Alterations in histone acetylation following exposure to <Superscript>60</Superscript>Co γ-rays and their relationship with chromosome damage in human lymphoblastoid cells

Chromosome damage is related to DNA damage and erroneous repair. It can cause cell dysfunction and ultimately induce carcinogenesis. Histone acetylation is crucial for regulating chromatin structure and DNA damage repair. Ionizing radiation (IR) can alter histone acetylation. However, variations in histone acetylation in response to IR exposure and the relationship between histone acetylation and IR-induced chromosome damage remains unclear. Hence, this study investigated the variation in the total acetylation levels of H3 and H4 in human lymphocytes exposed to 0–2 Gy ⁶⁰Co γ-rays. Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase (HDAC) inhibitor, was added to modify the histone acetylation state of irradiated cells. Then, the total acetylation level, enzyme activity, dicentric plus centric rings (dic?+?r) frequencies, and micronucleus (MN) frequencies of the treated cells were analyzed. Results indicated that the acetylation levels of H3 and H4 significantly decreased at 1 and 24 h, respectively, after radiation exposure. The acetylation levels of H3 and H4 in irradiated groups treated with SAHA were significantly higher than those in irradiated groups that were not treated with SAHA. SAHA treatment inhibited HDAC activity in cells exposed to 0–1 Gy ⁶⁰Co γ-rays. SAHA treatment significantly decreased dic?+?r/cell and MN/cell in cells exposed to 0.5 or 1.0 Gy ⁶⁰Co γ-rays relative to that in cells that did not receive SAHA treatment. In conclusion, histone acetylation is significantly affected by IR and is involved in chromosome damage induced by ⁶⁰Co γ-radiation.     

Chromosome aberrations and response to γ-ray challenge in lymphocytes of workers exposed to 1,3-butadiene

An integrated population monitoring study was initiated to investigate whether occupational exposure to current low levels of butadiene is mutagenic to workers. Ten exposed workers (mean production area concentration of 3.5 ppm) and 10 matched plant controls(mean exposure to 0.03 ppm) were selected and blood samples were collected for our study. The standard cytogenetic assay was used to determine chromosome aberration frequencies. In addition, a challenge assay was used to determine response to γ-rays as an indication of DNA repair deficiencies. In the latter assay, cells were exposed to γ-rays at the G1 phase of the cell cycle in vitro and the frequencies of chromosome aberrations in the first post-irradiation metaphase cells were quantitated. Based on results of the cytogenetic assay, the exposed group had a higher frequency of cells with chromosome aberrations and higher chromatid breaks per 100 cells compared with the control. However, the difference was not significant (p > 0.1). With the challenge assay, the exposed group had a higher frequency of aberrant cells (p < 0.04), chromatid breaks (p < 0.05), deletions (p < 0.07), and dicentrics (p < 0.02) than the controls. In addition, the dicentric frequencies from workers were significantly correlated with the presence of a butadiene metabolite [1,2-dihydroxy-4-(N-acetyl-cysteinyl-S)butane] in urine with a correlation of coefficient of 0.6 (p < 0.01). Two outliers were identified and our interpretation of their responses will be discussed. This study indicates that the workers had exposure-induced mutagenic effects. Together with the observation of gene mutation in a subset of the present population, this study indicates that the current occupational exposure to butadiene may not be safe to workers.     

THE RELATION BETWEEN DNA SYNTHESIS AND CHROMOSOME STRUCTURE AS RESOLVED BY X-RAY DAMAGE

Vicia faba root tip cells were treated for short periods with tritiated thymidine, either immediately before or after exposure of roots to x-rays, and autoradiograph preparations were analysed in an attempt to test the hypothesis that chromatid type (B') aberrations are induced only in those chromosome regions that have synthesized DNA prior to x-irradiation, whereas chromosome type (B') aberrations are induced only in unduplicated chromosome regions. Studying the relation between presence or absence of label at loci involved in aberrations, in cells irradiated at different development stages, and the pattern of labelling in cells carrying both types of aberration leads to the conclusion that B' aberrations are induced only in unreplicated chromosome regions. Following replication, only B' aberrations are induced, but these aberrations are also induced in chromosome regions preparing to incorporate DNA. It is suggested that the doubled response of the chromosome to x-rays prior to DNA incorporation might reflect a physical separation of replicating units prior to replication. The aberration yields in damaged cells which were irradiated in G₁ S, and early G₂ were in the ratio of 1.0:2.0:3.2. The data indicate that the increased yield of B' in early G₂ relative to S cells may be a consequence of changes in the spatial distribution of the chromosomes within the nucleus.     

