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Nucleic Acids Research Jan 2015Translesion synthesis (TLS) provides a highly conserved mechanism that enables DNA synthesis on a damaged template. TLS is performed by specialized DNA polymerases of...
Translesion synthesis (TLS) provides a highly conserved mechanism that enables DNA synthesis on a damaged template. TLS is performed by specialized DNA polymerases of which polymerase (Pol) κ is important for the cellular response to DNA damage induced by benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE), ultraviolet (UV) light and the alkylating agent methyl methanesulfonate (MMS). As TLS polymerases are intrinsically error-prone, tight regulation of their activity is required. One level of control is provided by ubiquitination of the homotrimeric DNA clamp PCNA at lysine residue 164 (PCNA-Ub). We here show that Polκ can function independently of PCNA modification and that Polη can function as a backup during TLS of MMS-induced lesions. Compared to cell lines deficient for PCNA modification (Pcna(K164R)) or Polκ, double mutant cell lines display hypersensitivity to MMS but not to BPDE or UV-C. Double mutant cells also displayed delayed post-replicative TLS, accumulate higher levels of replication stress and delayed S-phase progression. Furthermore, we show that Polη and Polκ are redundant in the DNA damage bypass of MMS-induced DNA damage. Taken together, we provide evidence for PCNA-Ub-independent activation of Polκ and establish Polη as an important backup polymerase in the absence of Polκ in response to MMS-induced DNA damage.
Topics: Animals; Ataxia Telangiectasia Mutated Proteins; Cell Survival; Cells, Cultured; Checkpoint Kinase 1; DNA Damage; DNA Replication; DNA-Directed DNA Polymerase; Methyl Methanesulfonate; Mice, Knockout; Mutation; Proliferating Cell Nuclear Antigen; Protein Kinases; S Phase; Ubiquitination
PubMed: 25505145
DOI: 10.1093/nar/gku1301 -
European Journal of Biochemistry Aug 1975Ether-permeabilized (nucleotide-permeable) cells of Escherichia coli show excision repair of their DNA after having been exposed to the carcinogens...
Carcinogen-induced DNA repair in nucleotide-permeable Escherichia coli cells. Induction of DNA repair by the carcinogens methyl and ethyl nitrosourea and methyl methanesulfonate.
Ether-permeabilized (nucleotide-permeable) cells of Escherichia coli show excision repair of their DNA after having been exposed to the carcinogens N-methyl-N-nitrosourea (MeNOUr), N-ethyl-N-nitrosourea (EtNOUr) and methyl methanesulfonate (MeSO2OMe) which are known to bind covalently to DNA. Defect mutations in genes uvrA, uvrB, uvrC, recA, recB, recC and rep did not inhibit this excision repair. Enzymic activities involved in this repair were identified by measuring size reduction of DNA, DNA degradation to acid-soluble nucleotides and repair polymerization. 1. In permeabilized cells methyl and ethyl nitrosourea induced endonucleolytic cleavage of endogenous DNA, as determined by size reduction of denatured DNA in neutral and alkaline sucrose gradients. An enzymic activity from E. coli K-12 cell extracts was purified (greater than 2000-fold) and was found to cleave preferentially methyl-nitrosourea-treated DNA and to convert the methylated supercoiled DNA duplex (RFI) of phage phiX 174 into the nicked circular form. 2. Degradation of alkylated cellular DNA to acid solubility was diminished in a mutant lacking the 5' leads to 3' exonucleolytic activity of DNA polymerase I but was not affected in a mutant which lacked the DNA polymerizing but retained the 5' leads 3' exonucleolytic activity of DNA polymerase I. 3. An easily measurable effect is carcinogen-induced repair polymerization, making it suitable for detection of covalent binding of carcinogens and potentially carcinogenic compounds.
Topics: Carcinogens; DNA Nucleotidyltransferases; DNA Repair; DNA Replication; Escherichia coli; Ethylnitrosourea; Mesylates; Methyl Methanesulfonate; Methylnitrosourea; Mitomycins; Nitrosourea Compounds; Nucleotides; Permeability; Radiation Effects; Ultraviolet Rays
PubMed: 170107
DOI: 10.1111/j.1432-1033.1975.tb02250.x -
PloS One 2021Living organisms are continuously under threat from a vast array of DNA-damaging agents, which impact genome DNA. DNA replication machinery stalls at damaged template...
