Effect of Dose Rate on the Induction of DNA Double-Strand Breaks in Eucaryotic Cells

Frankenberg-Schwager, M.; Frankenberg, D.; Adamczyk, C.; Blöcher, Detlef

doi:10.2307/3575532

Cited by 34 publications

(13 citation statements)

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“…The critical role of DNA double-strand breaks (DSB) and chromosome aberrations produced by ionizing radiation in causing cell death has long been recognised (9, 10). DSB formation results in rapid phosphorylation of histone H2AX (γH2AX).…”

Section: Introductionmentioning

confidence: 99%

A Small Interfering RNA Screen of Genes Involved in DNA Repair Identifies Tumor-Specific Radiosensitization by POLQ Knockdown

Higgins

Prevo²,

Lee³

et al. 2010

Cancer Research

126

109

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The effectiveness of radiotherapy treatment could be significantly improved if tumour cells could be rendered more sensitive to ionizing radiation without altering the sensitivity of normal tissues. However many of the key, therapeutically exploitable mechanisms that determine intrinsic tumour radiosensitivity are largely unknown. We have conducted a siRNA screen of 200 genes involved in DNA damage repair aimed at identifying genes whose knockdown increased tumour radiosensitivity. Parallel siRNA screens were conducted in irradiated and unirradiated tumour cells (SQ20B) and irradiated normal tissue cells (MRC5). Using γH2AX foci at 24 hours after ionising radiation we identified several genes such as BRCA2, Lig IV and XRCC5, whose knockdown is known to cause increased cell radiosensitivity thereby validating the primary screening endpoint. In addition we identified POLQ (DNA polymerase theta) as a potential tumour-specific target. Subsequent investigations demonstrated that POLQ knockdown resulted in radiosensitisation of a panel of tumour cell lines from different primary sites, whilst having little or no effect on normal tissue cell lines. These findings raise the possibility that POLQ inhibition might be used clinically to cause tumour specific radiosensitisation.

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Section: Introductionmentioning

confidence: 99%

A Small Interfering RNA Screen of Genes Involved in DNA Repair Identifies Tumor-Specific Radiosensitization by POLQ Knockdown

Higgins

Prevo²,

Lee³

et al. 2010

Cancer Research

126

109

View full text Add to dashboard Cite

show abstract

“…Early clonogenic cell survival studies in mammalian cells based on the fraction of cells surviving different rates of ionizing radiation showed that as the dose rate was lowered, cell survival increased for a given dose with the curves becoming progressively shallower and straighter (3, 5, 9). These findings were attributed to the repair of critical radiation damage (e.g., DSBs), which takes place during irradiation, and reduces the probability of interaction between two or more lesions that can have severe consequences, such as chromosomal aberrations (10). Later studies used pulsed-field gel electrophoresis (PFGE) to analyze the dose-rate effect on the induction and rejoining of DSBs (8, 11, 12).…”

Section: Introductionmentioning

confidence: 99%

Effect of Dose Rate on Residual γ-H2AX Levels and Frequency of Micronuclei in X-Irradiated Mouse Lymphocytes

et al. 2015

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The biological risks associated with low-dose-rate (LDR) radiation exposures are not yet well defined. To assess the risk related to DNA damage, we compared the yields of two established biodosimetry end points, γ-H2AX and micronuclei (MNi), in peripheral mouse blood lymphocytes after prolonged in vivo exposure to LDR X rays (0.31 cGy/min) vs. acute high-dose-rate (HDR) exposure (1.03 Gy/min). C57BL/6 mice were total-body irradiated with 320 kVP X rays with doses of 0, 1.1, 2.2 and 4.45 Gy. Residual levels of total γ-H2AX fluorescence in lymphocytes isolated 24 h after the start of irradiation were assessed using indirect immunofluorescence methods. The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was used to determine apoptotic cell frequency in lymphocytes sampled at 24 h. Curve fitting analysis suggested that the dose response for γ-H2AX yields after acute exposures could be described by a linear dependence. In contrast, a linear-quadratic dose-response shape was more appropriate for LDR exposure (perhaps reflecting differences in repair time after different LDR doses). Dose-rate sparing effects (P < 0.05) were observed at doses ≤2.2 Gy, such that the acute dose γ-H2AX and TUNEL-positive cell yields were significantly larger than the equivalent LDR yields. At the 4.45 Gy dose there was no difference in γ-H2AX expression between the two dose rates, whereas there was a two- to threefold increase in apoptosis in the LDR samples compared to the equivalent 4.45 Gy acute dose. Micronuclei yields were measured at 24 h and 7 days using the in vitro cytokinesis-blocked micronucleus (CBMN) assay. The results showed that MNi yields increased up to 2.2 Gy with no further increase at 4.45 Gy and with no detectable dose-rate effect across the dose range 24 h or 7 days post exposure. In conclusion, the γ-H2AX biomarker showed higher sensitivity to measure dose-rate effects after low-dose LDR X rays compared to MNi formation; however, confounding factors such as variable repair times post exposure, increased cell killing and cell cycle block likely contributed to the yields of MNi with accumulating doses of ionizing radiation.

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“…Radiation therapy causes cell death by inducing single- and double-strand DNA breaks 1, 2 . The rationale for treating tumor tissues with radiation without damaging normal tissues is that compared with normal cells, tumor cells are actively dividing and often have defects in DNA damage repair machinery, and thus are less able to repair DNA damage 3 .…”

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confidence: 99%

ATM-mediated stabilization of ZEB1 promotes DNA damage response and radioresistance through CHK1

et al. 2014

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Epithelial-mesenchymal transition (EMT) is associated with characteristics of breast cancer stem cells, including chemoresistance and radioresistance. However, it is unclear whether EMT itself or specific EMT regulators play causal roles in these properties. Here we identify an EMT-inducing transcription factor, zinc finger E-box binding homeobox 1 (ZEB1), as a regulator of radiosensitivity and DNA damage response (DDR). Radioresistant subpopulations of breast cancer cells derived from ionizing radiation exhibit hyperactivation of ATM and upregulation of ZEB1, and ZEB1 promotes tumor cell radioresistance in vitro and in vivo. Mechanistically, ATM kinase phosphorylates and stabilizes ZEB1 in response to DNA damage, and ZEB1 in turn directly interacts with USP7 and enhances its ability to deubiquitinate and stabilize CHK1, thereby promoting homologous recombination-dependent DNA repair and resistance to radiation. These findings identify ZEB1 as an ATM substrate linking ATM to CHK1 and as the mechanism underlying the association between EMT and radioresistance.

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Effect of Dose Rate on the Induction of DNA Double-Strand Breaks in Eucaryotic Cells

Cited by 34 publications

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A Small Interfering RNA Screen of Genes Involved in DNA Repair Identifies Tumor-Specific Radiosensitization by POLQ Knockdown

A Small Interfering RNA Screen of Genes Involved in DNA Repair Identifies Tumor-Specific Radiosensitization by POLQ Knockdown

Effect of Dose Rate on Residual γ-H2AX Levels and Frequency of Micronuclei in X-Irradiated Mouse Lymphocytes

ATM-mediated stabilization of ZEB1 promotes DNA damage response and radioresistance through CHK1

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