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For estimating the genetic effects of space radiation, an effort has been made to establish the methodology for detecting the influences of low-dose ionizing radiation at chromosome level. Human lymphoblastoid cell TK6-20C was irradiated with 10 cGy of X-rays or C-ions and mutation frequency (MF) at the heterozygous thymidine kinase (TK) locus was determined by judgment of TFT resistance. Although an increase in MF from 5.7 x 10(exp -6) to 6.9 x 10(exp -6) by X-ray irradiation was not statistically significant, C-ion exposure increased MF to 17.9 x 10(exp -6), about 3-fold induction over background level. This induction was due to the enhancement of TK mutants exhibiting hemizygous-type LOH (loss of heterozygosity). Surprisingly the radiation-specific LOH patterns were observed in more than half of these hemizygous-type LOH events. Such LOH mutants can be considered as a result of end-joining repair of DNA double-strand breaks (DSB). Recently the restriction enzyme site I-SceI was introduced into the thymidine kinase (tk) gene of human lymphoblastoid cell line TK6 and a system was established to investigate the fate of DSBs quantitatively and qualitatively at molecular level. In this proceeding, it is reported that the results of fate of site-directed DSB are well consistent with the above molecular analysis for LOH mutants obtained after low-dose ionizing radiation exposure. Here, also proposed is the analysis by introducing I-SceI site into the TK locus of the cells returned from International Space Station (ISS) and detecting whether the fate of DSBS can be modified by the stay in ISS. In other words, such long stay can be considered as priming effect in the adaptive response., 資料番号: AA0046917027

A major issue in radiation and space biology is whether gene expression levels are altered in cells exposed to gravity-changing stress. In the present study, genes up- or down-regulated in radiation-sensitive human RSa cells cultured under gravity-changing conditions, were identified using a PCR-based mRNA differential display method. Exposure of cells to gravity-changing stress was performed by free-fall with a drop-shaft facility. Among the candidates for gravity-changing stress-responsive genes obtained by the differential display analysis, the translocation-associated membrane protein (TRAM) and lactate dehydrogenase A (LDH-A) genes were confirmed by Northern blotting analysis to exhibit early increased expression. Thus, TRAM and LDH-A were found to be candidates for the genes which play a role in the cellular response to gravity-changing stress. TRAM is an endoplasmic reticulum (ER) stress protein, therefore, it is also suggested that ER is a candidate for cellular organs sensitive to gravity-changing stress., 資料番号: AA0045438002

宇宙利用シンポジウム 宇宙科学研究所 20030120-20030121 神奈川 日本, Space Utilization Symposium Institute of Space and Astronautical Science 20030120-20030121 Kanagawa Japan, 資料番号: AA0045438000

Effect of low dose irradiation was investigated in human neuronal progenitor cells. As a result, over 1 Gy X-ray irradiation caused apoptosis and lipid peroxidation. DNA array assay was tested using a smaller dose (0.5 Gy) than that of 1 Gy, and it was found that it still caused apoptosis related gene expressions., 資料番号: AA0046917025

It was previously found that protease activation just after UV irradiation is induced in cultured human UVAP-1 cells. It was here investigated whether UV-activated protease activity is affected by exposure of human UVAP-1 cells to gravity-changing stress prior to UV irradiation. Levels of UV-induced protease activity were found to be increased to more extent in UVAP-1 cells exposed to drop shaft prior to UV irradiation than in cells exposed to UV irradiation alone. The cell lysate that was exposed to mock-treatment, gravity-changing stress alone, UV irradiation alone and gravity-changing stress plus UV irradiation, was partially purified by TSKgel G2000SW column chromatography. Some fractions that show high protease activity were detected in separated samples treated with both gravity-changing stress and UV irradiation. Protease activities of the fractions were effectively inhibited by cysteine protease inhibitor, E-64. To purify E-64 sensitive protease, E-64 affinity column chromatography was carried out using the cell lysate treated with both of gravity-changing stress and UV irradiation. The identification and analysis of purified proteases are in progress., 資料番号: AA0045438001