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.

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.

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.

DNA damage induced by radiation exposure from cardiac catheterization – an analysis in patients and operators

Background

The biological effects of low-dose radiation from cardiac imaging or intervention 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.

Methods

Peripheral mononuclear cells (MNCs) were isolated from patients (n=52) and operators (n=35) before and after coronary angiography and/or percutaneous coronary intervention. Expression of gammaH2AX, 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.

Results

In the patient MNCs, the numbers of gammaH2AX foci and DICs increased after cardiac catheterization by 101±75% and 28±99%, respectively (P<0.05 for both). The mRNA expressions of interleukin (IL)-1α, IL-1β, leukemia inhibitory factor (LIF) and caspase-1 were significantly increased by radiation exposure from cardiac catheterization. The increase in IL-1β was significantly correlated with that of gammaH2AX, but not with dose area product. In the operators, neither gammaH2AX foci nor DICs level was changed, but IL-1β mRNA was significantly increased. Protein expression of IkappaBα was significantly decreased in both groups.

Conclusions

DNA damage was increased in the MNCs of patients, but not of operators, who underwent cardiac catheterization. Inflammatory cytokines were increased both in the patients and operators, presumably through activation of NF-kappaB. Further efforts to reduce radiation exposure from cardiac catheterization are necessary both for patients and operators.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Grants-in-Aid for Scientific Research (KAKENHI)

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-1β, leukemia inhibitory factor, and caspase-1 were significantly increased by radiation exposure from cardiac catheterization. The increase in IL-1β 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-1β 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.

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.

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.

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.

The motion and spatial reorganization of sub-nuclear domains have been extensively studied using microscopy, but the underlying mechanisms that promote the reorganization are still poorly understood. We found that dynamic nuclear deformation provides a driving force for long-range migration and aggressive clustering of chromocenters, which ultimately induces nuclear architecture reorganization. This study significantly contributes to an improved understanding of the role of nuclear deformation and reorganization of nuclear architecture that seems complex but is based on simple physical properties of the cell.

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.

RELATIVE BIOLOGICAL EFFECTIVENESS OF NEUTRONS DERIVED FROM THE EXCESS RELATIVE RISK MODEL WITH THE ATOMIC BOMB SURVIVORS DATA MANAGED BY HIROSHIMA UNIVERSITY

According to an analysis of the Life Span Study cohort data conducted by the Radiation Effects Research Foundation in Hiroshima and Nagasaki, the sex-averaged excess relative risk (ERR) of all solid cancers was 0.42 Gy-Eq-1. On the other hand, analysis of the atomic bomb survivors (ABS) cohort data at Hiroshima University indicated the ERR value was 0.28 Gy-Eq-1 in Hiroshima. In both cases, initial radiation doses were derived from the dosimetry system DS02, in which the relative biological effectiveness (RBE) of neutrons was assumed to be a constant value of 10. To clarify the validity of the RBE, the authors investigated the possibility of different contributions of neutrons by using the ABS. Although there were no statistically significant differences among the estimated value of RBE (=65) and the ordinal value (=10), the corresponding ERR decreased by 30%, which might affect the interpretation of radiation health assessments.

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.

Distinct roles of ATM and ATR in the regulation of ARP8 phosphorylation to prevent chromosome translocations

Chromosomal translocations are hallmarks of various types of cancers and leukemias. However, the molecular mechanisms of chromosome translocations remain largely unknown. The ataxia-telangiectasia mutated (ATM) protein, a DNA damage signaling regulator, facilitates DNA repair to prevent chromosome abnormalities. Previously, we showed that ATM deficiency led to the 11q23 chromosome translocation, the most frequent chromosome abnormalities in secondary leukemia. Here, we show that ARP8, a subunit of the INO80 chromatin remodeling complex, is phosphorylated after etoposide treatment. The etoposide-induced phosphorylation of ARP8 is regulated by ATM and ATR, and attenuates its interaction with INO80. The ATM-regulated phosphorylation of ARP8 reduces the excessive loading of INO80 and RAD51 onto the breakpoint cluster region. These findings suggest that the phosphorylation of ARP8, regulated by ATM, plays an important role in maintaining the fidelity of DNA repair to prevent the etoposide-induced 11q23 abnormalities.

