Marked Dependence on Growth State of Backup Pathways of NHEJ
- Institute of Medical Radiation Biology, University Duisburg-Essen Medical School, Essen (Germany)
Purpose: Backup pathways of nonhomologous end joining (B-NHEJ) enable cells to repair DNA double-strand breaks (DSBs) when DNA-PK-dependent NHEJ (D-NHEJ) is compromised. Recent evidence implicates growth signaling in the regulation of D-NHEJ. This study was intended to determine whether the ability to repair DSBs by B-NHEJ also depends on growth state. Methods and Materials: LIG4 {sup -/-} and wild type (WT) mouse embryo fibroblasts (MEFs) were used. Repair of DSBs was measured by pulsed-field agarose gel electrophoresis. G1 cells were selected by centrifugal elutriation. A plasmid assay was used to measure DNA end-joining activity in whole cell extracts. Results: Wild-type MEFs efficiently repaired DSBs by D-NHEJ in either the exponential or plateau phase of growth. Because of their defect in ligase IV, which compromises D-NHEJ, LIG4 {sup -/-} MEFs showed reduced repair capacity but were slowly able to rejoin a large proportion of DSBs via B-NHEJ. B-NHEJ was markedly reduced in the plateau phase of growth or at high radiation doses. Elutriated G1 cells from exponentially growing or plateau-phase LIG4 {sup -/-} cultures showed a response similar to nonelutriated cells, ruling out that the effect simply reflects redistribution in the cell cycle. An in vitro assay, gauging the activity of B-NHEJ, showed a reduction in DNA end joining during the plateau phase that could be corrected by recombinant DNA ligase III{alpha}. Conclusions: Suppression of growth signaling markedly compromises DSB repair by B-NHEJ. This effect is associated with a reduction in DNA ligase III mediated DNA end joining.
- OSTI ID:
- 20953605
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 68, Issue 5; Other Information: DOI: 10.1016/j.ijrobp.2007.04.038; PII: S0360-3016(07)00758-4; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
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