Living organisms are continuously under threat from a vast array of DNA-damaging agents, which impact genome DNA. DNA replication machinery stalls at damaged template DNA. The stalled replication fork is restarted via bypass replication by translesion DNA-synthesis polymerases, including the Y-family polymerases Polη, Polι, and Polκ, which possess the ability to incorporate nucleotides opposite the damaged template. To investigate the division of labor among these polymerases in vivo, we generated POLη-/-, POLι-/-, POLκ-/-, double knockout (KO), and triple knockout (TKO) mutants in all combinations from human TK6 cells. TKO cells exhibited a hypersensitivity to ultraviolet (UV), cisplatin (CDDP), and methyl methanesulfonate (MMS), confirming the pivotal role played by these polymerases in bypass replication of damaged template DNA. POLη-/- cells, but not POLι-/- or POLκ-/- cells, showed a strong sensitivity to UV and CDDP, while TKO cells showed a slightly higher sensitivity to UV and CDDP than did POLη-/- cells. On the other hand, TKO cells, but not all single KO cells, exhibited a significantly higher sensitivity to MMS than did wild-type cells. Consistently, DNA-fiber assay revealed that Polη plays a crucial role in bypassing lesions caused by UV-mimetic agent 4-nitroquinoline-1-oxide and CDDP, while all three polymerases play complementary roles in bypassing MMS-induced damage. Our findings indicate that the three Y-family polymerases play distinctly different roles in bypass replication, according to the type of DNA damage generated on the template strand.
Topics: Cell Line; Cisplatin; DNA; DNA Damage; DNA Repair; DNA Replication; DNA-Directed DNA Polymerase; Gene Knockout Techniques; Humans; Methyl Methanesulfonate; Ultraviolet Rays; DNA Polymerase iota
PubMed: 34061890
DOI: 10.1371/journal.pone.0252587 -
The Journal of Cell Biology Jul 2014Deoxyribonucleic acid (DNA) lesions encountered during replication are often bypassed using DNA damage tolerance (DDT) pathways to avoid prolonged fork stalling and...
Deoxyribonucleic acid (DNA) lesions encountered during replication are often bypassed using DNA damage tolerance (DDT) pathways to avoid prolonged fork stalling and allow for completion of DNA replication. Rad18 is a central E3 ubiquitin ligase in DDT, which exists in a monoubiquitinated (Rad18•Ub) and nonubiquitinated form in human cells. We find that Rad18 is deubiquitinated when cells are treated with methyl methanesulfonate or hydrogen peroxide. The ubiquitinated form of Rad18 does not interact with SNF2 histone linker plant homeodomain RING helicase (SHPRH) or helicase-like transcription factor, two downstream E3 ligases needed to carry out error-free bypass of DNA lesions. Instead, it interacts preferentially with the zinc finger domain of another, nonubiquitinated Rad18 and may inhibit Rad18 function in trans. Ubiquitination also prevents Rad18 from localizing to sites of DNA damage, inducing proliferating cell nuclear antigen monoubiquitination, and suppressing mutagenesis. These data reveal a new role for monoubiquitination in controlling Rad18 function and suggest that damage-specific deubiquitination promotes a switch from Rad18•Ub-Rad18 complexes to the Rad18-SHPRH complexes necessary for error-free lesion bypass in cells.
Topics: Animals; Binding Sites; Cell Line; DNA Damage; DNA-Binding Proteins; HEK293 Cells; Humans; Methyl Methanesulfonate; Mice; Mutagenesis; Protein Interaction Mapping; Ubiquitin-Protein Ligases; Ubiquitination
PubMed: 25023518
DOI: 10.1083/jcb.201311063 -
Cell Cycle (Georgetown, Tex.) 2015ELG1 is a conserved gene with important roles in the maintenance of genome stability. Elg1's activity prevents gross chromosomal rearrangements, maintains proper...
ELG1 is a conserved gene with important roles in the maintenance of genome stability. Elg1's activity prevents gross chromosomal rearrangements, maintains proper telomere length regulation, helps repairing DNA damage created by a number of genotoxins and participates in sister chromatid cohesion. Elg1 is evolutionarily conserved, and its Fanconi Anemia-related mammalian ortholog (also known as ATAD5) is embryonic lethal when lost in mice and acts as a tumor suppressor in mice and humans. Elg1 encodes a protein that forms an RFC-like complex that unloads the replicative clamp, PCNA, from DNA, mainly in its SUMOylated form. We have identified 2 different regions in yeast Elg1 that undergo phosphorylation. Phosphorylation of one of them, S112, is dependent on the ATR yeast ortholog, Mec1, and probably is a direct target of this kinase. We show that phosphorylation of Elg1 is important for its role at telomeres. Mutants unable to undergo phosphorylation suppress the DNA damage sensitivity of Δrad5 mutants, defective for an error-free post-replicational bypass pathway. This indicates a role of phosphorylation in the regulation of DNA repair. Our results open the way to investigate the mechanisms by which the activity of Elg1 is regulated during DNA replication and in response to DNA damage.
