RESUMO
We describe here an accelerator-based neutron irradiation facility, intended to expose blood or small animals to neutron fields mimicking those from an improvised nuclear device at relevant distances from the epicenter. Neutrons are generated by a mixed proton/deuteron beam on a thick beryllium target, generating a broad spectrum of neutron energies that match those estimated for the Hiroshima bomb at 1.5 km from ground zero. This spectrum, dominated by neutron energies between 0.2 and 9 MeV, is significantly different from the standard reactor fission spectrum, as the initial bomb spectrum changes when the neutrons are transported through air. The neutron and gamma dose rates were measured using a custom tissue-equivalent gas ionization chamber and a compensated Geiger-Mueller dosimeter, respectively. Neutron spectra were evaluated by unfolding measurements using a proton-recoil proportional counter and a liquid scintillator detector. As an illustration of the potential use of this facility we present micronucleus yields in single divided, cytokinesis-blocked human peripheral lymphocytes up to 1.5 Gy demonstrating 3- to 5-fold enhancement over equivalent X-ray doses. This facility is currently in routine use, irradiating both mice and human blood samples for evaluation of neutron-specific biodosimetry assays. Future studies will focus on dose reconstruction in realistic mixed neutron/photon fields.
Assuntos
Modelos Biológicos , Nêutrons , Guerra Nuclear , Animais , Humanos , Testes para MicronúcleosRESUMO
While gene expression studies have proved extremely important in understanding cellular processes, it is becoming more apparent that there may be differences in individual cells that are missed by studying the population as a whole. We have developed a qRT-PCR protocol that allows us to assay multiple gene products in small samples, starting at 100 cells and going down to a single cell, and have used it to study radiation responses at the single-cell level. Since the accuracy of qRT-PCR depends greatly on the choice of "housekeeping" genes used for normalization, initial studies concentrated on determining the optimal panel of such genes. Using an endogenous control array, it was found that for IMR90 cells, common housekeeping genes tend to fall into one of two categories-those that are relatively stably expressed regardless of the number of cells in the sample, e.g., B2M, PPIA, and GAPDH, and those that are more variable (again regardless of the size of the population), e.g., YWHAZ, 18S, TBP, and HPRT1. Further, expression levels in commonly studied radiation-response genes, such as ATF3, CDKN1A, GADD45A, and MDM2, were assayed in 100, 10, and single-cell samples. It is here that the value of single-cell analyses becomes apparent. It was observed that the expression of some genes such as FGF2 and MDM2 was relatively constant over all irradiated cells, while that of others such as FAS was considerably more variable. It was clear that almost all cells respond to ionizing radiation but the individual responses were considerably varied. The analyses of single cells indicate that responses in individual cells are not uniform and suggest that responses observed in populations are not indicative of identical patterns in all cells. This in turn points to the value of single-cell analyses.
Assuntos
Fibroblastos/citologia , Fibroblastos/efeitos da radiação , Análise de Célula Única , Fibroblastos/metabolismo , Humanos , Reação em Cadeia da Polimerase em Tempo Real , Transcriptoma/efeitos dos fármacosRESUMO
Exposure to ionizing radiation may induce a heritable genomic instability phenotype that results in a persisting and enhanced genetic and functional change among the progeny of irradiated cells. Since radiation-induced bystander effects have been demonstrated with a variety of biological end points under both in vitro and in vivo conditions, this raises the question whether cytoplasmic irradiation or the radiation-induced bystander effect can also lead to delayed genomic instability. In the present study, we used the Radiological Research Accelerator Facility charged-particle microbeam for precise nuclear or cytoplasmic irradiation. The progeny of irradiated and the bystander human hamster hybrid (A(L)) cells were analyzed using multicolor banding (mBAND) to examine persistent chromosomal changes. Our results showed that the numbers of metaphase cells involving changes of human chromosome 11 (including rearrangement, deletion and duplication) were significantly higher than that of the control in the progeny of both nuclear and cytoplasmic targeted cells. These chromosomal changes could also be detected among the progeny of bystander cells. mBAND analyses of clonal isolates from nuclear and cytoplasm irradiations as well as the bystander cell group showed that chromosomal unstable clones were generated. Analyses of clonal stability after long-term culture indicated no significant change in the number of unstable clones for the duration of culture in each irradiated group. These results suggest that genomic instability that is manifested after ionizing radiation exposure is not dependent on direct damage to the cell nucleus.
