Oncogenic bystander radiation effects in Patched heterozygous mouse cerebellum

Ionizing radiation-induced bystander effects, potential targets for modulation of radiotherapy

Cells exposed to ionizing radiation show DNA damage, apoptosis, chromosomal aberrations or increased mutation frequency and for a long time it was generally accepted that these effects resulted from ionization of cell structures and the action of reactive oxygen species formed by water radiolysis. In the last few years, however, it has appeared that cells exposed to ionizing radiation and other genotoxic agents can release signals that induce very similar effects in non-targeted neighboring cells, phenomena known as bystander effects. These signals are transmitted to the neighboring non-hit cells by intercellular gap-junction communication or are released outside the cell, in the case of cultured cells into the medium. The signaling is mutual, and irradiated cells can also receive signals from non-irradiated neighbors. Most experiments show a decrease in survival of unirradiated bystander cells, but some studies of the influence of unirradiated or low dose-irradiated cells on those irradiated with higher doses show that intercellular bystander signaling can also increase the survival of irradiated cell populations. In the last few years, communication between irradiated and non-irradiated cells has attracted interest in many studies as a possible target for modulation of radiotherapy. Understanding the mechanisms underlying bystander effects is important for radiation risk assessment and for evaluation of protocols for cancer radiotherapy. In this review we describe different aspects of ionizing radiation-induced bystander effects: experimental examples, types of DNA damage, situations in vivo, and their possible role in adaptive response to irradiation, and we discuss their possible significance for anticancer therapy.

Computer diagnosis in cardiology

This article reports upon the emergence of a novel cognitive, computer-based technology which may lead to significantly improved methods of cardiological diagnosis and a rapid and inexpensive method of cardiological screening.The technology 'Virtual Scanning' illustrates how, in blood, the reaction of proteins and their reactive substrates releases light; that the colour and intensity of this bioluminescence is unique to each reaction and it's rate; and that the development of pathologies influence cognition and visual perception. This illustrates that the function of the autonomic nervous system is linked to that of the physiological systems and that the rate of biochemical reactions, and the progression of disease, can be measured by a cognitive test procedure and used as an indication of the disease(s) affecting heart function.The article discusses the limitations of the conventional biomarker technique, and the potential value of non-invasive cognitive techniques, such as Virtual Scanning, to the medical practitioner. Finally, it discusses how the ability of Virtual Scanning to diagnose disease from its presymptomatic origins may lead to improved diagnostic accuracy and significantly reduced costs.

Assessing cancer risks of low-dose radiation

Ionizing radiation is considered a non-threshold carcinogen. However, quantifying the risk of the more commonly encountered low and/or protracted radiation exposures remains problematic and subject to uncertainty. Therefore, a major challenge lies in providing a sound mechanistic understanding of low-dose radiation carcinogenesis. This Perspective article considers whether differences exist between the effects mediated by high- and low-dose radiation exposure and how this affects the assessment of low-dose cancer risk.

Protein kinase C epsilon is involved in ionizing radiation induced bystander response in human cells

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.

Radiation-stimulated epigenetic reprogramming of adaptive-response genes in the lung: an evolutionary gift for mounting adaptive protection against lung cancer

Humans are continuously exposed to low-level ionizing radiation from natural sources. However, harsher radiation environments persisted during our planet's early years and mammals survived via an evolutionary gift--a system of radiation-induced natural protective measures (adaptive protection). This system includes antioxidants, DNA repair, apoptosis of severely damaged cells, epigenetically regulated apoptosis (epiapoptosis) pathways that selectively remove precancerous and other aberrant cells, and immunity against cancer. We propose a novel model in which the protective system is regulated at least in part via radiation-stress-stimulated epigenetic reprogramming (epireprogramming) of adaptive-response genes. High-dose radiation can promote epigenetically silencing of adaptive-response genes (episilencing), for example via promoter-associated DNA and/or histone methylation and/or histone deacetylation. Evidence is provided for low linear-energy-transfer (LET) radiation-activated natural protection (ANP) against high-LET alpha-radiation-induced lung cancer in plutonium-239 exposed rats and radon-progeny-exposed humans. Using a revised hormetic relative risk model for cancer induction that accounts for both epigenetic activation (epiactivation) and episilencing of genes, we demonstrate that, on average, >80% of alpha-radiation-induced rat lung cancers were prevented by chronic, low-rate gamma-ray ANP. Interestingly, lifetime exposure to residential radon at the Environmental Protection Agency's action level of 4 pCi L(-1) appears to be associated with on average a > 60% reduction in lung cancer cases, rather than an increase. We have used underlined italics to indicate newly introduced terminology.

