-
ELife Jun 2023The replication checkpoint is essential for accurate DNA replication and repair, and maintenance of genomic integrity when a cell is challenged with genotoxic stress....
The replication checkpoint is essential for accurate DNA replication and repair, and maintenance of genomic integrity when a cell is challenged with genotoxic stress. Several studies have defined the complement of proteins that change subcellular location in the budding yeast following chemically induced DNA replication stress using methyl methanesulfonate (MMS) or hydroxyurea (HU). How these protein movements are regulated remains largely unexplored. We find that the essential checkpoint kinases Mec1 and Rad53 are responsible for regulating the subcellular localization of 159 proteins during MMS-induced replication stress. Unexpectedly, Rad53 regulation of the localization of 52 proteins is independent of its known kinase activator Mec1, and in some scenarios independent of Tel1 or the mediator proteins Rad9 and Mrc1. We demonstrate that Rad53 is phosphorylated and active following MMS exposure in cells lacking Mec1 and Tel1. This noncanonical mode of Rad53 activation depends partly on the retrograde signaling transcription factor Rtg3, which also facilitates proper DNA replication dynamics. We conclude that there are biologically important modes of Rad53 protein kinase activation that respond to replication stress and operate in parallel to Mec1 and Tel1.
Topics: Protein Serine-Threonine Kinases; Cell Cycle Proteins; Saccharomyces cerevisiae Proteins; Intracellular Signaling Peptides and Proteins; Checkpoint Kinase 2; Saccharomyces cerevisiae; Phosphorylation; DNA Damage; Methyl Methanesulfonate; DNA Replication
PubMed: 37278514
DOI: 10.7554/eLife.82483 -
Journal of Medical Virology Apr 2023Epstein-Barr virus (EBV) infection is associated with the occurrence and development of gastric cancer (GC). Methyl methanesulfonate and ultraviolet-sensitive gene 81...
Epstein-Barr virus (EBV) infection is associated with the occurrence and development of gastric cancer (GC). Methyl methanesulfonate and ultraviolet-sensitive gene 81 (MUS81) is the catalytic component of a structure-specific endonuclease and plays an important role in chromosomal stability. However, the link between EBV infection and MUS81 remains unclear. In the present study, we found that MUS81 expression was much lower in EBV-associated GC cells than in EBV-negative GC. MUS81 acts as an oncogene in GC by inducing the cell migration and proliferation. Western blot and luciferase reporter assays revealed that miR-BART9-5p directly targeted MUS81 and downregulated its expression. Additionally, overexpression of MUS81 in EBV-positive GC cells inhibited the expression of EBV nuclear antigen 1 (EBNA1). EBNA1 is critical for the pathogenesis of EBV-associated tumors and the maintenance of a stable copy number of the viral genomes. Altogether, these results indicated that the lowering MUS81 expression might be a mechanism by EBV to maintain its latent infection.
Topics: Humans; Epstein-Barr Virus Infections; Herpesvirus 4, Human; Methyl Methanesulfonate; Down-Regulation; Stomach Neoplasms; MicroRNAs; Latent Infection; Cell Movement; Cell Proliferation; Cell Line, Tumor; DNA-Binding Proteins; Endonucleases
PubMed: 37185865
DOI: 10.1002/jmv.28725 -
Plant Cell Reports Aug 2023SMC5/6 complex subunit OsMMS21 is involved in cell cycle and hormone signaling and required for stem cell proliferation during shoot and root development in rice. The...
SMC5/6 complex subunit OsMMS21 is involved in cell cycle and hormone signaling and required for stem cell proliferation during shoot and root development in rice. The structural maintenance of chromosome (SMC)5/6 complex is required for nucleolar integrity and DNA metabolism. Moreover, METHYL METHANESULFONATE SENSITIVITY GENE 21 (MMS21), a SUMO E3 ligase that is part of the SMC5/6 complex, is essential for the root stem cell niche and cell cycle transition in Arabidopsis. However, its specific role in rice remains unclear. Here, OsSMC5 and OsSMC6 single heterozygous mutants were generated using CRISPR/Cas9 technology to elucidate the function of SMC5/6 subunits, including OsSMC5, OsSMC6, and OsMMS21, in cell proliferation in rice. ossmc5/ + and ossmc6/ + heterozygous single mutants did not yield homozygous mutants in their progeny, indicating that OsSMC5 and OsSMC6 both play necessary roles during embryo formation. Loss of OsMMS21 caused severe defects in both the shoot and roots in rice. Transcriptome analysis showed a significant decrease in the expression of genes involved in auxin signaling in the roots of osmms21 mutants. Moreover, the expression levels of the cycB2-1 and MCM genes, which are involved the cell cycle, were significantly lower in the shoots of the mutants, indicating that OsMMS21 was involved in both hormone signaling pathways and the cell cycle. Overall, these findings indicate that the SUMO E3 ligase OsMMS21 is required for both shoot and root stem cell niches, improving the understanding of the function of the SMC5/6 complex in rice.
