title: Delayed cell cycle progression in human lymphoblastoid cells after exposure to high-LET radiation correlates with extremely localized DNA damage.
abstract: To compare the genotoxic effects of high-LET ionizing radiation to those of low-LET radiation, we investigated the responses of human lymphoblastoid cells to DNA damage TK6 after treatment with either low-LET X rays or high-LET iron ions (1000 keV/microm). A highly localized distribution of gammaH2AX/RAD51 foci was observed in the nuclei of cells irradiated with iron ions, in sharp contrast to cells exposed to X rays, where the distribution of foci was much more uniform. This implied the occurrence of a relatively high frequency of closely spaced double-strand breaks, i.e. clustered DNA damage, after iron-ion exposure. Despite the well-established notion that clustered DNA damage is refractory to repair compared to isolated DNA lesions, there were no significant differences in the levels of clonogenic survival and apoptosis between cells treated with iron ions or X rays. Strikingly, however, cells accumulated in G(2)/M phase to a much lesser extent after iron-ion exposure than after X-ray exposure. This differential accumulation could be attributed to a much slower evacuation of the S-phase compartment in the case of cells irradiated with iron ions. Taken together, our results indicate that, relative to the situation for low-LET X rays, exposure to high-LET iron ions results in a substantially greater inhibition of S-phase progression as a result of a higher frequency of DNA replication-blocking clustered DNA damage.
authors.affiliation: Technology of Radioisotope, The Institute of Physical Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan.
authors.forename: Sachiko
authors.initials: S
authors.lastname: Goto
authors.forename: Masami
authors.initials: M
authors.lastname: Watanabe
authors.forename: Fumio
authors.initials: F
authors.lastname: Yatagai
mesh_terms: D017209:Apoptosis; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002453:Cell Cycle / Q000528:radiation effects*; D002470:Cell Survival; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D019084:Fluorescent Antibody Technique, Indirect; D016195:G2 Phase / Q000528:radiation effects; D006657:Histones / Q000096:biosynthesis; D006801:Humans; D007477:Ions; D007501:Iron; D008214:Lymphocytes / Q000528:radiation effects*; D008938:Mitosis / Q000528:radiation effects; D051135:Rad51 Recombinase; D011839:Radiation, Ionizing; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014965:X-Rays
chemical_list: D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D007477:Ions; D007501:Iron; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D001973:Bromodeoxyuridine