Topics: Carrier Proteins; DNA Damage; DNA Repair; Gene Expression Regulation; Intracellular Signaling Peptides and Proteins; Mass Spectrometry; Methyl Methanesulfonate; Phosphorylation; Protein Serine-Threonine Kinases; Saccharomyces cerevisiae Proteins; Telomere; Telomere Homeostasis
PubMed: 26177013
DOI: 10.1080/15384101.2015.1068475 -
DNA Repair Sep 2015Here we report identification of the lkh1 gene encoding a LAMMER kinase homolog (Lkh1) from a screen for DNA repair-deficient mutants in Ustilago maydis. The mutant...
Here we report identification of the lkh1 gene encoding a LAMMER kinase homolog (Lkh1) from a screen for DNA repair-deficient mutants in Ustilago maydis. The mutant allele isolated results from a mutation at glutamine codon 488 to a stop codon that would be predicted to lead to truncation of the carboxy-terminal kinase domain of the protein. This mutant (lkh1(Q488*)) is highly sensitive to ultraviolet light, methyl methanesulfonate, and hydroxyurea. In contrast, a null mutant (lkh1Δ) deleted of the entire lkh1 gene has a less severe phenotype. No epistasis was observed when an lkh1(Q488*)rad51Δ double mutant was tested for genotoxin sensitivity. However, overexpressing the gene for Rad51, its regulator Brh2, or the Brh2 regulator Dss1 partially restored genotoxin resistance of the lkh1Δ and lkh1(Q488*) mutants. Deletion of lkh1 in a chk1Δ mutant enabled these double mutant cells to continue to cycle when challenged with hydroxyurea. lkh1Δ and lkh1(Q488*) mutants were able to complete the meiotic process but exhibited reduced heteroallelic recombination and aberrant chromosome segregation. The observations suggest that Lkh1 serves in some aspect of cell cycle regulation after DNA damage or replication stress and that it also contributes to proper chromosome segregation in meiosis.
Topics: Cell Cycle; Chromosome Segregation; Cloning, Molecular; DNA Repair; Epistasis, Genetic; Fungal Proteins; Genetic Complementation Test; Genetic Testing; Genomic Instability; Hydroxyurea; Meiosis; Methyl Methanesulfonate; Mutation; Phenotype; Protein Kinases; Recombination, Genetic; Ultraviolet Rays; Ustilago
PubMed: 26176563
DOI: 10.1016/j.dnarep.2015.05.011 -
PloS One 2021The major human apurinic/apyrimidinic (AP) site endonuclease, APEX1, is a central player in the base excision DNA repair (BER) pathway and has a role in the regulation...
The major human apurinic/apyrimidinic (AP) site endonuclease, APEX1, is a central player in the base excision DNA repair (BER) pathway and has a role in the regulation of DNA binding by transcription factors. In vertebrates, APEX1 knockouts are embryonic lethal, and only a handful of knockout cell lines are known. To facilitate studies of multiple functions of this protein in human cells, we have used the CRISPR/Cas9 system to knock out the APEX1 gene in a widely used non-cancer hypotriploid HEK 293FT cell line. Two stable knockout lines were obtained, one carrying two single-base deletion alleles and one single-base insertion allele in exon 3, another homozygous in the single-base insertion allele. Both mutations cause a frameshift that leads to premature translation termination before the start of the protein's catalytic domain. Both cell lines totally lacked the APEX1 protein and AP site-cleaving activity, and showed significantly lower levels of the APEX1 transcript. The APEX1-null cells were unable to support BER on uracil- or AP site-containing substrates. Phenotypically, they showed a moderately increased sensitivity to methyl methanesulfonate (MMS; ~2-fold lower EC50 compared with wild-type cells), and their background level of natural AP sites detected by the aldehyde-reactive probe was elevated ~1.5-2-fold. However, the knockout lines retained a nearly wild-type sensitivity to oxidizing agents hydrogen peroxide and potassium bromate. Interestingly, despite the increased MMS cytotoxicity, we observed no additional increase in AP sites in knockout cells upon MMS treatment, which could indicate their conversion into more toxic products in the absence of repair. Overall, the relatively mild cell phenotype in the absence of APEX1-dependent BER suggests that mammalian cells possess mechanisms of tolerance or alternative repair of AP sites. The knockout derivatives of the extensively characterized HEK 293FT cell line may provide a valuable tool for studies of APEX1 in DNA repair and beyond.
