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Journal Cover Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
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   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0027-5107
   Published by Elsevier Homepage  [3175 journals]
  • The presence of KRAS, PPP2R1A and ARID1A mutations in 101 Chinese samples
           with ovarian endometriosis
    • Authors: Yang Zou; Jiang-Yan Zhou; Jiu-Bai Guo; Li-Qun Wang; Yong Luo; Zi-Yu Zhang; Fa-Ying Liu; Jun Tan; Feng Wang; Ou-Ping Huang
      Pages: 1 - 5
      Abstract: Publication date: May 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volume 809
      Author(s): Yang Zou, Jiang-Yan Zhou, Jiu-Bai Guo, Li-Qun Wang, Yong Luo, Zi-Yu Zhang, Fa-Ying Liu, Jun Tan, Feng Wang, Ou-Ping Huang
      Endometriosis is a potential premalignant disorder. The underlying molecular aberrations, however, are not fully understood. A recent exome sequencing study found that 25% (10/39) of deep infiltrating endometriosis harbored cancer driver gene mutations. However, it is unclear whether these mutations also exist in ovarian endometriosis. Here, a total of 101 ovarian endometriosis samples were analyzed for the presence of these gene mutations, including KRAS, PPP2R1A, PIK3CA and ARID1A. In addition, 6 other cancer-associated genes (BRAF, NRAS, HRAS, ERK1, ERK2 and PTEN) were also analyzed. In total, four somatic mutations were identified in three out of 101 ovarian endometriotic lesions (4%, 4/101), including a KRAS p.G12V, a PPP2R1A p.S256F and two ARID1A nonsense mutations (p.Q403* and p.G1926*); while no mutations were identified in the remaining 7 genes (BRAF, NRAS, HRAS, ERK1, ERK2, PTEN and PIK3CA). Note that the KRAS G12V and ARID1A Q403* mutations co-occurred in a 36-year-old sample who had a high serum CA125 (308.4 U/mL) and a late menarche age (18-year-old). Additionally, no mutations in any of the 10 genes were identified in either the healthy eutopic endometrial tissues from 85 control individuals without endometriosis, or in 62 healthy ovarian tissues from ovarian cysts samples (without endometriosis). Our study revealed, for the first time, the presence of classical cancer driver gene mutations in ovarian endometriosis. Furthermore, the co-occurrence of KRAS and ARID1A mutations was identified in a single individual for the first time. The observations of cancer driver gene mutations in our ovarian endometriosis samples, together with several prior observations, further support the notion that endometriosis is a premalignant disorder.

      PubDate: 2018-03-19T00:58:16Z
      DOI: 10.1016/j.mrfmmm.2018.03.001
      Issue No: Vol. 809 (2018)
  • Polymerase bypass of N7-guanine monoadducts of cisplatin, diepoxybutane,
           and epichlorohydrin
    • Authors: Jiayu Ye; Caitlin R. Farrington; Julie T. Millard
      Pages: 6 - 12
      Abstract: Publication date: May 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volume 809
      Author(s): Jiayu Ye, Caitlin R. Farrington, Julie T. Millard
      DNA oligonucleotides containing site-specific N7-guanine monoadducts of cisplatin, diepoxybutane, and epichlorohydrin were used as templates for DNA synthesis by two bacterial DNA polymerases and human polymerase β. These polymerases were able to bypass the lesions effectively, although the efficiency was decreased, with inhibition increasing with the size of the lesion. Fidelity of incorporation was essentially unaltered, suggesting that N7-guanine monoadducts do not significantly contribute to the mutational spectra of these agents.

      PubDate: 2018-04-15T03:44:33Z
      DOI: 10.1016/j.mrfmmm.2018.03.002
      Issue No: Vol. 809 (2018)
  • The first (6-4) photolyase with DNA damage repair activity from the
           Antarctic microalga Chlamydomonas sp. ICE-L
    • Authors: Meiling An; Zhou Zheng; Changfeng Qu; Xixi Wang; Hao Chen; Chongli Shi; Jinlai Miao
      Pages: 13 - 19
      Abstract: Publication date: May 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volume 809
      Author(s): Meiling An, Zhou Zheng, Changfeng Qu, Xixi Wang, Hao Chen, Chongli Shi, Jinlai Miao
      The psychrophilic microalga, Chlamydomonas sp. ICE-L, isolated from floating ice in the Antarctic, one of the most highly UV exposed ecosystems on Earth, displays an efficient DNA photorepair capacity. Here, the first known (6-4) photolyase gene (6-4CiPhr) from C. sp. ICE-L was identified. The 6-4CiPhr encoded 559-amino acid polypeptide with a pI of 8.86, and had a predicted Mw of 64.2 kDa. Real-time PCR was carried out to investigate the response of 6-4CiPhr to UVB exposure. The transcription of 6-4CiPhr was up-regulated continuously within 6 h, achieving a maximum of 62.7-fold at 6 h. Expressing 6-4CiPhr in a photolyase-deficient Escherichia coli strain improved survival rate of the strain. In vitro activity assays of purified protein demonstrated that 6-4CiPhr was a photolyase with 6-4PP repair activity. These findings improve understanding of photoreactivation mechanisms of (6-4) photolyase.

      PubDate: 2018-04-15T03:44:33Z
      DOI: 10.1016/j.mrfmmm.2018.03.004
      Issue No: Vol. 809 (2018)
  • Identification of nonsynonymous TP53 mutations in hydatidiform moles
    • Authors: Ka-Kui Chan; Esther Shuk-Ying Wong; Oscar Gee-Wan Wong; Hextan Yuen-Sheung Ngan; Annie Nga-Yin Cheung
      Pages: 20 - 23
      Abstract: Publication date: May 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volume 809
      Author(s): Ka-Kui Chan, Esther Shuk-Ying Wong, Oscar Gee-Wan Wong, Hextan Yuen-Sheung Ngan, Annie Nga-Yin Cheung
      Hydatidiform mole (HM), an unusual pregnancy with pure or predominant paternal genetic contribution, is the most common form of gestational trophoblastic disease. Most HM regress after uterine evacuation but some will develop into persistent disease or even frank malignancy. Although p53 is highly expressed in HM, TP53 mutations have rarely been detected in previous studies. Here we screened for specific missense mutations on several TP53 hotspots in 49 HMs using a highly sensitive pyrosequencing approach and revealed the significant existence of such mutations in HM tissues. A particularly high frequency (∼59% of the cases) of p53 inactivating mutation on exon 7 has been detected. Our identification of hitherto unreported TP53 mutations in HM suggests the presence of p53 mutants and reflects the advantages of using pyrosequencing for point mutation detection in clinical samples. Traditional sequencing method may have overlooked such mutations that only occur in a small population of trophoblasts.

      PubDate: 2018-04-15T03:44:33Z
      DOI: 10.1016/j.mrfmmm.2018.03.006
      Issue No: Vol. 809 (2018)
  • Effective discovery of rare variants by pooled target capture sequencing:
           A comparative analysis with individually indexed target capture sequencing
    • Authors: Seungjin Ryu; Jeehae Han; Trina M. Norden-Krichmar; Nicholas J. Schork; Yousin Suh
      Pages: 24 - 31
      Abstract: Publication date: Available online 30 March 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Seungjin Ryu, Jeehae Han, Trina M. Norden-Krichmar, Nicholas J. Schork, Yousin Suh
      Identification of all genetic variants associated with complex traits is one of the most important goals in modern human genetics. Genome-wide association studies (GWAS) have been successfully applied to identify common variants, which thus far explain only small portion of heritability. Interests in rare variants have been increasingly growing as an answer for this missing heritability. While next-generation sequencing allows detection of rare variants, its cost is still prohibitively high to sequence a large number of human DNA samples required for rare variant association studies. In this study, we evaluated the sensitivity and specificity of sequencing for pooled DNA samples of multiple individuals (Pool-seq) as a cost-effective and robust approach for rare variant discovery. We comparatively analyzed Pool-seq vs. individual-seq of indexed target capture of up to 960 genes in ~1,000 individuals, followed by independent genotyping validation studies. We found that Pool-seq was as effective and accurate as individual-seq in detecting rare variants and accurately estimating their minor allele frequencies (MAFs). Our results suggest that Pool-seq can be used as an efficient and cost-effective method for discovery of rare variants for population-based sequencing studies in individual laboratories.