Assuntos
Efeito Espectador/genética , Efeito Espectador/efeitos da radiação , Cromossomos Humanos Par 11/genética , Cromossomos Humanos Par 11/efeitos da radiação , Instabilidade Genômica/efeitos da radiação , Células Híbridas/citologia , Células Híbridas/efeitos da radiação , Animais , Células CHO , Núcleo Celular/genética , Núcleo Celular/efeitos da radiação , Células Clonais/citologia , Células Clonais/metabolismo , Células Clonais/efeitos da radiação , Cricetinae , Cricetulus , Citoplasma/genética , Citoplasma/efeitos da radiação , Humanos , Células Híbridas/metabolismo , Fatores de TempoRESUMO
Knowledge of cellular responses in tissue microenvironment is crucial for the accurate prediction of human health risks following chronic or acute exposure to ionizing radiation (IR). With this objective, we investigated the radio responses for the first time in three-dimensional (3D) artificial human skin tissue microenvironment after gamma-rays radiation. IR-induced DNA damage/repair response was assessed by immunological analysis of well-known DNA double strand break (DSB) repair proteins, i.e. 53BP1 and phosphorylated ataxia telangiectasia mutated(ser1981) (ATM(ser1981)). Efficient 53BP1 and phosphorylated ATM foci formation was observed in human EpiDerm tissue constructs after low and high doses of gamma-rays. Interestingly, EpiDerm tissue constructs displayed less 53BP1 and ATM foci number at all radiation doses (0.1, 1, 2.5 and 5 Gy) than that observed for 2D human fibroblasts. DSB repair efficiency judged by the disappearance of 53BP1 foci declined with increasing doses of gamma-rays and tissue constructs irradiated with 2.5 and 5 Gy of gamma-rays displayed 53BP1 foci persisting up to 72 h of analysis. Pretreatment of EpiDerm tissue constructs with LY294002, [an inhibitor of phosphatidylinositol-3 kinase and PI-3 kinase like kinases (PIKK)] completely abolished IR-induced 53BP1 foci formation and increased the apoptotic death. This observation indicates the importance of PIKK signalling pathway for efficient radiation responses in intact tissue constructs. In summary, we have successfully demonstrated the feasibility of monitoring the DNA damage response in human skin tissue microenvironment. In this system, 53BP1 can be used as a useful marker for monitoring the DSB repair efficiency.
Assuntos
Dano ao DNA/efeitos da radiação , Reparo do DNA/efeitos da radiação , Raios gama/efeitos adversos , Modelos Biológicos , Pele/efeitos da radiação , Biomarcadores/metabolismo , Linhagem Celular , Cromonas/farmacologia , Quebras de DNA de Cadeia Dupla/efeitos dos fármacos , Quebras de DNA de Cadeia Dupla/efeitos da radiação , Dano ao DNA/efeitos dos fármacos , Reparo do DNA/efeitos dos fármacos , Relação Dose-Resposta à Radiação , Inibidores Enzimáticos/farmacologia , Fibroblastos/efeitos dos fármacos , Fibroblastos/metabolismo , Fibroblastos/efeitos da radiação , Humanos , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Morfolinas/farmacologia , Fosfatidilinositol 3-Quinases/metabolismo , Radiação Ionizante , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/efeitos da radiação , Pele/efeitos dos fármacos , Pele/metabolismo , Proteína 1 de Ligação à Proteína Supressora de Tumor p53RESUMO
Our earlier study demonstrated the induction of PKC isoforms (betaII, PKC-alpha/beta, PKC-theta) by ionizing radiation induced bystander response in human cells. In this study, we extended our investigation to yet another important member of PKC family, PKC epsilon (PKCepsilon). PKCepsilon functions both as an anti-apoptotic and pro-apoptotic protein and it is the only PKC isozyme implicated in oncogenesis. Given the importance of PKCepsilon in oncogenesis, we wished to determine whether or not PKCepsilon is involved in bystander response. Gene expression array analysis demonstrated a 2-3-fold increase in PKCepsilon expression in the bystander human primary fibroblast cells that were co-cultured in double-sided Mylar dishes for 3h with human primary fibroblast cells irradiated with 5Gy of alpha-particles. The elevated PKCepsilon expression in bystander cells was verified by quantitative real time PCR. Suppression of PKCepsilon expression by small molecule inhibitor Bisindolylmaleimide IX (Ro 31-8220) considerably reduced the frequency of micronuclei (MN) induced both by 5Gy of gamma-rays (low LET) and alpha-particles (high LET) in bystander cells. Similar cytoprotective effects were observed in bystander cells after siRNA mediated silencing of PKCepsilon suggestive of its critical role in mediating some of the bystander effects (BE). Our novel study suggests the possibility that PKC signaling pathway may be a critical molecular target for suppression of ionizing radiation induced biological effects in bystander cells.
