DNA‐PKcs‐dependent NHEJ pathway supports the progression of topoisomerase II poison‐induced chromosome aberrant cells

Abstract

The role of DNA double strand break (DSB) repair pathways, non-homologous end joining (NHEJ), and homologous recombination (HR) was evaluated to prevent the chromosome instability induced by the topoisomerase II (Top2) poisons, idarubicin, and etoposide in Chinese hamster cell lines. XR-C1 (DNA-PKcs deficient) and V-C8 (BRCA2 deficient) showed higher sensitivity to increased concentrations of Top2 poisons compared with their normal counterparts, CHO9 and V79. Both proficient and deficient cells exhibited a marked DSB induction in all phases of the cell cycle. Additionally, deficient cells showed persistent DNA damage 24 hr post-treatment. Chromosomal aberrations increased in the first mitosis following Top2 poison-treatments in G1 or G2 in proficient and deficient cells. CHO9 and V79 demonstrated chromosome and chromatid exchanges following treatments in G1 and G2 phases, respectively. Deficient cells showed high frequencies of chromatid exchanges following treatments in G1 and G2. Simultaneously, we analyzed the micronuclei (MN) induction in interphase cells after treatments in G1, S, or G2 of the previous cell cycle. Both Top2 poisons induced an important increase in MN in CHO9, V79, and V-C8 cells. XR-C1 exhibited an increased MN frequency when cells were treated in G1 phase but not in S or G2. This MN reduction was due to a cell accumulation at G2/M and death in G2-treated cells. Our data suggest that NHEJ and HR operate differentially throughout the cell cycle to protect from Top2 poison-induced chromosome instability, and that DNA-PKcs-dependent NHEJ pathway allows the survival of chromosome damaged cells during S/G2 to the next interphase.

Mutagenic Effects of Perfluorooctanesulfonic Acid in gpt Delta Transgenic System Are Mediated by Hydrogen Peroxide

“…Nonhomologous end-joining is the predominant mechanism of DSB repair in eukaryotes and is often prone to error, which might lead to the amplification or loss of chromosomal material. At the late stage of DSB repair processes, if, for example, the deleted chromosomal regions remain in the cytoplasm, these events are likely to lead to MN formation . In this study, slight induction of MN formation by PFOS was observed in the bone marrow of gpt delta transgenic mice, which was consistent with previous observations in rats …”

“…At the late stage of DSB repair processes, if, for example, the deleted chromosomal regions remain in the cytoplasm, these events are likely to lead to MN formation. 36 In this study, slight induction of MN formation by PFOS was observed in the bone marrow of gpt delta transgenic mice, which was consistent with previous observations in rats. 37 It has been reported that the mutagenic potential PFOS was negative in S. typhimurium stains by bacterial reverse mutation assay (Ames test).…”

Progression of chromosomal damage induced by etoposide in G2 phase in a DNA-PKcs-deficient context

“…Moreover, our previous results have shown that D-NHEJ allows Chinese hamster cells that were treated with Top2 poisons during S/G2 to progress into the following interphase (Elguero et al 2012). Here, we evaluated the role of potentially error-prone D-NHEJ and B-NHEJ repair pathways in the conversion of persistent DNA damage to chromosomal rearrangements following ETO treatment in G2 phase, since these pathways may be associated with cancer development.…”