ABSTRACT
The human NTHL1 gene encodes a DNA glycosylase that plays a key role in the base excision repair (BER) pathway, repairing oxidative DNA damage and maintaining genome integrity. The physiological activity of NTHL1 is crucial in preventing genetic alterations that can lead to cancer. In this study, we employed an innovative targeted DNA sequencing (DNA-seq) methodology to explore the transcriptional landscape of the NTHL1 gene, revealing previously uncharacterized alternative splicing events and novel exons. Our designed approach provided significantly improved sequencing depth and coverage, enabling the identification of novel NTHL1 mRNA transcripts. Bioinformatics analysis confirmed all annotated splice junctions of the main NTHL1 transcripts (v.1 - v.3) and revealed novel mRNA transcripts (NTHL1 v.4 - v.9) derived from splicing events between annotated exons as well as mRNAs containing previously uncharacterized exons (NTHL1 v.10 - v.14). Quantitative PCR analysis highlighted a diverse expression pattern of these novel transcripts across different human cell lines, suggesting cell-specific roles and regulatory mechanisms. Notably, NTHL1 v.5 was overexpressed in luminal A breast cancer cells (MCF-7), while v.13 was prominent in triple negative (BT-20), HER2 + breast cancer (SK-BR-3), prostate, colorectal cancer cells and HEK-293 cells. Our findings suggest that specific novel NTHL1 transcripts may encode protein isoforms with distinct structural features, as indicated by ribosome profiling datasets, while others containing premature termination codons could function as long non-coding RNAs. These insights enhance our understanding of NTHL1 regulatory role and its potential as a biomarker and therapeutic target in human malignancies. This study underscores the importance of exploring the transcriptional diversity of NTHL1 to fully elucidate its role in cancer pathobiology.
Subject(s)
Alternative Splicing , Deoxyribonuclease (Pyrimidine Dimer) , Exons , RNA, Messenger , Humans , RNA, Messenger/genetics , RNA, Messenger/metabolism , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Deoxyribonuclease (Pyrimidine Dimer)/metabolism , Exons/genetics , MCF-7 Cells , Cell Line, Tumor , Sequence Analysis, DNA/methods , Gene Expression Regulation, Neoplastic , FemaleABSTRACT
A substantial number of hereditary colorectal cancer (CRC) and colonic polyposis cannot be explained by alteration in confirmed predisposition genes, such as mismatch repair (MMR) genes, APC and MUTYH. Recently, a certain number of potential predisposition genes have been suggested, involving each a small number of cases reported so far. Here, we describe the detection of rare variants in the NTLH1, AXIN2, RNF43, BUB1, and TP53 genes in nine unrelated patients who were suspected for inherited CRC and/or colonic polyposis. Seven of them were classified as pathogenic or likely pathogenic variants (PV/LPV). Clinical manifestations of carriers were largely consistent with reported cases with, nevertheless, distinct characteristics. PV/LPV in these uncommon gene can be responsible for up to 2.7% of inherited CRC or colonic polyposis syndromes. Our findings provide supporting evidence for the role of these genes in cancer predisposition, and contribute to the determination of related cancer spectrum and cancer risk for carriers, allowing for the establishment of appropriate screening strategy and genetic counseling in affected families.
Subject(s)
Adenomatous Polyposis Coli , Genetic Predisposition to Disease , Humans , Female , Male , Middle Aged , Adult , Adenomatous Polyposis Coli/genetics , Ubiquitin-Protein Ligases/genetics , Axin Protein/genetics , Colorectal Neoplasms/genetics , Tumor Suppressor Protein p53/genetics , Aged , Protein Serine-Threonine Kinases/genetics , DNA-Binding Proteins/genetics , Deoxyribonuclease (Pyrimidine Dimer)ABSTRACT
The functionalities of proteins rely on protein conformational changes during many processes. Identification of the protein conformations and capturing transitions among different conformations are important but extremely challenging in both experiments and simulations. In this work, we develop a machine learning based approach to identify a reaction coordinate that accelerates the exploration of protein conformational changes in molecular simulations. We implement our approach to study the conformational changes of human NTHL1 during DNA repair. Our results identified three distinct conformations: open (stable), closed (unstable), and bundle (stable). The existence of the bundle conformation can rationalize recent experimental observations. Comparison with an NTHL1 mutant demonstrates that a closely packed cluster of positively charged residues in the linker could be a factor to search when screening for genetic abnormalities. Results will lead to a better modulation of the DNA repair pathway to protect against carcinogenesis.