Assuntos
Fibroblastos/metabolismo , Proteína Quinase C-épsilon/antagonistas & inibidores , Apoptose/efeitos dos fármacos , Apoptose/efeitos da radiação , Efeito Espectador , Citoproteção/efeitos dos fármacos , Citoproteção/efeitos da radiação , Fibroblastos/efeitos dos fármacos , Fibroblastos/patologia , Fibroblastos/efeitos da radiação , Humanos , Indóis/farmacologia , Proteína Quinase C-épsilon/imunologia , RNA Interferente Pequeno/genética , Radiação IonizanteRESUMO
Recent developments in microbeam technology have made drastic improvements in particle delivery, focusing, image processing and precision to allow for rapid advances in our knowledge in radiation biology. The unequivocal demonstration that targeted cytoplasmic irradiation results in mutations in the nuclei of hit cells and the presence of non-targeted effects, all made possible using a charged particle microbeam, results in a paradigm shift in our basic understanding of the target theory and other radiation-induced low dose effects. The demonstration of a bystander effect in 3D human tissue and whole organisms have shown the potential relevance of the non-targeted response in human health. The demonstration of delayed mutations in the progeny of bystander cells suggest that genomic instability induced following ionizing radiation exposure is not dependent on direct damage to cell nucleus. The identification of specific signaling pathways provides mechanistic insight on the nature of the bystander process.
Assuntos
Bioensaio/métodos , Bioensaio/tendências , Efeito Espectador/efeitos da radiação , Técnicas de Cultura de Células/métodos , Técnicas de Cultura de Células/tendências , Radiobiologia/métodos , Radiobiologia/tendências , Animais , Bioensaio/instrumentação , Efeito Espectador/fisiologia , Técnicas de Cultura de Células/instrumentação , Relação Dose-Resposta à Radiação , Desenho de Equipamento , Humanos , Doses de Radiação , Radiobiologia/instrumentaçãoRESUMO
The radiation-induced bystander effect represents a paradigm shift in our understanding of the radiobiological effects of ionizing radiation, in that extranuclear and extracellular events may also contribute to the final biological consequences of exposure to low doses of radiation. Although radiation-induced bystander effects have been well documented in a variety of biological systems, the mechanism is not known. It is likely that multiple pathways are involved in the bystander phenomenon, and different cell types respond differently to bystander signalling. Using cDNA microarrays, a number of cellular signalling genes, including cyclooxygenase-2 (COX-2), have been shown to be causally linked to the bystander phenomenon. The observation that inhibition of the phosphorylation of extracellular signal-related kinase (ERK) suppressed the bystander response further confirmed the important role of the mitogen-activated protein kinase (MAPK) signalling cascade in the bystander process. Furthermore, cells deficient in mitochondrial DNA showed a significantly reduced response to bystander signalling, suggesting a functional role of mitochondria in the signalling process. Inhibitors of nitric oxide (NO) synthase (NOS) and mitochondrial calcium uptake provided evidence that NO and calcium signalling are part of the signalling cascade. The bystander observations imply that the relevant target for various radiobiological endpoints is larger than an individual cell. A better understanding of the cellular and molecular mechanisms of the bystander phenomenon, together with evidence of their occurrence in-vivo, will allow us to formulate a more accurate model for assessing the health effects of low doses of ionizing radiation.
Assuntos
Efeito Espectador , DNA/efeitos da radiação , Junções Comunicantes/efeitos da radiação , Mutação , Transdução de Sinais/efeitos da radiação , Animais , Células Cultivadas , Conexina 43/metabolismo , Meios de Cultivo Condicionados/metabolismo , Ciclo-Oxigenase 2/metabolismo , Citocinas/metabolismo , DNA Mitocondrial/metabolismo , Relação Dose-Resposta à Radiação , Junções Comunicantes/metabolismo , Humanos , Mitocôndrias/metabolismo , Mitocôndrias/efeitos da radiação , Modelos Biológicos , NF-kappa B/metabolismo , Doses de Radiação , Espécies Reativas de Oxigênio/metabolismoRESUMO
Studies over the last several years have revealed the existence of a biological phenomenon known as "bystander effect", wherein cells that are not exposed to radiation elicit a similar response to that of irradiated cells. Understanding the mechanism(s) underlying the bystander effect is important not only for radiation risk assessment but also for evaluation of protocols for cancer radiotherapy. Evaluation of signaling pathways in bystander cells may provide an insight to understand the molecular mechanisms(s) responsible for this complex phenomenon. With this objective, the time course kinetics of intracellular distribution of protein kinase C (PKC isoforms PKC-betaII, PKC-alpha/beta, PKC-theta) was investigated in total and subcellular (cytosolic and nuclear) fractions of human lung fibroblast (MRC-5) cells. MRC-5 cells were either irradiated or treated with the irradiated conditioned medium collected 1h after 1 or 10 Gy of gamma-irradiation. The radiation dose selected was in the range of therapeutic usage of radiation for the human cancer treatment. Unexpectedly, bystander cells showed higher activation of protein kinase C isoforms as compared to irradiated and sham-treated control cells. Protein kinase C isoforms were more enriched in the nuclear fraction than the cytosolic fraction proteins. Induction of PKC isoforms in bystander cells are due to post-translational modifications as shown by the non-phosphorylated protein kinase C level in both irradiated and bystander cells did not differ from the sham-treated control cells. The specific activation of protein kinase C isoforms in bystander cells as demonstrated for the first time in this study may help to identify the effect of therapeutically used radiation exposure for the tumor destructions along with its implications for adjacent non-irradiated cells and organs.