      PubDate: 2018-04-15T03:44:33Z
      DOI: 10.1016/j.mrfmmm.2018.03.007
      Issue No: Vol. 809 (2018)
  • Quantification of DNA damage products by gas chromatography tandem mass
           spectrometry in lung cell lines and prevention effect of thyme
           antioxidants on oxidative induced DNA damage
    • Authors: Önder Aybastıer; Sam Dawbaa; Cevdet Demir; Oğuzhan Akgün; Engin Ulukaya; Ferda Arı
      Pages: 1 - 9
      Abstract: Publication date: March 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volume 808
      Author(s): Önder Aybastıer, Sam Dawbaa, Cevdet Demir, Oğuzhan Akgün, Engin Ulukaya, Ferda Arı
      Lung cancer has a high treatment cost and poor prognosis in comparison to other types of cancers. This work was involved in studying oxidative DNA base damage inhibition. Accordingly, standard carvacrol, thymol, thymoquinone with water and water-methanol extract of thyme (Origanum vulgare L. subsp. hirtum (link.) Ietswaart), thyme oil and thyme water were prepared and investigated for their efficacy to inhibit DNA oxidative damage formed by H2O2 in malignant lung cells (A549). The antioxidant capacity by ABTS assay was 271.73 ± 11.45 mg trolox equivalent/mL for thyme oil. HPLC analysis was carried out to determine the contents of different thyme extracts, results showing the presence of carvacrol, thymol, protocatechuic acid, caffeic acid, epicatechin and rosmarinic acid in water and water-methanol extracts while only carvacrol and thymol were found in thyme oil and thyme water. After DNA isolation from the cultured cells, the formed oxidative induced DNA damage products were analysed using GC–MS/MS. It was proven that the antioxidants in the cell culture media have succeeded to inhibit oxidative DNA base damage. Thymoquinone was shown to be the best protectant antioxidant among other antioxidants against the formation of oxidative DNA damage, whereas water-methanol extract of thyme was the best among the plant-sourced samples. Thymoquinone and thyme water-methanol extract were investigated for their efficacy on cultured healthy lung cells (BEAS-2B), and it was proven that they are efficient in protection against the oxidation of DNA of healthy lung cells too.
      Graphical abstract image

      PubDate: 2018-01-25T02:06:55Z
      DOI: 10.1016/j.mrfmmm.2018.01.004
      Issue No: Vol. 808 (2018)
  • NOTCH1 modulates activity of DNA-PKcs
    • Authors: Marek Adamowicz; Fabrizio d’Adda di Fagagna; Jelena Vermezovic
      Pages: 20 - 27
      Abstract: Publication date: March 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volume 808
      Author(s): Marek Adamowicz, Fabrizio d’Adda di Fagagna, Jelena Vermezovic
      DNA-dependent protein kinase catalytic subunit (DNA-PKcs) controls one of the most frequently used DNA repair pathways in a cell, the non-homologous end joining (NHEJ) pathway. However, the exact role of DNA-PKcs in NHEJ remains poorly defined. Here we show that NOTCH1 attenuates DNA-PKcs-mediated autophosphorylation, as well as the phosphorylation of its specific substrate XRCC4. Surprisingly, NOTCH1-expressing cells do not display any significant impairment in the DNA damage repair, nor cellular survival, and remain sensitive to small molecule DNA-PKcs inhibitor. Additionally, in vitro DNA-PKcs kinase assay shows that NOTCH1 does not inhibit DNA-PKcs kinase activity, implying that NOTCH1 acts on DNA-PKcs through a different mechanism. Together, our set of results suggests that NOTCH1 is a physiological modulator of DNA-PKcs, and that it can be a useful tool to clarify the mechanisms by which DNA-PKcs governs NHEJ DNA repair.

      PubDate: 2018-04-15T03:44:33Z
      DOI: 10.1016/j.mrfmmm.2018.01.003
      Issue No: Vol. 808 (2018)
  • A change in structural integrity of c-Kit mutant D816V causes constitutive
    • Authors: Pawan Kumar Raghav; Ajay Kumar Singh; Gurudutta Gangenahalli
      Pages: 28 - 38
      Abstract: Publication date: March 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volume 808
      Author(s): Pawan Kumar Raghav, Ajay Kumar Singh, Gurudutta Gangenahalli
      Several signaling pathways, ligands, and genes that regulate proliferative and self-renewal properties of the Hematopoietic Stem Cells (HSCs) have been studied meticulously. One of the signaling pathways that play a crucial role in the process of hematopoiesis is the Stem Cell Factor (SCF) mediated c-Kit pathway. The c-Kit is a Receptor Tyrosine Kinase (RTK), which is expressed in the cells including HSCs. It undergoes dimerization upon binding with its cognate ligand SCF. As a result, phosphorylation of the Juxtamembrane (JM) domain of c-Kit takes place at Tyr568 and Tyr570 residues. These phosphorylated residues become the docking sites for protein tyrosine phosphatases (PTPs) namely SHP-1 and SHP-2, which in turn cause dephosphorylation and negative regulation of the downstream signaling responsible for the cell proliferation. Interestingly, it has been reported that the mutation of c-Kit at D816V makes it independent of SCF stimulation and SHP-1/SHP-2 inhibition, thereby, causing its constitutive activation. The present study was commenced to elucidate the structural behavior of this mutation in the JM and A-loop region of c-Kit using Molecular Dynamics (MD) simulations of the wild-type and mutant c-Kit in unphosphorylated and phosphorylated states. The energy difference computed between the wild type and mutant (D816V) c-Kit, and protein–protein docking and complex analysis revealed the impact of this single residue mutation on the integrity dynamics of c-Kit that makes it independent of SHP-1/SHP-2 negative regulation.
      Graphical abstract image

      PubDate: 2018-02-25T23:56:41Z
      DOI: 10.1016/j.mrfmmm.2018.02.001
      Issue No: Vol. 808 (2018)
  • Effect of age at exposure on chromosome abnormalities in MIC-exposed
           Bhopal population detected 30 years post-disaster
    • Authors: Bani Bandana Ganguly; Shouvik Mandal; Nalok Banerjee; Nitin N. Kadam; Rita Abbi
      Abstract: Publication date: Available online 29 March 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Bani Bandana Ganguly, Shouvik Mandal, Nalok Banerjee, Nitin N. Kadam, Rita Abbi
      Follow-up cytogenetic study was carried out on 145 individuals from areas stratified by Indian Council of Medical Research, for evaluation of the effect of age-at-exposure and its interaction with exposure status on chromosomal aberrations (CA) in blood-lymphocytes. CA was presented as abnormal cell (Abc), aberrations (Abn) and number of aberration/abnormal cell (Abn/Abc), and correlated with age-at-exposure (childhood: <1-10 years; young: 11-26 years; adult: >27 years). Age related increase in abnormalities (Abc, Abn, Abn/Abc) was observed in all exposure strata, except moderately exposed adult-group, which has exhibited lower Abn/Abc than similarly exposed childhood and young age-groups. Elevation of CA was also related to exposure status. Abn/Abc frequency was significantly higher in the severely exposed young and adult groups compared to the controls of the same age. Two-way ANOVA revealed significant abnormalities between the exposed groups; however, interaction of age and exposure was not statistically significant. Significant difference in group-means of Abc and Abn was also observed between adult and childhood in Tukey HSD test. Altogether, a significant interaction of age and MIC-exposure on CA could not be established due to inter-individual variation and lack of baseline information on CA. Significantly higher Abn was observed in people consuming tobacco; however, interaction of lifestyle with additional environmental/occupational exposures during last 30 years against a background exposure to MIC remained un-elucidated. Nevertheless, the study was important for demonstration of the correlation of the current status of CA in circulating lymphocytes with age and exposure status of the MIC-exposed survivors.

      PubDate: 2018-04-15T03:44:33Z
      DOI: 10.1016/j.mrfmmm.2018.03.005
  • Mitochondrial mutations associated with hearing and balance disorders
    • Authors: Iman Ibrahim; Mev Dominguez-Valentin; Bernard Segal; Anthony Zeitouni; Sabrina Daniela da Silva
      Abstract: Publication date: Available online 10 March 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Iman Ibrahim, Mev Dominguez-Valentin, Bernard Segal, Anthony Zeitouni, Sabrina Daniela da Silva
      Hearing and balance disorders are related to the inner ear and are among the major cause of falls in older adults. Hearing loss that commonly occurs with aging (aka presbyacusis) can result from noise exposure, smoking, ototoxic drugs and genetic factors such as mutations in nuclear and mitochondrial genes. Mutations in mitochondrial DNA (mtDNA) have been reported to play an important role in cell function by providing energy, as well as, cell death (apoptosis). This study aims to systematically review mitochondrial mutations associated with presbyacusis and suggests preventive measurements to improve the quality of life in older adults.

      PubDate: 2018-03-19T00:58:16Z
      DOI: 10.1016/j.mrfmmm.2018.03.003
  • Is inflammation a direct response to dsDNA breaks'
    • Authors: Shahid Chaudhary; Gorantla Venkata Raghuram; Indraneel Mittra
      Abstract: Publication date: Available online 22 February 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Shahid Chaudhary, Gorantla Venkata Raghuram, Indraneel Mittra
      Recent research shows that extra-nuclear cell-free chromatin (cfCh) released from dying cells can freely enter into healthy cells and integrate into their genomes. Genomic integration of cfCh leads to dsDNA breaks and activation of inflammatory cytokines both of which occur concurrently with similar kinetics and that induction of inflammation can be abrogated by preventing DNA breaks with the use of cfCh inactivating agents. The proposal is put forward that inflammatory cytokines are a new family of DDR proteins that are activated following dsDNA breaks inflicted by genomic integration of cfCh.

