A possible role for proinflammatory activation via cGAS-STING pathway in atherosclerosis induced by accumulation of DNA double-strand breaks.

DNA damage contributes to atherosclerosis. However, causative links between DNA double-strand breaks (DSBs) and atherosclerosis have yet to be established. Here, we investigated the role of DSBs in atherosclerosis using mice and vascular cells deficient in Ku80, a DSB repair protein. After 4 weeks of a high-fat diet, Ku80-deficient apolipoprotein E knockout mice (Ku80+/-ApoE-/-) displayed increased plaque size and DSBs in the aorta compared to those of ApoE-/- control. In the preatherosclerotic stages (two-week high-fat diet), the plaque size was similar in both the Ku80+/-ApoE-/- and ApoE-/- control mice, but the number of DSBs and mRNA levels of inflammatory cytokines such as IL-6 and MCP-1 were significantly increased in the Ku80+/-ApoE-/- aortas. We further investigated molecular links between DSBs and inflammatory responses using vascular smooth muscle cells isolated from Ku80 wild-type and Ku80+/- mice. The Ku80+/- cells displayed senescent features and elevated levels of inflammatory cytokine mRNAs. Moreover, the cytosolic DNA-sensing cGAS-STING pathway was activated in the Ku80+/- cells. Inhibiting the cGAS-STING pathway reduced IL-6 mRNA level. Notably, interferon regulatory factor 3 (IRF3), a downstream effector of the cGAS-STING pathway, was activated, and the depletion of IRF3 also reduced IL-6 mRNA levels in the Ku80+/- cells. Finally, DSBs accumulation in normal cells also activated the cGAS-STING-IRF3 pathway. In addition, cGAS inhibition attenuated DNA damage-induced IL-6 expression and cellular senescence in these cells. These results suggest that DSBs accumulation promoted atherosclerosis by upregulating proinflammatory responses and cellular senescence via the cGAS-STING (-IRF3) pathway.

Impact of lifting the mandatory evacuation order after the Fukushima Daiichi Nuclear Power Plant accident on the emergency medical system: a retrospective observational study at Minamisoma City with machine learning analysis.

OBJECTIVES: This study aimed to identify factors that delayed emergency medical services (EMS) in evacuation order zones after the 2011 Great East Japan Earthquake and Fukushima Daiichi Nuclear Power Plant accident and to investigate how the lifting of the evacuation affected these factors over time. DESIGN: This research was a retrospective observational study. The primary outcome measure was onsite EMS time. A gradient boosting model and a decision tree were used to find the boundary values for factors that reduce EMS. SETTING: The target area was Minamisoma City, Fukushima, Japan that was partly designated as an evacuation order zone after the 2011 Fukushima disaster, which was lifted due to decreased radiation. PARTICIPANTS: This study included patients transferred by EMS from 1 January 2013 through 31 October 2018. Patients who were not transported and those transported for community events, interhospital patient transfer and natural disasters were excluded. OUTCOME MEASURES: This study evaluated the total EMS time using on-site time which is the time from arrival at the scene to departure to the destination, and other independent factors. RESULTS: The total number of transports was 12 043. The decision tree revealed that the major factors that prolonged onsite time were time of day and latitude, except for differences by year. While latitude was a major factor in extending on-site time until 2016, the effect of latitude decreased and that of time of day became more significant since 2017. The boundary was located at N37.695° latitude. CONCLUSIONS: The onsite time delay in EMS in evacuation order zones is largely due to regional factors from north to south and the time of day. However, the north-south regional factor decreased with the lifting of evacuation orders.

Klotho protects chromosomal DNA from radiation-induced damage.

