Mechanistic insights into the survival curve of HeLa cells with a short shoulder and their S phase-specific sensitivity†

HeLa cells are a cell line with two unique cellular features: a short-shouldered survival curve and two peaks of radioresistance during the cell cycle phase, while their underlying mechanisms remain unclear. We herein proposed that these radiobiological features are due to a common mechanism by which radiation suppresses homologous recombination repair (HRR) in a dose-dependent manner. This radio-suppression of HRR is mediated by an intra-S checkpoint and reduces survivals of cells in S phase, especially early S phase, resulting in both short shoulder and radioresistance with two peaks in the cell cycle. This new explanation may not be limited to HeLa cells since a similar close association of these features is also observed in other type of cells.

Dynamin-related protein 2 interacts with the membrane-associated methyltransferase domain of plantago asiatica mosaic virus replicase and promotes viral replication

Positive-strand RNA viruses replicate their RNA in the viral replication complex, a spherical structure formed by remodeling of host intracellular membranes. This process also requires the interaction between viral membrane-associated replication proteins and host factors. We previously identified the membrane-associated determinant of the replicase of plantago asiatica mosaic virus (PlAMV), a positive-strand RNA virus of the genus Potexvirus, in its methyltransferase (MET) domain, and suggested that its interaction with host factors is required to establish viral replication. Here we identified Nicotiana benthamiana dynamin-related protein 2 (NbDRP2) as an interactor of the MET domain of the PlAMV replicase by co-immunoprecipitation (Co-IP) and mass spectrometry analysis. NbDRP2 is closely related to the DRP2 subfamily proteins in Arabidopsis thaliana, AtDRP2A and AtDRP2B. Confocal microscopy observation and Co-IP confirmed the interaction between the MET domain and NbDRP2. Also, the expression of NbDRP2 was induced by PlAMV infection. PlAMV accumulation was reduced when the expression of NbDRP2 gene was suppressed by virus-induced gene silencing. In addition, PlAMV accumulation was reduced in protoplasts treated with dynamin inhibitor. These results indicate a proviral role of the interaction of NbDRP2 with the MET domain in PlAMV replication.

Induction of somatic mutations by low concentrations of tritiated water (HTO): evidence for the possible existence of a dose-rate threshold

Tritium is a low energy beta emitter and is discharged into the aquatic environment primarily in the form of tritiated water (HTO) from nuclear power plants or from nuclear fuel reprocessing plants. Although the biological effects of HTO exposures at significant doses or dose rates have been extensively studied, there are few reports concerning the biological effects of HTO exposures at very low dose rates. In the present study using a hyper-sensitive assay system, we investigated the dose rate effect of HTO on the induction of mutations. Confluent cell populations were exposed to HTO for a total dose of 0.2 Gy at dose rates between 4.9 mGy/day and 192 mGy/day by incubating cells in medium containing HTO. HTO-induced mutant frequencies and mutation spectra were then investigated. A significant inflection point for both the mutant frequency and mutation spectra was found between 11 mGy/day and 21.6 mGy/day. Mutation spectra analysis revealed that a mechanistic change in the nature of the mutation events occurred around 11 mGy/day. The present observations and published experimental results from oral administrations of HTO to mice suggest that a threshold dose-rate for HTO exposures might exist between 11 mGy/day and 21.6 mGy/day where the nature of the mutation events induced by HTO becomes similar to those seen in spontaneous events.

RIF1 controls replication initiation and homologous recombination repair in a radiation dose-dependent manner

RIF1 controls both DNA replication timing and the DNA double-strand break (DSB) repair pathway to maintain genome integrity. However, it remains unclear how RIF1 links these two processes following exposure to ionizing radiation (IR). Here, we show that inhibition of homologous recombination repair (HRR) by RIF1 occurs in a dose-dependent manner and is controlled via DNA replication. RIF1 inhibits both DNA end resection and RAD51 accumulation after exposure to high doses of IR. Contrastingly, HRR inhibition by RIF1 is antagonized by BRCA1 after a low-dose IR exposure. At high IR doses, RIF1 suppresses replication initiation by dephosphorylating MCM helicase. Notably, the dephosphorylation of MCM helicase inhibits both DNA end resection and HRR, even without RIF1. Thus, our data show the importance of active DNA replication for HRR and suggest a common suppression mechanism for DNA replication and HRR at high IR doses, both of which are controlled by RIF1.This article has an associated First Person interview with the first author of the paper.

Utility of state-level influenza disease burden and severity estimates to investigate an apparent increase in reported severe cases of influenza A(H1N1) pdm09 - Arizona, 2015-2016

The Arizona Department of Health Services identified unusually high levels of influenza activity and severe complications during the 2015-2016 influenza season leading to concerns about potential increased disease severity compared with prior seasons. We estimated state-level burden and severity to compare across three seasons using multiple data sources for community-level illness, hospitalisation and death. Severity ratios were calculated as the number of hospitalisations or deaths per community case. Community influenza-like illness rates, hospitalisation rates and mortality rates in 2015-2016 were higher than the previous two seasons. However, ratios of severe disease to community illness were similar. Arizona experienced overall increased disease burden in 2015-2016, but not increased severity compared with prior seasons. Timely estimates of state-specific burden and severity are potentially feasible and may provide important information during seemingly unusual influenza seasons or pandemic situations.

Radiation-Induced Myofibroblasts Promote Tumor Growth via Mitochondrial ROS-Activated TGFβ Signaling

Fibroblasts are a key stromal cell in the tumor microenvironment (TME) and promote tumor growth via release of various growth factors. Stromal fibroblasts in cancer, called cancer-associated fibroblasts (CAF), are related to myofibroblasts, an activated form of fibroblast. While investigating the role of stroma fibroblasts on radiation-related carcinogenesis, it was observed following long-term fractionated radiation (FR) that the morphology of human diploid fibroblasts changed from smaller spindle shapes to larger flat shapes. These cells expressed smooth muscle actin (α-SMA) and platelet-derived growth factor receptors, markers of myofibroblasts and CAFs, respectively. Long-term FR induces progressive damage to the fibroblast nucleus and mitochondria via increases in mitochondrial reactive oxygen species (ROS) levels. Here, it is demonstrated that long-term FR-induced α-SMA-positive cells have decreased mitochondrial membrane potential and activated oxidative stress responses. Antioxidant N-acetyl cysteine suppressed radiation-induced mitochondrial damage and generation of myofibroblasts. These results indicate that mitochondrial ROS are associated with the acquisition of myofibroblasts after long-term FR. Mechanistically, mitochondrial ROS activated TGFβ signaling which in turn mediated the expression of α-SMA in radiation-induced myofibroblasts. Finally, in vivo tumor growth analysis in a human tumor xenograft model system revealed that long-term FR-induced myofibroblasts promote tumor growth by enhancing angiogenesis.Implications: Radiation affects malignant cancer cells directly and indirectly via molecular alterations in stromal fibroblasts such as activation of TGFβ and angiogenic signaling pathways. Mol Cancer Res; 16(11); 1676-86. ©2018 AACR.