      PubDate: 2018-02-25T23:56:41Z
      DOI: 10.1016/j.mrfmmm.2018.02.002
  • Drosophila Bendless catalyzes K63-linked polyubiquitination and is
           involved in the response to DNA damage
    • Authors: Zhiqiang Bai; Zhouhua Li; Wei Xiao
      Abstract: Publication date: Available online 21 February 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Zhiqiang Bai, Zhouhua Li, Wei Xiao
      In this study, we report the identification and functional characterization of the Drosophila ben/ubc13 gene, encoding a unique ubiquitin-conjugating enzyme (Ubc or E2), in DNA-damage response. Ben forms a heterodimer with DmUev1a, the only Ubc/E2 variant (Uev) in Drosophila. Ben and DmUev1a act together to catalyze K63-linked polyubiquitination in vitro. ben can functionally rescue the yeast ubc13 null mutant from killing by DNA-damaging agents. We also find that BenP97S, which was previously described to affect the connectivity between the giant fiber and the tergotrochanter motor neuron, fails to interact with the RING protein Chfr but retains interaction with DmUev1a as well as Uevs from other species. The corresponding yeast Ubc13P97S interacts with Mms2 but fails to bind Rad5. Consequently, neither benP97S nor ubc13P97S is able to complement the yeast ubc13 mutant defective in error-free DNA-damage tolerance. More importantly, the benP97S mutant flies are more sensitive to a DNA-damaging agent, suggesting that Ben functions in a manner similar to its yeast and mammalian counterparts. Collectively, our observations imply that Ben-DmUev1a-promoted K63-linked polyubiquitination and involvement in DNA-damage response are highly conserved in eukaryotes including flies.

      PubDate: 2018-02-25T23:56:41Z
      DOI: 10.1016/j.mrfmmm.2018.02.003
  • Replication stress in mitochondria
    • Authors: Miria Ricchetti
      Abstract: Publication date: Available online 1 February 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Miria Ricchetti
      Mitochondrial DNA (mtDNA), which is essential for mitochondrial and cell function, is replicated and transcribed in the organelle by proteins that are entirely coded in the nucleus. Replication of mtDNA is challenged not only by threats related to the replication machinery and orchestration of DNA synthesis, but also by factors linked to the peculiarity of this genome. Indeed the architecture, organization, copy number, and location of mtDNA, which are markedly distinct from the nuclear genome, require ad hoc and complex regulation to ensure coordinated replication. As a consequence sub-optimal mtDNA replication, which results from compromised regulation of these factors, is generally associated with mitochondrial dysfunction and disease. Mitochondrial DNA replication should be considered in the context of the organelle and the whole cell, and not just a single genome or a single replication event. Major threats to mtDNA replication are linked to its dependence on both mitochondrial and nuclear factors, which require exquisite coordination of these crucial subcellular compartments. Moreover, regulation of replication events deals with a dynamic population of multiple mtDNA molecules rather than with a fixed number of genome copies, as it is the case for nuclear DNA. Importantly, the mechanistic aspects of mtDNA replication are still debated. We describe here major challenges for human mtDNA replication, the mechanistic aspects of the process that are to a large extent original, and their consequences on disease.

      PubDate: 2018-02-05T02:51:54Z
      DOI: 10.1016/j.mrfmmm.2018.01.005
  • The roles of human MTH1, MTH2 and MTH3 proteins in maintaining genome
           stability under oxidative stress
    • Authors: Kazunari Hashiguchi; Michio Hayashi; Mutsuo Sekiguchi; Keiko Umezu
      Abstract: Publication date: Available online 31 January 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Kazunari Hashiguchi, Michio Hayashi, Mutsuo Sekiguchi, Keiko Umezu
      The hydrolysis of nucleotides containing 8-oxo-7,8-dihydroguanine (8-oxoG) is important in the maintenance of genome stability. Human cells possess three types of proteins, MTH1 (NUDT1), MTH2 (NUDT15) and MTH3 (NUDT18), which have the potential to hydrolyze deoxyribonucleoside di- and triphosphates containing 8-oxoG to the monophosphate, the form of which is unusable for DNA synthesis. To elucidate the physiological roles of these enzymes, we constructed single knockout (KO) cell lines for each of the MTH1, MTH2 and MTH3 genes and MTH1 and MTH2-double KO cell lines from the human HeLa S3 line using CRISPR/Cas9. With the exception of MTH3-KO, all of the KO cell lines showed similar proliferation rates to the parental line, HeLa S3, indicating that the MTH1 and MTH2 functions are dispensable for cell growth. On the other hand, the MTH3-KO cells showed a significantly slower growth rate, suggesting that MTH3 has a definite role in cell growth in addition to the cleavage of 8-oxoG-containing deoxyribonucleotide. MTH1-KO, MTH2-KO and MTH1- MTH2-KO cells exhibited increased sensitivity to hydrogen peroxide, whereas MTH3-KO did not. MTH1-KO cells showed only a slight increase in mutant frequency in comparison to the parental HeLa S3 line. The overproduction of MTH1 and MTH2 suppressed the mutator phenotype of mutT-deficient E. coli cells, whereas the overproduction of MTH3 did not show such a suppressive effect. Our findings suggest that both MTH1 and MTH2 are involved in the maintaining genome stability in human cells against oxidative stress, while MTH3 may play some other role(s).

      PubDate: 2018-02-05T02:51:54Z
      DOI: 10.1016/j.mrfmmm.2018.01.002
  • Special Section: Replication Stress, a threat to the nuclear and
           mitochondrial genome
    • Authors: Lisa Wiesmüller; Karin Scharffetter-Kochanek; Hartmut Geiger
      Abstract: Publication date: Available online 5 January 2018
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Lisa Wiesmüller, Karin Scharffetter-Kochanek, Hartmut Geiger

      PubDate: 2018-01-15T01:45:21Z
      DOI: 10.1016/j.mrfmmm.2018.01.001
  • Trimethoprim-sulfamethoxazole treatment increases the Pig-a mutant
           frequency in peripheral blood from severely malnourished rats
    • Authors: Monserrat Elsa; del Carmen
      Abstract: Publication date: Available online 30 December 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): M. Monserrat Pacheco-Martínez, Elsa Cervantes-Ríos, María del Carmen García-Rodríguez, Rocío Ortiz-Muñiz
      Severe malnutrition is a complex condition that increases susceptibility to infections. Thus, drugs are extensively used in malnutrition cases. In the present study, we assessed the mutagenic effects of combined trimethoprim and sulfamethoxazole (TMP-SMX) treatment in undernourished (UN) and well-nourished (WN) rats. Six-week-old UN and WN Han-Wistar rats were treated with TMP-SMX at a daily dose of 10 mg/kg/d TMP and 50 mg/kg/d SMX for 5 or 10 days. Blood was collected from the tail vein one day before (day −1) and 15, 30, and 45 days after TMP-SMX administration. The Pig-a mutant frequencies (MFs) in peripheral blood reticulocytes (RETs) and erythrocytes (RBCs) were measured through flow cytometry. Severe malnutrition increased the basal MFs in RETs (RET CD59-) and RBC (RBCs CD59-). These findings support the hypothesis that severe malnutrition is mutagenic even in the absence of exposure to an exogenous mutagen. UN and WN rats treated for 5 or 10 consecutive days with TMP-SMX had significantly increased and sustained Pig-a mutant frequencies, demonstrating the mutagenic effects of this drug.

      PubDate: 2018-01-03T20:29:14Z
  • Strategies for identification of mutations induced by carbon-ion beam
           irradiation in Arabidopsis thaliana by whole genome re-sequencing
    • Authors: Yan Shanwei; Luo Lixia Tao Cui Xia Chen Jiangyan Yang
      Abstract: Publication date: Available online 9 December 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Yan Du, Shanwei Luo, Lixia Yu, Tao Cui, Xia Chen, Jiangyan Yang, Xin Li, Wenjian Li, Jufang Wang, Libin Zhou
      Heavy-ion beam irradiation is a powerful physical mutagen that has been used to create numerous mutant materials in plants. These materials are an essential resource for functional genomics research in the post-genome era. The advent of next-generation sequencing (NGS) technology has promoted the study of functional genomics and molecular breeding. A wealth of information can be gathered from whole genome re-sequencing; however, understanding the molecular mutation profile at genome wide, as well as identifying causal genes for a given phenotype are big challenging issues for researchers. The huge outputs created by NGS make it difficult to capture key information. It is worthy to explore an effective and efficient data-sieving strategy for mutation scanning at whole genome scale. Re-sequencing data from one laboratory wild type (Columbia) and eleven M3 Arabidopsis thaliana lines derived from carbon-ion beam irradiation were used in present study. Both the number and different combinations of samples used for analysis affected the sieving results. The result indicated that using six samples was sufficient to filter out the shared mutation (background interference) sites as well as to identify the true mutation sites in the whole genome. The final number of candidate mutation sites could be further narrowed down by combining traditional rough map-based cloning. Our results demonstrated the feasibility of a parallel sequencing analysis as an efficient tool for the identification of mutations induced by carbon-ion beam irradiation. For the first time, we presented different analysis strategies for handling massive parallel sequencing data sets to detect the mutations induced by carbon-ion beam irradiation in Arabidopsis thaliana with low false-positive rate, as well as to identify the causative nucleotide changes responsible for a mutant phenotype.

