Oct 27, 2011

Tatsuhiko Imaoka (National Institute of Radiological Sciences)

Childhood exposure to carcinogens renders a higher risk of breast cancer. The molecular mechanisms underlying cancer development after such exposure are not, however, well understood. Here we examined how the mechanism of cancer development relates to the age at exposure to ionizing radiation (IR) or the carcinogen 1-methyl-1-nitrosourea (MNU). Pre- and postpubertal (3- and 7-week-old, respectively) female Sprague-Dawley rats were whole-body gamma-irradiated (2 Gy), injected intraperitoneally with MNU (20 mg/kg) or left untreated and were autopsied at 50 weeks of age. Mammary carcinomas were examined for estrogen receptor (ER) alpha, progesterone receptor (PR) and ErbB ligand expression and for expression microarrays. Early histological changes of the ovaries were also evaluated. The incidence of mammary cancer was higher after postpubertal, rather than prepubertal, IR exposure; the inverse was true for MNU. Most cancers were positive for both ERalpha and PR except for the prepubertal IR group. Cancers of the prepubertal IR group expressed a different set of ErbB ligands from those of the other groups and did not overexpress Areg, which encodes an estrogen-regulated ErbB ligand, or other developmentally related genes including those for hormonally regulated mammary gland development. Prepubertal IR exposure resulted in ovarian dysfunction as revealed by a reduced follicular pool. Evidence thus suggests that mammary carcinogenesis induced by prepubertal IR exposure is independent of ovarian hormones but requires certain ErbB ligands; induction by postpubertal exposure depends on ovarian hormones and different ErbB ligands. In contrast, the mechanism of MNU-induced carcinogenesis was less influenced by the age at exposure.

References:
Imaoka et al. Pre- and Postpubertal Irradiation Induces Mammary Cancers with Distinct Expression of Hormone Receptors, ErbB Ligands and Developmental Genes in Rats.
Mol Carcinog 50, 539-52 (2011) doi:10.1002/mc.20746

Oct 27, 2011

Tokuhisa Hirouchi (Institute for Environmental Sciences)

It is well known that radiation exposure induces acute myeloid leukemia (AML) in humans and mice. However, a mechanism for the radiation-induced AML is unclear in comparison with that for spontaneous AML. Previous reports studying various types of spontaneous leukemias showed that all of leukemic cells expanded in a patient/diseased animal were arisen from a cell having both self-renewal and multiple cell-differentiation potentials, called “leukemic stem cell”. Since normal hematopoietic stem cells (HSCs) also possess both the self-renewal potentials and multipotencies, it is assumed that a first AML stem cell was appeared in HSC pool. To investigate whether radiation-induced AML stem cells were also originated from HSCs, we identified and analyzed AML stem cells of murine radiation-induced AMLs. We injected 100 cells of each of 7 cell populations corresponding to different 7 hematopoietic cell-differentiation stages involving HSC stage and compared the latencies of AMLs induced in recipient mice. Differently from murine spontaneous AML stem cells, the identified radiation-induced AML stem cells were frequently similar with common myeloid progenitors (CMPs) of normal mice. In bone marrow, the number of the CMP-like radiation-induced AML stem cells was significantly higher than that of CMP in normal mice. However, the progenies of CMP in radiation-induced AML mice were fewer than those in normal mice. Additionally, we demonstrated that normal CMPs were most radiosensitive in the other immature hematopoietic cells, and that the number of CMP in irradiated mice was lower than that in non-irradiated mice 70 days after radiation exposure. This study suggests a possibility that murine radiation-induced AML stem cells are arisen from radiosensitive CMP pool. The mechanism of occurrence of radiation-induced AML stem cell is not exactly same as that of spontaneous AML stem cell.