Pressure-induced stacking disorder in boehmite

The structure of an aluminum layered hydroxide, boehmite (γ-AlOOH), as a function of pressure was studied by using in situ synchrotron X-ray and neutron diffraction. Peak broadening, which is only found for hkl (h ≠ 0) peaks in the X-ray diffraction patterns, is explained by stacking disorder accompanying a continuously increasing displacement of the AlO6 octahedral layer along the a-axis. This finding could be the first experimental result for pressure-induced stacking disorder driven by continuous layer displacement. The magnitude of the layer displacement was estimated from the X-ray scattering profile calculation based on the stacking disordered structure model. Hydrogen bond geometries of boehmite, obtained by structure refinements of the observed neutron diffraction patterns for the deuterated sample up to 10 GPa, show linearly approaching O-D covalent and DO hydrogen bond distances and they merge below 26 GPa. Pressure-induced stacking disorder makes the electrostatic potential of hydrogen bonds asymmetric, yielding less chance for proton-tunnelling.

Frequency-Domain Multiplexing Readout with a Self-Trigger System for Pulse Signals from Kinetic Inductance Detectors

We present the development of a frequency-domain multiplexing readout of kinetic inductance detectors (KIDs) for pulse signals with a self-trigger system. The KIDs consist of an array of superconducting resonators that have different resonant frequencies individually, allowing us to read out multiple channels in the frequency domain with a single wire using a microwave-frequency comb. The energy deposited to the resonators break Cooper pairs, changing the kinetic inductance and, hence, the amplitude and the phase of the probing microwaves. For some applications such as X-ray detections, the deposited energy is detected as a pulse signal shaped by the time constants of the quasiparticle lifetime, the resonator quality factor, and the ballistic phonon lifetime in the substrate, ranging from microseconds to milliseconds. A readout system commonly used converts the frequency-domain data to the time-domain data. For the short pulse signals, the data rate may exceed the data transfer bandwidth, as the short time constant pulses require us to have a high sampling rate. In order to overcome this circumstance, we have developed a KID readout system that contains a self-trigger system to extract relevant signal data and reduces the total data rate with a commercial off-the-shelf FPGA board. We have demonstrated that the system can read out pulse signals of 15 resonators simultaneously with about 10 Hz event rate by irradiating α particles from 241 Am to the silicon substrate on whose surface aluminum KID resonators are formed.

Induction of somatic mutations by low-dose X-rays: the challenge in recognizing radiation-induced events

It is difficult to distinguish radiation-induced events from spontaneous events during induction of stochastic effects, especially in the case of low-dose or low-dose-rate exposures. By using a hypersensitive system for detecting somatic mutations at the HPRT1 locus, we investigated the frequency and spectrum of mutations induced by low-dose X-rays. The mutant frequencies induced by doses of >0.15 Gy were statistically significant when compared with the spontaneous frequency, and a clear dose dependency was also observed for mutant frequencies at doses of >0.15 Gy. In contrast, mutant frequencies at doses of <0.1 Gy occurred at non-significant levels. The mutation spectrum in HPRT-deficient mutants revealed that the type of mutations induced by low-dose exposures was similar to that seen in spontaneous mutants. An apparent change in mutation type was observed for mutants induced by doses of >0.2 Gy. Our observations suggest that there could be a critical dose for mutation induction at between 0.1 Gy and 0.2 Gy, where mutagenic events are induced by multiple DNA double-strand breaks (DSBs). These observations also suggest that low-dose radiation delivered at doses of <0.1 Gy may not result in DSB-induced mutations but may enhance spontaneous mutagenesis events.

Abstract P2-01-08: Enumeration of heterogeneous circulating tumor cells (CTCs) using size-based method in early, and metastatic, breast cancer patients

Background

The detection of circulating tumor cells (CTCs) in peripheral blood is an independent predictor of the efficacy of systemic therapy, and also a prognostic marker for patients with metastatic breast cancer. One of the main methods to detect CTCs is CellSearch system, which uses immune-magnetic separation followed by immunocytochemistry. A microdevice (CTChip from ClearCell system) can capture and enumerate CTCs based on distinctive physiological differences (size and deformability) between cancer cells and blood cells. CTChip thus obtains a larger CTC yield than affinity-based separation, which enriches a particular subgroup of cells expressing EpCAM. In this study, we enumerate CTCs in peripheral blood from early and metastatic breast cancer patients using a size-based method.

Patients and methods

We examined blood samples from a total of 18 early and metastatic breast cancer patients, after obtaining written informed consent. Blood samples were taken in sodium EDTA tubes after discarding the first 1ml of blood from the syringe. Two ml blood samples were applied to CTChip (ClearCell system), and CTCs were eventually trapped in the microwells of the CTChip. Trapped cells were analyzed by immunocytochemistry with monoclonal antibodies specific for leukocytes (CD45) and epithelial cells (CK8/18), along with 4',6-diamidino-2-phenylindole (DAPI) for nuclei: CK8/18-positive, DAPI-positive and CD45-negative cells more than 10 μm in diameter were defined as CTCs. Eight patients were examined using both the CTChip and CellSearch system to compare the yield of CTCs.

Results

Of 18 patients, 6 were de novo stage IV, 6 were recurrent and 6 were early stage breast cancer patients. Of primary tumors, 8 were HER2- and ER and/or PR +, 6 were HER2-and ER- and PR-, 3 were HER2+ and ER and/or PR +, and one was HER2+ and ER- and PR-. Using CTChip, detected CTCs ranged from 3 - 107 cells/2 ml in all cases: 3 - 83 for early stage, 19 - 156 for stage IV and 21 - 146 for recurrent. The number of CTCs found in recurrent patients tended to be higher than in early stage patients. Size-based method using CTChip clearly showed high sensitivity compared with the CellSearch system, which detected CTCs in only 2 cases out of 8. In analysis by immunochemistry, we found CK-negative, CD45-negative and DAPI positive cells with larger diameter (&gt;16 μm) than CK-positive CTCs in most patients, and the numbers were higher in stage IV (8.5 cells of median value) and recurrent (13 cells) patients than in early stage patients (1.5 cells). Our study suggested that CK-negative large cells might be CTCs with epithelial–mesenchymal transition (EMT).