Subject(s)
Molecular Dynamics Simulation , Proteins , Humans , Proteins/chemistry , Protein Conformation , Deoxyribonuclease (Pyrimidine Dimer)ABSTRACT
Endonuclease V (EndoV) is a single-metal-dependent enzyme that repairs deaminated DNA nucleobases in cells by cleaving the phosphodiester bond, and this enzyme has proven to be a powerful tool in biotechnology and medicine. The catalytic mechanism used by EndoV must be understood to design new disease detection and therapeutic solutions and further exploit the enzyme in interdisciplinary applications. This study has used a mixed molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) approach to compare eight distinct catalytic pathways and provides the first proposed mechanism for bacterial EndoV. The calculations demonstrate that mechanisms involving either direct or indirect metal coordination to the leaving group of the substrate previously proposed for other nucleases are unlikely for EndoV, regardless of the general base (histidine, aspartate, and substrate phosphate moiety). Instead, distinct catalytic pathways are characterized for EndoV that involve K139 stabilizing the leaving group, a metal-coordinated water stabilizing the transition structure, and either H214 or a substrate phosphate group activating the water nucleophile. In silico K139A and H214A mutational results support the newly proposed roles of these residues. Although this is a previously unseen combination of general base, general acid, and metal-binding architecture for a one-metal-dependent endonuclease, our proposed catalytic mechanisms are fully consistent with experimental kinetic, structural, and mutational data. In addition to substantiating a growing body of literature, suggesting that one metal is enough to catalyze P-O bond cleavage in nucleic acids, this new fundamental understanding of the catalytic function will promote the exploration of new and improved applications of EndoV.
Subject(s)
Nucleic Acids , Deoxyribonuclease (Pyrimidine Dimer)/chemistry , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Deoxyribonuclease (Pyrimidine Dimer)/metabolism , Lysine , Metals , Phosphates , WaterABSTRACT
Polyketide synthase (pks) island harboring Escherichia coli are, under the right circumstances, able to produce the genotoxin colibactin. Colibactin is a risk factor for the development of colorectal cancer and associated with mutational signatures SBS88 and ID18. This study explores colibactin-associated mutational signatures in biallelic NTHL1 and MUTYH patients. Targeted Next Generation Sequencing (NGS) was performed on colorectal adenomas and carcinomas of one biallelic NTHL and 12 biallelic MUTYH patients. Additional fecal metagenomics and genome sequencing followed by mutational signature analysis was conducted for the NTHL1 patient. Targeted NGS of the NTHL1 patient showed somatic APC variants fitting SBS88 which was confirmed using WGS. Furthermore, fecal metagenomics revealed pks genes. Also, in 1 out of 11 MUTYH patient a somatic variant was detected fitting SBS88. This report shows that colibactin may influence development of colorectal neoplasms in predisposed patients.
Subject(s)
Adenomatous Polyposis Coli , Colorectal Neoplasms , Humans , Adenomatous Polyposis Coli/genetics , Adenomatous Polyposis Coli/pathology , Mutation , Colorectal Neoplasms/genetics , Colorectal Neoplasms/pathology , Deoxyribonuclease (Pyrimidine Dimer)/geneticsABSTRACT
In search of novel breast cancer (BC) risk variants, we performed a whole-exome sequencing and variant analysis of 69 Finnish BC patients as well as analysed loss-of-function variants identified in DNA repair genes in the Finns from the Genome Aggregation Database. Additionally, we carried out a validation study of SERPINA3 c.918-1G>C, recently suggested for BC predisposition. We estimated the frequencies of 41 rare candidate variants in 38 genes by genotyping them in 2482-4101 BC patients and in 1273-3985 controls. We further evaluated all coding variants in the candidate genes in a dataset of 18,786 BC patients and 182,927 controls from FinnGen. None of the variants associated significantly with cancer risk in the primary BC series; however, in the FinnGen data, NTHL1 c.244C>T p.(Gln82Ter) associated with BC with a high risk for homozygous (OR = 44.7 [95% CI 6.90-290], P = 6.7 × 10-5) and a low risk for heterozygous women (OR = 1.39 [1.18-1.64], P = 7.8 × 10-5). Furthermore, the results suggested a high risk of colorectal, urinary tract, and basal-cell skin cancer for homozygous individuals, supporting NTHL1 as a recessive multi-tumour susceptibility gene. No significant association with BC risk was detected for SERPINA3 or any other evaluated gene.