Klotho is an anti-aging, single-pass transmembrane protein found mainly in the kidney. Although aging is likely to be associated with DNA damage, the involvement of Klotho in protecting cells from DNA damage is still unclear. In this study, we examined DNA damage in human kidney cells and mouse kidney tissue after ionizing radiation (IR). The depletion and overexpression of Klotho in human kidney cells reduced and increased the cell survival rates after IR, respectively. The formation of γ-H2AX foci, representing DNA damage, was significantly elevated immediately after IR in cells with Klotho depletion and decreased in cells overexpressing Klotho. These results were confirmed in mouse renal tissues after IR. Quantification of DNA damage by a comet assay revealed that the Klotho knockdown significantly increased the amount of DNA damage immediately after IR, suggesting that Klotho protects chromosomal DNA from the induction of damage, rather than facilitating DNA repair. Consistent with this notion, Klotho was detected in both the nucleus and cytoplasm. In the nucleus, Klotho may serve to protect chromosomal DNA from damage, leading to its anti-aging effects.

Cigarette smoke induces mitochondrial DNA damage and activates cGAS-STING pathway: application to a biomarker for atherosclerosis.

Cigarette smoking is a major risk factor for atherosclerosis. We previously reported that DNA damage was accumulated in atherosclerotic plaque, and was increased in human mononuclear cells by smoking. As vascular endothelial cells are known to modulate inflammation, we investigated the mechanism by which smoking activates innate immunity in endothelial cells focusing on DNA damage. Furthermore, we sought to characterize the plasma level of cell-free DNA (cfDNA), a result of mitochondrial and/or genomic DNA damage, as a biomarker for atherosclerosis. Cigarette smoke extract (CSE) increased DNA damage in the nucleus and mitochondria in human endothelial cells. Mitochondrial damage induced minority mitochondrial outer membrane permeabilization, which was insufficient for cell death but instead led to nuclear DNA damage. DNA fragments, derived from the nucleus and mitochondria, were accumulated in the cytosol, and caused a persistent increase in IL-6 mRNA expression via the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway. cfDNA, quantified with quantitative PCR in culture medium was increased by CSE. Consistent with in vitro results, plasma mitochondrial cfDNA (mt-cfDNA) and nuclear cfDNA (n-cfDNA) were increased in young healthy smokers compared with age-matched nonsmokers. Additionally, both mt-cfDNA and n-cfDNA were significantly increased in patients with atherosclerosis compared with the normal controls. Our multivariate analysis revealed that only mt-cfDNA predicted the risk of atherosclerosis. In conclusion, accumulated cytosolic DNA caused by cigarette smoke and the resultant activation of the cGAS-STING pathway may be a mechanism of atherosclerosis development. The plasma level of mt-cfDNA, possibly as a result of DNA damage, may be a useful biomarker for atherosclerosis.

DNA Damage Induced by Radiation Exposure from Cardiac Catheterization.

Almost 40% of medical radiation exposure is related to cardiac imaging or intervention. However, the biological effects of low-dose radiation from medical imaging remain largely unknown. This study aimed to evaluate the effects of ionized radiation from cardiac catheterization on genomic DNA integrity and inflammatory cytokines in patients and operators.Peripheral mononuclear cells (MNCs) were isolated from patients (n = 51) and operators (n = 35) before and after coronary angiography and/or percutaneous coronary intervention. The expression of γH2AX, a marker for DNA double-strand breaks, was measured by immunofluorescence. Dicentric chromosomes (DICs), a form of chromosome aberrations, were assayed using a fluorescent in situ hybridization technique.In the patient MNCs, the numbers of γH2AX foci and DICs increased after cardiac catheterization by 4.5 ± 9.4-fold and 71 ± 122%, respectively (P < 0.05 for both). The mRNA expressions of interleukin (IL)-1α, IL-1ß, leukemia inhibitory factor, and caspase-1 were significantly increased by radiation exposure from cardiac catheterization. The increase in IL-1ß was significantly correlated with that of γH2AX, but not with the dose area product. In the operators, neither γH2AX foci nor the DIC level was changed, but IL-1ß mRNA was significantly increased. The protein expression of IκBα was significantly decreased in both groups.DNA damage was increased in the MNCs of patients, but not of operators, who underwent cardiac catheterization. Inflammatory cytokines were increased in both the patients and operators, presumably through NF-κB activation. Further efforts to reduce radiation exposure from cardiac catheterization are necessary for both patients and operators.