The effects of X-rays on the chromosomes of locust embryos

The variation in yield and the dose-response for chromatid aberration types following x-irradiation of Schistocerca gregaria embryo cells is described. Marked variations in yield are found for all aberration types during the G₂ and latter part of S stages of interphase. Only gaps appear to follow similar curves, other aberration types having unique patterns of response. The dose exponents for the various chromatid aberration types are similar to, but lower than, those reported for other organisms. Chromatid “breaks” appear to have a dose exponent greater than 1.0 — a fact which is in conformation with the exchange hypothesis. The chromosome radiosensitivity of this organism is similar to that reported for other organisms.     

Excess processing of oxidative damaged bases causes hypersensitivity to oxidative stress and low dose rate irradiation

Abstract

Ionizing radiations such as X-ray and γ-ray can directly or indirectly produce clustered or multiple damages in DNA. Previous studies have reported that overexpression of DNA glycosylases in Escherichia coli (E. coli) and human lymphoblast cells caused increased sensitivity to γ-ray and X-ray irradiation. However, the effects and the mechanisms of other radiation, such as low dose rate radiation, heavy-ion beams, or hydrogen peroxide (H₂O₂), are still poorly understood. In the present study, we constructed a stable HeLaS3 cell line overexpressing human 8-oxoguanine DNA N-glycosylase 1 (hOGG1) protein. We determined the survival of HeLaS3 and HeLaS3/hOGG1 cells exposed to UV, heavy-ion beams, γ-rays, and H₂O₂. The results showed that HeLaS3 cells overexpressing hOGG1 were more sensitive to γ-rays, OH^?, and H₂O₂, but not to UV or heavy-ion beams, than control HeLaS3. We further determined the levels of 8-oxoG foci and of chromosomal double-strand breaks (DSBs) by detecting γ-H2AX foci formation in DNA. The results demonstrated that both γ-rays and H₂O₂ induced 8-oxoguanine (8-oxoG) foci formation in HeLaS3 cells. hOGG1-overexpressing cells had increased amounts of γ-H2AX foci and decreased amounts of 8-oxoG foci compared with HeLaS3 control cells. These results suggest that excess hOGG1 removes the oxidatively damaged 8-oxoG in DNA more efficiently and therefore generates more DSBs. Micronucleus formation also supported this conclusion. Low dose-rate γ-ray effects were also investigated. We first found that overexpression of hOGG1 also caused increased sensitivity to low dose rate γ-ray irradiation. The rate of micronucleus formation supported the notion that low dose rate irradiation increased genome instability.     

Mitotic recombination induced by chemical and physical agents in the yeast Saccharomyces cerevisiae

The treatment of diploid cultures of yeast with ultraviolet light (UV), γ-rays, nitrous acid (NA) and ethyl methane sulphonate (EMS) results in increases in cell death, mitotic gene conversion and crossing-over. Acridine orange (AO) treatment, in contrast, was effective only in increasing the frequency of gene conversion. The individual mutagens were effective in the order UV > NA > γ-rays > AO > EMS. Prior treatment of yeast cultures in starvation medium produced a significant reduction in the yield of induced gene conversion.The results have been interpreted on the basis of a general model of mitotic gene conversion which involves the post-replication repair of induced lesions involving de novo DNA synthesis without genetic exchange. In contrast mitotic crossing-over appears to involve the action of a repair system independent from excision or post-replication repair which involves genetic exchange between homologous chromosomes.     

Cytochrome P-450 and the activation of promutagens in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae the cellular content of cytochrome P-450 was investigated and shown to be related to the growth phase of aerobic cultures when glucose was the carbon source. When grown on glucose medium the log-phase cells of the diploid strain D5 contained about 9× more cytochrome P-450 than log-phase cells of the diploid strain D4. The D4 cells grown on medium containing glucose contained about 10× more cytochrome P-450 than D4 cell grown on medium containing galactose as carbon source. Cells of strain D4, harvested from log-phase cultures grown on glucose, were capable of metabolizing aflatoxin B₁, dimethylnitrosamine, β-naphthylamine, ethyl carbamate, cyclophosphamide and dimethylsulphoxide to products active genetically in the same cells. The metabolism of the compounds tested was attributed to cyctochrome P-450-dependent mixed-function oxidation since genetic activity was high in log cells grown on medium containing glucose but negligible in log cells grown on medium containing galactose. However, aflatoxin B₁ differed from the other promutagens tested since the genetic activity of this compound in cells grown on galactose medium was similar to the activity in cells grown on glucose medium. This result is discussed in relation to enzyme systems which could metabolize aflatoxin B₁. The results of treating log-phase cells of the strain D5, grown on medium containing glucose, with aflatoxin B₁ and dimethylnitrosamine are presented and compared with the results from the strain D4.     