      PubDate: 2017-12-12T02:22:03Z
    • Abstract: Publication date: December 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volume 806

      PubDate: 2017-12-08T02:08:12Z
  • Association of H3K79 monomethylation (an epigenetic signature) with
           arsenic-induced skin lesions
    • Authors: Pritha Bhattacharjee; Somnath Paul; Sandip Bhattacharjee; Ashok K. Giri; Pritha Bhattacharjee
      Abstract: Publication date: Available online 14 November 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Pritha Bhattacharjee, Somnath Paul, Sandip Bhattacharjee, Ashok K. Giri, Pritha Bhattacharjee
      Arsenic, a non mutagenic carcinogen, poses a profound health risk upon prolonged exposure. The objective of the study was to analyze the post-translational modifications of the major histone H3 and the associated molecular crosstalk to identify the epigenetic signature of arsenic susceptibility. Herein, we identified significant upregulation of H3K79me1, in individuals with arsenic-induced skin lesion (WSL), and H3K79me1 was found to be regulated by the upstream methyltransferase DOT1L. Moreover, the downstream target molecule 53BP1, a tumor suppressor protein that has a docking preference for H3K79me1 at a site of a double-strand break (DSB), was downregulated, indicating greater DNA damage in the WSL group. Western blot data confirmed higher levels of γH2AX, a known marker of DSBs, in group WSL. In vitro dose–response analysis also confirmed the association of the H3K79me1 signature with arsenic toxicity. Taken together, our findings revealed that H3K79me1 and DOT1L could be a novel epigenetic signature of the arsenic-exposed WSL group.

      PubDate: 2017-11-16T12:14:26Z
      DOI: 10.1016/j.mrfmmm.2017.11.001
  • Molecular criteria for mutagenesis by DNA methylation: some computational
    • Authors: Tejeshwori Salam; S. Premila Devi; R.H. Duncan Lyngdoh
      Abstract: Publication date: Available online 10 November 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Tejeshwori Salam, S. Premila Devi, R.H. Duncan Lyngdoh
      Alkylating agents and N-nitroso compounds are well-known mutagens and carcinogens which act by alkylating DNA at the nucleobase moieties. Criteria for mutagenicity through DNA alkylation include (a) absence of the Watson-Crick (N1-guanine and N3-thymine) protons, (b) rotation of the alkyl group away from the H-bonding zone, (c) configuration of the alkylated base pair close to the Watson-Crick type. This computational study brings together these three molecular criteria for the first time. Three methylated DNA bases − N7-methylguanine, O6-methylguanine and O4-methylthymine − are studied using computational chemical methods. Watson-Crick proton loss is predicted more feasible for the mutagenic O6-methylguanine and O4-methylthymine than for the non-mutagenic N7-methylguanine in agreement with the observed trend for pKa values. Attainment of a conformer conducive to mutagenesis is more feasible for O6-methylguanine than for O4-methylthymine, though the latter is more mutagenic. These methylated bases yield 9 H-bonded pairs with normal DNA bases. At biological pH, O6-methylguanine and O4-methylthymine would yield stable mutagenic pairs having Watson-Crick type configuration by H-bonded pairing with thymine and guanine respectively, while N7-methylguanine would yield a non-mutagenic pair with cytosine. The three criteria thus well differentiate the non-mutagenic N7-methylguanine from the mutagenic O6-methylguanine and O4-methylthymine in good accord with experimental observations.

      PubDate: 2017-11-16T12:14:26Z
      DOI: 10.1016/j.mrfmmm.2017.10.004
  • Biological effects of carbon ion beams with various LETs on budding yeast
           Saccharomyces cerevisiae
    • Authors: Youichirou Matuo; Yoshinobu Izumi; Yoshiya Furusawa; Kikuo Shimizu
      Abstract: Publication date: Available online 7 November 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Youichirou Matuo, Yoshinobu Izumi, Yoshiya Furusawa, Kikuo Shimizu
      It has been established that irradiation with higher linear energy transfer (LET) increases lethality and mutagenicity more than that with lower LET. However, the characteristics specific to carbon ion beam have not yet been elucidated. Yeast cells were irradiated with carbon ions with an LET of 13 or 50 keV/μm, and cell survival and mutation frequency were analyzed. The results, combined with our previous findings for ions with an LET of 107 keV/μm, demonstrated that, in conjunction with an increase in LET, cell survival decreased, while mutation frequency increased. This indicates that a carbon ion beam with a higher LET is more mutagenic than one with a lower LET.

      PubDate: 2017-11-09T11:45:04Z
      DOI: 10.1016/j.mrfmmm.2017.10.003
  • DNA replication stress drives fragile site instability
    • Authors: Michal Irony-Tur Sinai; Batsheva Kerem
      Abstract: Publication date: Available online 18 October 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Michal Irony-Tur Sinai, Batsheva Kerem
      DNA replication stress is one of the early drivers enabling the ongoing acquisition of genetic changes arising during tumorigenesis. As such, it is a feature of most pre-malignant and malignant cells. In this review article, we focus on the early events initiating DNA replication stress and the preferential sensitivity of common fragile sites (CFSs) to this stress. CFSs are specific genomic regions within the normal chromosomal structure, which appear as gaps and breaks in the metaphase chromosomes of cells grown under mild replication stress conditions. The main characteristics predisposing CFSs to instability include late replication timing, delayed replication completion, failure to activate additional origins, origin paucity along large genomic regions, collision between replication and transcription complexes along large genes, and the presence of AT-dinucleotide rich sequences. The contribution of these features to instability at CFSs during early cancer development is discussed.

      PubDate: 2017-10-26T10:54:07Z
      DOI: 10.1016/j.mrfmmm.2017.10.002
  • Replication stress in hematopoietic stem cells in mouse and man
    • Authors: Johanna Flach; Michael Milyavsky
      Abstract: Publication date: Available online 18 October 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Johanna Flach, Michael Milyavsky
      Life-long blood regeneration relies on a rare population of self-renewing hematopoietic stem cells (HSCs). These cells’ nearly unlimited self-renewal potential and lifetime persistence in the body signifies the need for tight control of their genome integrity. Their quiescent state, tightly linked with low metabolic activity, is one of the main strategies employed by HSCs to preserve an intact genome. On the other hand, HSCs need to be able to quickly respond to increased blood demands and rapidly increase their cellular output in order to fight infection-associated inflammation or extensive blood loss. This increase in proliferation rate, however, comes at the price of exposing HSCs to DNA damage inevitably associated with the process of DNA replication. Any interference with normal replication fork progression leads to a specialized molecular response termed replication stress (RS). Importantly, increased levels of RS are a hallmark feature of aged HSCs, where an accumulating body of evidence points to causative relationships between RS and the aging-associated impairment of the blood system’s functional capacity. In this review, we present an overview of RS in HSCs focusing on its causes and consequences for the blood system of mice and men.

      PubDate: 2017-10-26T10:54:07Z
      DOI: 10.1016/j.mrfmmm.2017.10.001
    • Abstract: Publication date: October 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis, Volumes 803–805

      PubDate: 2017-10-03T06:57:29Z
  • Efficient repair of DNA double strand breaks in individuals from high
           level natural radiation areas of Kerala coast, south-west India
    • Authors: Vinay Jain; Divyalakshmi Saini; P.R. Vivek Kumar; G. Jaikrishan; Birajalaxmi Das
      Abstract: Publication date: Available online 20 September 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Vinay Jain, Divyalakshmi Saini, P.R. Vivek Kumar, G. Jaikrishan, Birajalaxmi Das
      High level natural radiation areas (HLNRA) of Kerala coastal strip (55km long and 0.5km wide) in southwest India exhibit wide variations in the level of background dose (< 1.0 to 45.0mGy/year) due to thorium deposits in the beach sand. The areas with ≤1.5mGy/year are considered as normal level natural radiation area (NLNRA), whereas areas with >1.5mGy/year are HLNRA. Individuals belonging to HLNRA were stratified into two groups, Low dose group (LDG: 1.51–5.0mGy/year) and high dose group (HDG: >5.0mGy/year). The mean annual dose received by the individuals from NLNRA, LDG and HDG was 1.3±0.1, 2.7±0.9 and 9.4±2.3mGy/year, respectively. Induction and repair of DNA double strand breaks (DSBs) in terms of gamma-H2AX positive cells were analysed in peripheral blood mononuclear cells (PBMCs) using flow cytometry. Induction of DSBs was studied at low (0.25Gy) and high challenge doses (1.0 and 2.0Gy) of gamma radiation in 78 individuals {NLNRA, N=23; HLNRA (LDG, N=21 and HDG, N=34)}. Repair kinetics of DSBs were evaluated in PBMCs of 30 individuals belonging to NLNRA (N=8), LDG (N=7) and HDG (N=15) at low (0.25Gy) and high doses (2.0Gy) of gamma radiation. Transcriptional profile of DNA damage response (DDR) and DSB repair genes involved in non-homologous end joining (NHEJ) and homologous recombination repair (HRR) pathways was analysed after a challenge dose of 2.0Gy in PBMCs of NLNRA (N=10) and HDG, HLNRA (N=10) group. Our results revealed significantly lower induction and efficient repair of DSBs in HLNRA groups as compared to NLNRA. Transcription profile of DCLRE1C, XRCC4, NBS1 and CDK2 showed significant up-regulation (p≤0.05) in HDG at a challenge dose of 2.0Gy indicating active involvement of DDR and DSB repair pathways. In conclusion, lower induction and efficient repair of DNA DSBs in HLNRA groups is suggestive of an in vivo radio-adaptive response due to priming effect of chronic low dose radiation prevailing in this area.