Biological and internal dosimetry for radiation medicine: current status and future perspectives.

The International Atomic Energy Agency (IAEA) and Hiroshima International Council for Health Care of the Radiation-Exposed (HICARE) jointly organized two relevant workshops in Hiroshima, Japan, i.e. a Training Meeting 'Biodosimetry in the 21st century' (BIODOSE-21) on 10-14 June 2013 and a Workshop on 'Biological and internal dosimetry: recent advance and clinical applications' which took place between 17 and 21 February 2020. The main objective of the first meeting was to develop the ability of biodosimetry laboratories to use mature and novel techniques in biological dosimetry for the estimation of radiation doses received by individuals and populations. This meeting had a special focus on the Asia-Pacific region and was connected with the then on-going IAEA Coordinated Research Project (CRP) E35008 'Strengthening of "Biological dosimetry" in IAEA Member States: Improvement of current techniques and intensification of collaboration and networking among the different institutes' (2012-17). The meeting was attended by 25 participants, which included 11 lecturers. The 14 trainees for this meeting came from India, Indonesia, Japan, Malaysia, Philippines, Republic of Korea, Singapore, Thailand and Vietnam. During the meeting 13 lectures by HICARE and IAEA invited lecturers were delivered besides eight research reports presented by the IAEA CRP E35008 network centers from the Asia-Pacific region. Two laboratory exercises were also undertaken, one each at Hiroshima University and the Radiation Effects Research Foundation (RERF). The second training workshop aimed to discuss with the participants the use of mature and novel techniques in biological and internal dosimetry for the estimation of radiation effects by accidental, environmental and medical exposures. The workshop was attended by 19 participants from Indonesia, Jordan, Oman, Philippines, Singapore, Syrian Arab Republic, Thailand, UAE, USA and Yemen. The main outcome of both meetings was a review of the state-of-the-art of biodosimetry and internal dosimetry and their future perspectives in medical management. This report highlights the learning outcome of two meetings for the benefit of all stake-holders in the field of biological and internal dosimetry.

A Combination of Iohexol Treatment and Ionizing Radiation Exposure Enhances Kidney Injury in Contrast-Induced Nephropathy by Increasing DNA Damage.

Contrast media has been shown to induce nephropathy (i.e., contrast-induced nephropathy) after various types of radiological examinations. The molecular mechanism of contrast-induced nephropathy has been unclear. In this study, we investigated the mechanism of contrast-induced nephropathy by examining the effects of combined treatment of contrast medium and ionizing radiation on kidney cells in vitro and kidney tissue in vivo. In human renal tubular epithelium cells, immunofluorescence analysis revealed that iohexol increased the numbers of radiation-induced γH2AX nuclear foci. The numbers of γH2AX nuclear foci remained high at 24 h, suggesting that some radiation-induced double-strand breaks remain unrepaired in the presence of iohexol. We established a mouse model of contrast-induced nephropathy, then showed that iohexol and ionizing radiation synergistically reduced renal function and induced double-strand breaks. Importantly, iohexol induced significant macrophage accumulation and oxidative DNA damage in the kidneys of contrast-induced nephropathy model mice in the absence of ionizing radiation; these effects were amplified by ionizing radiation. The results suggest that underlying inflammation and oxidative DNA damage caused by iohexol contribute to the enhancement of radiation-induced double-strand breaks, leading to contrast-induced nephropathy.

Piwi-piRNA complexes induce stepwise changes in nuclear architecture at target loci.

