Abstract
BackgroundDNA-dependent protein kinase (DNA-PK), consisting of a Ku heterodimer (Ku70/80) and a large catalytic subunit (DNA-PKcs), plays an important role in the repair of DNA double-strand breaks via non-homologous end-joining (NHEJ) in mammalian cells. Severe combined immunodeficient (scid) mice carry a mutation in the gene encoding DNA-PKcs and are sensitive to ionizing radiation. To examine the roles of DNA-PKcs in the generation of deletion mutations in vivo, we crossed scid mice with gpt delta transgenic mice for detecting mutations.ResultsThe scid and wild-type (WT) gpt delta transgenic mice were irradiated with a single X-ray dose of 10 Gy, and Spi− mutant frequencies (MFs) were determined in the brain and spleen 2 days after irradiation. Irradiation with X-rays significantly enhanced Spi− MF in both organs in the scid and WT mice. The MFs in the brain of irradiated scid mice were significantly lower than those in WT mice, i.e., 2.9 ± 1.0 × 10− 6 versus 5.0 ± 1.1 × 10− 6 (P < 0.001), respectively. In the spleen, however, both mouse strains exhibited similar MFs, i.e., 4.1 ± 1.8 × 10− 6 versus 4.8 ± 1.4 × 10− 6. Unirradiated scid and WT mice did not exhibit significant differences in MFs in either organ.ConclusionsDNA-PKcs is unessential for the induction of deletion mutations in the spleen, while it plays a role in this in the brain. Therefore, the contribution of DNA-PKcs to NHEJ may be organ-specific.
Highlights
The repair of DNA double-strand breaks (DSBs) is critical for the maintenance of genomic integrity
We have demonstrated that the Sensitive to P2 interference (Spi)− mutant frequency (MF) is substantially increased by ionizing radiation (IR) and chemical treatments, and suggested that nonhomologous end-joining (NHEJ) repair plays an important role in the induction of Spi− deletion mutants [28, 31, 32]
WT and scid mice were exposed to X-ray irradiation at a dose of 10 Gy and Spi− MFs were determined in the brain and spleen (Fig. 1, Supplementary Table 1 and 2)
Summary
The repair of DNA double-strand breaks (DSBs) is critical for the maintenance of genomic integrity. DSBs are repaired by the homologous recombination and/or the nonhomologous end-joining (NHEJ) pathways [1–3]. DSBs induced by ionizing radiation (IR) are mainly repaired through NHEJ pathway. This is true in non-dividing cells and in G1 cells due to the absence of sister chromatids, the preferred substrate for homologous recombination. DNA-dependent protein kinase (DNA-PK) consists of three components, the catalytic subunit DNA-PKcs and the heterodimeric Ku70 and Ku80 proteins, and is involved in NHEJ of DNA DSBs and V(D)J recombination [5–9]. DNA-dependent protein kinase (DNA-PK), consisting of a Ku heterodimer (Ku70/80) and a large catalytic subunit (DNA-PKcs), plays an important role in the repair of DNA double-strand breaks via nonhomologous end-joining (NHEJ) in mammalian cells. To examine the roles of DNA-PKcs in the generation of deletion mutations in vivo, we crossed scid mice with gpt delta transgenic mice for detecting mutations
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