Induction of genetic instability by transfer of a UV-A-irradiated chromosome

Urushibara, Ayumi*; Kodama, Seiji*; Yokoya, Akinari

Mutation Research; Genetic Toxicology And Environmental Mutagenesis, 766, p.29 - 34, 2014/05

https://doi.org/10.1016/j.mrgentox.2014.02.005

Chemical repair of base lesions, AP sites, and strand breaks on plasmid DNA in dilute aqueous solution by ascorbic acid

Hata, Kuniki; Urushibara, Ayumi; Yamashita, Shinichi; Shikazono, Naoya; Yokoya, Akinari; Katsumura, Yosuke*

Biochemical and Biophysical Research Communications, 434(2), p.341 - 345, 2013/05

https://doi.org/10.1016/j.bbrc.2013.03.075

A Novel technique using DNA denatureation to detect multiplly induced single-strand breaks in a hydrated plasmid DNA molecule by X-ray and He ion irradiation

Yokoya, Akinari; Shikazono, Naoya; Fujii, Kentaro; Noguchi, Miho; Urushibara, Ayumi

Radiation Protection Dosimetry, 143(2-4), p.219 - 225, 2011/02

https://doi.org/10.1093/rpd/ncq540

Multiple single-strand breaks (m-SSBs), which are predicted to be preferentially induced by high LET radiation, would be underestimated if one uses the conventional method using plasmid DNA, because m-SSBs will not cause additionally conformational changes if they are on the same or on the opposite strand but separated each other sufficiently so as not to induce a double strand break. In order to observe the invisible m-SSBs, we have developed a novel technique using DNA denaturation. The m-SSBs arising in both strands of DNA are revealed as molecular size change in single strand DNA (SS-DNA) by gel electrophoresis. We have applied this method to the X- and He ion irradiated sample of hydrated pUC18 plasmid DNA. A half of SS-DNA population remains as intact within the experimental resolution ( 140 bases) for both irradiations. Contrary to our initial expectation, these results indicate that SSBs are not multiply induced over 140 bp even by high-LET irradiation.

The Yield, processing, and biological consequences of clustered DNA damage induced by ionizing radiation

Shikazono, Naoya; Noguchi, Miho; Fujii, Kentaro; Urushibara, Ayumi*; Yokoya, Akinari

Journal of Radiation Research, 50(1), p.27 - 36, 2009/01

https://doi.org/10.1269/jrr.08086

After living cells are exposed to ionizing radiation, a variety of chemical modifications of DNA are induced either directly by ionization of DNA or indirectly through interactions with water-derived radicals. Clustered DNA damage, which is defined as two or more of such lesions within one to two helical turns of DNA induced by a single radiation track, is considered to be a unique feature of ionizing radiation. A double strand break (DSB) is a type of clustered DNA damage. Formation and repair of DSBs have been studied in great detail over the years as they have been linked to important biological endpoints. Although non-DSB clustered DNA damage has received less attention, there is growing evidence of its biological significance. This review focuses on the current understanding of (1) the yield of non-DSB clustered damage induced by ionizing radiation (2) the processing, and (3) biological consequences of non-DSB clustered DNA damage.

Unrepairable DNA damage site composed of clustered lesions along ion particle tracks

Yokoya, Akinari; Shikazono, Naoya; Fujii, Kentaro; Ushigome, Takeshi*; Suzuki, Masao*; Urushibara, Ayumi; Watanabe, Ritsuko

Proceedings of the 27th Symposium on Materials Science and Engineering, Research Center of Ion Beam Technology Hosei University, 8 Pages, 2008/12

It has been indicated that ion particle irradiation to living cells causes a clustered DNA damage site, defined as two or more lesions formed within a few nano meters, in a cell nuclei. The clustered damage is less readily repaired by enzymatic repair system so that it induces biological effects, such as mutation induction. We have studied the mechanism of clustered damage induction by biochemical approaches using closed circular plasmid DNA as a model molecule to be irradiated with He ions from TIARA. We have used base excision repair proteins as enzymatic probes to quantify base lesions. We have also applied a novel method using DNA denaturation to visualize multiple single strand breaks which hardly be detected by conventional method. Our recent results will be reported in this seminar.

LET dependence of the yield of single-, double-strand breaks and base lesions in fully hydrated plasmid DNA films by He ion irradiation

Urushibara, Ayumi*; Shikazono, Naoya; O'Neill, P.*; Fujii, Kentaro; Wada, Seiichi*; Yokoya, Akinari

International Journal of Radiation Biology, 84(1), p.23 - 33, 2008/01

https://doi.org/10.1080/09553000701616072

To characterize the complexity of radiation damage to DNA, fully hydrated plasmid DNA was irradiated with He ions. From quantification of the conformational changes of the irradiated samples, the yields of single-(SSB) and double strand break (DSB) were obtained. Base lesions were visualized as additional strand breaks by treatment with base excision repair enzymes. The yield of prompt SSBs does not depend significantly on LET of the He ions, whereas the yield of prompt DSBs increases with increasing LET. The yields of isolated base lesions, revealed by enzymes as additional SSBs, decrease drastically with increasing LET. The sum of the yields of DSB and additional DSBs revealed by the enzymes increase with increasing LET of the He ions except at the highest LET investigated. These results indicate that the yields of clustered damage, revealed as DSB and non-DSB clustered damage sites, increase with increasing ionization density of radiation.

