Differential effects of p53 on bystander phenotypes induced by gamma ray and high LET heavy ion radiation

The cross-talk between Bax, Bcl2, caspases, and DNA damage in bystander HepG2 cells is regulated by γ-radiation dose and time of conditioned media transfer

Although radiation-induced bystander effects have been broadly explored in various biological systems, the molecular mechanisms and the consequences of different regulatory factors (dose, time, cell type) on bystander responses are not clearly understood. This study investigates the effects of irradiated cell-conditioned media (ICCM) collected at different times post-irradiation on bystander cancer cells regarding DNA damage and apoptosis induction. Human hepatocellular carcinoma HepG2 cells were exposed to γ-ray doses of 2 Gy, 5 Gy, and 8 Gy. In the early and late stages (1 h, 2 h, and 24 h) after irradiation, the ICCM was collected and transferred to unirradiated cells. Compared to control, bystander cells showed an increased level of H2AX phosphorylation, mitochondrial membrane depolarization, and elevation of intrinsic apoptotic pathway mediators such as p53, Bax, cas9, cas-3, and PARP cleavage. These results were confirmed by phosphatidylserine (PS) externalization and scanning electron microscopic observations, suggesting a rise in bystander HepG2 cell apoptosis. Anti-apoptotic Bcl2-level and viability were lower in bystander cells compared to control. The highest effects were observed in 8 Gy γ radiation-induced bystander cells. Even though the bystander effect was persistent at all time points of the study, ICCM at the early time points (1 or 2 h) had the most significant impact on the apoptosis markers in bystander cells. Nevertheless, 24 h ICCM induced the highest increase in H2AX and p53 phosphorylation and Bax levels. The effects of ICCM of irradiated HepG2 cells were additionally studied in normal liver cells BRL-3A to simulate actual radiotherapy conditions. The outcomes suggest that the expression of the signaling mediators in bystander cells is highly dynamic. A cross-talk between those signaling mediators regulates bystander responses depending on the radiation dose and time of incubation post-irradiation.

Identification of two downregulated circRNAs in patients with acute B-lymphocytic leukemia

Acute B-lymphocytic leukemia (B-ALL) is associated with a high mortality rate, with no effective treatment strategies available. The identification of diagnostic and prognostic biomarkers of B-ALL can contribute to the development of novel therapeutic methods and drugs, which can improve the survival outcomes of patients with B-ALL. The present study aimed to identify downregulated circular RNAs (circRNAs) in patients with B-ALL. RNA sequencing was performed to construct the circRNA expression profiles in B-ALL cells and normal human lymphoblasts. The Database for Annotation, Visualization and Integrated Discovery was used to perform Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses. In addition, reverse transcription-quantitative (RT-q)PCR analysis was performed to detect the expression levels of the downregulated circRNAs. A total of 263 differentially expressed circRNAs were identified, including 76 upregulated and 187 downregulated circRNAs, respectively. The upregulated circRNAs were mainly enriched in ‘macromolecule modification’, ‘protein modification’ and ‘cellular protein modification processes’, while the downregulated circRNAs were mainly enriched in the ‘negative regulation of RNA biosynthetic processes’, ‘natural killer cell-mediated cytotoxicity’ and ‘viral carcinogenesis’. RT-qPCR analysis demonstrated that two of the downregulated circRNAs (hsa_circ_0000745 and chr15:87949594-87966067-), identified during microarray analysis were also significantly downregulated in Ball-1 cells and B-ALL bone marrow samples. Thus, these circRNAs may serve as biomarkers for patients with B-ALL.