Carrageenan-induced decline of natural killer activity: II. Inhibition of cytolysis by adherent non-T Ia-negative suppressor cells activated in vivo

The intravenous injection of 1 to 2 mg of ι-carrageenan (CAR) into (C57BL/6 × C3H)F₁ or BALB/c mice causes a prompt and substantial decline of splenic natural killer (NK) activity against YAC-1 lymphoma targets lasting approximately 1 week in F₁ mice. During this time, NK activity can be enhanced by administration of the interferon inducer polyinosinic-polycytidilic acid. The in vivo effect of CAR requires neither an intact thymus nor unimpaired proliferative capacity of lymphomyeloid cells, according to experiments in congenitally athymic BALB/c.nu/nu mice and in preirradiated (700 rad of γ-rays) F₁ hybrids. The splenic cytotoxic activity lowered in vivo by CAR can be restored in vitro by removing subpopulations of cells that adhere to glass wool or carbonyl iron particles, but not to Sephadex G-10. Thus, the lytic function of mature NK cells is reversibly inhibited in the spleens of CAR-treated animals; differentiation and maturation of NK precursors are not inhibited, as judged by the enhancing effect on NK activity of the interferon inducer. Splenocytes of CAR-treated donors suppress cytotoxic effectors of untreated mice in cell mixing experiments. Athymic and preirradiated animals given CAR are fully competent donors of suppressor cells. Suppressor function is insensitive to irradiation (2000 rad of γ-rays in vitro) and to anti Thy-1 or anti-Ia antibody plus complement. Inhibition of NK cytolysis is not restricted by the major histocompatibility complex and can also be mediated by cell-free supernatants in which suppressor cells were incubated. This model of reversible inhibition of NK activity suggests that activation of thymus-independent suppressor cells is one of the regulatory mechanisms of natural cytotoxic activity in vivo.     

温度胁迫对白车轴草水浸提液化感作用的影响

采用蚕豆根尖细胞微核试验和染色体畸变试验,研究了温度胁迫下白车轴草水浸提液对蚕豆根尖细胞的化感作用。结果表明:不同温度(5℃、25℃和35℃)处理后的白车轴草的水浸提液对蚕豆根尖细胞有丝分裂指数的影响为低浓度促进,高浓度抑制。在白车轴草水浸提液的作用下,蚕豆根尖细胞内出现了多种染色体畸变,如微核、染色体断片、染色体桥、落后染色体等,对微核率和染色体畸变率的诱导效应表现为随水浸提液浓度的增大而增大。温度胁迫后的化感作用明显大于胁迫前,其化感效应表现为低温(5℃)下白车轴草水浸提液高温(35℃)常温(25℃)白车轴草水浸提液。推测原因可能是温度胁迫改变和增加了化感物质的释放。     

Radiation-induced chromosomal aberrations in human lymphocytes. I. Dependence on the dose of gamma-rays and an anomaly at low doses

Cultures of human lymphocytes obtained from blood of healthy adult donors were irradiated with different doses of ⁶⁰Co γ-rays and the irradiated cells were analysed in metaphase 50 h after irradiation. The effect (total yield of abberations of chromosome type, or total yield of exchange type abberations) produced by the lowest dose (5 rad) appears to be statistically significant in a sample of 1500 cells. In the usual dose range (25–400 rad), both parabolic and linear-quadratic equations give a satisfactory fit of experimental data (dicentrics, fragments, or all aberrations of chromosome type). Low doses of γ-rays, however, produced more aberrations than expected, if one extrapolates dose-effect curves from higher doses. Both relations should be considered, therefore, merely as empirical equations. Dicentrics show at low doses (10–30 rad) a plateau which appears to be statistically significant. Some indications are obtained that the total number of chromosome-type aberrations is a more reliable criterion of cytogenetic damage than the usually accepted yeild of dicientrics and rings.     