Estimation of the effects of medical diagnostic radiation exposure based on DNA damage

X-rays are widely applied in the medical field for the diagnosis and treatment of diseases. Among the uses of X-rays in diagnosis, computed tomography (CT) has been established as one of the most informative diagnostic radiology examinations. Moreover, recent advances in CT scan technology have made this examination much easier and more informative and increased its application, especially in Japan. However, the radiation dose of CT scans is higher than that of simple X-ray examinations. Therefore, the health risk of a CT scan has been discussed in various studies, but is still controversial. Consequently, the biological and cytogenetic effects of CT scans are being analyzed. Here, we summarize the recent findings concerning the biological and cytogenetic effects of ionizing radiation from a CT scan, by focusing on DNA damage and chromosome aberrations.

Exploration of genetic basis underlying individual differences in radiosensitivity within human populations using genome editing technology

DNA double-strand breaks (DSBs) induced by ionizing radiation (IR) are the initial and critical step in major alteration of genetic information and cell death. To prevent deleterious effects, DNA repair systems recognize and re-join DNA DSBs in human cells. It has been suggested that there are individual differences in radiosensitivity within human populations, and that variations in DNA repair genes might contribute to this heterogeneity. Because confounding factors, including age, gender, smoking, and diverse genetic backgrounds within human populations, also influence the cellular radiosensitivity, to accurately measure the effect of candidate genetic variations on radiosensitivity, it is necessary to use human cultured cells with a uniform genetic background. However, a reverse genetics approach in human cultured cells is difficult because of their low level of homologous recombination. Engineered endonucleases used in genome editing technology, however, can enable the local activation of DNA repair pathways at the human genome target site to efficiently introduce genetic variations of interest into human cultured cells. Recently, we used this technology to demonstrate that heterozygous mutations of the ATM gene, which is responsible for a hyper-radiosensitive genetic disorder, ataxia-telangiectasia, increased the number of chromosomal aberrations after IR. Thus, understanding the heterozygous mutations of radiosensitive disorders should shed light on the genetic basis underlying individual differences in radiosensitivity within human populations.

SUMO modification system facilitates the exchange of histone variant H2A.Z-2 at DNA damage sites

Histone exchange and histone post-translational modifications play important roles in the regulation of DNA metabolism, by re-organizing the chromatin configuration. We previously demonstrated that the histone variant H2A.Z-2 is rapidly exchanged at damaged sites after DNA double strand break induction in human cells. In yeast, the small ubiquitin-like modifier (SUMO) modification of H2A.Z is involved in the DNA damage response. However, whether the SUMO modification regulates the exchange of human H2A.Z-2 at DNA damage sites remains unclear. Here, we show that H2A.Z-2 is SUMOylated in a damage-dependent manner, and the SUMOylation of H2A.Z-2 is suppressed by the depletion of the SUMO E3 ligase, PIAS4. Moreover, PIAS4 depletion represses the incorporation and eviction of H2A.Z-2 at damaged sites. These findings demonstrate that the PIAS4-mediated SUMOylation regulates the exchange of H2A.Z-2 at DNA damage sites.

Evaluation of ATM heterozygous mutations underlying individual differences in radiosensitivity using genome editing in human cultured cells

Ionizing radiation (IR) induces DNA double-strand breaks (DSBs), which are an initial step towards chromosomal aberrations and cell death. It has been suggested that there are individual differences in radiosensitivity within human populations, and that the variations in DNA repair genes might determine this heterogeneity. However, it is difficult to quantify the effect of genetic variants on the individual differences in radiosensitivity, since confounding factors such as smoking and the diverse genetic backgrounds within human populations affect radiosensitivity. To precisely quantify the effect of a genetic variation on radiosensitivity, we here used the CRISPR-ObLiGaRe (Obligate Ligation-Gated Recombination) method combined with the CRISPR/Cas9 system and a nonhomologous end joining (NHEJ)-mediated knock-in technique in human cultured cells with a uniform genetic background. We generated ATM heterozygous knock-out (ATM ^+/-) cell clones as a carrier model of a radiation-hypersensitive autosomal-recessive disorder, ataxia-telangiectasia (A-T). Cytokinesis-blocked micronucleus assay and chromosome aberration assay showed that the radiosensitivity of ATM ^+/- cell clones was significantly higher than that of ATM ^+/+ cells, suggesting that ATM gene variants are indeed involved in determining individual radiosensitivity. Importantly, the differences in radiosensitivity among the same genotype clones were small, unlike the individual differences in fibroblasts derived from A-T-affected family members.