Avoidance or adaptation of radiotherapy in patients with cancer with Li-Fraumeni and heritable TP53-related cancer syndromes

The management of patients with cancer and Li-Fraumeni or heritable TP53-related cancer syndromes is complex because of their increased risk of developing second malignant neoplasms after genotoxic stresses such as systemic treatments or radiotherapy (radiosusceptibility). Clinical decision making also integrates the risks of normal tissue toxicity and sequelae (radiosensitivity) and tumour response to radiotherapy (radioresistance and radiocurability). Radiotherapy should be avoided in patients with cancer and Li-Fraumeni or heritable TP53 cancer-related syndromes, but overall prognosis might be poor without radiotherapy: radioresistance in these patients seems similar to or worse than that of the general population. Radiosensitivity in germline TP53 variant carriers seems similar to that in the general population. The risk of second malignant neoplasms according to germline TP53 variant and the patient's overall oncological prognosis should be assessed during specialised multidisciplinary staff meetings. Radiotherapy should be avoided whenever other similarly curative treatment options are available. In other cases, it should be adapted to minimise the risk of second malignant neoplasms in patients who still require radiotherapy despite its genotoxicity, in view of its potential benefit. Adaptations might be achieved through the reduction of irradiated volumes using proton therapy, non-ionising diagnostic procedures, image guidance, and minimal stray radiation. Non-ionising imaging should become more systematic. Radiotherapy approaches that might result in a lower probability of misrepaired DNA damage (eg, particle therapy biology and tumour targeting) are an area of investigation.

Effect of Carbon Ion Radiation Induces Bystander Effect on Metastasis of A549 Cells and Metabonomic Correlation Analysis

Objective

To analyze the effect of carbon ion (¹²C⁶⁺) radiation may induce bystander effect on A549 cell metastasis and metabonomics.

Methods

A549 cell was irradiated with carbon ion to establish the clone survival model and the transwell matrix assay was applied to measure the effect of carbon ion on cell viability, migration, and invasion, respectively. Normal human embryonic lung fibroblasts (WI-38) were irradiated with carbon ions of 0 and 2 Gy and then transferred to A549 cell co-culture medium for 24 h. The migration and invasion of A549 cells were detected by the Transwell chamber. The analysis of metabonomic information in transfer medium by liquid phase mass spectrometry (LC-MS), The differential molecules were obtained by principal pomponent analysis (PCA) and the target proteins of significant differences (p = 1.7 × 10⁻³) obtained by combining with the STICH database. KEGG pathway was used to analyze the enrichment of the target protein pathway.

Results

Compared with 0 Gy, the colony formation, migration, and invasion of A549 cells were significantly inhibited by carbon ion 2 and 4 Gy irradiation, while the inhibitory effect was not significant after 1 Gy irradiation. Compared with 0 Gy, the culture medium 24 h after carbon ion 2 Gy irradiation significantly inhibited the metastasis of tumor cells (p = 0.03). LC-MS analysis showed that 23 differential metabolites were obtained in the cell culture medium 24 h after carbon ion 0 and 2 Gy irradiation (9 up-regulated and 14 down-regulated). Among them, two were up-regulated and two down-regulated (p = 2.9 × 10⁻³). 41 target proteins were corresponding to these four differential molecules. Through the analysis of the KEGG signal pathway, it was found that these target molecules were mainly enriched in purine metabolism, tyrosine metabolism, cysteine and methionine metabolism, peroxisome, and carbon metabolism. Neuroactive ligand-receptor interaction, calcium signaling pathway, arachidonic acid metabolism, and Fc epsilon RI signaling pathway.

Conclusion

The bystander effect induced by 2 Gy carbon ion radiation inhibits the metastasis of tumor cells, which indicates that carbon ions may change the metabolites of irradiated cells, so that it may indirectly affect the metabolism of tumor cell growth microenvironment, thus inhibiting the metastasis of malignant tumor cells.

Macrophage-Mediated Bystander Effects after Different Irradiations through a p53-dependent Pathway

