title: Nuclear accumulation of cyclin D1 following long-term fractionated exposures to low-dose ionizing radiation in normal human diploid cells.
abstract: Cyclin D1 is a mitogenic sensor that responds to growth signals from the extracellular environment and regulates the G 1-to-S cell cycle transition. When cells are acutely irradiated with a single dose of 10 Gy, cyclin D1 is degraded, causing cell cycle arrest at the G 1/S checkpoint. In contrast, cyclin D1 accumulates in human tumor cells that are exposed to long-term fractionated radiation (0.5 Gy/fraction of X-rays). In this study we investigated the effect of fractionated low-dose radiation exposure on cyclin D1 localization in 3 strains of normal human fibroblasts. To specifically examine the nuclear accumulation of cyclin D1, cells were treated with a hypotonic buffer containing detergent to remove cytoplasmic cyclin D1. Proliferating cell nuclear antigen (PCNA) immunofluorescence was used to identify cells in S phase. With this approach, we observed S-phase nuclear retention of cyclin D1 following low-dose fractionated exposures, and found that cyclin D1 nuclear retention increased with exposure time. Cells that retained nuclear cyclin D1 were more likely to have micronuclei than non-retaining cells, indicating that the accumulation of nuclear cyclin D1 was associated with genomic instability. Moreover, inhibition of the v-akt murine thymoma viral oncogene homolog (AKT) pathway facilitated cyclin D1 degradation and eliminated cyclin D1 nuclear retention in cells exposed to fractionated radiation. Thus, cyclin D1 may represent a useful marker for monitoring long-term effects associated with exposure to low levels of radiation.
authors.affiliation: Department of Environmental Health; National Institute of Public Health; Wako, Saitama, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Shimura
authors.affiliation: Radiation Safety Research Center; Nuclear Technology Research Laboratory; Central Research Institute of Electric Power Industry (CRIEPI); Tokyo, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Hamada
authors.affiliation: Department of Experimental Oncology; Research Center for Radiation Genome Medicine; Research Institute for Radiation Biology and Medicine (RIRBM); Hiroshima University; Hiroshima, Japan.
authors.forename: Megumi
authors.initials: M
authors.lastname: Sasatani
authors.affiliation: Department of Experimental Oncology; Research Center for Radiation Genome Medicine; Research Institute for Radiation Biology and Medicine (RIRBM); Hiroshima University; Hiroshima, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Kamiya
authors.affiliation: Department of Environmental Health; National Institute of Public Health; Wako, Saitama, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Kunugita
mesh_terms: D002021:Buffers; D002467:Cell Nucleus / Q000378:metabolism / Q000528:radiation effects*; D002478:Cells, Cultured; D056741:Cyclin D / Q000378:metabolism* / Q000528:radiation effects; D004171:Diploidy; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts; D006801:Humans; D051058:Oncogene Protein v-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D059807:S Phase Cell Cycle Checkpoints / Q000528:radiation effects
chemical_list: D002021:Buffers; D056741:Cyclin D; D018809:Proliferating Cell Nuclear Antigen; D051058:Oncogene Protein v-akt
keywords: AKT; Cyclin D1; double-strand breaks; long-term exposure; low-dose radiation