Junko Tatsumi-Miyajima

ESR dosimetry for atomic bomb survivors and radiologic technologists

Abstract An individual absorbed dose for atomic bomb (A-bomb) survivors and radiologic technologists has been estimated using a new personal dosimetry. This dosimetry is based on the electron spin resonance (ESR) spectroscopy of the CO 3 3− radicals, which are produced in their teeth by radiation. Measurements were carried out to study the characteristics of the dosimetry; the ESR signals of the CO 3 3− radicals were stable and increased linearly with the radiation dose. In the evaluation of the absorbed dose, the ESR signals were considered to be a function of photon energy. The absorbed doses in ten cases of A-bomb victims and eight cases of radiologic technologists were determined. For A-bomb survivors, the adsorbed doses, which were estimated using the ESR dosimetry, were consistent with the ones obtained using the calculations of the tissue dose in air of A-bomb, and also with the ones obtained using the chromosome measurements. For radiologic technologists, the absorbed doses, which were estimated using the ESR dosimetry, agreed with the ones calculated using the information on the occupational history and conditions. The advantages of this method are that the absorbed dose can be directly estimated by measuring the ESR signals obtained from the teeth of persons, who are exposed to radiation. Therefore, the ESR dosimetry is useful to estimate the accidental exposure and the long term cumulative dose.

Trans-dominant inhibition of poly(ADP-ribosyl)ation potentiates alkylation-induced shuttle-vector mutagenesis in Chinese hamster cells

In most eukaryotic cells, the catalytic activation of poly(ADP-ribose) polymerase (PARP) represents one of the earliest cellular responses to the infliction of DNA damage. To study the biological function(s) of poly(ADP-ribosyl)ation, we have established stable transfectants (COM3 cells) of the SV40-transformed Chinese hamster cell line C060 which conditionally overexpress the PARP DNA-binding domain upon addition of dexamethasone. We could demonstrate that DNA-binding domain overexpression, which leads to trans-dominant inhibition of poly(ADP-ribosyl)ation, potentiates the cytotoxicity of alkylation treatment and of γ-radiation [21]. Likewise, carcinogen-induced gene amplification, viewed as a manifestation of genomic instability, was potentiated by the overexpression of the PARP DNA-binding domain [22]. Recently, we studied the effect of trans-dominant PARP inhibition on mutagenesis by employing a shuttle-vector assay in which mutagen-exposed plasmid pYZ289 is electroporated into COM3 cells. We could show that dexamethasone-induced overexpression of the PARP DNA-binding domain in COM3 cells potentiates the mutagenicity of the alkylating agent N-methyl-N-nitrosourea, while no effect of dexamethasone treatment on mutation frequency was recorded in control cells lacking the PARP DNA-binding domain transgene. Taken together, our results further substantiate the role of poly(ADP-ribosyl)ation in the maintenance of genomic integrity and stability under conditions of genotoxic stress.

Analysis of mutations caused by DNA double-strand breaks produced by a restriction enzyme in shuttle vector plasmids propagated in ataxia telangiectasia cells

Rejoining of DNA double-strand breaks (DSB) produced by a restriction endonuclease AvaI in the supF gene in a plasmid pZ189Ava, and mutations presumably due to the altered rejoinings were analyzed. After allowing the rejoining and replication of the plasmids in human cells originating from normal subjects and ataxia telangiectasia (AT) patients, the plasmids were retrieved and those containing mutated supF were screened in an indicator strain of Escherichia coli. The proportion of correctly rejoined plasmids was significantly lower in AT cells than in normal cells, suggesting that AT cells have lower fidelity in rejoining DSB. DNA sequencing of the mutated supF genes revealed that all mutations were deletions or insertions occurring exactly or closely at the rejoining site in both normal and AT cells. In AT cells, the majority of mutations were deletions, while deletions and insertions were evenly formed in normal cells. AT cells may be deficient in the mechanism to protect the broken ends of DNA strands from the exonucleolytic digestion.

Transition of Phenotypic Dimorphism with Regard to Spontaneous Sister Chromatid Exchange in Epstein‐Barr Virus‐transformed Bloom's Syndrome Lymphoblastoid Cell Lines

We recently established four lymphoblastoid cell lines (LCLs) by infecting the peripheral blood of four Japanese patients suffering from Blooms syndrome (BS) with Epstein‐Barr virus (EBV). During the course of propagating these cell lines, two of them exhibited dimorphism regarding spontaneous sister chromatid exchange (SCE), i.e., a mixed population consisted of cells with extremely high SCE levels characteristic of BS and cells with low SCE levels indistinguishable from that of normal control cells. On the other hand, the other two cell lines maintained a monomorphic population with high SCE levels at least until 30 weeks after EBV infection. The proportion of the cells with high SCE levels in the cell lines with dual phenotype declined as the population doubling numbers (PDN) increased with time and they became ultimately undetectable. The proportion of cells with low SCE levels at the time of EBV infection was estimated in one of these LCLs as 0.075% by extrapolating the linear regression of the logit for the proportion plotted against PDN. In view of the well‐known stability of the monomorphic phenotype in representative BS LCLs during extended cultivation, together with the present observations on the dual phenotype, we conclude that the frequent establishment of BS LCLs exclusively with low spontaneous SCE levels is attributable to the various proportions of low‐SCE cells existing in vivo in the B‐lymphocytes pool of BS individuals and to the selective pressure against the high‐SCE cells in in vitro cultures.