The goal of this work was to elucidate the mechanisms of bystander effects outside the localized irradiation field and their potential hematological toxicity. In this study, an in vitro multicellular co-culture system was used to investigate the intercellular commutation and related signaling pathways between either irradiated A549 cells or Beas-2B cells and bystander lymphoblast TK6 cells with or without macrophage U937 cells as an intermediator. Results showed that the proliferation ability of bystander TK6 cells was inhibited after co-culture with A549 cells irradiated with γ rays rather than carbon ions. When macrophages were contained in the co-culture system, the cell viability damage to the bystander TK6 cells were further enhanced. However, the proliferation inhibition of bystander TK6 cells after co-culture with irradiated Beas-2B cells was observed only when intermediator macrophages existed in the cell co-culture system. More serious cell injury was detected after carbon-ion irradiation compared with γ-ray irradiation. The p53-relevant apoptosis pathway was activated in both irradiated A549 and Beas-2B cells, each to a different extent. When the p53 pathway of irradiated cells was inhibited by PFT-α, PFTµ or p53 siRNA, the bystander damage to TK6 cells were clearly alleviated. In conclusion, the bystander lymphoblast damage was induced in different cells using different LET radiations. An amplified bystander response was modulated by the intermediator macrophage. The underlying molecular mechanisms of these bystander effects were dependent on the activation of p53 and its relevant apoptosis pathway in the irradiated cells. These results suggest that the bystander and macrophage-mediated bystander effects contribute to the common acute side effect of lymphocytopenia after local irradiation.

Silencing of ARL14 Gene Induces Lung Adenocarcinoma Cells to a Dormant State

Recently, a growing number of ADP ribosylation factor (ARF) family members has been suggested to be critical in tumorigenesis. However, the effects of most ARF members on lung adenocarcinoma pathogenesis are still not well disclosed yet. In this study, ARF-like GTPase 14 (ARL14) was screened as an important prognostic factor of lung adenocarcinoma from The Cancer Genome Atlas (TCGA) database and validated by our in vitro experiments. It was found that silencing of ARL14 gene inhibited cell proliferation and the abilities of cell migration and invasion, and it also attenuated radiation damage of lung adenocarcinoma cells but had no effect on the proliferation of normal lung cells. Notably, ARL14 siRNA blocked the extracellular signal-regulated kinase (ERK)/p38 signaling pathway and induced cell cycle arrest in G0 phase, ultimately leading to cell dormancy. Moreover, ARL14 siRNA enhanced the expression of cell death activator DFFA-like effector (CIDEC) that had opposite roles in cell proliferation and migration to ALR14. Collectively, our results suggest that ARL14 has an important role in the pathogenesis of lung adenocarcinoma through CIDEC/ERK/p38 signaling pathway, and thus it could be applied as a new candidate of prognosis indicator and/or therapeutic target of lung adenocarcinoma.

Current status of space radiobiological studies in China

After successfully launching two space laboratories, namely, Tiangong-1 and Tiangong-2, China has announced her next plan of constructing the Chinese Space Station (CSS) in 2022. The CSS will provide not only platforms for Chinese scientists to carry out experimental studies in outer space but also opportunities for open international cooperation. In this article, we review the development of China's manned space exploration missions and the preliminary plan for CSS. Additionally, China has initiated space radiation research decades ago with both ground-based simulation research platform and space vehicles and has made noticeable progresses in several aspects. These include studies on human health risk assessment using mammalian cell cultures and animals as models. Furthermore, there have been numerous studies on assessing the space environment in plant breeding.

Bystander effectors of chondrosarcoma cells irradiated at different LET impair proliferation of chondrocytes

While the dose-response relationship of radiation-induced bystander effect (RIBE) is controversial at low and high linear energy transfer (LET), mechanisms and effectors of cell-to-cell communication stay unclear and highly dependent of cell type. In the present study, we investigated the capacity of chondrocytes in responding to bystander factors released by chondrosarcoma cells irradiated at different doses (0.05 to 8 Gy) with X-rays and C-ions. Following a medium transfer protocol, cell survival, proliferation and DNA damages were quantified in bystander chondrocytes. The bystander factors secreted by chondrosarcoma cells were characterized. A significant and major RIBE response was observed in chondrocyte cells (T/C-28a2) receiving conditioned medium from chondrosarcoma cells (SW1353) irradiated with 0.1 Gy of X-rays and 0.05 Gy of C-ions, resulting in cell survivals of 36% and 62%, respectively. Micronuclei induction in bystander cells was observed from the same low doses. The cell survival results obtained by clonogenic assays were confirmed using impedancemetry. The bystander activity was vanished after a heat treatment or a dilution of the conditioned media. The cytokines which are well known as bystander factors, TNF-α and IL-6, were increased as a function of doses and LET according to an ELISA multiplex analysis. Together, the results demonstrate that irradiated chondrosarcoma cells can communicate stress factors to non-irradiated chondrocytes, inducing a wide and specific bystander response related to both doses and LET.