Topics: Saccharomyces cerevisiae Proteins; Oryza; Cell Cycle Proteins; SUMO-1 Protein; Ubiquitin-Protein Ligases; Cell Division; Hormones
PubMed: 37178216
DOI: 10.1007/s00299-023-03030-9 -
Genes and Environment : the Official... Apr 2023The use of organotypic human tissue models in genotoxicity has increased as an alternative to animal testing. Genotoxicity is generally examined using a battery of in...
BACKGROUND
The use of organotypic human tissue models in genotoxicity has increased as an alternative to animal testing. Genotoxicity is generally examined using a battery of in vitro assays such as Ames and micronucleus (MN) tests that cover gene mutations and structural and numerical chromosome aberrations. At the 7th International Workshop on Genotoxicity Testing, working group members agreed that the skin models have reached an advanced stage of maturity, while further efforts in liver and airway models are needed [Pfuhler et al., Mutat. Res. 850-851 (2020) 503135]. Organotypic human airway model is composed of fully differentiated and functional respiratory epithelium. However, because cell proliferation in organotypic airway models is thought to be less active, assessing their MN-inducing potential is an issue, even in the cytokinesis-blocking approach using cytochalasin B (CB) [Wang et al., Environ. Mol. Mutagen. 62 (2021) 306-318]. Here, we developed a MN test using EpiAirway™ in which epidermal growth factor (EGF) was included as a stimulant of cell division.
RESULTS
By incubating EpiAirway™ tissue with medium containing various concentrations of CB, we found that the percentage of binucleated cells (%BNCs) almost plateaued at 3 μg/mL CB for 72 h incubation. Additionally, we confirmed that EGF stimulation with CB incubation produced an additional increase in %BNCs with a peak at 5 ng/mL EGF. Transepithelial electrical resistance measurement and tissue histology revealed that CB incubation caused the reduced barrier integrity and cyst formation in EpiAirway™. Adenylate kinase assay confirmed that the cytotoxicity increased with each day of culture in the CB incubation period with EGF stimulation. These results indicated that chemical treatment should be conducted prior to CB incubation. Under these experimental conditions, it was confirmed that the frequency of micronucleated cells was dose-dependently increased by apical applications of two clastogens, mitomycin C and methyl methanesulfonate, and an aneugen, colchicine, at the subcytotoxic concentrations assessed in %BNCs.
CONCLUSIONS
Well-studied genotoxicants demonstrated capability in an organotypic human airway model as a MN test system. For further utilization, investigations of aerosol exposure, repeating exposure protocol, and metabolic activation are required.
PubMed: 37046355
DOI: 10.1186/s41021-023-00269-2 -
Mutation Research. Genetic Toxicology... Apr 2023The fat mass and obesity-associated protein FTO is an "eraser" of N6-methyladenosine, the most abundant mRNA modification. FTO plays important roles in tumorigenesis....
The fat mass and obesity-associated protein FTO is an "eraser" of N6-methyladenosine, the most abundant mRNA modification. FTO plays important roles in tumorigenesis. However, its activities have not been fully elucidated and its possible involvement in DNA damage - the early driving event in tumorigenesis - remains poorly characterized. Here, we have investigated the role of FTO in the DNA damage response (DDR) and its underlying mechanisms. We demonstrate that FTO responds to various DNA damage stimuli. FTO is overexpressed in mice following exposure to the promutagens aristolochic acid I and benzo[a]pyrene. Knockout of the FTO gene in TK6 cells, via CRISPR/Cas9, increased genotoxicity induced by DNA damage stimuli (micronucleus and TK mutation assays). Cisplatin- and diepoxybutane-induced micronucleus frequencies and methyl methanesulfonate- and azathioprine-induced TK mutant frequencies were also higher in FTO KO cells. We investigated the potential roles of FTO in DDR. RNA sequencing and enrichment analysis revealed that FTO deletion disrupted the p38 MAPK pathway and inhibited the activation of nucleotide excision repair and cell-cycle-related pathways following cisplatin (DNA intrastrand cross-links) treatment. These effects were confirmed by western blotting and qRT-PCR. FTO deletion impaired cell-cycle arrest at the G2/M phase following cisplatin and diepoxybutane treatment (flow cytometry analysis). Our findings demonstrated that FTO is involved in several aspects of DDR, acting, at least in part, by impairing cell cycle progression.