Assuntos
Efeito Espectador , Fibroblastos/enzimologia , Isoenzimas/metabolismo , Isoenzimas/efeitos da radiação , Proteína Quinase C-alfa/metabolismo , Proteína Quinase C-alfa/efeitos da radiação , Proteína Quinase C/metabolismo , Proteína Quinase C/efeitos da radiação , Ciclo Celular/fisiologia , Ciclo Celular/efeitos da radiação , Linhagem Celular , Núcleo Celular/metabolismo , Meios de Cultivo Condicionados , Citosol/metabolismo , Relação Dose-Resposta à Radiação , Ativação Enzimática/efeitos da radiação , Fibroblastos/ultraestrutura , Humanos , Pulmão/citologia , Proteína Quinase C beta , Proteína Quinase C-theta , Processamento de Proteína Pós-Traducional , Radiação Ionizante , Transdução de SinaisRESUMO
Multiphoton microscopy has been added to the array of imaging techniques at the endstation for the Microbeam II cell irradiator at Columbia University's Radiological Research Accelerator Facility (RARAF). This three-dimensional (3D), laser-scanning microscope functions through multiphoton excitation, providing an enhanced imaging routine during radiation experiments with tissuelike samples, such as small living animals and organisms. Studies at RARAF focus on radiation effects; hence, this multiphoton microscope was designed to observe postirradiation cellular dynamics. This multiphoton microscope was custom designed into an existing Nikon Eclipse E600-FN research fluorescence microscope on the irradiation platform. Design details and biology applications using this enhanced 3D-imaging technique at RARAF are reviewed.
Assuntos
Imageamento Tridimensional/métodos , Microscopia de Fluorescência por Excitação Multifotônica/instrumentação , Microscopia de Fluorescência por Excitação Multifotônica/métodos , Animais , Calibragem , Bovinos , Núcleo Celular/metabolismo , Células Cultivadas , Células Endoteliais/citologia , Desenho de Equipamento , Humanos , Aumento da Imagem/instrumentação , Aumento da Imagem/métodos , Lasers , Óptica e Fotônica , Fótons , Artéria Pulmonar/citologiaRESUMO
PURPOSE: This investigation is aimed to determine the role of low LET (linear energy transfer, gamma-rays) and high LET (alpha-particles) radiations on bystander effect of using the same type of cells and its implications on colony-forming efficiency from a single cell. MATERIALS AND METHODS: Normal human fetal lung (MRC-5), immortalized repair deficient ataxia telangiectasia mutated (ATM) (GM5,849C) and normal (GM637H) fibroblast cells were used. Colony-forming efficiency in bystander cells (GM637H) was studied using the medium transfer technique from the two donor (MRC-5 and GM5,849C) cells and the procedure followed for bystander treatment is presented schematically in Figure 1. Evidence of change in colony formation in bystander cells, was assessed by scavenging nitric oxide (NO). RESULTS: Enhancement of 10 - 30% in colony-forming efficiency was observed in bystander GM637H cells treated with irradiated conditioned medium (ICM) from MRC-5 cells collected 1 h after different doses of either gamma-rays (1, 2.5, 5 and 10 Gy) or alpha particles (0.25, 0.5, 1 and 2.5 Gy) irradiation. Similar results were obtained when ICM derived from the ATM (GM5,849C) cells. However, the stimulation was not dose dependent. Furthermore, we also show that the increase in dilutions of ICM (1:1, 1:5 and 1:10) showed an inverse correlation with cloning efficiency. Treatment of MRC-5 cells with PTIO (2-phenyl-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide) a NO scavenger, 1 h prior to irradiation reduced the enhancement of ICM mediated cell survival. CONCLUSIONS: In the present study, though both the low and high LET radiations enhanced the clonogenic potential of the bystander recipient cells, medium from the ATM defective (GM5,849C) cells after gamma-irradiation showed less stimulating effect than the medium from the normal (MRC-5) cells. However, after alpha-irradiation an inverse effect was seen. NO may play an important role in enhancing the growth potential in these bystander cells.