Molecular Signaling in Response to Charged Particle Exposures and its Importance in Particle Therapy

Energetic, charged particles elicit an orchestrated DNA damage response (DDR) during their traversal through healthy tissues and tumors. Complex DNA damage formation, after exposure to high linear energy transfer (LET) charged particles, results in DNA repair foci formation, which begins within seconds. More protein modifications occur after high-LET, compared with low-LET, irradiation. Charged-particle exposure activates several transcription factors that are cytoprotective or cytodestructive, or that upregulate cytokine and chemokine expression, and are involved in bystander signaling. Molecular signaling for a survival or death decision in different tumor types and healthy tissues should be studied as prerequisite for shaping sensitizing and protective strategies. Long-term signaling and gene expression changes were found in various tissues of animals exposed to charged particles, and elucidation of their role in chronic and late effects of charged-particle therapy will help to develop effective preventive measures.

Protection of normal cells from irradiation bystander effects by silica-flufenamic acid nanoparticles

The development of a myriad of nanoparticles types has opened new possibilities for the diagnostics and treatment of many diseases, especially for cancer. However, most of the researches done so far do not focus on the protection of normal cells surrounding a tumor from irradiation bystander effects that might lead to cancer recurrence. Gap-junctions are known to be involved in this process, which leads to genomic instability of neighboring normal cells, and flufenamic acid (FFA) is included in a new group of gap-junction blockers recently discovered. The present work explores the use of mesoporous silica nanoparticles MCM-41 functionalized with 3-Aminopropyltriethoxysilane (APTES) for anchoring the flufenamic acid for its prolonged and controlled release and protection from radiation bystander effects. MCM-41 and functionalized samples were structurally and chemically characterized with multiple techniques. The biocompatibility of all samples was tested in a live/dead assay performed in cultured MRC-5 and HeLa cells. HeLa cells cultured were exposed to 50 Gy of gamma-rays and the media transferred to fibroblast cells cultured separately. Our results show that MCM-41 and functionalized samples have high biocompatibility with MCR-5 and HeLa cells, and most importantly, the FFA delivered by these NPs was able to halt apoptosis, one of main bystander effects.

Enhanced DNA double-strand break repair of microbeam targeted A549 lung carcinoma cells by adjacent WI38 normal lung fibroblast cells via bi-directional signaling

Understanding the mechanisms underlying the radiation-induced bystander effect (RIBE) and bi-directional signaling between irradiated carcinoma cells and their surrounding non-irradiated normal cells is relevant to cancer radiotherapy. The present study investigated propagation of RIBE signals between human lung carcinoma A549 cells and normal lung fibroblast WI38 cells in bystander cells, either directly or indirectly contacting irradiated A549 cells. We prepared A549-GFP/WI38 co-cultures and A549-GFP/A549 co-cultures, in which A549-GFP cells stably expressing H2BGFP were co-cultured with either A549 cells or WI38 cells, respectively. Using the SPICE-NIRS microbeam, only the A549-GFP cells were irradiated with 500 protons per cell. The level of γ-H2AX, a marker for DNA double-strand breaks (DSB), was subsequently measured for up to 24h post-irradiation in three categories of cells: (1) "targeted"/irradiated A549-GFP cells; (2) "neighboring"/non-irradiated cells directly contacting the "targeted" cells; and (3) "distant"/non-irradiated cells, which were not in direct contact with the "targeted" cells. We found that DSB repair in targeted A549-GFP cells was enhanced by co-cultured WI38 cells. The bystander response in A549-GFP/A549 cell co-cultures, as marked by γ-H2AX levels at 8h post-irradiation, showed a decrease to non-irradiated control level when approaching 24h, while the neighboring/distant bystander WI38 cells in A549-GFP/WI38 co-cultures was maintained at a similar level until 24h post-irradiation. Surprisingly, distant A549-GFP cells in A549-GFP/WI38 co-cultures showed time dependency similar to bystander WI38 cells, but not to distant cells in A549-GFP/A549 co-cultures. These observations indicate that γ-H2AX was induced in WI38 cells as a result of RIBE. WI38 cells were not only involved in rescue of targeted A549, but also in the modification of RIBE against distant A549-GFP cells. The present results demonstrate that radiation-induced bi-directional signaling had extended a profound influence on cellular sensitivity to radiation as well as the sensitivity to RIBE.