PIWI-interacting RNAs (piRNAs) are germline-specific small RNAs that form effector complexes with PIWI proteins (Piwi-piRNA complexes) and play critical roles for preserving genomic integrity by repressing transposable elements (TEs). Drosophila Piwi transcriptionally silences specific targets through heterochromatin formation and increases histone H3K9 methylation (H3K9me3) and histone H1 deposition at these loci, with nuclear RNA export factor variant Nxf2 serving as a co-factor. Using ChEP and DamID-seq, we now uncover a Piwi/Nxf2-dependent target association with nuclear lamins. Hi-C analysis of Piwi or Nxf2-depleted cells reveals decreased intra-TAD and increased inter-TAD interactions in regions harboring Piwi-piRNA target TEs. Using a forced tethering system, we analyze the functional effects of Piwi-piRNA/Nxf2-mediated recruitment of piRNA target regions to the nuclear periphery. Removal of active histone marks is followed by transcriptional silencing, chromatin conformational changes, and H3K9me3 and H1 association. Our data show that the Piwi-piRNA pathway can induce stepwise changes in nuclear architecture and chromatin state at target loci for transcriptional silencing.

OASIS/CREB3L1 is a factor that responds to nuclear envelope stress.

The nuclear envelope (NE) safeguards the genome and is pivotal for regulating genome activity as the structural scaffold of higher-order chromatin organization. NE had been thought as the stable during the interphase of cell cycle. However, recent studies have revealed that the NE can be damaged by various stresses such as mechanical stress and cellular senescence. These types of stresses are called NE stress. It has been proposed that NE stress is closely related to cellular dysfunctions such as genome instability and cell death. Here, we found that an endoplasmic reticulum (ER)-resident transmembrane transcription factor, OASIS, accumulates at damaged NE. Notably, the major components of nuclear lamina, Lamin proteins were depleted at the NE where OASIS accumulates. We previously demonstrated that OASIS is cleaved at the membrane domain in response to ER stress. In contrast, OASIS accumulates as the full-length form to damaged NE in response to NE stress. The accumulation to damaged NE is specific for OASIS among OASIS family members. Intriguingly, OASIS colocalizes with the components of linker of nucleoskeleton and cytoskeleton complexes, SUN2 and Nesprin-2 at the damaged NE. OASIS partially colocalizes with BAF, LEM domain proteins, and a component of ESCRT III, which are involved in the repair of ruptured NE. Furthermore, OASIS suppresses DNA damage induced by NE stress and restores nuclear deformation under NE stress conditions. Our findings reveal a novel NE stress response pathway mediated by OASIS.

Lessons from the Fukushima Daiichi nuclear power plant accident -from a research perspective.

Since the accident at Fukushima Daiichi nuclear power plant, there has been a focus on the impact of low-dose radiation exposure due to nuclear disasters and radiology on human bodies. In order to study very low levels of impact on the human body from low-dose radiation exposure, a system with high detection sensitivity is needed. Until now, the most well-established biological radiation effect detection system in the field of emergency radiation medicine has been chromosomal analysis. However, chromosomal analysis requires advanced skills, and it is necessary to perform chromosomal analysis of a large number of cells in order to detect slight effects on the human body due to low-dose radiation exposure. Therefore, in order to study the effects of low-dose radiation exposure on the human body, it is necessary to develop high-throughput chromosome analysis technology. We have established the PNA-FISH method, which is a fluorescence in-situ hybridisation method using a PNA probe, as a high-throughput chromosome analysis technique. Using this method, the detection of dicentrics and ring chromosomes has become very efficient. Using this technology, chromosomal analysis was performed on peripheral blood before and after computed tomography (CT) examination of patients at Hiroshima University Hospital, and it was possible to detect chromosomal abnormalities due to low-dose radiation exposure in the CT examination. Furthermore, it was shown that there may be individual differences in the increase in chromosomal abnormalities due to low-dose radiation exposure, suggesting the need to build a next-generation medical radiation exposure management system based on individual differences in radiation sensitivity. If techniques such as chromosomal analysis, which have been used for biological dose evaluation in emergency radiation medicine, can be used for general radiology, such as radiodiagnosis and treatment, that will be a contribution to radiology from an unprecedented angle. This article will discuss the clinical application of new biological dose evaluation methods that have been developed in the field of emergency radiation medicine.