Assuntos
Efeito Espectador/efeitos da radiação , Fibroblastos/efeitos da radiação , Transferência Linear de Energia , Pulmão/efeitos da radiação , Partículas alfa , Efeito Espectador/fisiologia , Sobrevivência Celular/fisiologia , Sobrevivência Celular/efeitos da radiação , Óxidos N-Cíclicos/farmacologia , Relação Dose-Resposta à Radiação , Fibroblastos/citologia , Fibroblastos/fisiologia , Sequestradores de Radicais Livres/farmacologia , Raios gama , Humanos , Imidazóis/farmacologia , Pulmão/citologia , Pulmão/fisiologia , Óxido Nítrico/metabolismo , Radiação IonizanteRESUMO
OBJECTIVE: There is growing recognition that the effects of ionizing radiation may extend to more than those cells that directly suffer damage to DNA in the cell nucleus. Data from several investigators have indicated that cells neighboring those that are irradiated also demonstrate several responses seen in hit cells--the so-called bystander effect. The microbeam facility at the Center for Radiological Research is particularly well suited for the study of this bystander effect, since it has the ability to place known numbers of charged particles (protons or alpha-particles at LETs from 20 to 180 KeV/microm) at defined positions relative to individual cells. That is, some known fraction of cells in a population can be irradiated through the nucleus, or the cytoplasm or even adjacent to cells through the media. Therefore, using the microbeam it is possible to examine individual cell responses in both hit and nonhit cells in the same population. METHOD AND RESULTS: Alterations in the cyclin-dependent kinase inhibitor CDKN1a (p21/Cip1/WAF1) were quantified at the mRNA level in single normal human fibroblasts following precise delivery of 0 or 10 alpha-particles per cell at 90 KeV/microm to 50% of cells in a population. Semiquantitative RT-PCR of individual hit cells demonstrated increases in the levels of CDKN1A message that followed the kinetics previously described for irradiated populations. Furthermore, nonhit bystander cells also showed increased (though lesser) levels of CDKN1a message. CONCLUSION: Data presented here demonstrate the power of this approach, which combines the ability of the microbeam to irradiate specific cells in a population and the ability to quantify the response to the irradiation in individual targeted and bystander cells.
Assuntos
Partículas alfa , Efeito Espectador/efeitos da radiação , Fibroblastos/metabolismo , Regulação da Expressão Gênica/efeitos da radiação , Inibidor de Quinase Dependente de Ciclina p21/biossíntese , Dano ao DNA/efeitos da radiação , Relação Dose-Resposta à Radiação , Humanos , Doses de Radiação , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fatores de TempoRESUMO
The cellular response to ionizing radiation is not limited to cells irradiated directly but can be demonstrated in neighboring "bystander" populations. The ability of mouse embryonic stem (ES) cells to express a bystander effect and the role of the radioresistance gene Rad9 were tested. Mouse ES cells differing in Rad9 status were exposed to broad-beam 125 keV/ microm 3He alpha particles. All populations, when confluent, demonstrated a dose-independent bystander effect with respect to cell killing, and the Rad9-/- genotype did not selectively alter that response or cell killing after direct exposure to this high-LET radiation. In contrast, relative to Rad9+/+ cells, the homozygous mutant was sensitive to direct exposure to alpha particles when in log phase, providing evidence of a role for Rad9 in repair of potentially lethal damage. Direct exposure to alpha particles induced an increase in the frequency of apoptosis and micronucleus formation, regardless of Rad9 status, although the null mutant showed high spontaneous levels of both end points. All populations demonstrated alpha-particle-induced bystander apoptosis, but that effect was most prominent in Rad9-/- cells. Minimal alpha-particle induction of micronuclei in bystander cells was observed, except for the Rad9-/- mutant, where a significant increase above background was detected. Therefore, the Rad9 null mutation selectively sensitizes mouse ES cells to spontaneous and high-LET radiation-induced bystander apoptosis and micronucleus formation, but it has much less impact on cell killing by direct or bystander alpha-particle exposure. Results are presented in the context of defining the function of Rad9 in the cellular response to radiation and its differential effects on individual bystander end points.