Radiation-induced bystander signalling in cancer therapy

Our understanding of how radiation kills normal and tumour cells has been based on an intimate knowledge of the direct induction of DNA damage and its cellular consequences. What has become clear is that, as well as responses to direct DNA damage, cell-cell signalling -- known as the bystander effect -- mediated through gap junctions and inflammatory responses may have an important role in the response of cells and tissues to radiation exposure and also chemotherapy agents. This Review outlines the key aspects of radiation-induced intercellular signalling and assesses its relevance for existing and future radiation-based therapies.

Physical, heritable and age-related factors as modifiers of radiation cancer risk in patched heterozygous mice

PURPOSE

To address the tumorigenic potential of exposure to low/intermediate doses of ionizing radiation and to identify biological factors influencing tumor response in a mouse model highly susceptible to radiogenic cancer.

METHODS AND MATERIALS

Newborn Ptc1 heterozygous mice were exposed to X-ray doses of 100, 250, and 500 mGy, and tumor development was monitored for their lifetime. Additional groups were irradiated with the same doses and sacrificed at fixed times for determination of short-term endpoints, such as apoptosis and early preneoplastic lesions in cerebellum. Finally, groups of Ptc1 heterozygous mice were bred on the C57BL/6 background to study the influence of common variant genes on radiation response.

RESULTS

We have identified a significant effect of low-intermediate doses of radiation (250 and 500 mGy) in shortening mean survival and inducing early and more progressed stages of tumor development in the cerebellum of Ptc1(+/-) mice. In addition, we show that age at exposure and heritable factors are potent modifiers of radiation-related cancer risk.

CONCLUSIONS

The Ptc1 knockout mouse model offers a highly sensitive system that may potentially help to improve understanding and quantification of risk at low doses, such as doses experienced in occupational and medical exposures, and clarify the complex interactions between genetic and environmental factors underlying cancer susceptibility.

Global gene expression analyses of bystander and alpha particle irradiated normal human lung fibroblasts: synchronous and differential responses

Background

The existence of a radiation bystander effect, in which non-irradiated cells respond to signals from irradiated cells, is now well established. It raises concerns for the interpretation of risks arising from exposure to low doses of ionizing radiation. However, the regulatory mechanisms involved in the bystander response have not been well elucidated. To provide insight into the signaling pathways responding in bystanders, we have measured global gene expression four hours after bystander and direct alpha particle exposure of primary human lung fibroblasts.

Results

Although common p53-regulated radiation response genes like CDKN1A were expressed at elevated levels in the directly exposed cultures, they showed little or no change in the bystanders. In contrast, genes regulated by NFκB, such as PTGS2 (cyclooxygenase-2), IL8 and BCL2A1, responded nearly identically in bystander and irradiated cells. This trend was substantiated by gene ontology and pathway analyses of the microarray data, which suggest that bystander cells mount a full NFκB response, but a muted or partial p53 response. In time-course analyses, quantitative real-time PCR measurements of CDKN1A showed the expected 4-hour peak of expression in irradiated but not bystander cells. In contrast, PTGS2, IL8 and BCL2A1 responded with two waves of expression in both bystander and directly irradiated cells, one peaking at half an hour and the other between four and six hours after irradiation.

Conclusion

Two major transcriptional hubs that regulate the direct response to ionizing radiation are also implicated in regulation of the bystander response, but to dramatically different degrees. While activation of the p53 response pathway is minimal in bystander cells, the NFκB response is virtually identical in irradiated and bystander cells. This alteration in the balance of signaling is likely to lead to different outcomes in irradiated cells and their bystanders, perhaps leading to greater survival of bystanders and increased risk from any long-term damage they have sustained.

Radiation Induced Bystander Effect in vivo

Radiation-induced bystander effect is defined as the induction of biological effects in cells that are not directly traversed by radiation, but merely in the presence of cells that are. Although radiation induced bystander effects have been well defined in a variety of in vitro models using a range of endpoints including clonogenic survival, mutations, neoplastic transformation, apoptosis, micronucleus, chromosomal aberrations and DNA double strand beaks, the mechanism(s) as well as the presence of such an effect in vivo are not well described. In this review, we summarize the evidence of radiation induced bystander effect in various in vivo systems including rodents, fish and plants. Many biological endpoints such as epigenetic changes, DNA damage, miRNA, apoptosis, cell proliferation, gene expression and tumorgenesis have been demonstrated in the non-targeted regions in vivo. Although the bystander effect is evolutionarily conserved in rodent systems, the bystander response depends on gender, tissue and strain. However, the studies about mechanism of radiation induced bystander effect in vivo are still limited.