Replication-stress-associated DSBs induced by ionizing radiation risk genomic destabilization and associated clonal evolution.

Exposure to ionizing radiation is associated with cancer risk. Although multiple types of DNA damage are caused by radiation, it remains unknown how this damage is associated with cancer risk. Here, we show that after repair of double-strand breaks (DSBs) directly caused by radiation (dir-DSBs), irradiated cells enter a state at higher risk of genomic destabilization due to accumulation of replication-stress-associated DSBs (rs-DSBs), ultimately resulting in clonal evolution of cells with abrogated defense systems. These effects were observed over broad ranges of radiation doses (0.25-2 Gy) and dose rates (1.39-909 mGy/min), but not upon high-dose irradiation, which caused permanent cell-cycle arrest. The resultant genomic destabilization also increased the risk of induction of single-nucleotide variants (SNVs), including radiation-associated SNVs, as well as structural alterations in chromosomes. Thus, the radiation-associated risk can be attributed to rs-DSB accumulation and resultant genomic destabilization.

Evaluating Individual Radiosensitivity for the Prediction of Acute Toxicities of Chemoradiotherapy in Esophageal Cancer Patients.

In this work, individual radiosensitivity was evaluated using DNA damage response and chromosomal aberrations (CAs) in peripheral blood lymphocytes (PBLs) for the prediction of acute toxicities of chemoradiotherapy (CRT) in esophageal cancer patients. Eighteen patients with esophageal cancer were enrolled in this prospective study. Prescribed doses were 60 Gy in 11 patients and 50 Gy in seven patients. Patients received 2 Gy radiotherapy five days a week. PBLs were obtained during treatment just before and 15 min after 2 Gy radiation therapy on the days when the cumulative dose reached 2, 20, 40 Gy and 50 or 60 Gy. PBLs were also obtained four weeks and six months after radiotherapy in all and 13 patients, respectively. Dicentric and ring chromosomes in PBLs were counted to evaluate the number of CAs. Gamma-H2AX foci per cell were scored to assess DNA double-strand breaks. We analyzed the association between these factors and adverse events. The number of γ-H2AX foci before radiotherapy showed no significant increase during CRT, while their increment was significantly reduced with the accumulation of radiation dose. The mean number of CAs increased during CRT up to 1.04 per metaphase, and gradually decreased to approximately 60% six months after CRT. Five patients showed grade 3 toxicities during or after CRT (overreactors: OR), while 13 had grade 2 or less toxicities (non-overreactors: NOR). The number of CAs was significantly higher in the OR group than in the NOR group at a cumulative dose of 20 Gy (mean value: 0.63 vs. 0.34, P = 0.02), 40 Gy (mean value: 0.90 vs. 0.52, P = 0.04), and the final day of radiotherapy (mean value: 1.49 vs. 0.84, P = 0.005). These findings suggest that number of CAs could be an index for predicting acute toxicities of CRT for esophageal cancer.

Bach1 plays an important role in angiogenesis through regulation of oxidative stress.