Assuntos
Efeito Espectador/efeitos da radiação , Proteínas de Ciclo Celular/fisiologia , Partículas alfa , Animais , Apoptose/efeitos da radiação , Dano ao DNA , Camundongos , Micronúcleos com Defeito Cromossômico/efeitos da radiaçãoRESUMO
The radiation-induced bystander effect is defined as "the induction of biological effects in cells that are not directly traversed by a charged particle but are in close proximity to cells that are." Although these bystander effects have been demonstrated with a variety of biological endpoints in both human and rodent cell lines (as well as in 3D tissue samples), the mechanism of the phenomenon is not known. Although gap junction communication and the presence of soluble mediator(s) are both known to play important roles in the bystander response, the precise signaling molecules have yet to be identified. By using the Columbia University charged particle beam in conjunction with a strip dish design, we show here that the cyclooxygenase-2 (COX-2, also known as prostaglandin endoperoxide synthase-2) signaling cascade plays an essential role in the bystander process. Treatment of bystander cells with NS-398, which suppresses COX-2 activity, significantly reduced the bystander effect. Because the critical event of the COX-2 signaling is the activation of the mitogen-activated protein kinase pathways, our finding that inhibition of the extracellular signal-related kinase phosphorylation suppressed bystander response further confirmed the important role of mitogen-activated protein kinase signaling cascade in the bystander process. These results provide evidence that the COX-2-related pathway, which is essential in mediating cellular inflammatory response, is the critical signaling link for the bystander phenomenon.
Assuntos
Efeito Espectador/efeitos da radiação , Ciclo-Oxigenase 2/metabolismo , Transdução de Sinais/efeitos da radiação , Partículas alfa , Western Blotting , Efeito Espectador/efeitos dos fármacos , Efeito Espectador/fisiologia , Inibidores de Ciclo-Oxigenase 2/farmacologia , Análise Mutacional de DNA , Primers do DNA , Fibroblastos , Humanos , Hipoxantina Fosforribosiltransferase/genética , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Nitrobenzenos/farmacologia , Análise de Sequência com Séries de Oligonucleotídeos , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de Sinais/fisiologia , Sulfonamidas/farmacologiaRESUMO
A central tenet in understanding the biological effects of ionizing radiation has been that the initially affected cells were directly damaged by the radiation. By contrast, evidence has emerged concerning "bystander" responses involving damage to nearby cells that were not themselves directly traversed by the radiation. These long-range effects are of interest both mechanistically and for assessing risks from low-dose exposures, where only a small proportion of cells are directly hit. Bystander effects have been observed largely by using single-cell in vitro systems that do not have realistic multicellular morphology; no studies have as yet been reported in three-dimensional, normal human tissue. Given that the bystander phenomenon must involve cell-to-cell interactions, the relevance of such single-cell in vitro studies is questionable, and thus the significance of bystander responses for human health has remained unclear. Here, we describe bystander responses in a three-dimensional, normal human-tissue system. Endpoints were induction of micronucleated and apoptotic cells. A charged-particle microbeam was used, allowing irradiation of cells in defined locations in the tissue yet guaranteeing that no cells located more than a few micrometers away receive any radiation exposure. Unirradiated cells up to 1 mm distant from irradiated cells showed a significant enhancement in effect over background, with an average increase in effect of 1.7-fold for micronuclei and 2.8-fold for apoptosis. The surprisingly long range of bystander signals in human tissue suggests that bystander responses may be important in extrapolating radiation risk estimates from epidemiologically accessible doses down to very low doses where nonhit bystander cells will predominate.
Assuntos
Partículas alfa/efeitos adversos , Dano ao DNA , Queratinócitos/efeitos da radiação , Apoptose/efeitos da radiação , Humanos , Queratinócitos/patologia , Testes para MicronúcleosRESUMO
Long-lived, sensitive, and specific biomarkers of particular mutagenic agents are much sought after and potentially have broad applications in the fields of cancer biology, epidemiology, and prevention. Many clastogens induce a spectrum of chromosome aberrations, and some of them can be exploited as biomarkers of exposure. Densely ionizing radiation, for example, alpha particle radiation (from radon or plutonium) and neutron radiation, preferentially induces complex chromosome aberrations, which can be detected by the 24-color multifluor fluorescence in situ hybridization (mFISH) technique. We report the detection and quantification of stable complex chromosome aberrations in lymphocytes of healthy former nuclear-weapons workers, who were exposed many years ago to plutonium, gamma rays, or both, at the Mayak weapons complex in Russia. We analyzed peripheral-blood lymphocytes from these individuals for the presence of persistent complex chromosome aberrations. A significantly elevated frequency of complex chromosome translocations was detected in the highly exposed plutonium workers but not in the group exposed only to high doses of gamma radiation. No such differences were found for simple chromosomal aberrations. The results suggest that stable complex chromosomal translocations represent a long-lived, quantitative, low-background biomarker of densely ionizing radiation for human populations exposed many years ago.