Chromatin remodeling modulates radiosensitivity of the daughter cells derived from cell population exposed to low- and high-LET irradiation

Radiation effects are dependent of linear energy transfer (LET), but it is still obscure whether the daughter cells (DCs) derived from irradiated population are radioresistance and much less the underlying mechanism. With the measurements of survival, proliferation and γH2AX foci, this study shows that the DCs from γ-ray irradiated cells (DCs-γ) became more radioresistant than its parent control without irradiation, but the radiosensitivity of DCs from α-particle irradiated cells (DCs-α) was not altered. After irradiation with equivalent doses of γ-rays and α-particles, the foci number of histone H3 lysine 9 dimethylation (H3K9me3) and the activity of histone deacetylase (HDAC) in DCs-γ was extensively higher than these in DCs-α and its parent control, indicating that a higher level of heterochromatin was formed in DCs-γ but not in DCs-α. Treatment of cells with SAHA (an inhibitor of HDAC) decreased the level of heterochromatin domains by inhibiting the expressions of H3K9m3 and HP-1a proteins and triggering the expression of acetylated core histone H3 (Ac-H3). When cells were treated with SAHA, the radioresistance phenotype of DCs-γ was eliminated so that the radiosensitivities of DCs-γ, DCs-α and their parent cells approached to same levels. Our current results reveal that γ-rays but not α-particles could induce chromatin remodeling and heterochromatinization which results in the occurrence of radioresistance of DCs, indicating that the combination treatment of irradiation and HDAC inhibitor could serve as a potential cancer therapy strategy, especially for the fraction radiotherapy of low-LET irradiation.

Evaluating biomarkers to model cancer risk post cosmic ray exposure

Robust predictive models are essential to manage the risk of radiation-induced carcinogenesis. Chronic exposure to cosmic rays in the context of the complex deep space environment may place astronauts at high cancer risk. To estimate this risk, it is critical to understand how radiation-induced cellular stress impacts cell fate decisions and how this in turn alters the risk of carcinogenesis. Exposure to the heavy ion component of cosmic rays triggers a multitude of cellular changes, depending on the rate of exposure, the type of damage incurred and individual susceptibility. Heterogeneity in dose, dose rate, radiation quality, energy and particle flux contribute to the complexity of risk assessment. To unravel the impact of each of these factors, it is critical to identify sensitive biomarkers that can serve as inputs for robust modeling of individual risk of cancer or other long-term health consequences of exposure. Limitations in sensitivity of biomarkers to dose and dose rate, and the complexity of longitudinal monitoring, are some of the factors that increase uncertainties in the output from risk prediction models. Here, we critically evaluate candidate early and late biomarkers of radiation exposure and discuss their usefulness in predicting cell fate decisions. Some of the biomarkers we have reviewed include complex clustered DNA damage, persistent DNA repair foci, reactive oxygen species, chromosome aberrations and inflammation. Other biomarkers discussed, often assayed for at longer points post exposure, include mutations, chromosome aberrations, reactive oxygen species and telomere length changes. We discuss the relationship of biomarkers to different potential cell fates, including proliferation, apoptosis, senescence, and loss of stemness, which can propagate genomic instability and alter tissue composition and the underlying mRNA signatures that contribute to cell fate decisions. Our goal is to highlight factors that are important in choosing biomarkers and to evaluate the potential for biomarkers to inform models of post exposure cancer risk. Because cellular stress response pathways to space radiation and environmental carcinogens share common nodes, biomarker-driven risk models may be broadly applicable for estimating risks for other carcinogens.