      PubDate: 2017-09-20T17:13:09Z
      DOI: 10.1016/j.mrfmmm.2017.09.003
  • p.Val19Glyfs*21 and p.Leu228* variants in the survival of motor neuron 1
           trigger nonsense-mediated mRNA decay causing the SMN1 PTC+ transcripts
    • Authors: Yu-jin Qu; Lin Ge; Jin-li Bai; Yan-yan Cao; Yu-wei Jin; Hong Wang; Lan Yang; Fang Song
      Abstract: Publication date: Available online 15 September 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Yu-jin Qu, Lin Ge, Jin-li Bai, Yan-yan Cao, Yu-wei Jin, Hong Wang, Lan Yang, Fang Song
      Spinal Muscular Atrophy (SMA) results from loss-of-function mutations in the survival of motor neuron 1 (SMN1) gene. Our previous research showed that 40% of variants were nonsense or frameshift variants and SMN1 mRNA levels in the patients carrying these variants were significantly decreased. Here we selected one rare variant (p.Val19Glyfs*21) and one common variant (p.Leu228*) to explore the degradation mechanism of mutant transcripts. The levels of full-length (FL)-SMN1 transcripts and SMN protein in the cell lines from the patients with these variants were both significantly reduced (p<0.01). Treatment with two translation inhibitors (puromycin and Cycloheximide (CHX)) markedly increased the levels of FL-SMN1 transcripts with premature translation termination codons (PTCs) (p<0.01) and showed time-dependent (10h>5.5h) but not dose-dependent effects. Moreover, the knockdown of UPF1, a key factor in nonsense-mediated mRNA decay (NMD) by lentivirus, led to a 3.08-fold increase (p<0.01) in FL-SMN1 transcript levels in patient fibroblasts. Our research provides evidence that these two PTC-generating variants (p.Val19Glyfs*21 and p.Leu228*) can trigger NMD, causing rapid degradation of SMN1 transcripts thereby resulting in SMN protein deficiency. These two variants are highly pathogenic and are associated with more severe SMA phenotypes. Varying NMD efficiency after treatment with puromycin and CHX in different cell types was also observed.

      PubDate: 2017-09-20T17:13:09Z
      DOI: 10.1016/j.mrfmmm.2017.09.005
  • Beyond interstrand crosslinks repair: contribution of FANCD2 and other
           Fanconi Anemia proteins to the replication of DNA
    • Authors: Maria B. Federico; Paola Campodónico; Natalia S. Paviolo; Vanesa Gottifredi
      Abstract: Publication date: Available online 14 September 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Maria B. Federico, Paola Campodónico, Natalia S. Paviolo, Vanesa Gottifredi
      Biallelic mutations of FANCD2 and other components of the Fanconi Anemia (FA) pathway cause a disease characterized by bone marrow failure, cancer predisposition and a striking sensitivity to agents that induce crosslinks between the two complementary DNA strands (inter-strand crosslinks-ICL). Such genotoxins were used to characterize the contribution of the FA pathway to the genomic stability of cells, thus unravelling the biological relevance of ICL repair in the context of the disease. Notwithstanding this, whether the defect in ICL repair as the sole trigger for the multiple physiological alterations observed in FA patients is still under investigation. Remarkably, ICL-independent functions of FANCD2 and other components of the FA pathway were recently reported. FANCD2 contributes to the processing of very challenging double strand ends (DSEs: one ended DSBs created during DNA replication). Other ICL-independent functions of FANCD2 include prevention of DNA breakage at stalled replication forks and facilitation of chromosome segregation at the end of M phase. The current understanding of replication-associated functions of FANCD2 and its relevance for the survival of genomically stable cells is herein discussed.

      PubDate: 2017-09-20T17:13:09Z
      DOI: 10.1016/j.mrfmmm.2017.09.004
  • Integration of the TGx-28.65 genomic biomarker with the flow cytometry
           micronucleus test to assess the genotoxicity of disperse orange and
           1,2,4-benzenetriol in human TK6 cells
    • Authors: Julie K. Buick; Andrew Williams; Byron Kuo; John W. Wills; Carol D. Swartz; Leslie Recio; Heng-Hong Li; Albert J. Fornace; Jiri Aubrecht; Carole L. Yauk
      Abstract: Publication date: Available online 13 September 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Julie K. Buick, Andrew Williams, Byron Kuo, John W. Wills, Carol D. Swartz, Leslie Recio, Heng-Hong Li, Albert J. Fornace, Jiri Aubrecht, Carole L. Yauk
      In vitro gene expression signatures to predict toxicological responses can provide mechanistic context for regulatory testing. We previously developed the TGx-28.65 genomic biomarker from a database of gene expression profiles derived from human TK6 cells exposed to 28 well-known compounds. The biomarker comprises 65 genes that can classify chemicals as DNA damaging or non-DNA damaging. In this study, we applied the TGx-28.65 genomic biomarker in parallel with the in vitro micronucleus (MN) assay to determine if two chemicals of regulatory interest at Health Canada, disperse orange (DO: the orange azo dye 3-[[4-[(4-Nitrophenyl)azo]phenyl] benzylamino]propanenitrile) and 1,2,4-benzenetriol (BT: a metabolite of benzene) are genotoxic or non-genotoxic. Both chemicals caused dose-dependent declines in relative survival and increases in apoptosis. A strong significant increase in MN induction was observed for all concentrations of BT; the top two concentrations of DO also caused a statistically significant increase in MN, but these increases were <2-fold above controls. TGx-28.65 analysis classified BT as genotoxic at all three concentrations and DO as genotoxic at the mid and high concentrations. Thus, although DO only induced a small increase in MN, this response was sufficient to induce a cellular DNA damage response. However, benchmark dose modeling confirmed that BT is much more potent than DO. The results strongly suggest that follow-up work is required to assess whether DO and BT are also genotoxic in vivo. This is particularly important for DO, which may require metabolic activation by bacterial gut flora to fully induce its genotoxic potential. Our previously published data and this proof of concept study suggest that the TGx-28.65 genomic biomarker has the potential to add significant value to existing approaches used to assess genotoxicity.

      PubDate: 2017-09-14T13:02:49Z
      DOI: 10.1016/j.mrfmmm.2017.09.002
  • Effect of Modeled Microgravity on UV-C-induced Interplant Communication of
           Arabidopsis thaliana
    • Authors: Ting Wang; Wei Xu; Huasheng Li; Chenguang Deng; Hui Zhao; Yuejin Wu; Min Liu; Lijun Wu; Jinying Lu; Po Bian
      Abstract: Publication date: Available online 6 September 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Ting Wang, Wei Xu, Huasheng Li, Chenguang Deng, Hui Zhao, Yuejin Wu, Min Liu, Lijun Wu, Jinying Lu, Po Bian
      Controlled ecological life support systems (CELSS) will be an important feature of long-duration space missions of which higher plants are one of the indispensable components. Because of its pivotal role in enabling plants to cope with environmental stress, interplant communication might have important implications for the ecological stability of such CELSS. However, the manifestations of interplant communication in microgravity conditions have yet to be fully elucidated. To address this, a well-established Arabidopsis thaliana co-culture experimental system, in which UV-C-induced airborne interplant communication is evaluated by the alleviation of transcriptional gene silencing (TGS) in bystander plants, was placed in microgravity modeled by a two-dimensional rotating clinostat. Compared with plants under normal gravity, TGS alleviation in bystander plants was inhibited in microgravity. Moreover, TGS alleviation was also prevented when plants of the pgm-1 line, which are impaired in gravity sensing, were used in either the UV-C-irradiated or bystander group. In addition to the specific TGS-loci, interplant communication-shaped genome-wide DNA methylation in bystander plants was altered under microgravity conditions. These results indicate that interplant communications might be modified in microgravity. Time course analysis showed that microgravity interfered with both the production of communicative signals in UV-C-irradiated plants and the induction of epigenetic responses in bystander plants. This was further confirmed by the experimental finding that microgravity also prevented the response of bystander plants to exogenous methyl jasmonate (JA) and methyl salicylate (SA), two well-known airborne signaling molecules, and down-regulated JA and SA biosynthesis in UV-C-irradiated plants.

