Homologous Recombination Contributes to the Repair of DNA Double-Strand Breaks Induced by High-Energy Iron Ions

Abstract

Zafar F., Seidler S.B., Kronenberg A., Schild D. and Wiese C. Homologous recombination contributes to the repair of DNA double-strand breaks induced by high-energy iron ions. Radiat. Res.To test the contribution of homologous recombinational repair (HRR) in repairing DNA damaged sites induced by high-energy iron ions, we used: 1) HRR-deficient rodent cells carrying a deletion in the RAD51D gene and 2) syngeneic human cells impaired for HRR by RAD51D or RAD51 knockdown using RNA interference. We show that in response to iron ions, HRR contributes to cell survival in rodent cells, and that HRR-deficiency abrogates RAD51 foci formation. Complementation of the HRR defect by human RAD51D rescues both enhanced cytotoxicity and RAD51 foci formation. For human cells irradiated with iron ions, cell survival is decreased, and, in p53 mutant cells, the levels of mutagenesis are increased when HRR is impaired. Human cells synchronized in S phase exhibit more pronounced resistance to iron ions as compared with cells in G1 phase, and this increase in radioresistance is diminished by RAD51 knockdown. These results implicate a role for RAD51-mediated DNA repair (i.e. HRR) in removing a fraction of clustered lesions induced by charged particle irradiation. Our results are the first to directly show the requirement for an intact HRR pathway in human cells in ensuring DNA repair and cell survival in response to high-energy high LET radiation.3

Distinct Roles of Ape1 Protein, an Enzyme Involved in DNA Repair, in High or Low Linear Energy Transfer Ionizing Radiation-induced Cell Killing

“…Interestingly, in an NHEJ-deficient genetic background, where HRR is the main mechanism for repair, the RBE for high LET radiation is close to 1 (6 -8), suggesting that HRR is not subject to inhibition by whatever mechanism interferes with NHEJ in high LETirradiated cells. This has been demonstrated in vivo (9) and confirmed by another group (10).…”

“…This conclusion has been verified by our group (8,9,36) and another group (10). The mechanism involves high LET IR-generated small DNA fragments (Յ40 bp) whose size prevents Ku from simultaneously binding to the two ends of one DNA fragment to initiate efficient NHEJ (8).…”

DNA end resection is needed for the repair of complex lesions in G1-phase human cells

“…37 Complex DSBs are mainly repaired by the slow component, 27,35 which in G2-phase represents resection-dependent HR. 27,38 Recent data on the repair of covalently blocked DSB ends or IR-induced DSBs in DT40 B cells suggest a function of CtIP and MRE11 also in G1. 17,19 This is in line with the observed recruitment of RPA to complex DSBs in G1 ( Fig.…”

Alpha Particle Emitter Radiolabeled Antibody for Metastatic Cancer: What Can We Learn from Heavy Ion Beam Radiobiology?

“…Zafar et al tested the contribution of homologous recombination pathway to repair DNA DSB induced by high LET radiation using RAD51D-deficient CHO cells and found that rad51d −/− cells are more sensitive than wild type CHO cells [103]. Moreover, studies of ataxia telangiectasia-mutated (ATM) protein, functioning upstream of both NHEJ and HR repair pathways, with ATM deficient cells and ATM inhibitors have also shown that lack of ATM significantly reduced cell survival after treatment with high LET carbon ion radiation [54,104].…”