Types and frequencies of chromosomal aberrations induced by irradiation of different parts of interphase in Crepis capillaris

Quantitative and qualitative estimates of chromosomal damage in roots of Crepis capillaris were made in metaphase cells at many time intervals after irradiation with 200 or 400 rad of ⁶⁰Co gamma-rays. The results have confirmed the general pattern described for cells of other organisms, and have revealed in addition the following new facts. (1) The formation of aberrations of chromosome and chromatid type is not determined by the time of chromosome duplication alone. (2) The relative frequencies of different types of discontinuity form peaks with the following time succession: single gaps, chromatid breaks, isolocus breaks. (3) The location of peaks does not depend on the radiation dose, and shows no correlation which the time of synthesis. (4) Irradiation of G₂ induces a significant number of chromosome-type exchanges in Crepis. (5) Higher doses of radiation in G₂ favour the formation of chromatid over chromosome exchanges and of isochromatid breaks over chromosome breaks. A new interpretation of the production of certain types of aberration is discussed.     

The impact of autophagy on cell death modalities in CRL-5876 lung adenocarcinoma cells after their exposure to γ-rays and/or erlotinib

In most patients with lung cancer radiation treatment is used either as single agent or in combination with radiosensitizing drugs. However, the mechanisms underlying combined therapy and its impact on different modes of cell death have not yet been fully elucidated. We aimed to examine effects of single and combined treatments with γ-rays and erlotinib on radioresistant CRL-5876 human lung adenocarcinoma cells with particular emphasis on cell death. CRL-5876 cells were treated with γ-rays and/or erlotinib and changes in cell cycle, DNA repair dynamics, ultrastructure, nuclear morphology and protein expression were monitored at different time points. To reveal the relationship between types of cell death that arise after these treatments, autophagy was blocked with chloroquine. We found that higher dose of γ-rays causes G2/M arrest while adding of erlotinib to this treatment decreases the number of cells in S phase. Impact of erlotinib on kinetics of disappearance of irradiation-induced DNA double strand breaks is reflected in the increase of residual γ-H2AX foci after 24 h. γ-rays provoke cytoprotective autophagy which precedes development of senescence. Erlotinib predominantly induces apoptosis and enlarges the number of apoptotic cells in the irradiated CRL-5876 cells. Chloroquine improved cytotoxicity induced by radiation and erlotinib, increased apoptosis and decreased senescence in the CRL-5876 cells. The results obtained on CRL-5876 cells indicate significant radiosensitizing effect of erlotinib and suggest that chloroquine in the combination with the above treatments may have an additional antitumor effect in lung adenocarcinoma.     

The mutagenic activity of aflatoxin B1 in the Cricetulus griseus hamster and Macaca mulatta monkey

Chromosome aberrations were scored in bone marrow cells of Cricetulus griseus hamsters and Macaca mulatta monkeys given a single i.p. injection of aflatoxin B1 (AFB1). The mutagenic activity of AFB1 was assessed by the percentage of cells bearing aberrations and by the total frequency of chromosome and chromatid breaks. Chinese hamsters were treated with five different doses of AFB1 ranging from 1 microgram to 5 mg/kg (LD50/30 = 12.2 mg/kg) and the aberration yields at each AFB1 dose level tested were determined at 24 h intervals for 5 consecutive days. Compared to controls the increase in the two types of chromosome abnormalities was significant in all tests. At 5 mg/kg of AFB1 the tests were carried out over a period of 92 days to assure the analysis of aberration yields with time. All chromosome aberration assays conducted during this period showed significant increases in the frequencies of aberrant cells and chromosome and chromatid breaks in comparison to controls. Macaque monkeys were treated in the same fashion using 0.1 and 1.0 mg/kg of AFB1 and the dynamics of chromosome aberration yields was analyzed for a period of 730 days. Similarly as in the case of Chinese hamsters the percentage of cells with aberrations and the frequency of chromosome and chromatid breaks were always higher in this period than the control value. Long-term aberration yield data obtained experimentally were expressed in the form of analytical curves which allowed to establish the time when the yields of aberrant cells reached their maxima and when they returned to the control level. In both animal species tested the courses of analytical curves had a similar dynamics. Factors that might be responsible for a long-term persistence and relatively great fluctuations of the chromosome aberration yields encountered after a single injection of AFB1 are discussed in detail.     

