| Affiliation: | 1.Laboratory of Immunology and Molecular Physiology, Zoology Department, Faculty of Science,Assiut University,Assiut,Egypt;2.Department of Molecular Biology and Biotechnology,University of Sheffield,Sheffield,UK;3.Institut für Radiobiologie der Bundeswehr in Verb. mit der Universitat Ulm,Munich,Germany;4.Department of Histology,University of Navarra,Pamplona,Spain;5.Institute of Radiation Biology, Helmholtz Zentrum München,Neuherberg,Germany |
| Abstract: | Noncycling and terminally differentiated (TD) cells display differences in radiosensitivity and DNA damage response. Unlike other TD cells, Sertoli cells express a mixture of proliferation inducers and inhibitors in vivo and can reenter the cell cycle. Being in a G1-like cell cycle stage, TD Sertoli cells are expected to repair DSBs by the error-prone nonhomologous end-joining pathway (NHEJ). Recently, we have provided evidence for the involvement of Ku-dependent NHEJ in protecting testis cells from DNA damage as indicated by persistent foci of the DNA double-strand break (DSB) repair proteins phospho-H2AX, 53BP1, and phospho-ATM in TD Sertoli cells of Ku70-deficient mice. Here, we analyzed the kinetics of 53BP1 foci induction and decay up to 12 h after 0.5 Gy gamma irradiation in DNA-PKcs-deficient (Prkdc scid ) and wild-type Sertoli cells. In nonirradiated mice and Prkdc scid Sertoli cells displayed persistent DSBs foci in around 12 % of cells and a fivefold increase in numbers of these DSB DNA damage-related foci relative to the wild type. In irradiated mice, Prkdc scid Sertoli cells showed elevated levels of DSB-indicating foci in 82 % of cells 12 h after ionizing radiation (IR) exposure, relative to 52 % of irradiated wild-type Sertoli cells. These data indicate that Sertoli cells respond to and repair IR-induced DSBs in vivo, with repair kinetics being slow in the wild type and inefficient in Prkdc scid . Applying the same dose of IR to Prdkc ?/? and Ku ?/? mouse embryonic fibroblast (MEF) cells revealed a delayed induction of 53BP1 DSB-indicating foci 5 min post-IR in Prdkc ?/? cells. Inefficient DSB repair was evident 7 h post-IR in DNA-PKcs-deficient cells, but not in Ku ?/? MEFs. Our data show that quiescent Sertoli cells repair genotoxic DSBs by DNA-PKcs-dependent NEHJ in vivo with a slower kinetics relative to somatic DNA-PKcs-deficient cells in vitro, while DNA-PKcs deficiency caused inefficient DSB repair at later time points post-IR in both conditions. These observations suggest that DNA-PKcs contributes to the fast and slow repair of DSBs by NHEJ. |
