title: Characteristics of DNA repair induced by DNA polymerase β in hepatoma cells after γ-ray irradiation.
abstract: OBJECTIVE
  To investigate the effects of DNA repair induced by DNA polymerase β in hepatoma cells after γ-ray irradiation.
  
  
  METHODS
  Cell nuclei were prepared from mouse model (SMMC LTNM), in which human hepatoma cells are transplanted on nude mice. The nuclei were then irradiated with (60)Co-γ rays at different dose levels or dose rates. A selective inhibitor test was then used to detect the effects of the radiation on DNA repair using N-ethylmaleimide (NEM) and ddTTP as selective inhibitors to DNA polymerases γ and β respectively.
  
  
  RESULTS
  (3)H-TTP incorporation into irradiated nuclei or calf thymus DNA was significantly higher than that the rate at which it is incorporated into non-irradiated nuclei when either DNA polymerase β or γ was inhibited. When both NEM and ddTTP are present, the (3)H-TTP incorporation in irradiated DNA was not significantly different from the non-irradiated nuclei. Furthermore, (3)H-TTP incorporation into DNA of SMMC-LTNM hepatoma nuclei was higher than that of normal hepatocyte nuclei (P < 0.01). This suggests that DNA repair induced by DNA polymerase β was more active in hepatoma cell nuclei than in normal hepatocyte nuclei.
  
  
  CONCLUSIONS
  DNA polymerase β may be more responsive to DNA damage in some tumor cells than that in normal cells, which may facilitate the cells to repair DNA damages from radiation more efficiently.
authors.affiliation: Jian-Ming Cai, Xiu-Long Zheng, Jian-Guo Gao, Department of Radiation Medicine, Second Military Medical University, Shanghai 200433, China.
authors.forename: J M
authors.initials: JM
authors.lastname: Cai
authors.affiliation: Jian-Ming Cai, Xiu-Long Zheng, Jian-Guo Gao, Department of Radiation Medicine, Second Military Medical University, Shanghai 200433, China.
authors.forename: X L
authors.initials: XL
authors.lastname: Zheng
authors.affiliation: Jian-Ming Cai, Xiu-Long Zheng, Jian-Guo Gao, Department of Radiation Medicine, Second Military Medical University, Shanghai 200433, China.
authors.forename: C
authors.initials: C
authors.lastname: Luo
authors.affiliation: Jian-Ming Cai, Xiu-Long Zheng, Jian-Guo Gao, Department of Radiation Medicine, Second Military Medical University, Shanghai 200433, China.
authors.forename: J G
authors.initials: JG
authors.lastname: Gao
authors.affiliation: Jian-Ming Cai, Xiu-Long Zheng, Jian-Guo Gao, Department of Radiation Medicine, Second Military Medical University, Shanghai 200433, China.
authors.forename: T M
authors.initials: TM
authors.lastname: Cheng
keywords: DNA polymerases; DNA repair γ-rays; Liver neoplasms; Liver/radiation effects