Assuntos
Aberrações Cromossômicas/efeitos da radiação , Cromossomos Humanos/efeitos da radiação , Exposição Ocupacional , Radiação Ionizante , Translocação Genética , Humanos , Hibridização in Situ Fluorescente , Reatores Nucleares , Plutônio , Radônio , Federação RussaRESUMO
There is increasing evidence biological responses to ionizing radiation are not confined to those cells that are directly hit, but may be seen in the progeny at subsequent generations (genomic instability) and in non-irradiated neighbors of irradiated cells (bystander effects). These so called non-targeted phenomena would have significant contributions to radiation-induced carcinogenesis, especially at low doses where only a limited number of cells in a population are directed hit. Here we present data using a co-culturing protocol examining chromosomal instability in alpha-irradiated and bystander human fibroblasts BJ1-htert. At the first cell division following exposure to 0.1 and 1Gy alpha-particles, irradiated populations demonstrated a dose dependent increase in chromosome-type aberrations. At this time bystander BJ1-htert populations demonstrated elevated chromatid-type aberrations when compared to controls. Irradiated and bystander populations were also analyzed for chromosomal aberrations as a function of time post-irradiation. When considered over 25 doublings, all irradiated and bystander populations had significantly higher frequencies of chromatid aberrations when compared to controls (2-3-fold over controls) and were not dependent on dose. The results presented here support the link between the radiation-induced phenomena of genomic instability and the bystander effect.
Assuntos
Partículas alfa , Efeito Espectador , Instabilidade Cromossômica , Fibroblastos/efeitos da radiação , Animais , Linhagem Celular , Aberrações Cromossômicas , Técnicas de Cocultura , Análise Citogenética , Relação Dose-Resposta à Radiação , Humanos , Fatores de TempoRESUMO
The bystander effect is a biological phenomenon whereby cells not directly targeted by DNA-damaging agents elicit a response similar to that of targeted cells. Understanding the mechanisms underlying the bystander effect is important not only for radiation risk assessment but also for evaluation of protocols for radiotherapy of tumors. Identification of DNA repair and signal transduction proteins that are induced specifically in bystander cells may help in deducing the molecular mechanism(s) responsible for this complex phenomenon. With this objective, we have studied the expression of replication protein A (RPA), which is involved in various DNA metabolic activities such as replication, repair and recombination. We analyzed RPA expression by immunofluorescence and Western blot techniques in both gamma-irradiated primary human fibroblast cells and bystander cells that were recipients of conditioned growth medium harvested from gamma-irradiated cell cultures. A two- to threefold induction of RPA was observed in bystander MRC5 cells treated with conditioned medium collected from gamma-irradiated WI38 or MRC5 cells. Lack of induction of RPA in sham-manipulated MRC5 cells treated with irradiated medium alone (without cells) indicates that the signal elicited from the irradiated cells is responsible for induction of RPA in bystander cells. RPA was induced more effectively in bystander cells than in irradiated cells at the earliest time analyzed (30 min), and the RPA level declined to that of sham-treated control cells by 24 h after treatment. In addition to RPA, apurinic/apyrimidinic endonuclease (APE, a key enzyme of the base excision repair pathway) also showed enhanced expression in bystander cells. Our findings suggest that the induction of RPA and APE is due to a combination of DNA strand breaks and oxidized base lesions in the genomic DNA of bystander cells.