References:
Hirouchi et al. Cell Surface Marker Phenotypes and Gene Expression Profiles of Murine Radiation-Induced Acute Myeloid Leukemia Stem Cells are Similar to Those of Common Myeloid Progenitors.
Radiat Res 176, 311-22 (2011)

Oct 12, 2011

Hisakatsu Nawata (Research Reactor Institute, Kyoto University)

A change in chromosome number, known as aneuploidy, is a common characteristic of cancer. Aneuploidy disrupts gene expression in human cancer cells and immortalized human epithelial cells, but not in normal human cells. However, the relationship between aneuploidy and cancer remains unclear. To study the effects of aneuploidy in normal human cells, we generated artificial cells of human primary fibroblast having three chromosome 8 (trisomy 8 cells) by using microcell-mediated chromosome transfer technique. In addition to decreased proliferation, the trisomy 8 cells lost contact inhibition and reproliferated after exhibiting senescence-like characteristics that are typical of transformed cells. Furthermore, the trisomy 8 cells exhibited chromosome instability, and the overall gene expression profile based on microarray analyses was significantly different from that of diploid human primary fibroblasts. Our data suggest that aneuploidy, even a single chromosome gain, can be introduced into normal human cells and causes, in some cases, a partial cancer phenotype due to a disruption in overall gene expression.

References:
Nawata et al. Dysregulation of Gene Expression in the Artificial Human Trisomy Cells of Chromosome 8 Associated with Transformed Cell Phenotypes
PLoS One 2011;6(9):e25319.

Sep 06, 2011

Mikio Shimada (Radiation Biology Center, Kyoto University)

The centrosome is a cytoplasmic organelle which duplicates once during each cell cycle, and the presence of excess centrosomes promote chromosome instability through chromosome missegregation following cytokinesis. Ionizing radiation (IR) can induce extra centrosomes by permitting the continuation of CDK2/Cyclin-A/E-mediated centrosome duplication when cells are arrested in the cell cycle after irradiation. The work described here shows that, in addition to IR, extra centrosomes were induced in human U2OS and mouse NIH3T3 cells after treatment with agents which include DNA adduct-forming chemicals: benzopyrene (BP), 4-nitroquinoline 1-oxide (4NQO), a DNA cross linker: cis-diamminedichloro-platinum (cisplatin), topoisomerase inhibitors: camptothecin, etoposide, genistein, and ultra-violet light (UV). These agents were divided into two categories with respect to the regulation of p21, which is an inhibitor of CDK2/Cyclin-A/E: specifically, p21 was up-regulated by an IR exposure and treatment with topoisomerase inhibitors. However, UV, BP, 4NQO and cisplatin down-regulated p21 below basal levels. When cells were irradiated with IR in combination with all of these agents, except genistein, enhanced induction of extra centrosomes was observed, regardless of the nature of p21 expression. Genistein significantly suppressed the frequency of IR-induced extra centrosomes in a dose-dependent manner, and 20μg/ml of genistein reduced this frequency to 66%. Consistent with this, genistein substantially up-regulated p21 expression over the induction caused by IR alone, while other agents down-regulated or marginally affected this. This suggests the inhibitory effect of genistein on the induction of extra centrosomes occurs through the inactivation of CDK2/Cyclin-A/E via p21 up-regulation. This hypothesis is supported by the observation that p21 knockdown with siRNA reduced the activity of CDK2/Cyclin-A/E and restored the enhanced effect of a combined treatment with genistein and IR. These results demonstrate the preventive effect of genistein and a crucial role for p21 in IR-induced excess centrosomes.

References:
Simada et al. Genistein, isoflavonoids in soybeans, prevents the formation of excess radiation-induced centrosomes via p21 up-regulation
Mutat Res. 2011 Aug 5. [Epub ahead of print]

Jul 25, 2011

Takahiro Kataoka (Graduate School of Health Sciences, Okayama University)

Our previous studies showed the possibility that activation of the antioxidative function alleviates various oxidative damages, which are related to lifestyle diseases. Results showed that, low-dose X-ray irradiation activated superoxide dismutase and inhibits oedema following ischaemia-reperfusion. To alleviate ischaemia-reperfusion injury with transplantation, the changes of the antioxidative function in liver graft using low-dose X-ray irradiation immediately after exenteration were examined. Results showed that liver grafts activate the antioxidative function as a result of irradiation. In addition, radon inhalation enhances the antioxidative function in some organs, and alleviates alcohol-induced oxidative damage of mouse liver. Moreover, in order to determine the most effective condition of radon inhalation, mice inhaled radon before or after carbon tetrachloride (CCl4) administration. Results showed that radon inhalation alleviates CCl4-induced hepatopathy, especially prior inhalation. It is highly possible that adequate activation of antioxidative functions induced by low-dose irradiation can contribute to preventing or reducing oxidative damages, which are related to lifestyle diseases.