Conclusion

This size-based technology enables us to capture CTCs regardless of EpCAM expression. Enumerated CTCs varied in size and positivity of CK8/18, suggesting the heterogeneity of CTCs. Further research, especially focusing on EMT will be crucial to understand the key mechanism of metastasis and drug resistance.

Citation Format: Tozuka K, Nagai SE, Kubo K, Komatsu K, Takai K, Inoue K, Matsumoto H, Hayashi Y, Tsuboi M, Yamada Y, Wang X, Suganuma M. Enumeration of heterogeneous circulating tumor cells (CTCs) using size-based method in early, and metastatic, breast cancer patients [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-01-08.

ATM-mediated mitochondrial damage response triggered by nuclear DNA damage in normal human lung fibroblasts

Ionizing radiation (IR) elevates mitochondrial oxidative phosphorylation (OXPHOS) in response to the energy requirement for DNA damage responses. Reactive oxygen species (ROS) released during mitochondrial OXPHOS may cause oxidative damage to mitochondria in irradiated cells. In this paper, we investigated the association between nuclear DNA damage and mitochondrial damage following IR in normal human lung fibroblasts. In contrast to low-doses of acute single radiation, continuous exposure of chronic radiation or long-term exposure of fractionated radiation (FR) induced persistent Rad51 and γ-H2AX foci at least 24 hours after IR in irradiated cells. Additionally, long-term FR increased mitochondrial ROS accompanied with enhanced mitochondrial membrane potential (ΔΨm) and mitochondrial complex IV (cytochrome c oxidase) activity. Mitochondrial ROS released from the respiratory chain complex I caused oxidative damage to mitochondria. Inhibition of ATM kinase or ATM loss eliminated nuclear DNA damage recognition and mitochondrial radiation responses. Consequently, nuclear DNA damage activates ATM which in turn increases ROS level and subsequently induces mitochondrial damage in irradiated cells. In conclusion, we demonstrated that ATM is essential in the mitochondrial radiation responses in irradiated cells. We further demonstrated that ATM is involved in signal transduction from nucleus to the mitochondria in response to IR.

Note: Development of a new Bridgman-type high pressure cell for accurate dielectric measurements

We developed a new high pressure cell which allows us to perform accurate dielectric measurements above 3 GPa. The developed cell is based on Bridgman type opposed anvil cells with electrodes immersed into holes in the anvils in order to make the electrode area constant under compression. As a feasibility experiment, dielectric measurements for H₂O were conducted up to 6.6 GPa and obtained dielectric constants are well consistent with previous studies.

A comparison of radiation-induced mitochondrial damage between neural progenitor stem cells and differentiated cells

Mitochondria play a key role in maintaining cellular homeostasis during stress responses, and mitochondrial dysfunction contributes to carcinogenesis, aging, and neurologic disease. We here investigated ionizing radiation (IR)-induced mitochondrial damage in human neural progenitor stem cells (NSCs), their differentiated counterparts and human normal fibroblasts. Long-term fractionated radiation (FR) with low doses of X-rays for 31 d enhanced mitochondrial activity as evident by elevated mitochondrial membrane potential (ΔΨm) and mitochondrial complex IV (cytochrome c oxidase) activity to fill the energy demands for the chronic DNA damage response in differentiated cells. Subsequent reduction of the antioxidant glutathione via continuous activation of mitochondrial oxidative phosphorylation caused oxidative stress and genomic instability in differentiated cells exposed to long-term FR. In contrast, long-term FR had no effect on the mitochondrial activity in NSCs. This cell type showed efficient DNA repair, no mitochondrial damage, and resistance to long-term FR. After high doses of acute single radiation (SR) (> 5 Gy), cell cycle arrest at the G2 phase was observed in NSCs and human fibroblasts. Under this condition, increase in mitochondria mass, mitochondrial DNA, and intracellular reactive oxygen species (ROS) levels were observed in the absence of enhanced mitochondrial activity. Consequently, cellular senescence was induced by high doses of SR in differentiated cells. In conclusion, we demonstrated that mitochondrial radiation responses differ according to the extent of DNA damage, duration of radiation exposure, and cell differentiation.

Severe mitochondrial damage associated with low-dose radiation sensitivity in ATM- and NBS1-deficient cells

Low-dose radiation risks remain unclear owing to a lack of sufficient studies. We previously reported that low-dose, long-term fractionated radiation (FR) with 0.01 or 0.05 Gy/fraction for 31 d inflicts oxidative stress in human fibroblasts due to excess levels of mitochondrial reactive oxygen species (ROS). To identify the small effects of low-dose radiation, we investigated how mitochondria respond to low-dose radiation in radiosensitive human ataxia telangiectasia mutated (ATM)- and Nijmegen breakage syndrome (NBS)1-deficient cell lines compared with corresponding cell lines expressing ATM and NBS1. Consistent with previous results in normal fibroblasts, low-dose, long-term FR increased mitochondrial mass and caused accumulation of mitochondrial ROS in ATM- and NBS1-complemented cell lines. Excess mitochondrial ROS resulted in mitochondrial damage that was in turn recognized by Parkin, leading to mitochondrial autophagy (mitophagy). In contrast, ATM- and NBS1-deficient cells showed defective induction of mitophagy after low-dose, long-term FR, leading to accumulation of abnormal mitochondria; this was determined by mitochondrial fragmentation and decreased mitochondrial membrane potential. Consequently, apoptosis was induced in ATM- and NBS1-deficient cells after low-dose, long-term FR. Antioxidant N-acetyl-L-cysteine was effective as a radioprotective agent against mitochondrial damage induced by low-dose, long-term FR among all cell lines, including radiosensitive cell lines. In conclusion, we demonstrated that mitochondria are target organelles of low-dose radiation. Mitochondrial response influences radiation sensitivity in human cells. Our findings provide new insights into cancer risk estimation associated with low-dose radiation exposure.

Transcatheter Embolization of Testicular Vein for Varicocele Testis

Percutaneous transcatheter embolization of the testicular vein was performed on 28 patients with angiographically proven varicocele testis. In 2 patients bilateral and in 26 only the left vein was embolized using 3-, 5-, or 8-mm stainless steel coils. All patients had clinically palpable varicoceles and male infertility. The grade of varicoceles improved after embolization in 23 of 28 cases (82%). Effective sperm count increased significantly from 34.5 ± 44.6 to 65.1 ± 71.0 following embolization. However, pregnancy was achieved only in one of 28 cases. Technically, the basilic vein approach was felt to be superior to the femoral vein or jugular vein approach for this procedure.