Antagonizing effect of CLPABP on the function of HuR as a regulator of ARE-containing leptin mRNA stability and the effect of its depletion on obesity in old male mouse

Cardiolipin and phosphatidic acid-binding protein (CLPABP) is a pleckstrin homology domain-containing protein and is localized on the surface of mitochondria of cultured cells as a large protein-RNA complex. To analyze the physiological functions of CLPABP, we established and characterized a CLPABP knockout (KO) mouse. Although expression levels of CLPABP transcripts in the developmental organs were high, CLPABP KO mice were normal at birth and grew normally when young. However, old male mice presented a fatty phenotype, similar to that seen in metabolic syndrome, in parallel with elevated male- and age-dependent CLPABP gene expression. One of the reasons for this obesity in CLPABP KO mice is dependence on increases in leptin concentration in plasma. The leptin transcripts were also upregulated in the adipose tissue of KO mice compared with wild-type (WT) mice. To understand the difference in levels of the transcriptional product, we focused on the effect of CLPABP on the stability of mRNA involving an AU-rich element (ARE) in its 3'UTR dependence on the RNA stabilizer, human antigen R (HuR), which is one of the CLPABP-binding proteins. Increase in stability of ARE-containing mRNAs of leptin by HuR was antagonized by the expression of CLPABP in cultured cells. Depletion of CLPABP disturbed the normal subcellular localization of HuR to stress granules, and overexpression of CLPABP induced instability of leptin mRNA by inhibiting HuR function. Consequently, leptin levels in old male mice might be regulated by CLPABP expression, which might lead to body weight control.

A new application of the phase-field method for understanding the mechanisms of nuclear architecture reorganization

Specific features of nuclear architecture are important for the functional organization of the nucleus, and chromatin consists of two forms, heterochromatin and euchromatin. Conventional nuclear architecture is observed when heterochromatin is enriched at nuclear periphery, and it represents the primary structure in the majority of eukaryotic cells, including the rod cells of diurnal mammals. In contrast to this, inverted nuclear architecture is observed when the heterochromatin is distributed at the center of the nucleus, which occurs in the rod cells of nocturnal mammals. The inverted architecture found in the rod cells of the adult mouse is formed through the reorganization of conventional architecture during terminal differentiation. Although a previous experimental approach has demonstrated the relationship between these two nuclear architecture types at the molecular level, the mechanisms underlying long-range reorganization processes remain unknown. The details of nuclear structures and their spatial and temporal dynamics remain to be elucidated. Therefore, a comprehensive approach, using mathematical modeling, is required, in order to address these questions. Here, we propose a new mathematical approach to the understanding of nuclear architecture dynamics using the phase-field method. We successfully recreated the process of nuclear architecture reorganization, and showed that it is robustly induced by physical features, independent of a specific genotype. Our study demonstrates the potential of phase-field method application in the life science fields.