      PubDate: 2017-09-08T18:22:55Z
      DOI: 10.1016/j.mrfmmm.2017.09.001
  • Investigating mutation-specific biological activities of small molecules
           using quantitative structure-activity relationship for epidermal growth
           factor receptor in cancer
    • Authors: P. Anoosha; R. Sakthivel; M. Michael Gromiha
      Abstract: Publication date: Available online 26 August 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): P. Anoosha, R. Sakthivel, M. Michael Gromiha
      Epidermal Growth Factor Receptor (EGFR) is a potential drug target in cancer therapy. Missense mutations play major roles in influencing the protein function, leading to abnormal cell proliferation and tumorigenesis. A number of EGFR inhibitor molecules targeting ATP binding domain were developed from the past two decades. Unfortunately, they become inactive due to resistance caused by new mutations in patients, and previous studies have also reported noticeable differences in inhibitor binding to distinct known driver mutants as well. Hence, there is a high demand for identification of EGFR mutation-specific inhibitors. In our present study, we derived a set of anti-cancer compounds with biological activities against eight typical EGFR known driver mutations and developed quantitative structure-activity relationship (QSAR) models for each separately. The compounds are grouped based on their functional scaffolds, which enhanced the correlation between compound features and respective biological activities. The models for different mutants performed well with a correlation coefficient, (r) in the range of 0.72–0.91 on jack-knife test. Further, we analyzed the selected features in different models and observed that hydrogen bond and aromaticity-related features play important roles in predicting the biological activity of a compound. This analysis is complimented with docking studies, which showed the binding patterns and interactions of ligands with EGFR mutants that could influence their activities.
      Graphical abstract image

      PubDate: 2017-09-03T18:10:12Z
      DOI: 10.1016/j.mrfmmm.2017.08.003
  • Role of specialized DNA polymerases in the limitation of replicative
           stress and DNA damage transmission
    • Authors: Elodie Bournique; Marina Dall’Osto; Jean-Sébastien Hoffmann; Valérie Bergoglio
      Abstract: Publication date: Available online 14 August 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Elodie Bournique, Marina Dall’Osto, Jean-Sébastien Hoffmann, Valérie Bergoglio
      Replication stress is a strong and early driving force for genomic instability and tumor development. Beside replicative DNA polymerases, an emerging group of specialized DNA polymerases is involved in the technical assistance of the replication machinery in order to prevent replicative stress and its deleterious consequences. During S-phase, altered progression of the replication fork by endogenous or exogenous impediments induces replicative stress, causing cells to reach mitosis with genomic regions not fully duplicated. Recently, specific mechanisms to resolve replication intermediates during mitosis with the aim of limiting DNA damage transmission to daughter cells have been identified. In this review, we detail the two major actions of specialized DNA polymerases that limit DNA damage transmission: the prevention of replicative stress by non-B DNA replication and the recovery of stalled replication forks.

      PubDate: 2017-08-24T17:24:33Z
      DOI: 10.1016/j.mrfmmm.2017.08.002
  • Automatic detection of micronuclei by cell microscopic image processing
    • Authors: Mohammad Taghi Bahreyni Toossi; Hosein Azimian; Omid Sarrafzadeh; Shokoufeh Mohebbi; Shokouhozaman Soleymanifard
      Abstract: Publication date: Available online 12 August 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Mohammad Taghi Bahreyni Toossi, Hosein Azimian, Omid Sarrafzadeh, Shokoufeh Mohebbi, Shokouhozaman Soleymanifard
      With the development and applications of ionizing radiation in medicine, the radiation effects on human health get more and more attention. Ionizing radiation can lead to various forms of cytogenetic damage, including increased frequencies of micronuclei (MNi) and chromosome abnormalities. The cytokinesis block micronucleus (CBMN) assay is widely used method for measuring MNi to determine chromosome mutations or genome instability in cultured human lymphocytes. The visual scoring of MNi is time-consuming and scorer fatigue can lead to inconsistency. In this work, we designed software for the scoring of in vitro CBMN assay for biomonitoring on Giemsa-stained slides that overcome many previous limitations. Automatic scoring proceeds in four stages as follows. First, overall segmentation of nuclei is done. Then, binucleated (BN) cells are detected. Next, the entire cell is estimated for each BN as it is assumed that there is no detectable cytoplasm. Finally, MNi are detected within each BN cell. The designed Software is even able to detect BN cells with vague cytoplasm and MNi in peripheral blood smear. Our system is tested on a self-provided dataset and is achieved high sensitivities of about 98% and 82% in recognizing BN cells and MNi, respectively. Moreover, in our study less than 1% false positives were observed that makes our system reliable for practical MNi scoring.

      PubDate: 2017-08-14T16:48:48Z
      DOI: 10.1016/j.mrfmmm.2017.07.012
  • Regulation of repair pathway choice at two-ended DNA double-strand breaks
    • Authors: Atsushi Shibata
      Abstract: Publication date: Available online 29 July 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Atsushi Shibata
      A DNA double-strand break (DSB) is considered to be a critical DNA lesion because its misrepair can cause severe mutations, such as deletions or chromosomal translocations. For the precise repair of DSBs, the repair pathway that is optimal for the particular circumstance needs to be selected. Non-homologous end joining (NHEJ) functions in G1/S/G2 phase, while homologous recombination (HR) becomes active only in S/G2 phase after DNA replication. DSB end structure is another factor affecting the repair pathway. For example, one-ended DSBs in S phase are mainly repaired by HR due to the lack of a partner DSB end for NHEJ. In contrast, two-ended DSBs, which are mainly induced by ionizing radiation, are repaired by either NHEJ or HR in G2 cells. Under the current model in terms of DSB repair pathway usage in G2 phase, NHEJ repairs ∼70% of two-ended DSBs, whereas HR repairs only ∼30%. Recent studies propose that NHEJ factors can bind all the DSB ends and are then either used to progress that pathway of DSB repair, or the repair proceeds by HR. In addition, molecular regulation by BRCA1 and 53BP1 has also been proposed. At DSB sites, BRCA1 functions to alleviate the 53BP1 barrier to resection by promoting 53BP1 dephosphorylation, followed by RIF1 release and 53BP1 repositioning. This timely 53BP1 repositioning may be important for the establishment of a chromatin environment that promotes the recruitment of EXO1 for resection in HR. This review summarizes current knowledge on factors regulating DSB repair pathway choice in terms of spatiotemporal regulation by focusing on the repair events at two-ended DSBs in G2 cells.

      PubDate: 2017-08-04T16:17:40Z
      DOI: 10.1016/j.mrfmmm.2017.07.011
  • Paths from DNA damage and signaling to genome rearrangements via
           homologous recombination
    • Authors: Jac A. Nickoloff
      Abstract: Publication date: Available online 24 July 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Jac A. Nickoloff
      DNA damage is a constant threat to genome integrity. DNA repair and damage signaling networks play a central role maintaining genome stability, suppress tumorigenesis, and determine tumor response to common cancer chemotherapeutic agents and radiotherapy. DNA double-strand breaks (DSBs) are critical lesions induced by ionizing radiation and when replication forks encounter damage. DSBs can result in mutations and large-scale genome rearrangements reflecting mis-repair by non-homologous end joining or homologous recombination. Ionizing radiation induces genetic change immediately, and it also triggers delayed events weeks or even years after exposure, long after the initial damage has been repaired or diluted through cell division. This review covers DNA damage signaling and repair pathways and cell fate following genotoxic insult, including immediate and delayed genome instability and cell survival/cell death pathways.

      PubDate: 2017-07-25T15:27:57Z
      DOI: 10.1016/j.mrfmmm.2017.07.008
  • The Emerging Roles of the Ubiquitination/deubiquitination System in Tumor
           Radioresistance regarding DNA damage responses, cell cycle regulation,
           hypoxic responses, and antioxidant properties: Insight into the
           Development of Novel Radiosensitizing Strategies
    • Authors: Yoko Goto; Sho Kpyasu; Minoru Kobayashi; Hiroshi Harada
      Abstract: Publication date: Available online 22 July 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Yoko Goto, Sho Kpyasu, Minoru Kobayashi, Hiroshi Harada
      Radiation therapy is one of the first-line treatments for many cancers, with no less than half of cancer patients receiving it in the US. Despite the development of innovative and high-precision radiation therapy strategies, many patients still experience local tumor recurrence after the treatment, at least in part, due to the existence of radioresistant cells in malignant tumor tissues. Among the various biological processes known to induce radioresistance, a post-translational protein modification, ubiquitination, has received marked attention in recent years. Ubiquitination, in which highly conserved ubiquitin polypeptides are covalently attached to their target proteins, has long been recognized as a system to tag unnecessary proteins for 26S proteasome-dependent proteolysis. However, accumulating lines of evidence recently revealed that it acts as a signal molecule in diverse biological processes as well, and its functional disorder was found to cause not only tumor development and various diseases but also tumor radioresistance. The present review summarizes the latest knowledge about how the cancer-related disorder of the ubiquitination systems induces the radioresistance of cancer cells by influencing intrinsic pathways, each of which potentially affects the radioresistance/radiosensitivity of cells, such as DNA damage responses, cell cycle regulation, hypoxic responses, and antioxidant properties. In addition, this review aims to provide insights into how we can exploit the disorders in order to develop novel radiosensitizing strategies.

