title: Factors influencing the removal of thymine glycol from DNA in gamma-irradiated human cells.
abstract: The toxic and mutagenic effects of ionizing radiation are believed to be caused by damage to cellular DNA. We have made use of a novel immunoassay for thymine glycol to examine the removal of this lesion from the DNA of irradiated human cells. Because of the sensitivity of the assay, we have been able to keep the radiation doses at or below the standard clinical dose of 2 Gy. Our initial observations indicated that although removal of thymine glycol is > 80% complete by 4 h post-irradiation with 2 Gy, there is a lag of 30-60 min before repair commences. However, if cells are irradiated with 0.25 Gy 4 h prior to the 2-Gy dose, removal of the thymine glycols commences immediately after the second irradiation, suggesting that repair of thymine glycol is inducible. Our current studies are directed at two aspects of the repair process, (1) factors involved in the repair process leading up to and including glycosylase-mediated removal of thymine glycol and (2) the control of the inducible response. We have observed that mutation of the XPG gene drastically reduced the level and rate of global removal of thymine glycol (induced by 2-Gy irradiation), and there was no evidence for an inducible response. Similar results were seen with a Cockayne syndrome B (CSB) cell line. We have also examined repair in quiescent and phytohemagglutinin-stimulated human lymphocytes. Both show similar kinetics for the rate of removal of thymine glycol under induced and noninduced conditions.
authors.affiliation: Experimental Oncology Cross Cancer Institute, Edmonton, Alberta T6G 1Z2, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Weinfeld
authors.forename: J Z
authors.initials: JZ
authors.lastname: Xing
authors.forename: J
authors.initials: J
authors.lastname: Lee
authors.forename: S A
authors.initials: SA
authors.lastname: Leadon
authors.forename: P K
authors.initials: PK
authors.lastname: Cooper
authors.forename: X C
authors.initials: XC
authors.lastname: Le
mesh_terms: D000818:Animals; D002478:Cells, Cultured / Q000528:radiation effects; D003057:Cockayne Syndrome / Q000235:genetics / Q000473:pathology; D004247:DNA / Q000378:metabolism* / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair; D004270:DNA, Circular / Q000528:radiation effects; D004274:DNA, Recombinant / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D004307:Dose-Response Relationship, Radiation; D019075:Electrophoresis, Capillary; D004720:Endonucleases; D019084:Fluorescent Antibody Technique, Indirect; D005720:Gamma Rays; D006801:Humans; D008213:Lymphocyte Activation / Q000235:genetics; D008214:Lymphocytes / Q000378:metabolism / Q000528:radiation effects; D051379:Mice; D009687:Nuclear Proteins; D010957:Plasmids / Q000528:radiation effects; D051381:Rats; D016192:Resting Phase, Cell Cycle; D012680:Sensitivity and Specificity; D013941:Thymine / Q000031:analogs & derivatives* / Q000032:analysis / Q000378:metabolism*; D014157:Transcription Factors; D014983:Xeroderma Pigmentosum / Q000235:genetics / Q000473:pathology; D000099250:DNA Excision Repair Protein ERCC-5
chemical_list: D004247:DNA; D004270:DNA, Circular; D004274:DNA, Recombinant; D004268:DNA-Binding Proteins; D004720:Endonucleases; D009687:Nuclear Proteins; D013941:Thymine; D014157:Transcription Factors; D000099250:DNA Excision Repair Protein ERCC-5; C029389:thymine glycol