Cytogenetic effects of radioiodine therapy: a 20-year follow-up study

The purpose of this study was to compare cytogenetic data in a patient before and after treatment with radioiodine to evaluate the assays in the context of biological dosimetry. We studied a 34-year-old male patient who underwent a total thyroidectomy followed by ablation therapy with (131)I (19.28 GBq) for a papillary thyroid carcinoma. The patient provided blood samples before treatment and then serial samples at monthly intervals during the first year period and quarterly intervals for 5 years and finally 20 years after treatment. A micronucleus assay, dicentric assay, FISH method and G-banding were used to detect and measure DNA damage in circulating peripheral blood lymphocytes of the patient. The results showed that radiation-induced cytogenetic effects persisted for many years after treatment as shown by elevated micronuclei and chromosome aberrations as a result of exposure to (131)I. At 5 years after treatment, the micronucleus count was tenfold higher than the pre-exposure frequency. Shortly after the treatment, micronucleus counts produced a dose estimate of 0.47 ± 0.09 Gy. The dose to the patient evaluated retrospectively using FISH-measured translocations was 0.70 ± 0.16 Gy. Overall, our results show that the micronucleus assay is a retrospective biomarker of low-dose radiation exposure. However, this method is not able to determine local dose to the target tissue which in this case was any residual thyroid cells plus metastases of thyroidal origin.

Analysis of individual differences in radiosensitivity using genome editing

Current standards for radiological protection of the public have been uniformly established. However, individual differences in radiosensitivity are suggested to exist in human populations, which could be caused by nucleotide variants of DNA repair genes. In order to verify if such genetic variants are responsible for individual differences in radiosensitivity, they could be introduced into cultured human cells for evaluation. This strategy would make it possible to analyse the effect of candidate nucleotide variants on individual radiosensitivity, independent of the diverse genetic background. However, efficient gene targeting in cultured human cells is difficult due to the low frequency of homologous recombination (HR) repair. The development of artificial nucleases has enabled efficient HR-mediated genome editing to be performed in cultured human cells. A novel genome editing strategy, 'transcription activator-like effector nuclease (TALEN)-mediated two-step single base pair editing', has been developed, and this was used to introduce a nucleotide variant associated with a chromosomal instability syndrome bi-allelically into cultured human cells to demonstrate that it is the causative mutation. It is proposed that this editing technique will be useful to investigate individual radiosensitivity.

Enhanced gefitinib-induced repression of the epidermal growth factor receptor pathway by ataxia telangiectasia-mutated kinase inhibition in non-small-cell lung cancer cells

The epidermal growth factor receptor (EGFR) tyrosine kinase signaling pathways regulate cellular activities. The EGFR tyrosine kinase inhibitors (EGFR‐TKIs) repress the EGFR pathway constitutively activated by somatic EGFR gene mutations and have drastically improved the prognosis of non‐small‐cell lung cancer (NSCLC) patients. However, some problems, including resistance, remain to be solved. Recently, combination therapy with EGFR‐TKIs and cytotoxic agents has been shown to improve the prognosis of NSCLC patients. To enhance the anticancer effects of EGFR‐TKIs, we examined the cross‐talk of the EGFR pathways with ataxia telangiectasia‐mutated (ATM) signaling pathways. ATM is a key protein kinase in the DNA damage response and is known to phosphorylate Akt, an EGFR downstream factor. We found that the combination of an ATM inhibitor, KU55933, and an EGFR‐TKI, gefitinib, resulted in synergistic cell growth inhibition and induction of apoptosis in NSCLC cell lines carrying the sensitive EGFR mutation. We also found that KU55933 enhanced the gefitinib‐dependent repression of the phosphorylation of EGFR and/or its downstream factors. ATM inhibition may facilitate the gefitinib‐dependent repression of the phosphorylation of EGFR and/or its downstream factors, to exert anticancer effects against NSCLC cells with the sensitive EGFR mutation.

hCAS/CSE1L regulates RAD51 distribution and focus formation for homologous recombinational repair

Homologous recombinational repair (HR) is one of the major repair systems for DNA double-strand breaks. RAD51 is a key molecule in HR, and the RAD51 concentration in the cell nucleus increases after DNA damage induction. However, the mechanism that regulates the intracellular distribution of RAD51 is still unclear. Here, we show that hCAS/CSE1L associates with RAD51 in human cells. We found that hCAS/CSE1L negatively regulates the nuclear protein level of RAD51 under normal conditions. hCAS/CSE1L is also required to repress the DNA damage-induced focus formation of RAD51. Moreover, we show that hCAS/CSE1L plays roles in the regulation of the HR activity and in chromosome stability. These findings suggest that hCAS/CSE1L is responsible for controlling the HR activity by directly interacting with RAD51.