Ice VII from aqueous salt solutions: From a glass to a crystal with broken H-bonds

It has been known for decades that certain aqueous salt solutions of LiCl and LiBr readily form glasses when cooled to below ≈160 K. This fact has recently been exploited to produce a « salty » high-pressure ice form: When the glass is compressed at low temperatures to pressures higher than 4 GPa and subsequently warmed, it crystallizes into ice VII with the ionic species trapped inside the ice lattice. Here we report the extreme limit of salt incorporation into ice VII, using high pressure neutron diffraction and molecular dynamics simulations. We show that high-pressure crystallisation of aqueous solutions of LiCl∙RH₂O and LiBr∙RH₂O with R = 5.6 leads to solids with strongly expanded volume, a destruction of the hydrogen-bond network with an isotropic distribution of water-dipole moments, as well as a crystal-to-amorphous transition on decompression. This highly unusual behaviour constitutes an interesting pathway from a glass to a crystal where translational periodicity is restored but the rotational degrees of freedom remaining completely random.

NBS1 and multiple regulations of DNA damage response

DNA damage response is finely tuned, with several pathways including those for DNA repair, chromatin remodeling and cell cycle checkpoint, although most studies to date have focused on single pathways. Genetic diseases characterized by genome instability have provided novel insights into the underlying mechanisms of DNA damage response. NBS1, a protein responsible for the radiation-sensitive autosomal recessive disorder Nijmegen breakage syndrome, is one of the first factors to accumulate at sites of DNA double-strand breaks (DSBs). NBS1 binds to at least five key proteins, including ATM, RPA, MRE11, RAD18 and RNF20, in the conserved regions within a limited span of the C terminus, functioning in the regulation of chromatin remodeling, cell cycle checkpoint and DNA repair in response to DSBs. In this article, we reviewed the functions of these binding proteins and their comprehensive association with NBS1.

Detection and differentiation of Fusarium oxysporum f. sp. lycopersici race 1 using loop-mediated isothermal amplification with three primer sets

Fusarium oxysporum f. sp. lycopersici (Fol) causes tomato wilt. Based on the difference in pathogenicity towards tomato cultivars, Fol is classified into three races. In this study, a rapid method is developed for the detection and discrimination of Fol race 1 using a loop-mediated isothermal amplification (LAMP) assay with two primer sets targeting a region of the nucleotide sequence of the SIX4 gene specific for race 1 and a primer set targeting the SIX5 gene, conserved in all known Fol isolates. Upon LAMP reaction, amplification using all three primer sets was observed only when DNA of Fol race 1 was used as a template, and not when DNA of other Fol races or other fungal species was used. This method could detect 300 fg of Fol race 1 DNA, a 100-fold higher sensitivity than that obtained by conventional PCR. The method can also detect DNA extracted from soil artificially infested with Fol race 1. It is now possible to detect Fol race 1 in colonies and infected tomato stems without DNA isolation. This method is a rapid and simple tool for discrimination of Fol race 1.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study developed a loop-mediated isothermal amplification (LAMP) assay for detection and differentiation of Fusarium oxysporum f. sp. lycopersici (Fol) race 1 by using three primer sets targeting for the SIX4 and SIX5 genes. These genes are present together only in Fol race 1. This method can detect Fol race 1 in infected tomato stems without DNA extraction, affording an efficient diagnosis of Fusarium wilt on tomatoes in the field.

Partially ordered state of ice XV

Most ice polymorphs have order–disorder “pairs” in terms of hydrogen positions, which contributes to the rich variety of ice polymorphs; in fact, three recently discovered polymorphs— ices XIII, XIV, and XV—are ordered counter forms to already identified disordered phases. Despite the considerable effort to understand order–disorder transition in ice crystals, there is an inconsistency among the various experiments and calculations for ice XV, the ordered counter form of ice VI, i.e., neutron diffraction observations suggest antiferroelectrically ordered structures, which disagree with dielectric measurement and theoretical studies, implying ferroelectrically ordered structures. Here we investigate in-situ neutron diffraction measurements and density functional theory calculations to revisit the structure and stability of ice XV. We find that none of the completely ordered configurations are particular favored; instead, partially ordered states are established as a mixture of ordered domains in disordered ice VI. This scenario in which several kinds of ordered configuration coexist dispels the contradictions in previous studies. It means that the order–disorder pairs in ice polymorphs are not one-to-one correspondent pairs but rather have one-to-n correspondence, where there are n possible configurations at finite temperature.

Induction of Excess Centrosomes in Neural Progenitor Cells during the Development of Radiation-Induced Microcephaly

The embryonic brain is one of the tissues most vulnerable to ionizing radiation. In this study, we showed that ionizing radiation induces apoptosis in the neural progenitors of the mouse cerebral cortex, and that the surviving progenitor cells subsequently develop a considerable amount of supernumerary centrosomes. When mouse embryos at Day 13.5 were exposed to γ-rays, brains sizes were reduced markedly in a dose-dependent manner, and these size reductions persisted until birth. Immunostaining with caspase-3 antibodies showed that apoptosis occurred in 35% and 40% of neural progenitor cells at 4 h after exposure to 1 and 2 Gy, respectively, and this was accompanied by a disruption of the apical layer in which mitotic spindles were positioned in unirradiated mice. At 24 h after 1 Gy irradiation, the apoptotic cells were completely eliminated and proliferation was restored to a level similar to that of unirradiated cells, but numerous spindles were localized outside the apical layer. Similarly, abnormal cytokinesis, which included multipolar division and centrosome clustering, was observed in 19% and 24% of the surviving neural progenitor cells at 48 h after irradiation with 1 and 2 Gy, respectively. Because these cytokinesis aberrations derived from excess centrosomes result in growth delay and mitotic catastrophe-mediated cell elimination, our findings suggest that, in addition to apoptosis at an early stage of radiation exposure, radiation-induced centrosome overduplication could contribute to the depletion of neural progenitors and thereby lead to microcephaly.

Abstract P2-02-20: Enumeration of heterogeneous circulating tumor cells (CTCs) in metastatic breast cancer patients based on size and deformability

Background :

The detection of circulating tumor cells (CTCs) in peripheral blood is an independent predictor of the efficacy of systemic therapy and a prognostic marker for patients with metastatic breast cancer. One of the leading techniques to detect CTCs uses immune-magnetic separation followed by immunocytochemistry. A microdevice can capture and enumerate CTCs using distinctive physiological difference (size and deformability) between cancer cells and blood cells. This microdevice thus obtains a larger CTC yield than that of affinity based separation which enriches the samples from a particular subgroup of cells based on biomarker (EpCAM) used. In this study, we investigated CTCs in peripheral blood from metastatic breast cancer patients using this microdevice.