Yields of strand breaks and base lesions induced by soft X-rays in plasmid DNA

Yokoya, Akinari; Fujii, Kentaro; Ushigome, Takeshi; Shikazono, Naoya; Urushibara, Ayumi; Watanabe, Ritsuko

Radiation Protection Dosimetry, 122(1-4), p.86 - 88, 2006/12

https://doi.org/10.1093/rpd/ncl408

We have studied yields of DNA damages induced by soft X-rays obtained from a conventional soft X-ray machine in a LET region between -rays and ultrasoft X-rays. Practically soft X-rays with a broad energy spectrum emitted from a target of heavy metal, such as tungsten, have been widely used not only for radiobiological experiments but also for medical application such as mammography. Radiation weighting factors for these soft X-rays have been assigned to be 1 by ICRP. However, the fraction of a large number of low energy photons in the spectrum (below several tens keV) provided by bremsstrahlung is expected to be more effective for DNA damage induction than -rays since low energy photo- and Auger electrons predominantly ejected in consequence of a photoelectric effect can produce dense clusters of ionization/excitation on DNA molecules. We have examined the yield of DNA strand breaks induced by white soft X-rays (150 kVp, tungsten target). Yields of base lesions revealed by base excision repair enzymes will be also presented.

Clustered DNA damage induced by ionizing radiaton

Yokoya, Akinari; Shikazono, Naoya; Urushibara, Ayumi; Fujii, Kentaro; Akamatsu, Ken; Watanabe, Ritsuko

Hoshasen Seibutsu Kenkyu, 40(2), p.168 - 184, 2005/06

http://ci.nii.ac.jp/naid/40006828265

Ionizing radiation causes modifications in a DNA molecule depending on the characteristic tack-structure in which two or more isolated lesions arise in a few nm scale (1 or 2 helical turn of DNA), known as "clustered DNA damage". These clustered DNA damages could be distinct from those by reactive oxygen species (ROS) endogenously induced on their severity of induction of biological effects such as mutation. However, the studies on the nature and repair mechanism of clustered DNA damage have still been behind because of the technical difficulties on determination of the chemical structure and yield. This article reviews some experimental evidences of the clustered DNA damages in this research field, as well as our recent progress on the studies on the clustered DNA damages using both molecular biological techniques and synchrotron spectroscopic method.

DNA damages induced by photons and ion particles with various LETs

Yokoya, Akinari; Ushigome, Takeshi; Shikazono, Naoya; Fujii, Kentaro; Urushibara, Ayumi; Suzuki, Masao*; Tauchi, Hiroshi*; Watanabe, Ritsuko

no journal, , 

The yields of single- and double-strand breaks (SSB and DSB), base lesions and clustered damage induced in DNA were measured after exposing to various kinds of radiation. To focus on the effect of direct energy deposition from radiation track, we prepared hydrated DNA as well as solution sample with various scavenging capacities. Base excision repair enzymes, EndoIII and Fpg, were used to detect oxidative base lesions. The obtained results show that (1) the yield of directly induced SSB by the soft X-irradiation is about 30 percent of total SSBs in a cell mimetic condition and (2) the SSB yield does not significantly depend on the quality of radiation. On the other hand, (3) the yields of base lesions show a maximum by soft X-irradiation and drastically decreases with increasing of LET. (4) Soft X-rays are more effective in inducing base lesions than ions with similar LET, and (5) EndoIII treatment gives significantly higher SSB yield than those by Fpg treatment.

The Mutation frequency of 8-oxo-7,8-dihydroguanine when single strand break is closely present on the same or the opposite strand

Noguchi, Miho; Urushibara, Ayumi*; Yokoya, Akinari; Shikazono, Naoya

no journal, , 

Ionizing radiation induces clustered DNA damage which is defined as two or more lesions induced within 1-2 helical turns (10-20bp) of DNA by a single radiation track. Recent in vitro studies predict that the non-DSB clustered damage shows high biological effects. It is, however, technically difficult to directly detect non-DSB clustered damage site as well as its effect in living cells. In this study, we investigated the potential of single strand break (SSB) to influence the mutagenicity of base lesions in Escherichia coli. We used plasmid based assay to measure the mutation frequency induced by bistranded clustered damage. As models of clustered damage, we used synthesized oligonucleotides carrying a SSB and 8-oxo-7,8-dihydroguanine (8-oxoG) at a restriction enzyme recognition site. Damaged DNA was transfected into wild-type or glycosylase-deficient strains (fpg, mutY, fpg mutY) of E coli and mutation frequency was assessed by the inability to cut by the restriction enzyme. Clustered damage containing 8-oxoG and SSB located on opposite strand raised mutation frequencies. However, clustered damage containing 8-oxoG and SSB positioned in tandem gave lower mutation frequency than single 8-oxoG lesion. We propose that the mutagenic potential of 8-oxoG depends on whether SSB is located on either strand, same or opposite, to 8-oxoG.