Regulation of homologous recombinational repair by lamin B1 in radiation-induced DNA damage

DNA double-strand breaks (DSBs) are the major lethal lesion induced by ionizing radiation (IR). RAD51-dependent homologous recombination (HR) is one of the most important pathways in DSB repair and genome integrity maintenance. However, the mechanism of HR regulation by RAD51 remains unclear. To understand the mechanism of RAD51-dependent HR, we searched for interacting partners of RAD51 by a proteomics analysis and identified lamin B1 in human cells. Lamins are nuclear lamina proteins that play important roles in the structural organization of the nucleus and the regulation of chromosome functions. Immunoblotting analyses revealed that siRNA-mediated lamin B1 depletion repressed the DNA damage-dependent increase of RAD51 after IR. The repression was abolished by the proteasome inhibitor MG132, suggesting that lamin B1 stabilizes RAD51 by preventing proteasome-mediated degradation in cells with IR-induced DNA damage. We also showed that lamin B1 depletion repressed RAD51 focus formation and decreased the survival rates after IR. On the basis of these results, we propose that lamin B1 promotes DSB repair and cell survival by maintaining the RAD51 protein levels for HR upon DSB induction after IR.

Structural basis for ubiquitin recognition by ubiquitin-binding zinc finger of FAAP20

Several ubiquitin-binding zinc fingers (UBZs) have been reported to preferentially bind K63-linked ubiquitin chains. In particular, the UBZ domain of FAAP20 (FAAP20-UBZ), a member of the Fanconi anemia core complex, seems to recognize K63-linked ubiquitin chains, in order to recruit the complex to DNA interstrand crosslinks and mediate DNA repair. By contrast, it is reported that the attachment of a single ubiquitin to Rev1, a translesion DNA polymerase, increases binding of Rev1 to FAAP20. To clarify the specificity of FAAP20-UBZ, we determined the crystal structure of FAAP20-UBZ in complex with K63-linked diubiquitin at 1.9 Å resolution. In this structure, FAAP20-UBZ interacts only with one of the two ubiquitin moieties. Consistently, binding assays using surface plasmon resonance spectrometry showed that FAAP20-UBZ binds ubiquitin and M1-, K48- and K63-linked diubiquitin chains with similar affinities. Residues in the vicinity of Ala168 within the α-helix and the C-terminal Trp180 interact with the canonical Ile44-centered hydrophobic patch of ubiquitin. Asp164 within the α-helix and the C-terminal loop mediate a hydrogen bond network, which reinforces ubiquitin-binding of FAAP20-UBZ. Mutations of the ubiquitin-interacting residues disrupted binding to ubiquitin in vitro and abolished the accumulation of FAAP20 to DNA damage sites in vivo. Finally, structural comparison among FAAP20-UBZ, WRNIP1-UBZ and RAD18-UBZ revealed distinct modes of ubiquitin binding. UBZ family proteins could be divided into at least three classes, according to their ubiquitin-binding modes.

The International Nucleome Consortium

The eukaryotic genome adopts in the cell nucleus a 3-dimensional configuration that varies with cell types, developmental stages and environmental condition as well as between normal and pathological states. Understanding genome function will therefore require the elucidation of the structure-function relationship of the cell nucleus as a complex, dynamic biological system, referred to as the nucleome. This exciting and timely task calls for a multi-faceted, interdisciplinary and multi-national effort. We propose the establishment of an International Nucleome Consortium to coordinate this effort worldwide.

The transcription repressors Bach2 and Bach1 promote B cell development by repressing the myeloid program

Mature lymphoid cells express the transcription repressor Bach2, which imposes regulation on humoral and cellular immunity. Here we found critical roles for Bach2 in the development of cells of the B lineage, commencing from the common lymphoid progenitor (CLP) stage, with Bach1 as an auxiliary. Overexpression of Bach2 in pre-pro-B cells deficient in the transcription factor EBF1 and single-cell analysis of CLPs revealed that Bach2 and Bach1 repressed the expression of genes important for myeloid cells ('myeloid genes'). Bach2 and Bach1 bound to presumptive regulatory regions of the myeloid genes. Bach2(hi) CLPs showed resistance to myeloid differentiation even when cultured under myeloid conditions. Our results suggest that Bach2 functions with Bach1 and EBF1 to promote B cell development by repressing myeloid genes in CLPs.