Patients and methods:

We examined blood samples of 9 patients with heavily treated locally recurrent or metastatic breast cancer. Informed consent from these patients was obtained before blood extraction. Blood samples were taken into sodium EDTA tubes after discarding the first 1ml of blood samples. Two ml whole blood were subjected to the microdevice (Clear cell system), and CTCs were trapped in the microwells: Trapped cells were analyzed by immunocytochemistry with monoclonal antibodies specific for leukocytes (CD45) and epithelial cells (CK8/18), along with 4,2-diamidino-2-phenylndole dihydrochloride (DAPI) for nuclei. CK8/18- positive, DAPI-positive and CD45-negative cells were defined as CTCs. Three patients were examined using both this microdevice and affinity-based separation with EpCAM, to compare the yield of CTCs.

Results:

Of the 9 patients: 7 had ER-positive primary tumors, and 6 had PgR-positive ones, HER2 overexpression was detected in 2 primary tumors. CTCs were detected in 8 patients. The single patient in whom CTCs were not detected suffered from local recurrence (axillary lymph node metastasis) only, with no distant metastases. We were also unable to detect CTCs using EpCAM affinity method for this patient. The number of detected CTCs in the other patients ranged from 19/2ml to 156/2ml (mean 90/2ml), and the sizes of CTCs varied from 5 to 16μm. CK8/18-negative and DAPI positive were detected in most patients, and these cells tended to be larger than CK8/18-positive cells, suggesting that epithelial–mesenchymal transition (EMT) might occur in CTCs. The total number of CTCs detected by the microdevice from 2 patients was larger than that of CTCs detected by EpCAM affinity method (107/2ml vs 1/7.5ml, and 19/2ml vs 39/7.5ml).

Conclusion:

CTCs detected by this microdevice varied in regard to the size of trapped cells and characteristics examined by immunochemistry, suggesting the heterogeneity of CTCs. Further research on this heterogeneity is vital in order to develop personalized treatment for patients with metastatic breast cancer.

Citation Format: Tozuka K, Nagai SE, Inoue K, Komatsu K, Matsumoto H, Hayashi Y, Kurozumi S, Suganuma M. Enumeration of heterogeneous circulating tumor cells (CTCs) in metastatic breast cancer patients based on size and deformability. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-02-20.

Abstract P4-14-17: Prognostic value of tumor-infiltrating lymphocytes in residual tumors after neoadjuvant chemotherapy concomitant with trastuzumab for HER2-positive breast cancer

Background:

Neoadjuvant chemotherapy (NAC) with taxanes, followed by fluorouracil, epirubicin, and cyclophosphamide (FEC), with concurrent trastuzumab is known to achieve a high pCR rate of more than 60% for HER2-positive breast cancer (BC) as well as good prognoses in those obtaining pCR. On the other hand, the prognostic significance of tumor-infiltrating lymphocytes (TILs) has recently been described in triple-negative BC. However, the prognostic and predictive values of TILs in HER2-positive BC remain unclear. In the present study, we examined the grades of TILs in pre-treatment cancer tissues and residual tumors after NAC with trastuzumab, and also investigated its predictive utility for pCR and prognostic power for HER2-positive BC.

Patients and Methods:

A total of 128 Japanese women with HER2-positive BC received either paclitaxel or docetaxel followed by FEC, with concomitant trastuzumab. The proportional grades of stromal (Str)-TILs in pre-treatment biopsy specimens and residual tumors after NAC with trastuzumab were determined as follows: low grade (0-10%), intermediate grade (10-40%), and high grade (40-90%), using the criteria of the International Working Group for TILs in BC. Analysis 1: The relationship between the grades of Str-TILs in pre-treatment tumors and pCR rates was investigated. Relapse-free survival (RFS) and cancer-specific survival (CSS) were analyzed for a correlation with pre-treatment Str-TILs. Analysis 2: Alterations in the grade of Str-TILs were examined in the residual tumors of non-pCR patients, and RFS and CSS were analyzed for a correlation with residual Str-TILs.

Results:

pCR was achieved in 83 out of the 128 patients (pCR rate, 64.8%) who received NAC with trastuzumab, and RFS was significantly better in the pCR group than in the non-pCR group (p = 0.0071). Analysis 1: The patient distribution of the Str-TILs grade in pre-treatment tumors was as follows: high: 24 (18.8%); intermediate: 38 (29.7%); and low: 66 (51.6%). pCR rates correlated with the Str-TILs grade in pre-treatment tumors: 83.3% in the high group, 71.1% in the intermediate group, and 54.5% in the low group (p = 0.026); however, the Str-TILs grade in pre-treatment tumors did not correlate with survival. Analysis 2: In 45 non-pCR patients, the distribution of the Str-TILs grade in residual tumors was as follows: high: 9 (20.0%); intermediate: 8 (17.8%); and low: 28 (62.2%), respectively. In non-pCR patients, the rate of a high Str-TILs grade was greater in residual tumors than in pre-treatment tumors (residual, 20.0%, pre-treatment, 8.9%). RFS was significantly better with a high grade than with a low grade of residual Str-TILs (p = 0.033).

Conclusions:

The status of TILs in pre-treatment tumors predicted responses to NAC concomitant with trastuzumab in HER2-positive BC. The grade of TILs was higher in residual tumors than in pre-treatment tumors, and, among non-pCR patients, the prognosis of patients with a high residual-TILs grade was better prognosis than that of patients with a low residual-TILs grade. We speculate that an examination of TILs in residual tumors after NAC with trastuzumab may be necessary for selecting patients with a good prognosis from non-pCR patients.

Citation Format: Kurozumi S, Inoue K, Matsumoto H, Hayashi Y, Tozuka K, Kubo K, Komatsu K, Takai K, Nagai SE, Oba H, Horiguchi J, Takeyoshi I, Kurosumi M. Prognostic value of tumor-infiltrating lymphocytes in residual tumors after neoadjuvant chemotherapy concomitant with trastuzumab for HER2-positive breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-14-17.

Cationized gelatin hydrogels mixed with plasmid DNA induce stronger and more sustained gene expression than atelocollagen at calvarial bone defects in vivo

Gene transduction of exogenous factors at local sites in vivo is a promising approach to promote regeneration of tissue defects owing to its simplicity and capacity for expression of a variety of genes. Gene transduction by viral vectors is highly efficient; however, there are safety concerns associated with viruses. As a method for nonviral gene transduction, plasmid DNA delivery is safer and simpler, but requires an efficient carrier substance. Here, we aimed to develop a simple, efficient method for bone regeneration by gene transduction and to identify optimal conditions for plasmid DNA delivery at bone defect sites. We focused on carrier substances and compared the efficiencies of two collagen derivatives, atelocollagen, and gelatin hydrogel, as substrates for plasmid DNA delivery in vivo. To assess the efficiencies of these substrates, we examined exogenous expression of green fluorescence protein (GFP) by fluorescence microscopy, polymerase chain reaction, and immunohistochemistry. GFP expression at the bone defect site was higher when gelatin hydrogel was used as a substrate to deliver plasmids than when atelocollagen was used. Moreover, the gelatin hydrogel was almost completely absorbed at the defect site, whereas some atelocollagen remained. When a plasmid harboring bone morphogenic protein 2 was delivered with the substrate to bony defect sites, more new bone formation was observed in the gelatin group than in the atelocollagen group. These results suggested that the gelatin hydrogel was more efficient than atelocollagen as a substrate for local gene delivery and may be a superior material for induction of bone regeneration.