Topics: CRISPR-Cas Systems; Cell Cycle Checkpoints; DNA Repair; DNA-(Apurinic or Apyrimidinic Site) Lyase; Gene Editing; HEK293 Cells; Humans; Hydrogen Peroxide; Methyl Methanesulfonate; Phenotype; RNA, Guide, CRISPR-Cas Systems
PubMed: 34529719
DOI: 10.1371/journal.pone.0257473 -
Infection and Immunity May 1985A UV-sensitive derivative was obtained from Streptococcus sanguis Challis. The organism could be transformed with a number of small streptococcal plasmids at frequencies...
A UV-sensitive derivative was obtained from Streptococcus sanguis Challis. The organism could be transformed with a number of small streptococcal plasmids at frequencies equal to, or 1 logarithm below, the transformation frequencies for the parent organism. However, transformation with chromosomal DNA was greatly impaired in the UV-sensitive derivative.
Topics: Methyl Methanesulfonate; Mutation; Plasmids; Recombination, Genetic; Streptococcus sanguis; Transformation, Bacterial; Ultraviolet Rays
PubMed: 3988349
DOI: 10.1128/iai.48.2.584-586.1985 -
Biology Letters Feb 2016Sea urchins are noted for the absence of neoplastic disease and represent a novel model to investigate cellular and systemic cancer protection mechanisms. Following...
Sea urchins are noted for the absence of neoplastic disease and represent a novel model to investigate cellular and systemic cancer protection mechanisms. Following intracoelomic injection of the DNA alkylating agent methyl methanesulfonate, DNA damage was detected in sea urchin cells and tissues (coelomocytes, muscle, oesophagus, ampullae and gonad) by the alkaline unwinding, fast micromethod. Gene expression analyses of the coelomocytes indicated upregulation of innate immune markers, including genes involved in NF-κB signalling. Results suggest that activation of the innate immune system following DNA damage may contribute to the naturally occurring resistance to neoplastic disease observed in sea urchins.
Topics: Animals; DNA Damage; Gene Expression; Immune System; Lytechinus; Methyl Methanesulfonate; Mutagens
PubMed: 26911343
DOI: 10.1098/rsbl.2015.1057 -
PloS One 2021Continuous culture systems allow for the controlled growth of microorganisms over a long period of time. Here, we develop a novel test for mutagenicity that involves...
Continuous culture systems allow for the controlled growth of microorganisms over a long period of time. Here, we develop a novel test for mutagenicity that involves growing yeast in continuous culture systems exposed to low levels of mutagen for a period of approximately 20 days. In contrast, most microorganism-based tests for mutagenicity expose the potential mutagen to the biological reporter at a high concentration of mutagen for a short period of time. Our test improves upon the sensitivity of the well-established Ames test by at least 20-fold for each of two mutagens that act by different mechanisms (the intercalator ethidium bromide and alkylating agent methyl methanesulfonate). To conduct the tests, cultures were grown in small, inexpensive continuous culture systems in media containing (potential) mutagen, and the resulting mutagenicity of the added compound was assessed via two methods: a canavanine-based plate assay and whole genome sequencing. In the canavanine-based plate assay, we were able to detect a clear relationship between the amount of mutagen and the number of canavanine-resistant mutant colonies over a period of one to three weeks of exposure. Whole genome sequencing of yeast grown in continuous culture systems exposed to methyl methanesulfonate demonstrated that quantification of mutations is possible by identifying the number of unique variants across each strain. However, this method had lower sensitivity than the plate-based assay and failed to distinguish the different concentrations of mutagen. In conclusion, we propose that yeast grown in continuous culture systems can provide an improved and more sensitive test for mutagenicity.
Topics: Canavanine; Culture Media; DNA, Fungal; Ethidium; Methyl Methanesulfonate; Mutagenicity Tests; Saccharomyces cerevisiae; Whole Genome Sequencing
PubMed: 33730086
DOI: 10.1371/journal.pone.0235303