title: Sorting the consequences of ionizing radiation: processing of 8-oxoguanine/abasic site lesions.
abstract: Clustered DNA damage is a hallmark of ionizing radiation. These complex lesions, composed of any combination of oxidized bases, abasic sites, or strand breaks within one helical turn, create a tremendous challenge for the base excision repair system, which must process the damage without generating cytotoxic double strand breaks (DSB). Clustered lesions affect the DNA incision activity of DNA glycosylases and AP endonucleases. Different levels of enzyme inhibition are dependent on lesion identity, orientation and separation. Very little is known about the simultaneous action of both classes of enzymes, which may lead to the creation of DSB. We have developed a novel substrate system of double-labeled hairpin duplexes, which allows the simultaneous determination of enzyme incision and formation of DBS. We use this system to study the processing of four clustered 8-oxoguanine/abasic site lesions by purified mouse Ogg1, human Ape1 and mouse embryonic stem cell nuclear extracts. Ape1 activity is least affected by the presence of a nearby oxidized base. In contrast, an abasic site inhibits the glycosylase and lyase activities of Ogg1 in an orientation-dependent manner. The combined action of both enzymes leads to the preferential formation of DSB with 5'-overhang ends. Processing of clusters by nuclear extracts displayed similar patter of enzyme inhibition and the same preference for avoiding double strand breaks with 3'-overhang ends.
authors.affiliation: Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794-8651, USA.
authors.forename: Kegui
authors.initials: K
authors.lastname: Tian
authors.forename: Monica
authors.initials: M
authors.lastname: McTigue
authors.forename: Carlos
authors.initials: C
authors.lastname: de los Santos
mesh_terms: D000818:Animals; D019757:Carbon-Oxygen Lyases / Q000378:metabolism; D004247:DNA / Q000235:genetics / Q000378:metabolism / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase; D043382:DNA-Formamidopyrimidine Glycosylase; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D009699:N-Glycosyl Hydrolases / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: C024829:8-hydroxyguanine; D006147:Guanine; D004247:DNA; D009699:N-Glycosyl Hydrolases; D043382:DNA-Formamidopyrimidine Glycosylase; D019757:Carbon-Oxygen Lyases; C085108:APEX1 protein, human; C486216:Apex1 protein, mouse; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase