Sep 28, 2015

Yu Abe (Department of Radiation Life Sciences, Fukushima Medical University School of Medicine) 

Excess risk of leukemia and brain tumors after CT scans in children has been reported. We performed dicentric chromosome assay (DCAs) before and after CT scan to assess effects of low-dose ionizing radiation on chromosomes. Peripheral blood (PB) lymphocytes were collected from 10 patients before and after a CT scan. DCA was performed by analyzing either 1,000 or 2,000 metaphases using both Giemsa staining and centromere-fluorescence in situ hybridization (Centromere-FISH). The increment of DIC formation was compared with effective radiation dose calculated using the computational dosimetry system, WAZA-ARI and dose length product (DLP) in a CT scan. Dicentric chromosome (DIC) formation increased significantly after a single CT scan, and increased DIC formation was found in all patients. A good correlation between the increment of DIC formation determined by analysis of 2,000 metaphases using Giemsa staining and those by 2,000 metaphases using Centromere-FISH was observed. However, no correlation was observed between the increment of DIC formation and the effective radiation dose. Therefore, these results suggest that chromosome cleavage may be induced by one CT scan, and we recommend 2,000 or more metaphases be analyzed in Giemsa staining or Centromere-FISH for DCAs in cases of low-dose radiation exposure. 

Reference:
Yu Abe, Tomisato Miura, Mitsuaki A Yoshida, Risa Ujiie, Yumiko Kurosu, Nagisa Kato, Atsushi Katafuchi, Naohiro Tsuyama, Takashi Ohba, Tomoko Inamasu, Fumio Shishido, Hideyoshi Noji, Kazuei Ogawa, Hiroshi Yokouchi, Kenya Kanazawa, Takashi Ishida, Satoshi Muto, Jun Ohsugi, Hiroyuki Suzuki, Tetsuo Ishikawa, Kenji Kamiya, and Akira Sakai. Increase in dicentric chromosome formation after a single CT scan in adults. 
Sci. Rep. 5, 13882; doi: 10.1038/srep13882 (2015). 

Sep 15, 2015

Huizi LI (National Institute of Radiological Sciences and Graduate School of Medical and Pharmaceutical Sciences, Chiba University) 

111In-labeled trastuzumab modified with nuclear localizing signal (NLS) peptides (111In-trastuzumab-NLS) efficiently delivers an Auger electron (AE) emitter 111In into the cell nucleus and is thus a promising radiopharmaceutical in AE-radioimmunotherapy (AE-RIT) for targeted killing of HER2-positive cancer. However, further improvement of its therapeutic efficacy is required. Here we show a transcriptomic approach to identify potential targets for enhancing the cytotoxic effects of 111In-trastuzumab-NLS. We generated two types of 111In-trastuzumab-NLS harboring different numbers of NLS peptides, 111In-trastuzumab-NLS-S and -L. These radioimmunoconjugates (230 and 460 kBq) showed a significant higher cytotoxicity to SKBR3 human breast cancer cells overexpressing HER2 compared to 111In-trastuzumab. Microarray analysis revealed that NF-kB related genes (38 genes) were significantly changed in transcription by 111In trastuzumab-NLS-L (230 kBq) treatment. qRT-PCR confirmed the microarray data by showing transcriptional alternation of selected NF-κB target genes in cells treated with 111In-trastuzumab-NLS-L. Interestingly, bortezomib, a drug known as a NF-κB modulator, significantly enhanced the cytotoxicity of 111In-trastuzumab-NLS-L in SKBR3 cells. Taken together, our transcriptome data suggest the possibility that the modulation of NF-kB signaling activity is a molecular signature of 111In-trastuzumab-NLS and co-administration of bortezomib may be efficacious in enhancement of AE-RIT with 111In-trastuzumab-NLS. 

Reference:
Li H, Morokoshi Y, Daino K, Furukawa T, Kamada T, Saga T and Hasegawa S. Transcriptomic signatures of Auger electron radioimmunotherapy using unclear targeted 111In-trastuzumab for potential combination therapies. 
Cancer Biother Radiopharm. 2015. in press. 

Sep 14, 2015

Kiichi KAMINAGA (Graduate School of Science and Engineering, Ibaraki University and Japan Atomic Energy Agency) 

To explore X-irradiation effects on the mammalian cell cycle, we performed to track single cells as live cell images observed by the time-lapse imaging technique. HeLa cells with fluorescent ubiquitination-based cell cycle indicator (FUCCI) were used as irradiation sample cells to visualize cell cycle because their nuclei show different colors, red for G1 and green for S/G2/(M). We exposed 5 Gy X-rays to the HeLa-Fucci cells and observed them using a fluorescent microscope. We accumulated cells images every 20 min for 48 h. We obtained evidences of cell cycle dynamics of irradiated and unirradiated cells. The period of G1 and S/G2/(M) phase were analyzed and it was revealed that the irradiated cells were split in two populations, one showing similar cell cycle dynamics with that of unirradiated cells, and another showing modified cell cycle with a prolonged interval before progressing next cell cycle. The heterogeneous mixture of populations of irradiated cells might be involved in finally biological effects such as cell lethality. 

Reference:
Kaminaga K, Noguchi M, Narita A, Sakamoto Y, Kanari Y, Yokoya A. VISUALIZATION OF CELL CYCLE MODIFICATION BY X-IRRADIATION IN SINGLE HELA CELLS USING FLUORESCENT UBIQUITINATION-BASED CELL CYCLE INDICATOR. 
Radiat. Prot. Dosim. (2015) 166(1-4): 91-94.doi: 10.1093/rpd/ncv168. 

Sep 01, 2015

Nobuyuki HAMADA (International Commission on Radiological Protection) 

The biological effects on humans of low dose and low dose rate exposures to ionizing radiation have always been of major interest. The most recent concept as suggested by the International Commission on Radiological Protection (ICRP) is to extrapolate existing epidemiological data at high doses and dose rates down to low doses and low dose rates relevant to radiological protection, using the so-called dose and dose rate effectiveness factor (DDREF). The present paper summarizes what was presented and discussed by experts from ICRP and Japan at a dedicated workshop on this topic held in May 2015 in Kyoto, Japan. This paper describes the historical development of the DDREF concept in light of emerging scientific evidence on dose and dose rate effects, summarizes the conclusions recently drawn by a number of international organizations (e.g. BEIR VII, ICRP, SSK, UNSCEAR, and WHO), mentions current scientific efforts to obtain more data on low dose and low dose rate effects at molecular, cellular, animal and human levels, and discusses future options that could be useful to improve and optimize the DDREF concept for the purpose of radiological protection.. 

Reference:
Werner Rühm, Gayle E. Woloschak, Roy E. Shore, Tamara V. Azizova, Bernd Grosche, Ohtsura Niwa, Suminori Akiba, Tetsuya Ono, Keiji Suzuki, Toshiyasu Iwasaki, Nobuhiko Ban, Michiaki Kai, Christopher H. Clement, Simon Bouffler, Hideki Toma, and Nobuyuki Hamada. Dose and dose rate effects of ionizing radiation: a discussion in light of radiological protection. 
Radiat. Environ. Biophys., in press, 2015. doi: 10.1007/s00411-015-0613-6. 

Aug 26, 2015

Nobuyuki HAMADA (Central Research Institute of Electric Power Industry) 

Ionizing radiation is a proven human carcinogen and cataractogen. The crystalline lens of the eye is among the most radiosensitive tissues in the body. A clouding of the normally transparent lens (i.e., cataract) is very common. Conversely, the lens continues to grow throughout life without developing tumors, suggesting that the lens possesses strong anti-carcinogenesis mechanisms. There is mounting evidence that mutations of oncogenes, tumor suppressor genes, DNA repair genes involved in base excision repair, nucleotide excision repair, and DNA double-strand break repair, and genes involved in intercellular interactions (e.g., via connexin gap junctions), and inflammation affect cataract development. Associations of these factors with cancer have long been recognized, highlighting that cataractogenesis shares some common mechanisms with carcinogenesis. This paper briefly overviews the current knowledge on the potential involvement of tumor related factors, DNA repair factors, intercellular interactions and inflammation in spontaneous cataractogenesis, and discusses its implications for cataractogenesis induced by targeted and nontargeted effects of ionizing irradiation. 

Reference:
Hamada N, Fujimichi Y. Role of carcinogenesis related mechanisms in cataractogenesis and its implications for ionizing radiation cataractogenesis. 
Cancer Lett. 2015. 368: 262-274, doi: 10.1016/j.canlet.2015.02.017. 

Aug 24, 2015

Mikio SHIMADA (Tokyo Institute of Technology, St. Jude Children’s Research Hospital)

Polynucleotide kinase–phosphatase (PNKP) is a DNA repair factor possessing both 5′‐kinase and 3′‐phosphatase activities to modify ends of a DNA break prior to ligation. Recently, decreased PNKP levels were identified as the cause of severe neuropathology present in the human microcephaly with seizures (MCSZ) syndrome. Utilizing novel murine Pnkp alleles that attenuate expression and a T424GfsX48 frame‐shift allele identified in MCSZ individuals, we determined how PNKP inactivation impacts neurogenesis. Mice with PNKP inactivation in neural progenitors manifest neurodevelopmental abnormalities and postnatal death. This severe phenotype involved defective base excision repair and non‐homologous end‐joining, pathways required for repair of both DNA single‐ and double‐strand breaks. Although mice homozygous for the T424GfsX48 allele were lethal embryonically, attenuated PNKP levels (akin to MCSZ) showed general neurodevelopmental defects, including microcephaly, indicating a critical developmental PNKP threshold. Directed postnatal neural inactivation of PNKP affected specific subpopulations including oligodendrocytes, indicating a broad requirement for genome maintenance, both during and after neurogenesis. These data illuminate the basis for selective neural vulnerability in DNA repair deficiency disease. 

Reference:
Mikio Shimada, Lavinia C Dumitrache, Helen R Russell, Peter J McKinnon. Polynucleotide kinase–phosphatase enables neurogenesis via multiple DNA repair pathways to maintain genome stability.
The EMBO Journal embj.201591363 DOI 10.15252/embj.201591363 | Published online 19.08.2015

Nov 10, 2014

Takaaki YASUHARA (Graduate School of Medicine, The University of Tokyo) 

The strength of the DNA damage checkpoint critically influences cell fate, yet themechanisms behind the fine tuning of checkpoint strength during the DNA damage response (DDR) are poorly understood. Here we show that Rad54B-a SNF2 helicase-like DNA-repair protein-limits the strength of both the G1/S and G2/M checkpoints. We find that Rad54B functions as a scaffold for p53 degradation via its direct interaction with the MDM2-MDMX ubiquitin-ligase complex. During the early phases of the DDR, Rad54B is upregulated, thereby maintaining low checkpoint strength and facilitating cell cycle progression. Once the p53-mediated checkpoint is established, Rad54B is downregulated, and high checkpoint strength is maintained. Constitutive upregulation of Rad54B activity, which is frequently observed in tumours, promotes genomic instability because of checkpoint override. Thus, the scaffolding function of Rad54B dynamically regulates the maintenance of genome integrity by limiting checkpoint strength. 

Reference:
Yasuhara T, Suzuki T, Katsura M, Miyagawa K. Rad54B serves as a scaffold in the DNA damage response that limits checkpoint strength.
Nat. Commun. 5:5426 doi: 10.1038/ncomms6426 (2014). PMID:25384516
http://www.nature.com/ncomms/2014/141111/ncomms6426/full/ncomms6426.html