Reorganization of damaged chromatin by the exchange of histone variant H2A.Z-2

PURPOSE

The reorganization of damaged chromatin plays an important role in the regulation of the DNA damage response. A recent study revealed the presence of 2 vertebrate H2A.Z isoforms, H2A.Z-1 and H2A.Z-2. However, the roles of the vertebrate H2A.Z isoforms are still unclear. Thus, in this study we examined the roles of the vertebrate H2A.Z isoforms in chromatin reorganization after the induction of DNA double-strand breaks (DSBs).

METHODS AND MATERIALS

To examine the dynamics of H2A.Z isoforms at damaged sites, we constructed GM0637 cells stably expressing each of the green fluorescent protein (GFP)-labeled H2A.Z isoforms, and performed fluorescence recovery after photobleaching (FRAP) analysis and inverted FRAP analysis in combination with microirradiation. Immunofluorescence staining using an anti-RAD51 antibody was performed to study the kinetics of RAD51 foci formation after 2-Gy irradiation of wild-type (WT), H2A.Z-1- and H2A.Z-2-deficient DT40 cells. Colony-forming assays were also performed to compare the survival rates of WT, H2A.Z-1-, and H2A.Z-2-deficient DT40 cells with control, and H2A.Z-1- and H2A.Z-2-depleted U2OS cells after irradiation.

RESULTS

FRAP analysis revealed that H2A.Z-2 was incorporated into damaged chromatin just after the induction of DSBs, whereas H2A.Z-1 remained essentially unchanged. Inverted FRAP analysis showed that H2A.Z-2 was released from damaged chromatin. These findings indicated that H2A.Z-2 was exchanged at DSB sites immediately after the induction of DSBs. RAD51 focus formation after ionizing irradiation was disturbed in H2A.Z-2-deficient DT40 cells but not in H2A.Z-1-deficient cells. The survival rate of H2A.Z-2-deficient cells after irradiation was lower than those of WT and H2A.Z-1- DT40 cells. Similar to DT40 cells, H2A.Z-2-depleted U2OS cells were also radiation-sensitive compared to control and H2A.Z-1-depleted cells.

CONCLUSIONS

We found that vertebrate H2A.Z-2 is involved in the regulation of the DNA damage response at a very early stage, via the damaged chromatin reorganization required for RAD51 focus formation.

Smoking cessation reverses DNA double-strand breaks in human mononuclear cells

OBJECTIVE

Cigarette smoking is a major risk factor for atherosclerotic cardiovascular disease, which is responsible for a significant proportion of smoking-related deaths. However, the precise mechanism whereby smoking induces this pathology has not been fully delineated. Based on observation of DNA double-strand breaks (DSBs), the most harmful type of DNA damage, in atherosclerotic lesions, we hypothesized that there is a direct association between smoking and DSBs. The goal of this study was to investigate whether smoking induces DSBs and smoking cessation reverses DSBs in vivo through examination of peripheral mononuclear cells (MNCs).

APPROACH AND RESULTS

Immunoreactivity of oxidative modification of DNA and DSBs were increased in human atherosclerotic lesions but not in the adjacent normal area. DSBs in human MNCs isolated from the blood of volunteers can be detected as cytologically visible "foci" using an antibody against the phosphorylated form of the histone H2AX (γ-H2AX). Young healthy active smokers (n = 15) showed increased γ-H2AX foci number when compared with non-smokers (n = 12) (foci number/cell: median, 0.37/cell; interquartile range [IQR], 0.31-0.58 vs. 4.36/cell; IQR, 3.09-7.39, p<0.0001). Smoking cessation for 1 month reduced the γ-H2AX foci number (median, 4.44/cell; IQR, 4.36-5.24 to 0.28/cell; IQR, 0.12-0.53, p<0.05). A positive correlation was noted between γ-H2AX foci number and exhaled carbon monoxide levels (r = 0.75, p<0.01).