A case-control study of risk factors for death from 2009 pandemic influenza A(H1N1): is American Indian racial status an independent risk factor?

Historically, American Indian/Alaska Native (AI/AN) populations have suffered excess morbidity and mortality from influenza. We investigated the risk factors for death from 2009 pandemic influenza A(H1N1) in persons residing in five states with substantial AI/AN populations. We conducted a case-control investigation using pandemic influenza fatalities from 2009 in Alaska, Arizona, New Mexico, Oklahoma and Wyoming. Controls were outpatients with influenza. We reviewed medical records and interviewed case proxies and controls. We used multiple imputation to predict missing data and multivariable conditional logistic regression to determine risk factors. We included 145 fatal cases and 236 controls; 22% of cases were AI/AN. Risk factors (P 45 years vs. <18 years], pre-existing medical conditions (mOR 7·1), smoking (mOR 3·0), delayed receipt of antivirals (mOR 6·5), and barriers to healthcare access (mOR 5·3). AI/AN race was not significantly associated with death. The increased influenza mortality in AI/AN individuals was due to factors other than racial status. Prevention of influenza deaths should focus on modifiable factors (smoking, early antiviral use, access to care) and identifying high-risk persons for immunization and prompt medical attention.

Relative contribution of four nucleases, CtIP, Dna2, Exo1 and Mre11, to the initial step of DNA double-strand break repair by homologous recombination in both the chicken DT40 and human TK6 cell lines

Homologous recombination (HR) is initiated by double-strand break (DSB) resection, during which DSBs are processed by nucleases to generate 3' single-strand DNA. DSB resection is initiated by CtIP and Mre11 followed by long-range resection by Dna2 and Exo1 in Saccharomyces cerevisiae. To analyze the relative contribution of four nucleases, CtIP, Mre11, Dna2 and Exo1, to DSB resection, we disrupted genes encoding these nucleases in chicken DT40 cells. CtIP and Dna2 are required for DSB resection, whereas Exo1 is dispensable even in the absence of Dna2, which observation agrees with no developmental defect in Exo1-deficient mice. Despite the critical role of Mre11 in DSB resection in S. cerevisiae, loss of Mre11 only modestly impairs DSB resection in DT40 cells. To further test the role of CtIP and Mre11 in other species, we conditionally disrupted CtIP and MRE11 genes in the human TK6 B cell line. As with DT40 cells, CtIP contributes to DSB resection considerably more significantly than Mre11 in TK6 cells. Considering the critical role of Mre11 in HR, this study suggests that Mre11 is involved in a mechanism other than DSB resection. In summary, CtIP and Dna2 are sufficient for DSB resection to ensure efficient DSB repair by HR.

Functional Role of NBS1 in Radiation Damage Response and Translesion DNA Synthesis

Nijmegen breakage syndrome (NBS) is a recessive genetic disorder characterized by increased sensitivity to ionizing radiation (IR) and a high frequency of malignancies. NBS1, a product of the mutated gene in NBS, contains several protein interaction domains in the N-terminus and C-terminus. The C-terminus of NBS1 is essential for interactions with MRE11, a homologous recombination repair nuclease, and ATM, a key player in signal transduction after the generation of DNA double-strand breaks (DSBs), which is induced by IR. Moreover, NBS1 regulates chromatin remodeling during DSB repair by histone H2B ubiquitination through binding to RNF20 at the C-terminus. Thus, NBS1 is considered as the first protein to be recruited to DSB sites, wherein it acts as a sensor or mediator of DSB damage responses. In addition to DSB response, we showed that NBS1 initiates Polη-dependent translesion DNA synthesis by recruiting RAD18 through its binding at the NBS1 C-terminus after UV exposure, and it also functions after the generation of interstrand crosslink DNA damage. Thus, NBS1 has multifunctional roles in response to DNA damage from a variety of genotoxic agents, including IR.

RNF20-SNF2H Pathway of Chromatin Relaxation in DNA Double-Strand Break Repair

Rapid progress in the study on the association of histone modifications with chromatin remodeling factors has broadened our understanding of chromatin dynamics in DNA transactions. In DNA double-strand break (DSB) repair, the well-known mark of histones is the phosphorylation of the H2A variant, H2AX, which has been used as a surrogate marker of DSBs. The ubiquitylation of histone H2B by RNF20 E3 ligase was recently found to be a DNA damage-induced histone modification. This modification is required for DSB repair and regulated by a distinctive pathway from that of histone H2AX phosphorylation. Moreover, the connection between H2B ubiquitylation and the chromatin remodeling activity of SNF2H has been elucidated. In this review, we summarize the current knowledge of RNF20-mediated processes and the molecular link to H2AX-mediated processes during DSB repair.

Y chromosome haplogroup D2a1 is significantly associated with high levels of luteinizing hormone in Japanese men

The association between the Y chromosome haplogroup D2 and risk of azoospermia and low sperm motility has been previously studied, and it was indicated that haplogroups DE (YAP lineage) are associated with prostate cancer risk in Japanese males. Our assumption had been that Y chromosome haplogroups may be associated with sex hormone levels, because sex hormones have been deemed responsible for spermatogenesis and carcinogenesis. In this study, we assessed the association between Y chromosome haplogroups and sex hormone levels, including those of testosterone, sex hormone-binding globulin (SHBG), follicle-stimulating hormone (FSH), luteinizing hormone (LH), inhibin-B, and calculated free testosterone (cFT), in 901 young men from the general Japanese population (cohort 1) and 786 Japanese men of proven fertility (cohort 2). We found that the haplogroup D2a1 was significantly associated with high LH levels in a combined analysis involving two cohorts (β = 0.068, SE = 0.025, p = 0.0075), following correction for multiple testing. To date, this result is the first evidence that implicates Y chromosome haplogroups in an association with sex hormone levels.