      PubDate: 2017-07-25T15:27:57Z
      DOI: 10.1016/j.mrfmmm.2017.07.007
  • DNA Damage Levels in Electronics Workers in Southern China: A Micro-Whole
           Blood Comet Assay
    • Authors: Zhiqiang Zhao; Xiumei Xing; Xiaoyan Ou; Xinxia Liu; Ridong Zhou; Huimin Zhang; Linqing Yang; Zhixiong Zhuang; Xiaolin Su; Yao Lu; Jun Jiang; Yarui Yang; Dong Cui; Yun He
      Abstract: Publication date: Available online 22 July 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Zhiqiang Zhao, Xiumei Xing, Xiaoyan Ou, Xinxia Liu, Ridong Zhou, Huimin Zhang, Linqing Yang, Zhixiong Zhuang, Xiaolin Su, Yao Lu, Jun Jiang, Yarui Yang, Dong Cui, Yun He
      We evaluated DNA damage levels of different categories of workers exposed to hazards inside electronics factories in Southern China. To find out the most dangerous risk factor, a cross-sectional study was conducted on a total of 584 exposed subjects and 138 controls in an electronics factory in Southern China, where the electronics industry is prevalent. The exposed hazards included isopropanol (IPO), lead, noise, video display terminals (VDT), lead in a high-temperature (high-temp) environment, and IPO in a high-temp environment. DNA damage detection was performed by the micro-whole blood comet assay using peripheral blood. DNA damage levels were estimated by percent tail DNA (%T). Linear regression models were used to test DNA damage differences between exposed groups and control group with adjustments for potential confounding factors. The level of DNA damage was more significant in both lead in a high-temp and IPO in a high-temp environment groups than in that of the controls (p< 0.05). The differences remained significant after stratifying by smoking status (p< 0.05). There were no significant differences between groups exposed to IPO, lead, noise, VDT environment and controls. In conclusion, we identified potential risk factors for DNA damage to electronics workers. Special attention should be paid to workers exposed to IPO and lead in a high-temp environment.

      PubDate: 2017-07-25T15:27:57Z
      DOI: 10.1016/j.mrfmmm.2017.07.005
  • Balancing act: To be or not to be ubiquitylated
    • Authors: Ryotaro Nishi
      Abstract: Publication date: Available online 21 July 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Ryotaro Nishi
      DNA double-strand breaks (DSBs) are one of the most deleterious DNA lesions. Appropriate repair of DSB either by homologous recombination or non-homologous end-joining is critical for maintaining genome stability and fitness. DSB repair cooperates with cellular signalling networks, namely DSB response (DDR), which plays pivotal roles in the choice of DSB repair pathway, orchestrating recruitment of DDR factors to site of damage, transcription suppression and cell cycle checkpoint activation. It has been revealed that these mechanisms are strictly regulated, in time and space, by complex and minute ubiquitylation-mediated reactions. Furthermore, balancing the ubiquitylation status of the DDR and DSB repair proteins by deubiquitylation, which is carried out by deubiquitylating enzymes (DUBs), is also found to be important. Recent findings have uncovered that DUBs are involved in various aspects of both DDR and DSB repair by counteracting non-proteolytic ubiquitylations in addition to protecting substrates from proteasomal degradation by removing proteolytic ubiquitylation. An advanced understanding of the detailed molecular mechanisms of the “balancing act” between ubiquitylation and deubiquitylation will provide novel therapeutic targets for diseases caused by dysfunction of DDR and DSB repair.

      PubDate: 2017-07-25T15:27:57Z
      DOI: 10.1016/j.mrfmmm.2017.07.006
  • Mutational signatures efficiently identify different mutational processes
           underlying cancers with similar somatic mutation spectra
    • Authors: Nan Zhou; Yuan Yuan; Xin Long; Chuanfang Wu; Jinku Bao
      Abstract: Publication date: Available online 19 July 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Nan Zhou, Yuan Yuan, Xin Long, Chuanfang Wu, Jinku Bao
      Compared to analyzing mutations with conventional spectra, deciphering mutational signatures provides much greater resolution of biological processes that generate somatic mutations during cancer development. Previous studies of bladder urothelial cancer (BLCA) and cervical squamous cell carcinoma (CESC) mutational signatures failed to uncover different mutational processes underlying the two cancers, which diminishes the capability of mutational signature to differentiate between the two cancers. In this study, we deciphered and compared the mutational signatures of BLCA and CESC. Four BLCA mutational signatures were deciphered from 37,098 somatic mutations of 130 exomes. Five CESC mutational signatures were deciphered from 44,206 somatic mutations of 194 exomes. Three BLCA mutational signatures were very similar to the three CESC signatures. These mutational signatures exhibited common endogenous mutational processes during BLCA and CESC development. The respective BLCA and CESC mutational signature 4 revealed the role of viral infection in both cancers. Noticeably, CESC mutational signature 4 is a novel one that has not been described in other studies. In summary, we have demonstrated the similarities and differences between BLCA and CESC by deciphering mutational signatures. This study will shed light on the use of mutational signatures to clarify the mechanisms of endogenous and exogenous carcinogens that cause somatic mutations in human cancers.

      PubDate: 2017-07-25T15:27:57Z
      DOI: 10.1016/j.mrfmmm.2017.07.004
  • Ubiquitin-like modifications in the DNA damage response
    • Authors: Zhifeng Wang; Wei-Guo Zhu; Xingzhi Xu
      Abstract: Publication date: Available online 11 July 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Zhifeng Wang, Wei-Guo Zhu, Xingzhi Xu
      Genomic DNA is damaged at an extremely high frequency by both endogenous and environmental factors. An improper response to DNA damage can lead to genome instability, accelerate the aging process and ultimately cause various human diseases, including cancers and neurodegenerative disorders. The mechanisms that underlie the cellular DNA damage response (DDR) are complex and are regulated at many levels, including at the level of post-translational modification (PTM). Since the discovery of ubiquitin in 1975 and ubiquitylation as a form of PTM in the early 1980s, a number of ubiquitin-like modifiers (UBLs) have been identified, including small ubiquitin-like modifiers (SUMOs), neural precursor cell expressed, developmentally down-regulated 8 (NEDD8), interferon-stimulated gene 15 (ISG15), human leukocyte antigen (HLA)-F adjacent transcript 10 (FAT10), ubiquitin-fold modifier 1 (UFRM1), URM1 ubiquitin-related modifier-1 (URM1), autophagy-related protein 12 (ATG12), autophagy-related protein 8 (ATG8), fan ubiquitin-like protein 1 (FUB1) and histone mono-ubiquitylation 1 (HUB1). All of these modifiers have known roles in the cellular response to various forms of stress, and delineating their underlying molecular mechanisms and functions is fundamental in enhancing our understanding of human disease and longevity. To date, however, the molecular mechanisms and functions of these UBLs in the DDR remain largely unknown. This review summarizes the current status of PTMs by UBLs in the DDR and their implication in cancer diagnosis, therapy and drug discovery.

      PubDate: 2017-07-19T15:09:59Z
      DOI: 10.1016/j.mrfmmm.2017.07.001
  • Mutagenic potential of hypoxanthine in live human cells
    • Authors: Stephen DeVito; Jordan Woodrick; Linze Song; Rabindra Roy
      Abstract: Publication date: Available online 28 June 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Stephen DeVito, Jordan Woodrick, Linze Song, Rabindra Roy
      Hypoxanthine (Hx) is a major DNA lesion generated by deamination of adenine during chronic inflammatory conditions, which is an underlying cause of various diseases including cancer of colon, liver, pancreas, bladder and stomach. There is evidence that deamination of DNA bases induces mutations, but no study has directly linked Hx accumulation to mutagenesis and strand-specific mutations yet in human cells. Using a site-specific mutagenesis approach, we report the first direct evidence of mutation potential and pattern of Hx in live human cells. We investigated Hx-induced mutations in human nonmalignant HEK293 and cancer HCT116 cell lines and found that Hx is mutagenic in both HEK293 and HCT116 cell lines. There is a strand bias for Hx-mediated mutations in both the cell lines; the Hx in lagging strand is more mutagenic than in leading strand. There is also some difference in cell types regarding the strand bias for mutation types; HEK293 cells showed largely deletion (>80%) mutations in both leading and lagging strand and the rest were insertions and A:T→G:C transition mutations in leading and lagging strands, respectively, whereas in HCT116 cells we observed 60% A:T→G:C transition mutations in the leading strand and 100% deletions in the lagging strand. Overall, Hx is a highly mutagenic lesion capable of generating A:T→G:C transitions and large deletions with a significant variation in leading and lagging strands in human cells. In recent meta-analysis study A→G (T→C) mutations were found to be a prominent signature in a variety of cancers, including a majority types that are induced by inflammation. The deletions are known to be a major cause of copy-number variations or CNVs, which is a major underlying cause of many human diseases including mental illness, developmental disorders and cancer. Thus, Hx, a major DNA lesion induced by different deamination mechanisms, has potential to initiate inflammation-driven carcinogenesis in addition to various human pathophysiological consequences.