CONCLUSIONS

Smoking induces DSBs in human MNCs in vivo, and importantly, smoking cessation for 1 month resulted in a decrease in DSBs to a level comparable to that seen in non-smokers. These data reinforce the notion that the cigarette smoking induces DSBs and highlight the importance of smoking cessation.

Nap1 stimulates homologous recombination by RAD51 and RAD54 in higher-ordered chromatin containing histone H1

Homologous recombination plays essential roles in mitotic DNA double strand break (DSB) repair and meiotic genetic recombination. In eukaryotes, RAD51 promotes the central homologous-pairing step during homologous recombination, but is not sufficient to overcome the reaction barrier imposed by nucleosomes. RAD54, a member of the ATP-dependent nucleosome remodeling factor family, is required to promote the RAD51-mediated homologous pairing in nucleosomal DNA. In higher eukaryotes, most nucleosomes form higher-ordered chromatin containing the linker histone H1. However, the mechanism by which RAD51/RAD54-mediated homologous pairing occurs in higher-ordered chromatin has not been elucidated. In this study, we found that a histone chaperone, Nap1, accumulates on DSB sites in human cells, and DSB repair is substantially decreased in Nap1-knockdown cells. We determined that Nap1 binds to RAD54, enhances the RAD54-mediated nucleosome remodeling by evicting histone H1, and eventually stimulates the RAD51-mediated homologous pairing in higher-ordered chromatin containing histone H1.

Role of DNA damage in cardiovascular disease

Patients with some progeroid syndromes, such as Werner syndrome, exhibit atherosclerotic cardiovascular disease (CVD) at a young age as a manifestation of premature aging. Recent studies have revealed that most progeroid syndromes are caused by genetic defects in specific molecules involved in the DNA damage response, a cornerstone of genome stability. Ionizing radiation is one of the most potent genotoxic stimuli and causes various kinds of DNA damage. Further, there is increasing evidence that therapeutic radiation treatments can cause cardiovascular complications. Here, we describe the DNA damage and subsequent response, review recent advances in the understanding of the molecular basis of progeroid syndromes (especially those syndromes that involve CVD), review the pathological and epidemiological analysis of radiation-induced CVD, and discuss the possible role of DNA damage and the DNA damage response in the pathogenesis of atherosclerotic CVD.

Involvement of homologous recombination in the synergism between cisplatin and poly (ADP-ribose) polymerase inhibition

Poly (ADP-ribose) polymerase (PARP) plays a critical role in responding to DNA damage, by activating DNA repair pathways responsible for cellular survival. Inhibition of PARP is used to treat certain solid cancers, such as breast and ovarian cancers. However, its effectiveness with other solid cancers, such as esophageal squamous cell carcinoma (ESCC), has not been clarified. We evaluated the effects of PARP inhibition on the survival of human esophageal cancer cells, with a special focus on the induction and repair of DNA double-strand breaks. The effects were monitored by colony formation assays and DNA damage responses, with immunofluorescence staining of γH2AX and RAD51. We found that PARP inhibition synergized with cisplatin, and the cells were highly sensitive, in a similar manner to the combination of cisplatin and 5-fluorouracil (5-FU). Comparable increases in RAD51 foci formation were observed after each combined treatment with cisplatin and either 3-aminobenzamide (3-AB) or 5-FU in three human esophageal cancer cell lines, TE11, TE14, and TE15. In addition, decreasing the amount of RAD51 by RNA interference rendered the TE11 cells even more hypersensitive to these treatments. Our findings suggested that the homologous recombinational repair pathway may be involved in the synergism between cisplatin and either 3-AB or 5-FU, and that 3-AB and 5-FU may similarly modify the cisplatin-induced DNA damage to types requiring the recruitment of RAD51 proteins for their repair. Understanding these mechanisms could be useful for improving the clinical outcome of ESCC patients who suffer from aggressive disease that presently lacks effective treatment options.