Increased oxidative stress in AOA3 cells disturbs ATM-dependent DNA damage responses

Ataxia telangiectasia (AT) is caused by a mutation in the ataxia-telangiectasia-mutated (ATM) gene; the condition is associated with hyper-radiosensitivity, abnormal cell-cycle checkpoints, and genomic instability. AT patients also show cerebellar ataxia, possibly due to reactive oxygen species (ROS) sensitivity in neural cells. The ATM protein is a key regulator of the DNA damage response. Recently, several AT-like disorders have been reported. The genes responsible for them are predicted to encode proteins that interact with ATM in the DNA-damage response. Ataxia with oculomotor apraxia types 1-3 (AOA1, 2, and 3) result in a neurodegenerative and cellular phenotype similar to AT; however, the basis of this phenotypic similarity is unclear. Here, we show that the cells of AOA3 patients display aberrant ATM-dependent phosphorylation and apoptosis following γ-irradiation. The ATM-dependent response to H2O2 treatment was abrogated in AOA3 cells. Furthermore, AOA3 cells had reduced ATM activity. Our results suggest that the attenuated ATM-related response is caused by an increase in endogenous ROS in AOA3 cells. Pretreatment of cells with pyocyanin, which induces endogenous ROS production, abolished the ATM-dependent response. Moreover, AOA3 cells had decreased homologous recombination (HR) activity, and pyocyanin pretreatment reduced HR activity in HeLa cells. These results indicate that excess endogenous ROS represses the ATM-dependent cellular response and HR repair in AOA3 cells. Since the ATM-dependent cell-cycle checkpoint is an important block to carcinogenesis, such inactivation of ATM may lead to tumorigenesis as well as neurodegeneration.

Constipation is not associated with colonic diverticula: a multicenter study in Japan

BACKGROUND

The association of diverticula with bowel habits is unclear. We therefore analyzed the association between diverticula and bowel habits in over 1000 Japanese individuals.

METHODS

Japanese subjects who underwent total colonoscopies at seven centers in Japan from June to September 2013 were analyzed. Bowel habits were evaluated using the Gastrointestinal Symptom Rating Scale, and stool form was assessed using a part of the Bristol Scale and Rome ΙΙΙ criteria. Diverticula were diagnosed by colonoscopy with a transparent soft-short hood.

KEY RESULTS

The study evaluated 1066 subjects, 648 males and 418 females (ratio, 1.55 : 1), of mean age 63.9 ± 13.0 years. After adjusting for age and sex, the presence of constipation was associated with a significantly reduced likelihood of diverticula (odds ratio [OR] = 0.70, 95% confidence interval [CI] 0.52-0.93). When assessed according to the location of diverticula, the presence of constipation was associated with a significantly decreased likelihood of left-sided (OR = 0.39, 95% CI 0.16-0.93), but not right-sided (OR = 1.10, 95% CI 0.48-2.53), diverticula. Furthermore, stool form was unrelated with the presence or absence of diverticula.

CONCLUSIONS & INFERENCES

The wide-spread hypothesis that constipation was associated with colonic diverticula was not supported. Rather, we found that the absence of diverticula was associated with constipation, suggesting the need to reassess the etiology of colonic diverticula.

DNA damage signaling guards against perturbation of cyclin D1 expression triggered by low-dose long-term fractionated radiation

Cyclin D1 expression is precisely controlled during cell-cycle progression. However, repeated exposure to low-dose fractionated radiation (FR) abrogates cell cycle-dependent cyclin D1 degradation by constitutive activation of AKT survival signaling in normal human fibroblasts. The resulting abnormal nuclear cyclin D1 accumulation induces defects in DNA replication and resulting DNA double-strand breaks, and is associated with induction of genomic instability in low-dose irradiated cells. Here, we investigated the role of DNA damage signaling against such perturbed cell-cycle control of cyclin D1 expression. Nuclear cyclin D1 accumulation was induced within 7 days after low-dose FR (0.01 Gy or 0.05 Gy per fraction) in ATM-deficient cells (AT5BIVA), but appeared later in AT5BIVA cells harboring human ATM cDNA. Thus, ATM prevents abnormal nuclear cyclin D1 accumulation at early time points after low-dose FR. We further demonstrated that ATM-mediated downregulation of protein phosphatase 2A activity caused activation of the AKT/cyclin D1 pathway after long-term FR. Perturbation of cyclin D1 expression induced Rad51 foci that indicate homologous recombination repair (HRR) in control cells, while ATM- and NBS1-deficient cells (GM7166) failed to induce Rad51 foci after long-term low-dose FR. After 21 days of FR, NBS1- and ATM-deficient cells showed a decrease in nuclear cyclin D1-positive cells, and an increase in apoptotic cells. Similarly, inhibition of ATM with KU55933 abrogated nuclear cyclin D1 accumulation by induction of apoptosis in ATM-complemented cells exposed to low-dose FR. In conclusion, we here demonstrate that ATM is involved in controlling cyclin D1 levels after low-dose FR. DNA damage signaling mitigates the harmful effects of low-dose long-term FR by suppression of cell death induced by perturbation of cyclin D1 expression.

Wilms' tumor gene WT1 promotes homologous recombination-mediated DNA damage repair

The Wilms' tumor gene WT1 is overexpressed in leukemia and various types of solid tumors and plays an oncogenic role in these malignancies. Alternative splicing at two sites yields four major isoforms, 17AA(+)KTS(+), 17AA(+)KTS(-), 17AA(-)KTS(+), and 17AA(-)KTS(-), and all the isoforms are expressed in the malignancies. However, among the four isoforms, function of WT1[17AA(-)KTS(+)] isoform still remains undetermined. In the present study, we showed that forced expression of WT1[17AA(-)KTS(+)] isoform significantly inhibited apoptosis by DNA-damaging agents such as Doxorubicin, Mitomycin, Camptothesisn, and Bleomycin in immortalized fibroblast MRC5SV and cervical cancer HeLa cells. Knockdown of Rad51, an essential factor for homologous recombination (HR)-mediated DNA repair canceled the resistance to Doxorubicin induced by WT1[17AA(-)KTS(+)] isoform. GFP recombination assay showed that WT1[17AA(-)KTS(+)] isoform alone promoted HR, but that three other WT1 isoforms did not. WT1[17AA(-)KTS(+)] isoform significantly upregulated the expression of HR genes, XRCC2, Rad51D, and Rad54. Knockdown of XRCC2, Rad51D, and Rad54 inhibited the HR activity and canceled resistance to Doxorubicin in MRC5SV cells with forced expression of WT1[17AA(-)KTS(+)] isoform. Furthermore, chromatin immunoprecipitation (ChIP) assay showed the binding of WT1[17AA(-)KTS(+)] isoform protein to promoters of XRCC2 and Rad51D. Immunohistochemical study showed that Rad54 and XRCC2 proteins were highly expressed in the majority of non-small-cell lung cancer (NSCLC) and gastric cancer, and that expression of these two proteins was significantly correlated with that of WT1 protein in NSCLCs. Our results presented here showed that WT1[17AA(-)KTS(+)] isoform had a function to promote HR-mediated DNA repair.