      PubDate: 2017-07-01T13:47:51Z
      DOI: 10.1016/j.mrfmmm.2017.06.005
  • Enhanced DNA double-strand break repair of microbeam targeted A549 lung
           carcinoma cells by adjacent WI38 normal lung fibroblast cells via
           bi-directional signaling
    • Authors: Alisa Kobayashi; Tengku Ahbrizal Farizal Tengku Ahmad; Narongchai Autsavapromporn; Masakazu Oikawa; Shino Homma-Takeda; Yoshiya Furusawa; Jun Wang; Teruaki Konishi
      Abstract: Publication date: Available online 23 June 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Alisa Kobayashi, Tengku Ahbrizal Farizal Tengku Ahmad, Narongchai Autsavapromporn, Masakazu Oikawa, Shino Homma-Takeda, Yoshiya Furusawa, Jun Wang, Teruaki Konishi
      Understanding the mechanisms underlying the radiation-induced bystander effect (RIBE) and bi-directional signaling between irradiated carcinoma cells and their surrounding non-irradiated normal cells is relevant to cancer radiotherapy. The present study investigated propagation of RIBE signals between human lung carcinoma A549 cells and normal lung fibroblast WI38 cells in bystander cells, either directly or indirectly contacting irradiated A549 cells. We prepared A549-GFP/WI38 co-cultures and A549-GFP/A549 co-cultures, in which A549-GFP cells stably expressing H2BGFP were co-cultured with either A549 cells or WI38 cells, respectively. Using the SPICE-NIRS microbeam, only the A549-GFP cells were irradiated with 500 protons per cell. The level of γ-H2AX, a marker for DNA double-strand breaks (DSB), was subsequently measured for up to 24h post-irradiation in three categories of cells: (1) “targeted”/irradiated A549-GFP cells; (2) “neighboring”/non-irradiated cells directly contacting the “targeted” cells; and (3) “distant”/non-irradiated cells, which were not in direct contact with the “targeted” cells. We found that DSB repair in targeted A549-GFP cells was enhanced by co-cultured WI38 cells. The bystander response in A549-GFP/A549 cell co-cultures, as marked by γ-H2AX levels at 8h post-irradiation, showed a decrease to non-irradiated control level when approaching 24h, while the neighboring/distant bystander WI38 cells in A549-GFP/WI38 co-cultures was maintained at a similar level until 24h post-irradiation. Surprisingly, distant A549-GFP cells in A549-GFP/WI38 co-cultures showed time dependency similar to bystander WI38 cells, but not to distant cells in A549-GFP/A549 co-cultures. These observations indicate that γ-H2AX was induced in WI38 cells as a result of RIBE. WI38 cells were not only involved in rescue of targeted A549, but also in the modification of RIBE against distant A549-GFP cells. The present results demonstrate that radiation-induced bi-directional signaling had extended a profound influence on cellular sensitivity to radiation as well as the sensitivity to RIBE.

      PubDate: 2017-07-01T13:47:51Z
      DOI: 10.1016/j.mrfmmm.2017.06.006
  • Regulation of DNA damage tolerance in mammalian cells by
           post-translational modifications of PCNA
    • Authors: Rie Kanao; Chikahide Masutani
      Abstract: Publication date: Available online 21 June 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Rie Kanao, Chikahide Masutani
      DNA damage tolerance pathways, which include translesion DNA synthesis (TLS) and template switching, are crucial for prevention of DNA replication arrest and maintenance of genomic stability. However, these pathways utilize error-prone DNA polymerases or template exchange between sister DNA strands, and consequently have the potential to induce mutations or chromosomal rearrangements. Post-translational modifications of proliferating cell nuclear antigen (PCNA) play important roles in controlling these pathways. For example, TLS is mediated by mono-ubiquitination of PCNA at lysine 164, for which RAD6–RAD18 is the primary E2–E3 complex. Elaborate protein–protein interactions between mono-ubiquitinated PCNA and Y-family DNA polymerases constitute the core of the TLS regulatory system, and enhancers of PCNA mono-ubiquitination and de-ubiquitinating enzymes finely regulate TLS and suppress TLS-mediated mutagenesis. The template switching pathway is promoted by K63-linked poly-ubiquitination of PCNA at lysine 164. Poly-ubiquitination is achieved by a coupled reaction mediated by two sets of E2–E3 complexes, RAD6–RAD18 and MMS2–UBC13–HTLF/SHPRH. In addition to these mono- and poly-ubiquitinations, simultaneous mono-ubiquitinations on multiple units of the PCNA homotrimeric ring promote an unidentified damage tolerance mechanism that remains to be fully characterized. Furthermore, SUMOylation of PCNA in mammalian cells can negatively regulate recombination. Other modifications, including ISGylation, acetylation, methylation, or phosphorylation, may also play roles in DNA damage tolerance and control of genomic stability.

      PubDate: 2017-06-22T13:14:08Z
  • Editorial
    • Authors: Minoru Takata
      Abstract: Publication date: Available online 10 June 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Minoru Takata

      PubDate: 2017-06-12T12:43:48Z
      DOI: 10.1016/j.mrfmmm.2017.06.001
  • Activation of the FA pathway mediated by phosphorylation and
    • Authors: Masamichi Ishiai; Koichi Sato; Junya Tomida; Hiroyuki Kitao; Hitoshi Kurumizaka; Minoru Takata
      Abstract: Publication date: Available online 5 May 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Masamichi Ishiai, Koichi Sato, Junya Tomida, Hiroyuki Kitao, Hitoshi Kurumizaka, Minoru Takata
      Fanconi anemia (FA) is a devastating hereditary condition that impacts genome integrity, leading to clinical features such as skeletal and visceral organ malformations, attrition of bone marrow stem cells, and carcinogenesis. At least 21 proteins, when absent or defective, have been implicated in this disorder, and they together constitute the FA pathway, which functions in detection and repair of, and tolerance to, endogenous DNA damage. The damage primarily handled by the FA pathway has been assumed to be related to DNA interstrand crosslinks (ICLs). The FA pathway is activated upon ICL damage, and a hallmark of this activation is the mono-ubiquitination events of the key FANCD2-FANCI protein complex. Recent data have revealed unexpectedly complex details in the regulation of FA pathway activation by ICLs. In this short review, we summarize the knowledge accumulated over the years regarding how the FA pathway is activated via protein modifications.

      PubDate: 2017-05-08T09:57:58Z
      DOI: 10.1016/j.mrfmmm.2017.05.003
  • The Legacy of William Morgan: The PNNL Years
    • Authors: Antone L. Brooks
      Abstract: Publication date: Available online 18 March 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Antone L. Brooks

      PubDate: 2017-03-21T06:13:29Z
      DOI: 10.1016/j.mrfmmm.2017.03.002
           AND HOW
    • Authors: R. Julian Preston
      Abstract: Publication date: Available online 8 March 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): R. Julian Preston
      The process of setting radiation protection standards requires the interaction of a number of international and national organizations that in turn require the input of scientific and regulatory experts. Bill Morgan served in an expert capacity for several of these organizations particularly for the application of radiation biology data to risk assessment. He brought great enthusiasm and dedication to these committee efforts. In fact, he really enjoyed this type of service. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), for example, provides comprehensive reviews of the input data for radiation risk assessments. In this context, they do not conduct risk assessments. In Europe, a research component of the risk assessment process is provided by the Multidisciplinary European Low Dose Initiative (MELODI). Specific issue areas are identified for which additional research can aid in reducing uncertainty in risk assessments. The International Commission for Radiological Protection (ICRP) uses these types of input data to develop nominal cancer risk estimates as input data for establishing dose limits for the public and workers. A similar regulatory role is provided in the US by the National Council on Radiation Protection and Measurements (NCRP). The NCRP Reports address the underlying principles for setting regulatory dose limits for the US public and workers; these differ to a limited extent from those of ICRP. The implementation of dose limits is conducted by individual countries but with significant guidance by the International Atomic Energy Agency (IAEA) through its Basic Safety Standards. The role of other national and international organizations are discussed in this same framework.

      PubDate: 2017-03-09T11:12:14Z
      DOI: 10.1016/j.mrfmmm.2017.03.004
  • Targeted Cytoplasmic Irradiation and Autophagy
    • Authors: Jinhua Wu; Bo Zhang; Yen-Ruh Wuu; Mercy M. Davidson; Tom K. Hei
      Abstract: Publication date: Available online 1 March 2017
      Source:Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
      Author(s): Jinhua Wu, Bo Zhang, Yen-Ruh Wuu, Mercy M. Davidson, Tom K. Hei
      The effect of ionizing irradiation on cytoplasmic organelles is often underestimated because the general dogma considers direct DNA damage in the nuclei to be the primary cause of radiation induced toxicity. Using a precision microbeam irradiator, we examined the changes in mitochondrial dynamics and functions triggered by targeted cytoplasmic irradiation with α-particles. Mitochondrial dysfunction induced by targeted cytoplasmic irradiation led to activation of autophagy, which degraded dysfunctional mitochondria in order to maintain cellular energy homeostasis. The activation of autophagy was cytoplasmic irradiation-specific and was not detected in nuclear irradiated cells. This autophagic process was oxyradical-dependent and required the activity of the mitochondrial fission protein dynamin related protein 1 (DRP1). The resultant mitochondrial fission induced phosphorylation of AMP activated protein kinase (AMPK) which leads to further activation of the extracellular signal-related kinase (ERK) 1/2 with concomitant inhibition of the mammalian target of rapamycin (mTOR) to initiate autophagy. Inhibition of autophagy resulted in delayed DNA damage repair and decreased cell viability, which supports the cytoprotective function of autophagy. Our results reveal a novel mechanism in which dysfunctional mitochondria are degraded by autophagy in an attempt to protect cells from toxic effects of targeted cytoplasmic radiation.

      PubDate: 2017-03-03T14:04:54Z
      DOI: 10.1016/j.mrfmmm.2017.02.004
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