Chromosome aberrations and radiation-induced cell death. I. Transmission and survival parameters of aberrations

Synchronous cultures of V₇₉ Chinese hamster cells were irradiated in G₁ with 300 rad of X-rays. Cells were collected for 2-h intervals after synchronization to include the first three post-irradiation divisions and were scored for chromosome aberrations. After the first post-irradiation division, asymmetrical exchanges were distributed according to the Poisson formula and both the asymmetrical exchange frequency and the acentric fragment frequency exhibited significant variations with collection time. Formulae derived from a previous mathematical analysis were used in conjunction with the aberration frequencies observed at the first, second, and third post-irradiation divisions to predict transmission and survival parameters for specific chromosomal aberrations.The probability, 2T, that an acentric fragment will be transmitted to a daughter cell at anaphase was found to be 0.57. The probability, W, that a two-break aberration (asymmetrical exchange) will be transmitted and observed at the next division was 0.56. Finally, the probability, P, that a cell will survive to a subsequent mitosis after losing a single acentric fragment was about 1.0 for one post-irradiation generation but somewhat less for two generations.     

Characteristics of γ-ray-induced chromosomal aberrations in mutagen-sensitive mutants of L5178Y cells

We have examined the chromosomal radiosensitivities of an ionizing-radiation- and MMS-sensitive mutant (M10), and a UV- and 4NQO-sensitive mutant (Q31), isolated from mouse lymphoma L5178Y cells, with regard to killing effects. In the first mitoses after 100 R γ-irradiations, it was found that M10 cells were highly radiosensitive in terms of chromosomal aberrations accompanying longer mitotic delay (3 h); the frequencies of both chromatid-type and chromosome-type aberrations were, respectively, about 7 and 4 times higher than that of wild-type L5178Y cells. Furthermore, chromatid exchanges, particularly triradials, isochromatid breaks with sister union, and chromatid gaps and breaks were markedly enhanced at G₁ phase of M10 cells. In contrast, the chromosomal radiosensitivity of Q31 cells after 100 R irradiation was similar to that of L5178Y cells. On the other hand, spontaneous aberration frequencies (overall breaks per cell) of M10 and Q31 cells were, respectively, 5.1 and 2.2 times higher than that of wild-type L5178Y cells. The chromosomal hypersensitivity to γ-rays in M10 cells is discussed in the light of knowledge obtained from ataxia telangiectasia cells.     

Aflatoxin formation,lipid synthesis,and glucose metabolism by Aspergillus parasiticus during incubation with and without agitation

Glucose utilization, growth of mold, and synthesis of aflatoxin and total lipid by Aspergillus parasiticus were studied with cultures that were incubated statically and with agitation. With both cultural conditions, maximal toxin formation occurred at 5 days which coincided with the end of rapid mold growth and rapid uptake of glucose. The toxin concentration decreased as incubation continued. The pattern for formation and depletion of total lipid was similar to that for aflatoxin. Maximal yields of toxin and of total lipid did not coincide with maximal production of mold mycelium. Incubation with agitation enhanced mold growth, consumption of glucose, and production of aflatoxin and total lipid during the first 3 days. Generally, more growht occured in agitated cultures, but maximal yields of aflatoxin and total lipid were lower than in quiescent cultures. The need for limited, but not excessive, O₂ for synthesis of aflatoxin and lipid also was demonstrated by varying the volume of medium in flasks that were incubated quiescently. Incorporation of [1-¹⁴C] glucose into aflatoxin indicated that limiting the O₂ supply and thereby favoring glucose catabolism via the Embden-Meyerhof pathway enhanced toxin formation. Aflatoxin formation also was greater when oxidative respiration of the mold was restricted by a metabolic inhibitor. Results suggest that the degree of aeration of the culture is important in controlling biosynthesis of aflatoxin.     

Enhancement of aflatoxin B1 cytotoxicity in differentiated rat hepatoma cultures by a prior glucocorticoid treatment of the monolayer.