Differential diagnosis of vertical root fractures using reconstructed three-dimensional models of bone defects

OBJECTIVES

The purpose of this study was to evaluate the accuracy of diagnosing vertical root fractures (VRFs) by comparing the volume of bone defects in VRFs with those in non-VRFs on reconstructed three-dimensional (3D) models (TDMs) using CBCT.

METHODS

32 maxillary pre-molars and anterior teeth with radiolucent areas were evaluated on pre-operative CBCT images. Of the 32 teeth, 16 had a fractured root (VRF group) and 16 had a non-fractured root (non-VRF group). The radiolucent area of each tooth was traced in each dimension [mesiodistal, buccolingual and horizontal (the apicoincisal aspect)] by two observers, and 3D images were reconstructed with the Amira(®) software (Visage Imaging Inc., Richmond, Australia). The volume, V, of the TDM was divided into the coronal side and the periapical side at the horizontal slice through the apical foramen, and v was defined as the volume of the coronal side. The values of v/V were calculated for all cases. The Mann-Whitney U test was used to compare values between the VRF group and the non-VRF group (p < 0.05). A receiver operating characteristic (ROC) curve was constructed to select the optimal cut-point.

RESULTS

There was a statistically significant difference in the value of v/V between the two groups (p < 0.05). With a cut-point derived from the ROC curve, and the sensitivity, specificity and accuracy of predicting the VRFs were 1.00, 0.75 and 0.88, respectively.

CONCLUSIONS

Lesions resulting from VRFs can be distinguished from those of non-VRFs on 3D CBCT images with a high degree of accuracy, based on their different 3D shapes.

Mutations in the FHA-domain of ectopically expressed NBS1 lead to radiosensitization and to no increase in somatic mutation rates via a partial suppression of homologous recombination

Ionizing radiation induces DNA double-strand breaks (DSBs). Mammalian cells repair DSBs through multiple pathways, and the repair pathway that is utilized may affect cellular radiation sensitivity. In this study, we examined effects on cellular radiosensitivity resulting from functional alterations in homologous recombination (HR). HR was inhibited by overexpression of the forkhead-associated (FHA) domain-mutated NBS1 (G27D/R28D: FHA-2D) protein in HeLa cells or in hamster cells carrying a human X-chromosome. Cells expressing FHA-2D presented partially (but significantly) HR-deficient phenotypes, which were assayed by the reduction of gene conversion frequencies measured with a reporter assay, a decrease in radiation-induced Mre11 foci formation, and hypersensitivity to camptothecin treatments. Interestingly, ectopic expression of FHA-2D did not increase the frequency of radiation-induced somatic mutations at the HPRT locus, suggesting that a partial reduction of HR efficiency has only a slight effect on genomic stability. The expression of FHA-2D rendered the exponentially growing cell population slightly (but significantly) more sensitive to ionizing radiation. This radiosensitization effect due to the expression of FHA-2D was enhanced when the cells were irradiated with split doses delivered at 24-h intervals. Furthermore, enhancement of radiation sensitivity by split dose irradiation was not seen in contact-inhibited G0/G1 populations, even though the cells expressed FHA-2D. These results suggest that the FHA domain of NBS1 might be an effective molecular target that can be used to induce radiosensitization using low molecular weight chemicals, and that partial inhibition of HR might improve the effectiveness of cancer radiotherapy.

Histone chaperone FACT regulates homologous recombination by chromatin remodeling through interaction with RNF20

The E3 ubiquitin ligase RNF20 regulates chromatin structure through ubiquitylation of histone H2B, so that early homologous recombination repair (HRR) proteins can access the DNA in eukaryotes during repair. However, it remains unresolved how RNF20 itself approaches the DNA in the presence of chromatin structure. Here, we identified the histone chaperone FACT as a key protein in the early steps of HRR. Depletion of SUPT16H, a component of FACT, caused pronounced defects in accumulations of repair proteins and, consequently, decreased HRR activity. This led to enhanced sensitivity to ionizing radiation (IR) and mitomycin-C in a fashion similar to RNF20-deficient cells, indicating that SUPT16H is essential for RNF20-mediated pathway. Indeed, SUPT16H directly bound to RNF20 in vivo, and mutation at the RING-finger domain in RNF20 abolished its interaction and accumulation, as well as that of RAD51 and BRCA1, at sites of DNA double-strand breaks (DSBs), whereas the localization of SUPT16H remained intact. Interestingly, PAF1, which has been implicated in transcription as a mediator of FACT and RNF20 association, was dispensable for DNA-damage-induced interaction of RNF20 with SUPT16H. Furthermore, depletion of SUPT16H caused pronounced defects in RNF20-mediated H2B ubiquitylation and thereby, impaired accumulation of the chromatin remodeling factor SNF2h. Consistent with this observation, the defective phenotypes of SUPT16H were effectively counteracted by enforced nucleosome relaxation. Taken together, our results indicate a primary role of FACT in RNF20 recruitment and the resulting chromatin remodeling for initiation of HRR.

ATM regulates Cdt1 stability during the unperturbed S phase to prevent re-replication

Ataxia-telangiectasia mutated (ATM) plays crucial roles in DNA damage responses, especially with regard to DNA double-strand breaks (DSBs). However, it appears that ATM can be activated not only by DSB, but also by some changes in chromatin architecture, suggesting potential ATM function in cell cycle control. Here, we found that ATM is involved in timely degradation of Cdt1, a critical replication licensing factor, during the unperturbed S phase. At least in certain cell types, degradation of p27^Kip1 was also impaired by ATM inhibition. The novel ATM function for Cdt1 regulation was dependent on its kinase activity and NBS1. Indeed, we found that ATM is moderately phosphorylated at Ser1981 during the S phase. ATM silencing induced partial reduction in levels of Skp2, a component of SCF^Skp2 ubiquitin ligase that controls Cdt1 degradation. Furthermore, Skp2 silencing resulted in Cdt1 stabilization like ATM inhibition. In addition, as reported previously, ATM silencing partially prevented Akt phosphorylation at Ser473, indicative of its activation, and Akt inhibition led to modest stabilization of Cdt1. Therefore, the ATM-Akt-SCF^Skp2 pathway may partly contribute to the novel ATM function. Finally, ATM inhibition rendered cells hypersensitive to induction of re-replication, indicating importance for maintenance of genome stability.