Bach1 is a known transcriptional repressor of the heme oxygenase-1 (HO-1) gene. The purpose of this study was to determine whether angiogenesis is accelerated by genetic ablation of Bach1 in a mouse ischemic hindlimb model. Hindlimb ischemia was surgically induced in wild-type (WT) mice, Bach1-deficient (Bach1-/-) mice, apolipoprotein E-deficient (ApoE-/-) mice, and Bach1/ApoE double-knockout (Bach1-/-/ApoE-/-) mice. Blood flow recovery after hindlimb ischemia showed significant improvement in Bach1-/- mice compared with that in WT mice. Bach1-/-/ApoE-/- mice showed significantly improved blood flow recovery compared with that in ApoE-/- mice to the level of that in WT mice. Migration of endothelial cells in ApoE-/- mice was significantly decreased compared with that in WT mice. Migration of endothelial cells significantly increased in Bach1-/-/ApoE-/- mice compared with that in ApoE-/- mice to the level of that in WT mice. The expression levels of HO-1, peroxisome proliferator-activated receptor γ co-activator-1α, angiopoietin 1, and fibroblast growth factor 2 in endothelial cells isolated from Bach1-/-/ApoE-/- mice were significantly higher than those in ApoE-/- mice. Oxidative stress assessed by anti-acrolein antibody staining in ischemic tissues and urinary 8-isoPGF2α excretion were significantly increased in ApoE-/- mice compared with those in WT and Bach1-/- mice. Oxidative stress was reduced in Bach1-/-/ApoE-/- mice compared with that in ApoE-/- mice. These findings suggest that genetic ablation of Bach1 plays an important role in ischemia-induced angiogenesis under the condition of increased oxidative stress. Bach1 could be a potential therapeutic target to reduce oxidative stress and potentially improve angiogenesis for patients with peripheral arterial disease.

Biological Effects of Low-Dose Chest CT on Chromosomal DNA.

Background Although the National Lung Screening Trial reported a significant reduction in lung cancer mortality when low-dose (LD) CT chest examinations are used for a diagnosis, their biologic effects from radiation exposure remain unclear. Purpose To compare LD CT and standard-dose (SD) CT for DNA double-strand breaks and chromosome aberrations (CAs) in peripheral blood lymphocytes. Materials and Methods Between March 2016 and June 2018, 209 participants who were referred to a respiratory surgery department for chest CT studies were prospectively enrolled in this study. Individuals were excluded if they had undergone radiography examinations within the last 3 days or had undergone chemotherapy or radiation therapy. Peripheral blood samples were obtained before and 15 minutes after CT. The number of γ-H2AX foci and unstable CAs in lymphocytes was quantified by immunofluorescent staining of γ-H2AX and by fluorescence in situ hybridization by using peptide nucleic acid probes for centromeres and telomeres, respectively. The Wilcoxon signed rank test was used for statistical analysis. Bonferroni correction was applied for multiple comparisons. Results Of the 209 participants (105 women, 104 men; mean age, 67.0 years ± 11.3 [standard deviation]), 107 underwent chest LD CT and 102 underwent chest SD CT. Sex distribution, age, and body size metrics were similar between the two groups. The median effective dose of LD CT and SD CT was 1.5 and 5.0 mSv, respectively. The number of double-strand breaks and CAs increased after a SD CT examination (γ-H2AX, P < .001; CAs, P = .003); the number of double-strand breaks and CAs before and after LD CT was not different (γ-H2AX, P = .45; CAs, P = .69). Conclusion No effect of low-dose CT on human DNA was detected. In the same setting, DNA double-strand breaks and chromosome aberrations increased after standard-dose CT. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Brenner in this issue.

Role of dynamic nuclear deformation on genomic architecture reorganization.

Higher-order genomic architecture varies according to cell type and changes dramatically during differentiation. One of the remarkable examples of spatial genomic reorganization is the rod photoreceptor cell differentiation in nocturnal mammals. The inverted nuclear architecture found in adult mouse rod cells is formed through the reorganization of the conventional architecture during terminal differentiation. However, the mechanisms underlying these changes remain largely unknown. Here, we found that the dynamic deformation of nuclei via actomyosin-mediated contractility contributes to chromocenter clustering and promotes genomic architecture reorganization during differentiation by conducting an in cellulo experiment coupled with phase-field modeling. Similar patterns of dynamic deformation of the nucleus and a concomitant migration of the nuclear content were also observed in rod cells derived from the developing mouse retina. These results indicate that the common phenomenon of dynamic nuclear deformation, which accompanies dynamic cell behavior, can be a universal mechanism for spatiotemporal genomic reorganization.

Matrin3 promotes homologous recombinational repair by regulation of RAD51.

