lastname: Hazra
authors.forename: T
authors.initials: T
authors.lastname: Izumi
authors.forename: L
authors.initials: L
authors.lastname: Maidt
authors.forename: R A
authors.initials: RA
authors.lastname: Floyd
authors.forename: S
authors.initials: S
authors.lastname: Mitra
mesh_terms: D019757:Carbon-Oxygen Lyases / Q000378:metabolism; D002460:Cell Line; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage; D045647:DNA Glycosylases; D011088:DNA Ligases / Q000235:genetics* / Q000378:metabolism*; D004260:DNA Repair / Q000235:genetics* / Q000502:physiology*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D043223:Deoxyribonuclease IV (Phage T4-Induced); D019204:GTP-Binding Proteins / Q000378:metabolism; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D009699:N-Glycosyl Hydrolases / Q000378:metabolism
chemical_list: C024829:8-hydroxyguanine; D006147:Guanine; D004247:DNA; D043223:Deoxyribonuclease IV (Phage T4-Induced); D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D019204:GTP-Binding Proteins; D019757:Carbon-Oxygen Lyases; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D011088:DNA Ligases