The cytotoxic effect of aflatoxin B₁ on cultures of a differentiated rat hepatoma cell line, Faza 967, has been evaluated by scoring the surviving colonies two weeks after briefly exposing the freshly plated cells to the mycotoxin. At the lowest concentration, aflatoxin B₁ exhibits no toxicity, unless the cultures have been pretreated with dexamethasone. HF-1, an hepatoma hybrid cell line exhibiting extinction of the hepatic functions and HF1-4, its subclone, that reexpresses all of these functions, have been compared. A 6hrs exposure to 60ng/ml aflatoxin B₁ is not toxic for HF₁ even after an hormonal treatment, while dexamethasone enhances the effect on HF₁-4. Glucocorticoïds have been shown previously to induce, in the differentiated clones, the hydroxylation of bile acid - a cytochrome P-450-mediated reaction ; in contrast, 3-methylcholanthrene, an inducer of benzopyrene hydroxylase in hepatoma cultures, is without effect on bile acid metabolism and on aflatoxin B₁ cytotoxicity. These results suggest that in the differentiated hepatoma cells, aflatoxin B₁ is converted into a cytotoxic metabolite by a glucocorticoïd-induced monooxygenase belonging to the cytochrome P-450-related group.     

Cytogenetic response to asbestos fibers in cultured human primary mesothelial cells from 10 different donors

The ability of amosite asbestos fibers to induce chromosomal aberrations in human primary mesothelial cells obtained from pleural effusions of 10 noncancerous patients was investigated. The glutathione S-transferase M1 (GSTM1) genotypes of the patients were determined, since the GSTM1 null genotype has been associated with increased susceptibility to lung cancer and chemically induced cytogenetic damage. Four of the patients represented the GSTM1 null genotype, and six the GSTM1 positive genotype. Successful chromosome aberration analyses were obtained from six cases, three of them with the GSTM1 null genotype. The level of aberrant cells in unexposed cultures ranged from 2.0% to 7.5%. Statistically significant increases (2.3–3.0-fold compared to controls) in the number of aberrant cells were observed in two cases only: in one case treated with 1 μg/cm² of amosite, and in another treated with 2 μg/cm² of amosite. Cell cultures from four individuals showed minor or no increases in the numbers of aberrant cells in the doses tested (1 and 2 μg/cm²). Chromosome breaks were the major type of aberration. The amosite exposed cells with significantly increased aberrations were from patients with GSTM1 positive genotypes. Two cases that showed no cytogenetic response to asbestos fibers were of the GSTM1 null genotype. Thus, our results suggest that the lack of the GSTM1 gene does not render human mesothelial cells more susceptible to chromosomal damage induced by asbestos. GSTM1 null cells appeared, however, to be more sensitive to the growth inhibitory effects of asbestos than did GSTM1 positive cells. Variation in the cytogenetic response of human primary mesothelial cells to asbestos fibers was observed to exist, but the fibers do not appear to be potent inducers of structural chromosomal aberrations in these cells. It remains to be established whether individual sensitivity to asbestos fibers, due to specific genetic traits, exists.     

Phloroglucinol (1,3,5-trihydroxybenzene) protects against ionizing radiation-induced cell damage through inhibition of oxidative stress in vitro and in vivo

Exposure of cells to γ-rays induces the production of reactive oxygen species (ROS) that play a main role in ionizing radiation damage. We have investigated the radioprotective effect of phloroglucinol (1,3,5-trihydroxybenzene), phlorotannin compound isolated from Ecklonia cava, against γ-ray radiation-induced oxidative damage in vitro and in vivo. Phloroglucinol significantly decreased the level of radiation-induced intracellular ROS and damage to cellular components such as the lipid, DNA and protein. Phloroglucinol enhanced cell viability that decreased after exposure to γ-rays and reduced radiation-induced apoptosis via inhibition of mitochondria mediated caspases pathway. Phloroglucinol reduced radiation-induced loss of the mitochondrial membrane action potential, reduced the levels of the active forms of caspase 9 and 3 and elevated the expression of bcl-2. Furthermore, the anti-apoptotic effect of phloroglucinol was exerted via inhibition of mitogen-activated protein kinase kinase-4 (MKK4/SEK1), c-Jun NH₂-terminal kinase (JNK) and activator protein-1 (AP-1) cascades induced by radiation exposure. Phloroglucinol restored the level of reduced glutathione (GSH) and protein expression of a catalytically active subunit of glutamate-cysteine ligase (GCL), which is a rate-limiting enzyme in GSH biosynthesis. In in vivo study, phloroglucinol administration in mice provided substantial protection against death and oxidative damage following whole-body irradiation. We examined survival with exposure to various radiation doses using the intestinal crypt assay and determined a dose reduction factor (DRF) of 1.24. Based on our findings, phloroglucinol may be possibly useful as a radioprotective compound.