Matrin3 is a highly conserved inner nuclear matrix protein involved in multiple stages of RNA metabolism. Although Matrin3 may also play a role in DNA repair, its precise roles have remained unclear. In this study, we showed that the depletion of Matrin3 led to decreased homologous recombination (HR) efficiency and increased radiation sensitivity of cells. Matrin3-depleted cells showed impaired DNA damage-dependent focus formation of RAD51, a key protein in HR. These findings suggest that Matrin3 promotes HR by regulating RAD51.

DNA Damage and Senescence-Associated Inflammation in Cardiovascular Disease.

DNA suffers various types of damage even in a normal condition, although they are rapidly repaired by mechanisms called DNA repair. Most progeroid syndromes are caused by genetic defects in specific molecules involved in the DNA repair. DNA damage activates a broad range of signaling pathway that leads to repair, cell cycle arrest, apoptosis and so on, which is called DNA damage response. Recent studies revealed that persistent DNA damage response triggers induction of cell senescence and senescence-associated secretory phenotype (SASP). Here, we review recent advances in the understanding of the molecular mechanisms by which SASP components are regulated, and discuss the possible roles of DNA damage and the DNA damage response, and SASP in the pathogenesis of cardiovascular disease.

Loss of Rim15p in shochu yeast alters carbon utilization during barley shochu fermentation.

Rim15p of the yeast Saccharomyces cerevisiae is a Greatwall-family protein kinase that inhibits alcoholic fermentation during sake brewing. To elucidate the roles of Rim15p in barley shochu fermentation, RIM15 was deleted in shochu yeast. The disruptant did not improve ethanol yield, but altered sugar and glycerol contents in the mash, suggesting that Rim15p has a novel function in carbon utilization.

Cancer-associated mutations of histones H2B, H3.1 and H2A.Z.1 affect the structure and stability of the nucleosome.

Mutations of the Glu76 residue of canonical histone H2B are frequently found in cancer cells. However, it is quite mysterious how a single amino acid substitution in one of the multiple H2B genes affects cell fate. Here we found that the H2B E76K mutation, in which Glu76 is replaced by Lys (E76K), distorted the interface between H2B and H4 in the nucleosome, as revealed by the crystal structure and induced nucleosome instability in vivo and in vitro. Exogenous production of the H2B E76K mutant robustly enhanced the colony formation ability of the expressing cells, indicating that the H2B E76K mutant has the potential to promote oncogenic transformation in the presence of wild-type H2B. We found that other cancer-associated mutations of histones, H3.1 E97K and H2A.Z.1 R80C, also induced nucleosome instability. Interestingly, like the H2B E76K mutant, the H3.1 E97K mutant was minimally incorporated into chromatin in cells, but it enhanced the colony formation ability. In contrast, the H2A.Z.1 R80C mutant was incorporated into chromatin in cells, and had minor effects on the colony formation ability of the cells. These characteristics of histones with cancer-associated mutations may provide important information toward understanding how the mutations promote cancer progression.

Chromosomal Abnormalities in Human Lymphocytes after Computed Tomography Scan Procedure.

The incidence of chromosomal abnormalities and cancer risk correlates well with the radiation dose after exposure to moderate- to high-dose ionizing radiation. However, the biological effects and health risks at less than 100 mGy, e.g., from computed tomography (CT) have not been ascertained. To investigate the biological effects of low-dose exposure from a CT procedure, we examined chromosomal aberrations, dicentric and ring chromosomes (dic+ring), in peripheral blood lymphocytes (PBLs), using FISH assays with telomere and centromere PNA probes. In 60 non-cancer patients exposed to CT scans, the numbers of dicentric and ring chromosomes were significantly increased with individual variation. The individual variations in the increment of dicentric and ring chromosomes after CT procedures were confirmed using PNA-FISH analysis of PBLs from 15 healthy volunteers after in vitro low-dose exposure using a 137Cs radiation device. These findings strongly suggest that appropriate medical use of low-dose radiation should consider individual differences in radiation sensitivity.