Page 134 - 2014 Printable Abstract Book
P. 134
1
1 ; and Yasuhiko Kobayashi, 1; 2 Japan Atomic Energy Agency, Takasaki, Japan and Gunma University
2
Graduate School of Medicine, Maebashi, Japan
To get the whole picture of heavy-ion induced bystander effects is necessary to better understand
the effect of low-dose irradiation during a manned space flight and the effect of localized irradiation in an
advanced radiotherapy. In the present study, we investigate the dependencies of bystander cell-killing
effect on irradiation dose and radiation quality, and elucidate its molecular mechanism. Normal human
fibroblast WI-38 cells were irradiated with 0.125-2 Gy of carbon ions or γ-rays. After irradiation, irradiated
cells and non-irradiated cells were co-cultured for 24 hours in the upper and lower parts of porous
membrane, respectively. The survival rates of bystander cells investigated by the colony formation assay
decreased with dose at lower than 0.5 Gy and bottomed out at around 80%. In addition, the survival rates
of bystander cells were not significantly different between carbon ions and γ-rays at the same doses. From
these results, it was clearly indicated that the bystander cell-killing effect is dependent in part on
irradiation dose but is independent of radiation quality. Treatment of carboxy-PTIO, a specific scavenger
of nitric oxides, effectively suppressed the reduction of survival rates of bystander cells. This result showed
that nitric oxide has an important role to induce the bystander cell-killing effect. The concentrations of
nitrite, an oxide of nitric oxides, were therefore measured by the modified Saltzman method. There were
negative relationships between the survival rates of bystander cells and the nitrite concentrations of the
medium. From this, it was suggested that the amounts of nitric oxide released to the medium are an
important factor related to the bystander cell-killing effect.
(PS1-60) The increasing spectrum of DNA double-strand break processing mechanisms and the
2
1
problematic of the DSB repair pathway selection. Emil Mladenov, PhD ; Christian Staudt, PhD ; and
1
George Iliakis, PhD, Institute of Medical Radiation Biology, University of Duisburg-Essen, Medical School,
1
Essen, Germany and Institut für Strahlenschutz,Helmholtz Zentrum München, Munich, Germany
2
In higher eukaryotes, the negative impact of double-strand breaks (DSBs) on cellular genome
stability is countered by at least two mechanistically distinct repair pathways: DNA-PK dependent non-
homologous end joining (D-NHEJ) and homologous recombination repair (HRR). Chemical inactivation,
genetic elimination or local failure of factors involved in D-NHEJ or HRR promote an alternative, error-
prone DNA-PK-independent end-joining pathway that serves as a backup (B-NHEJ). By utilizing the sister
chromatid as a template, HRR, is the only repair pathway, capable of fully restoring a DNA molecule that
has sustained a DSB; however HRR only operates in late S and the G2 phases of the cell cycle and is
considered to remove DSBs with relatively slow kinetics. In contrast, D-NHEJ is a fast process quickly
removing DSBs from the genome, in every phase of the cell cycle. However, D-NHEJ has no mechanisms
for restoring sequence information at the DSB, and is associated with base additions or losses that make
it error-prone. Like D-NHEJ, B-NHEJ is also functional throughout the cell cycle, although it shows higher
activity in G2 and drastically reduced activity in G0. B-NHEJ shows higher propensity for sequence
alterations at the junction and it is considered mainly responsible for translocation formation. In higher
eukaryotes, NHEJ appears to be preferred over HRR, even in the G2-phase of the cell cycle, which raises
the question as to why error-prone pathways are chosen over error-free ones. This question is particularly
relevant to our understanding of cellular responses to DNA damage and has been investigated for many
years in our laboratory. Here we will summarize the latest efforts in this direction in our laboratory and
will present a working model underlying repair pathway choice. Emphasis will be placed on the dose
132 | P a g e
1 ; and Yasuhiko Kobayashi, 1; 2 Japan Atomic Energy Agency, Takasaki, Japan and Gunma University
2
Graduate School of Medicine, Maebashi, Japan
To get the whole picture of heavy-ion induced bystander effects is necessary to better understand
the effect of low-dose irradiation during a manned space flight and the effect of localized irradiation in an
advanced radiotherapy. In the present study, we investigate the dependencies of bystander cell-killing
effect on irradiation dose and radiation quality, and elucidate its molecular mechanism. Normal human
fibroblast WI-38 cells were irradiated with 0.125-2 Gy of carbon ions or γ-rays. After irradiation, irradiated
cells and non-irradiated cells were co-cultured for 24 hours in the upper and lower parts of porous
membrane, respectively. The survival rates of bystander cells investigated by the colony formation assay
decreased with dose at lower than 0.5 Gy and bottomed out at around 80%. In addition, the survival rates
of bystander cells were not significantly different between carbon ions and γ-rays at the same doses. From
these results, it was clearly indicated that the bystander cell-killing effect is dependent in part on
irradiation dose but is independent of radiation quality. Treatment of carboxy-PTIO, a specific scavenger
of nitric oxides, effectively suppressed the reduction of survival rates of bystander cells. This result showed
that nitric oxide has an important role to induce the bystander cell-killing effect. The concentrations of
nitrite, an oxide of nitric oxides, were therefore measured by the modified Saltzman method. There were
negative relationships between the survival rates of bystander cells and the nitrite concentrations of the
medium. From this, it was suggested that the amounts of nitric oxide released to the medium are an
important factor related to the bystander cell-killing effect.
(PS1-60) The increasing spectrum of DNA double-strand break processing mechanisms and the
2
1
problematic of the DSB repair pathway selection. Emil Mladenov, PhD ; Christian Staudt, PhD ; and
1
George Iliakis, PhD, Institute of Medical Radiation Biology, University of Duisburg-Essen, Medical School,
1
Essen, Germany and Institut für Strahlenschutz,Helmholtz Zentrum München, Munich, Germany
2
In higher eukaryotes, the negative impact of double-strand breaks (DSBs) on cellular genome
stability is countered by at least two mechanistically distinct repair pathways: DNA-PK dependent non-
homologous end joining (D-NHEJ) and homologous recombination repair (HRR). Chemical inactivation,
genetic elimination or local failure of factors involved in D-NHEJ or HRR promote an alternative, error-
prone DNA-PK-independent end-joining pathway that serves as a backup (B-NHEJ). By utilizing the sister
chromatid as a template, HRR, is the only repair pathway, capable of fully restoring a DNA molecule that
has sustained a DSB; however HRR only operates in late S and the G2 phases of the cell cycle and is
considered to remove DSBs with relatively slow kinetics. In contrast, D-NHEJ is a fast process quickly
removing DSBs from the genome, in every phase of the cell cycle. However, D-NHEJ has no mechanisms
for restoring sequence information at the DSB, and is associated with base additions or losses that make
it error-prone. Like D-NHEJ, B-NHEJ is also functional throughout the cell cycle, although it shows higher
activity in G2 and drastically reduced activity in G0. B-NHEJ shows higher propensity for sequence
alterations at the junction and it is considered mainly responsible for translocation formation. In higher
eukaryotes, NHEJ appears to be preferred over HRR, even in the G2-phase of the cell cycle, which raises
the question as to why error-prone pathways are chosen over error-free ones. This question is particularly
relevant to our understanding of cellular responses to DNA damage and has been investigated for many
years in our laboratory. Here we will summarize the latest efforts in this direction in our laboratory and
will present a working model underlying repair pathway choice. Emphasis will be placed on the dose
132 | P a g e