Topics: Mice; Animals; Cisplatin; Mice, Knockout; Cell Division; DNA Damage; Carcinogenesis; Alpha-Ketoglutarate-Dependent Dioxygenase FTO
PubMed: 37003652
DOI: 10.1016/j.mrgentox.2023.503608 -
Toxicology Reports 2023Products derived from olives, such as the raw fruit and oils, are widely consumed due to their taste, and purported nutritional/health benefits. Phenolic compounds,...
Products derived from olives, such as the raw fruit and oils, are widely consumed due to their taste, and purported nutritional/health benefits. Phenolic compounds, especially hydroxytyrosol (HT), have been proposed as one of the key substances involved in these effects. An olive juice extract, standardized to contain 20% HT ("OE20HT"), was produced to investigate its health benefits. The aim of this study was to demonstrate the genotoxic safety of this ingredient based on Ames assay and micronucleus assay. Results indicated that OE20HT was not mutagenic at concentrations of up to 5000 µg/plate, with or without metabolic activation, and was neither aneugenic nor clastogenic after 3-hour exposure at concentrations of up to 60 µg/mL with or without metabolic activation, or after 24-hour exposure at concentrations of up to 40 µg/mL. To further substantiate the safety of OE20HT following ingestion without conducting additional animal studies, a comprehensive literature review was conducted. No safety concerns were identified based on acute or sub-chronic studies in animals, including reproductive and developmental studies. These results were supported by clinical studies demonstrating the absence of adverse effects after oral supplementation with olive extracts or HT. Based on data and the literature review, the OE20HT extract is therefore considered as safe for human consumption at doses up to 2.5 mg/kg body weight/day.
PubMed: 36852231
DOI: 10.1016/j.toxrep.2023.02.003 -
Life (Basel, Switzerland) Feb 2023The bioavailability of glucoside flavonoids is influenced by the nature of the sugar, glucosides being absorbed faster than rhamnoglucosides, for example. One strategy...
The bioavailability of glucoside flavonoids is influenced by the nature of the sugar, glucosides being absorbed faster than rhamnoglucosides, for example. One strategy to enhance the bioavailability is enzymatic hydrolysis. In this study, some kinetic parameters of hesperidinase-mediated hydrolysis of rutin were evaluated using an UHPLC/QTOF-MS analysis of the products of a bioconversion reaction. The resulting hydrolyzed rutins (after 4, 8 and 12 h of reaction) were submitted to anti-proliferative and Cytokinesis-Block Micronucleus (CBMN) assays in CHO-K1 cells. In the hesperidinase-mediated hydrolysis, the final concentration of quercetin-3-O-glucoside (Q3G) was directly proportional to the rutin concentration and inversely proportional to the reaction time. At an anti-proliferative concentration (2.5 μg/mL), hydrolyzed rutin derivatives did not show a mutagenic effect, except for the sample with a higher content of Q3G (after 4 h of the enzymatic hydrolysis of rutin). Moreover, the higher Q3G content in hydrolyzed rutin protected the CHO-K1 cells 92% of the time against methyl methanesulfonate-induced mutagenic damage. These results suggested that the anti-mutagenic effect of hydrolyzed rutin might be related to antioxidant and cell death induction. Presenting a good lipophilicity/hydrophilicity ratio, together with antioxidant and anti-mutagenic activities, the hesperidinase-mediated hydrolyzed rutin seemed to be a promisor raw material for the development of food supplements.
PubMed: 36836907
DOI: 10.3390/life13020549 -
Frontiers in Molecular Neuroscience 2022Retinitis pigmentosa (RP) is a group of neurodegenerative retinopathies causing blindness due to progressive and irreversible photoreceptor cell death. The alkylating...
INTRODUCTION
Retinitis pigmentosa (RP) is a group of neurodegenerative retinopathies causing blindness due to progressive and irreversible photoreceptor cell death. The alkylating agent methyl methanesulfonate (MMS) can induce selective photoreceptor cell death, which is used to establish RP animal models. MMS induces DNA base damage by adding alkyl groups to DNA, and epigenetic modifications influence DNA damage response. Here, we aimed to explore the relationship between DNA methylation and DNA damage response in dying photoreceptors of RP.
METHODS
The mouse RP model was established by a single intraperitoneal injection of MMS. The retinal structure and function were assessed by H&E, OCT, TUNEL, and ERG at several time points. The expression of DNA methylation regulators was assessed by qPCR and Western blot. DNMT inhibitor 5-aza-dC was applied to inhibit the activity of DNA methyltransferases and improve the retinal photoreceptor damage.
