Widespread Dependence of Backup NHEJ on Growth State: Ramifications for the Use of DNA-PK Inhibitors

Journal Article · Tue Feb 01 00:00:00 EST 2011 · International Journal of Radiation Oncology, Biology and Physics

DOI:https://doi.org/10.1016/j.ijrobp.2010.08.018· OSTI ID:21499713

Singh, Satyendra K; Wenqi, Wu; Lihua, Zhang; Klammer, Holger; Minli, Wang ^[1]; Iliakis, George ^[1]

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1. Institute of Medical Radiation Biology, University Duisburg-Essen Medical School, Essen (Germany)

Purpose: The backup pathway of nonhomologous end joining (B-NHEJ) enables cells to process DNA double-strand breaks (DSBs) when the DNA-PK-dependent pathway of NHEJ (D-NHEJ) is compromised. Our previous results show marked reduction in the activity of B-NHEJ when LIG4{sup -/-} mouse embryo fibroblasts (MEFs) cease to grow and enter a plateau phase. The dependence of B-NHEJ on growth state is substantially stronger than that of D-NHEJ and points to regulatory mechanisms or processing determinants that require elucidation. Because the different D-NHEJ mutants show phenotypes distinct in their details, it is necessary to characterize the dependence of their DSB repair capacity on growth state and to explore species-specific responses. Methods and Materials: DSB repair was measured in cells of different genetic background from various species using pulsed-field gel electrophoresis, or the formation of {gamma}-H2AX foci, at different stages of growth. Results: Using pulsed-field gel electrophoresis, we report a marked reduction of B-NHEJ during the plateau phase of growth in KU and XRCC4, mouse or Chinese hamster, mutants. Notably, this reduction is only marginal in DNA-PKcs-deficient cells. However, reduced B-NHEJ is also observed in repair proficient, plateau-phase cells after treatment with DNA-PK inhibitors. The reduction of B-NHEJ activity in the plateau phase of growth does not derive from the reduced expression of participating proteins, is detectable by {gamma}-H2AX foci analysis, and leads to enhanced cell killing. Conclusions: These results further document the marked dependence on growth state of an essential DSB repair pathway and show the general nature of the effect. Molecular characterization of the mechanism underlying this response will help to optimize the administration of DNA repair inhibitors as adjuvants in radiation therapy.

• OSTI ID: 21499713
• Journal Information: International Journal of Radiation Oncology, Biology and Physics, Vol. 79, Issue 2; Other Information: DOI: 10.1016/j.ijrobp.2010.08.018; PII: S0360-3016(10)03064-6; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0360-3016
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRONMENTAL POLLUTANT EFFECTS ON LIVING ORGANISMS AND BIOLOGICAL MATERIALS
BIOLOGICAL PATHWAYS
CELL CYCLE
CELL KILLING
DNA REPAIR
ELECTROPHORESIS
GELS
HAMSTERS
MICE
MUTANTS
RADIOTHERAPY
STRAND BREAKS
ANIMALS
BIOLOGICAL RECOVERY
BIOLOGICAL REPAIR
COLLOIDS
DISPERSIONS
DNA DAMAGES
MAMMALS
MEDICINE
NUCLEAR MEDICINE
RADIOLOGY
REPAIR
RODENTS
THERAPY
VERTEBRATES