Article

Repair of HZE-Particle-Induced DNA Double-Strand Breaks in Normal Human Fibroblasts

Division of Molecular Radiation Biology, Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Radiation Research (Impact Factor: 2.45). 05/2008; 169(4):437-46. DOI: 10.1667/RR1165.1
Source: PubMed

ABSTRACT DNA damage generated by high-energy and high-Z (HZE) particles is more skewed toward multiply damaged sites or clustered DNA damage than damage induced by low-linear energy transfer (LET) X and γ rays. Clustered DNA damage includes abasic sites, base damages and single- (SSBs) and double-strand breaks (DSBs). This complex DNA damage is difficult to repair and may require coordinated recruitment of multiple DNA repair factors. As a consequence of the production of irreparable clustered lesions, a greater biological effectiveness is observed for HZE-particle radiation than for low-LET radiation. To understand how the inability of cells to rejoin DSBs contributes to the greater biological effectiveness of HZE particles, the kinetics of DSB rejoining and cell survival after exposure of normal human skin fibroblasts to a spectrum of HZE particles was examined. Using γ-H2AX as a surrogate marker for DSB formation and rejoining, the ability of cells to rejoin DSBs was found to decrease with increasing Z; specifically, iron-ion-induced DSBs were repaired at a rate similar to those induced by silicon ions, oxygen ions and γ radiation, but a larger fraction of iron-ion-induced damage was irreparable. Furthermore, both DNA-PKcs (DSB repair factor) and 53BP1 (DSB sensing protein) co-localized with γ-H2AX along the track of dense ionization produced by iron and silicon ions and their focus dissolution kinetics was similar to that of γ-H2AX. Spatial co-localization analysis showed that unlike γ-H2AX and 53BP1, phosphorylated DNA-PKcs was localized only at very specific regions, presumably representing the sites of DSBs within the tracks. Examination of cell survival by clonogenic assay indicated that cell killing was greater for iron ions than for silicon and oxygen ions and γ rays. Collectively, these data demonstrate that the inability of cells to rejoin DSBs within clustered DNA lesions likely contributes to the greater biological effectiveness of HZE particles.

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    • "Particle radiation such as the HZE (High atomic number and energy ions) component of galactic cosmic rays, particle radiation therapy beams or natural radionuclides such as uranium and radon, impose damage through a particle track and by energy deposited radial to this track introducing clustered and complex lesions in the DNA more difficult to repair [2], [3], [4]. Structural damage to DNA is of major significance for cell function and triggers short term cellular responses including further ROS generation in the context of a cellular stress response, changes in gene transcription, signal transduction and induction of cell cycle arrest to ensure that most of the damage is repaired within a few hours [5], [6]. "
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    ABSTRACT: We report the functional and temporal relationship between cellular phenotypes such as oxidative stress, p38MAPK-dependent responses and genomic instability persisting in the progeny of cells exposed to sparsely ionizing low-Linear Energy Transfer (LET) radiation such as X-rays or high-charge and high-energy (HZE) particle high-LET radiation such as 56Fe ions. We found that exposure to low and high-LET radiation increased reactive oxygen species (ROS) levels as a threshold-like response induced independently of radiation quality and dose. This response was sustained for two weeks, which is the period of time when genomic instability is evidenced by increased micronucleus formation frequency and DNA damage associated foci. Indicators for another persisting response sharing phenotypes with stress-induced senescence, including beta galactosidase induction, increased nuclear size, p38MAPK activation and IL-8 production, were induced in the absence of cell proliferation arrest during the first, but not the second week following exposure to high-LET radiation. This response was driven by a p38MAPK-dependent mechanism and was affected by radiation quality and dose. This stress response and elevation of ROS affected genomic instability by distinct pathways. Through interference with p38MAPK activity, we show that radiation-induced stress phenotypes promote genomic instability. In contrast, exposure to physiologically relevant doses of hydrogen peroxide or increasing endogenous ROS levels with a catalase inhibitor reduced the level of genomic instability. Our results implicate persistently elevated ROS following exposure to radiation as a factor contributing to genome stabilization.
    PLoS ONE 10/2014; 9(10):e108234. DOI:10.1371/journal.pone.0108234 · 3.23 Impact Factor
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    • "Our results support previous studies which reported differential ATM kinase activation with varying radiation qualities [35]. It has been previously reported that DSB repair capacity of cells decrease with increasing LET [36]. The higher biological effectiveness of high LET radiation compared to ␥-rays is often explained theoretically by increased clustered ionizations within a small volume of the scale of the DNA helix and across the path of the particle increasing with LET [37]. "
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    • "These proteins, which appear as foci when detected by immunofluorescence staining, are considered to be surrogate markers of DSBs. Using these techniques, experiments reveal important differences in the characteristics of the spatial distribution and repair kinetics of DSBs induced by low-and high-LET radiations (Prise et al 2001, Desai et al 2005, Asaithamby et al 2008). Previously, we estimated the number and distribution of DSBs within nuclei, using amorphous track calculations of the radial dose combined with chromosome models simulated by random walk (RW) (Cucinotta et al 1997, Ponomarev et al 2010, Costes et al 2007). "
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