RESULTS
The outer nuclear layer (ONL) and IS/OS layer were significantly thinner and the retinal function was impaired after MMS treatment. The cell death was mainly located in the ONL. The retinal damage induced by MMS was accompanied by hyperexpression of DNMT3A/3B. The application of DNMT inhibitor 5-aza-dC could suppress the expression level of DNMT3A/3B, resulting in the remission of MMS-induced photoreceptor cell damage. The ONL and IS/OS layers were thicker than that of the control group, and the retinal function was partially restored. This protective effect of 5-aza-dC was associated with the down-regulated expression of DNMT3A/3B.
CONCLUSION
These findings identified a functional role of DNMT3A/3B in MMS-induced photoreceptor cell damage and provided novel evidence to support DNMTs as potential therapeutic targets in retinal degenerative diseases.Graphical Abstract.
PubMed: 36704326
DOI: 10.3389/fnmol.2022.1057365 -
Nucleic Acids Research Jan 2023Mycobacterium smegmatis Lhr exemplifies a novel clade of helicases composed of an N-terminal ATPase/helicase domain (Lhr-Core) and a large C-terminal domain (Lhr-CTD)...
Mycobacterium smegmatis Lhr exemplifies a novel clade of helicases composed of an N-terminal ATPase/helicase domain (Lhr-Core) and a large C-terminal domain (Lhr-CTD) that nucleates a unique homo-tetrameric quaternary structure. Expression of Lhr, and its operonic neighbor Nei2, is induced in mycobacteria exposed to mitomycin C (MMC). Here we report that lhr deletion sensitizes M. smegmatis to killing by DNA crosslinkers MMC and cisplatin but not to killing by monoadduct-forming alkylating agent methyl methanesulfonate or UV irradiation. Testing complementation of MMC and cisplatin sensitivity by expression of Lhr mutants in Δlhr cells established that: (i) Lhr-CTD is essential for DNA repair activity, such that Lhr-Core does not suffice; (ii) ATPase-defective mutant D170A/E171A fails to complement; (iii) ATPase-active, helicase-defective mutant W597A fails to complement and (iv) alanine mutations at the CTD-CTD interface that interdict homo-tetramer formation result in failure to complement. Our results instate Lhr's ATP-driven motor as an agent of inter-strand crosslink repair in vivo, contingent on Lhr's tetrameric quaternary structure. We characterize M. smegmatis Nei2 as a monomeric enzyme with AP β-lyase activity on single-stranded DNA. Counter to previous reports, we find Nei2 is inactive as a lyase at a THF abasic site and has feeble uracil glycosylase activity.
Topics: Mitomycin; Cisplatin; Bacterial Proteins; DNA Helicases; Mycobacterium; Adenosine Triphosphatases; DNA Repair; DNA, Single-Stranded
PubMed: 36610794
DOI: 10.1093/nar/gkac1222 -
Archives of Toxicology Mar 2023Although micronuclei are well-known biomarkers of genotoxic damage, the biological consequences of micronucleus induction are only poorly understood. To further...
Although micronuclei are well-known biomarkers of genotoxic damage, the biological consequences of micronucleus induction are only poorly understood. To further elucidate these consequences, HeLa cells stably expressing histone 2B coupled with green fluorescent protein were used for long-term live cell imaging to investigate the fate of micronuclei and micronucleated cells after treatment of cells with various genotoxic agents (doxorubicin (20, 30 and nM), tert-butyl hydroperoxide (tBHP, 50, 100 and 150 µM), radiation (0.5, 1 and 2 Gy), methyl methanesulfonate (MMS, 20, 25 and 30 µg/ml) and vinblastine (1, 2 and 3 nM)). Most micronuclei persist for multiple cell cycles or reincorporate while micronucleated cells were more prone to cell death, senescence and fatal mitotic errors compared to non-micronucleated cells, which is consistent with previous studies using etoposide. No clear substance-related effects on the fate of micronuclei and micronucleated cells were observed. To further investigate the fate of micronuclei, extrusion of micronuclei was studied with treatments reported as inducing the extrusion of micronuclei. Since extrusion was not observed in HeLa cells, the relevance of extrusion of micronuclei remains unclear. In addition, degradation of micronuclei was analysed via immunostaining of γH2AX, which demonstrated a high level of DNA damage in micronuclei compared to the main nuclei. Furthermore, transduction with two reporter genes (LC3B-dsRed and LaminB1-dsRed) was conducted followed by long-term live cell imaging. While autophagy marker LC3B was not associated with micronuclei, Lamin B1 was found in approximately 50% of all micronuclei. While degradation of micronuclei was not observed to be a frequent fate of micronuclei, the results show impaired stability of DNA and micronuclear envelope indicating rupture of micronuclei as a pre-step to chromothripsis.
Topics: Humans; HeLa Cells; Micronuclei, Chromosome-Defective; Cell Nucleus; DNA Damage; Histones; Micronucleus Tests
PubMed: 36564592
DOI: 10.1007/s00204-022-03433-9