References:
Kataoka et al. Studies on possibility for alleviation of lifestyle diseases by low-dose irradiation or radon inhalation.
Radiat Prot Dosimetry 146(1-3):360-3, 2011 May 3.
doi:10.1093/rpd/ncr189

Jun 10, 2011

Nobuyuki Hamada (Central Research Institute of Electric Power Industry)

As a guest editor, I edited the special issue on non-targeted radiation effects, which was published in June 2011 [1]. The issue consisting of six review articles provides a forum to grasp the current knowledge on the non-targeted effects and proposes its significance. I believe that the issue gives timely in-depth overviews to the readers and will contribute to progress in this research area. In my contribution [2], the manifestations of the bystander effects in vitro, in vivo and in humans shall be overviewed. Then, their cellular and molecular underpinnings shall be mentioned, especially focusing on the intercellular signaling from irradiated to bystander cells, and its downstream intracellular signaling in bystander cells. The potential contribution of the bystander effects to cancer radiotherapy shall also be discussed.

References:
[1] Hamada. Editorial. Evidence and significance of non-targeted effects of ionizing radiation.
Curr. Mol. Pharmacol. 4 (2011) 78.
[PMID: 21269270]
[2] Hamada et al. Signaling pathways underpinning the manifestations of ionizing radiation-induced bystander effects.
Curr. Mol. Pharmacol. 4 (2011) 79-95.
[PMID: 21143186]

Jun 05, 2011

Kyosuke Nakamura (Radiation Biology Center, Kyoto University)

The E3 ubiquitin ligase RNF20 regulates chromatin structure by monoubiquitinating histone H2B in transcription.Here, we show that RNF20 is localized to double-stranded DNA breaks (DSBs) independently of H2AX and is required for the DSB-induced H2B ubiquitination. In addition, RNF20 is required for the methylation of H3K4 at DSBs and the recruitment of the chromatin-remodeling factor SNF2h. Depletion of RNF20, depletion of SNF2h, or expression of theH2B mutant lacking the ubiquitination site (K120R) compromises resection of DNA ends and recruitment of RAD51 and BRCA1. Consequently, cells lacking RNF20 or SNF2h and cells expressing H2B K120R exhibit pronounced defects in homologous recombination repair (HRR) and enhanced sensitivity to radiation. Finally, the function of RNF20 in HRR can be partially bypassed by forced chromatin relaxation. Thus, the RNF20-mediated H2B ubiquitination at DSBs plays a critical role in HRR through chromatin remodeling .

References:
Nakamura et al. Regulation of Homologous Recombination by RNF20-Dependent H2B Ubiquitination
Molecular Cell 41, 515-528 (2011)

Jun 05, 2011

Mikio Shimada (Radiation Biology Center, Kyoto University)

Centrosome is an organelle to regulate microtubules and necessary for proper cell division in mammalian cells (Doxsey, 2001; Nigg, 2002; Nigg, 2007). The existence was first reported one hundreds year ago by Theodor Boveri (Boveri, 2008). It is built from two centrioles and surrounded by pericentriolar material (PCM). PCM provides a binding site for gamma-tubulin ring complex (g–TuRC) that acts as a microtubule nucleation template.　g–TuRC attaches to PCM and is originated for microtubules formation. The nember of centrosome is precisely regulated and the duplication cycle is synchronized with cell cycle. Centrosome duplicates once in S phase and matures in G2 phase. In M phase, centrosomes are divided by daughter cells. The number of centrosome and its' functions are regulated by many proteins including centrosome proteins, cell cycle proteins and DNA repair proteins. Recently, the role of DNA repair proteins for centrosome maintenance has been clarified. In this chapter, we introduce recent findings about the roles of DNA repair proteins in centrosome maintenance.