Assuntos
Efeito Espectador , Proteínas de Ligação a DNA/biossíntese , Linhagem Celular , Dano ao DNA , Reparo do DNA , DNA Liase (Sítios Apurínicos ou Apirimidínicos)/biossíntese , Proteínas de Ligação a DNA/genética , Humanos , Micronúcleos com Defeito Cromossômico , Proteína de Replicação A , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Human replication protein A (RPA p34), a crucial component of diverse DNA excision repair pathways, is implicated in DNA double-strand break (DSB) repair. To evaluate its role in DSB repair, the intranuclear dynamics of RPA was investigated after DNA damage and replication blockage in human cells. Using two different agents [ionizing radiation (IR) and hydroxyurea (HU)] to generate DSBs, we found that RPA relocated into distinct nuclear foci and colocalized with a well-known DSB binding factor, gamma-H2AX, at the sites of DNA damage in a time-dependent manner. Colocalization of RPA and gamma-H2AX foci peaked at 2 h after IR treatment and subsequently declined with increasing postrecovery times. The time course of RPA and gamma-H2AX foci association correlated well with the DSB repair activity detected by a neutral comet assay. A phosphatidylinositol-3 (PI-3) kinase inhibitor, wortmannin, completely abolished both RPA and gamma-H2AX foci formation triggered by IR. Additionally, radiosensitive ataxia telangiectasia (AT) cells harboring mutations in ATM gene product were found to be deficient in RPA and gamma-H2AX colocalization after IR. Transfection of AT cells with ATM cDNA fully restored the association of RPA foci with gamma-H2AX illustrating the requirement of ATM gene product for this process. The exact coincidence of RPA and gamma-H2AX in response to HU specifically in S-phase cells supports their role in DNA replication checkpoint control. Depletion of RPA by small interfering RNA (SiRNA) substantially elevated the frequencies of IR-induced micronuclei (MN) and apoptosis in human cells suggestive of a role for RPA in DSB repair. We propose that RPA in association with gamma-H2AX contributes to both DNA damage checkpoint control and repair in response to strand breaks and stalled replication forks in human cells.
Assuntos
Dano ao DNA/fisiologia , Proteínas de Ligação a DNA/metabolismo , Histonas/metabolismo , Apoptose/fisiologia , Dano ao DNA/efeitos da radiação , Reparo do DNA/fisiologia , Inativação Gênica , Histonas/genética , Humanos , Cinética , Micronúcleos com Defeito Cromossômico , Proteína de Replicação A , Fatores de TempoRESUMO
A multicolor banding (mBAND) fluorescence in situ hybridization technique was used to investigate the presence inhuman populations of a stable biomarker-intrachromosomal chromosome aberrations-of past exposure to high-LET radiation. Peripheral blood lymphocytes were taken from healthy Russian nuclear workers occupationally exposed from 1949 onward to either plutonium, gamma rays or both. Metaphase spreads were produced and chromosomes 1 and 2 were hybridized with mBAND FISH probes and scored for intra-chromosomal aberrations. A large yield of intrachromosomal aberrations was observed in both chromosomes of the individuals exposed to high doses of plutonium, whereas there was no significant increase over the (low) background control rate in the population who were exposed to high doses of gamma rays. Interchromosome aberration yields were similar in both the high plutonium and the high gamma-ray groups. These results for chromosome 1 and 2 confirm and extend data published previously for chromosome 5. Intrachromosomal aberrations thus represent a potential biomarker for past exposure to high-LET radiations such as alpha particles and neutrons and could possibly be used as a biodosimeter to estimate both the dose and type of radiation exposure in previously exposed populations.
Assuntos
Aberrações Cromossômicas/efeitos da radiação , Aberrações Cromossômicas/estatística & dados numéricos , Cromossomos Humanos/efeitos da radiação , Marcadores Genéticos/efeitos da radiação , Reatores Nucleares , Exposição Ocupacional/análise , Radiação Ionizante , Idoso , Idoso de 80 Anos ou mais , Carga Corporal (Radioterapia) , Bandeamento Cromossômico/métodos , Relação Dose-Resposta à Radiação , Feminino , Raios gama , Humanos , Leucócitos/metabolismo , Masculino , Pessoa de Meia-Idade , Plutônio , Doses de Radiação , Radiometria/métodos , Medição de Risco/métodos , Fatores de Risco , Federação Russa/epidemiologiaRESUMO
Normal human fibroblasts in plateau phase ( congruent with 95% G(1) phase) were stained with the vital nuclear dye Hoechst 33342 (blue fluorescence) or the vital cytoplasmic dye Cell Tracker Orange (orange fluorescence) and plated at a ratio of 1:1. Only the blue-fluorescing nuclei were microbeam-irradiated with a defined number of 90 keV/microm alpha particles. The orange-fluorescing cells were then "bystanders", i.e. not themselves hit but adjacent to cells that were. Hit cells showed a fluence-dependent induction of micronuclei as well as delays in progression from G(1) to S phase. Known bystander cells also showed enhanced frequencies of micronuclei (intermediate between those seen in irradiated and control cells) and transient cell cycle delays. However, the induction of micronuclei in bystander cells did not appear to be dependent on the fluence of the particles delivered to the neighboring hit cells. These are the first studies in which the bystander effect has been visualized directly rather than inferred. They indicate that the phenomenon has a quantitative basis and imply that the target for radiation effects cannot be considered to be the individual cell.