References:
Shimada et al. The potential roles of DNA repair proteins in centrosome maintentance
InTech DNA Repair Book4, in press

Apr 27, 2011

Shigeyoshi Saito (National Institute of Radiological Sciences)

Prenatal radiation-exposure induces various central nervous system (CNS) disorders depending on the dose, affected region and gestation-period. The goal of this study is to non-invasively assess a CNS development disorder induced by prenatal X-ray exposure using quantitative manganese-enhanced MRI (MEMRI) as well as apparent diffusion coefficient (ADC) and transverse relaxation time (T2) maps in comparison to immunohistological stainings. Changes in ΔR1 (increment of the relaxation rate before and after MnCl2 administration) induced by Mn2+ contrast agent were evaluated in the CNS of normal and prenatally irradiated rats. The ADC and T2 were also compared to histological results obtained using Hematoxylin-Eosin (HE; to estimate cell density), Activated Caspase-3 (apoptotic cells), and Glial fibrillary acidic protein (GFAP; proliferation of astrocytes/astroglia). We found that: 1) a decreased Mn2+ uptake (as indicated by smaller ΔR1) for radiation-exposed rats were predominantly correlated with a decrease of cell viability (apoptotic cytopathogenicity) and CNS cell density after prenatal radiation exposure; 2) longer T2 and ADC were associated with a decrease in CNS cell density and apoptotic alteration after radiation exposure. In addition to a slight proliferation of astroglia (+58%), a substantial decrease in cell density (-78%) and an excessive increase of apoptotic cells (+613%) observed in our prenatal radiation-exposure model. The results suggest that MEMRI in the prenatal X-ray exposure model predominantly reflected the decrease in cell density and viability rather than the proliferation of astroglia. In conclusion, quantitative MEMRI with ADC/T2 mapping provide objective information for in vivo assessment of cellular-level alterations by prenatal radiation-exposure, and potentially becoming a standard approach for evaluating cellular-damage of radiotherapy.

References:
Saito et al. Quantitative assessment of central nervous system disorder induced by prenatal X‐ray exposure using diffusion and manganese‐enhanced MRI.
NMR Biomed. 2011 Apr 28. [Epub ahead of print]
DOI: 10.1002/nbm.1715

Jan 14, 2011

Shigeyoshi Saito (National Institute of Radiological Sciences)

Our purpose was to noninvasively assess formation of the microvasculature, blood-brain barrier (BBB) and blood-CSF barrier formation of prenatal X-ray-induced CNS abnormalities using quantitative MRI. Eight pregnant female Sprague-Dawley rats were divided into two groups consisting of control and Xirradiated animals. After birth, 20 neonatal male rats were divided into four groups of five rats. To evaluate the development of the BBB, changes in T1 induced by Gd-DTPA were compared quantitatively in normal and prenatally irradiated animals in the formative period 1 to 2 weeks after birth. To assess the abnormalities of the microvasculature, quantitative perfusion MRI and MR angiography were also used. Histology was also performed to evaluate the BBB (albumin) and vascular endothelial cells (laminin). Decreased cerebral blood flow (CBF) and angioarchitectonic abnormalities were observed in the prenatally irradiated rats. However, abnormalities of the BBB and blood-CSF barrier were not observed using Gdenhanced MRI and albumin staining. Quantitative perfusion MRI, MR angiography and Gd-enhanced T1 mapping are useful for assessing CNS disturbance after prenatal exposure to radiation. These techniques provide important diagnostic information for assessing the condition of patients during the early stages of life after accidental or unavoidable prenatal exposure to radiation.

References:
Saito et al. Quantitative and Noninvasive Assessment of Prenatal X-Ray-Induced CNS Abnormalities Using Magnetic Resonance Imaging.
Radiat Res. 175:1-9 (2011)