Subject(s)
Breast Neoplasms , Genetic Predisposition to Disease , Humans , Female , Breast Neoplasms/genetics , Heterozygote , Breast , Finland , Deoxyribonuclease (Pyrimidine Dimer)/geneticsABSTRACT
Objective: To evaluate the role and molecular mechanism of Nei endonuclease VIII-like protein 3 (NEIL3) in hepatocellular carcinoma (HCC) through The Cancer Genome Atlas database. Methods: RNA sequencing of HCC samples was the first step in determining the level of gene NEIL3 expression in normal tissues and tumors. Then, NEIL3 was used for the Gene Ontology, the Kyoto Encyclopedia of Genes and Genomes, gene enrichment analysis, immune cell infiltration analysis. The samples were divided into high and low expression groups according to the median expression level of NEIL3 in liver cancer tissues. Logistic regression analysis, Kaplan-Meier analysis, univariate and multivariate Cox regression analysis, and a nomogram prognostic model were used to explore the clinical and prognostic significance of NEIL3 in HCC. Results: Compared with normal samples, NEIL3 was highly expressed in most malignant tumors, including HCC (P < 0.05). High expression of NEIL3 was related to cell cycle, DNA replication, and cell receptor pathways. In addition, the high expression of NEIL3 was significantly positively correlated with T-helper 2 lymphocytes and infiltration levels (R = 0.670, P < 0.001). Compared with the NEIL3 low expression group, the NEIL3 high expression group had a higher level of Th2 cell infiltration in tumor tissues (P < 0.001). Logistic regression analysis showed that NEIL3 overexpression was associated with high T stage, high pathological stage, high tissue grade, AFP > 400 µg/L and vascular invasion of HCC. The Kaplan-Meier analysis results showed that overall survival [hazard ratio (HR) = 2.53, P < 0.001)], disease-specific survival (HR = 2.52, P < 0.001), and progression-free interval (HR = 1.82, P < 0.001) in patients with HCC with high NEIL3 expression were unfavorable. Cox regression analysis results showed that high NEIL3 expression was an independent risk factor for an unfavorable prognosis in HCC patients (P = 0.002). The nomogram and calibration chart further demonstrated that high NEIL3 expression was one of the risk factors for an unfavorable prognosis in HCC patients. Conclusion: Elevated expression of NEIL3 is associated with an unfavorable prognosis and an increased proportion of immune cells in HCC, and it is likely to be used as a potential biomarker for evaluating the prognosis and immune infiltration level.
Subject(s)
Carcinoma, Hepatocellular , Liver Neoplasms , Humans , Deoxyribonuclease (Pyrimidine Dimer) , PrognosisABSTRACT
Multiple polyposes are heterogeneous diseases with different underlying molecular backgrounds, sharing a common symptom: the presence of transforming into cancerous intestinal polyps. Recent reports have indicated biallelic mutations in the NTHL1 gene, which is involved in base excision repair (BER), as predisposing to an elevated risk of colorectal cancer (CRC). We aimed to evaluate the significance of the p.Q82* truncating variant in predisposition to intestinal polyposis by assessing its frequency in polyposis patients. We genotyped 644 Polish patients and 634 control DNA samples using high-resolution melting analysis (HRM) and Sanger sequencing. We found the p.Q82* variant in four polyposis patients; in three, it was homozygous (OR = 6.90, p value = 0.202). Moreover, the p.R92C mutation was detected in one patient. We also looked more closely at the disease course in patients carrying NTHL1 mutations. Two homozygous patients also presented other neoplasia. In the family case, we noticed the earlier presence of polyps in the proband and early hepatoblastoma in his brother. We cannot univocally confirm the relationship of p.Q82* with an increased risk of CRC. However, homozygous p.Q82* was more frequent by 10-fold in patients without other mutations identified, which makes NTHL1 gene screening in this group reasonable.
Subject(s)
Adenomatous Polyposis Coli , Colorectal Neoplasms , Male , Humans , Adenomatous Polyposis Coli/genetics , Adenomatous Polyposis Coli/diagnosis , Poland , Genetic Predisposition to Disease , Colorectal Neoplasms/genetics , Colorectal Neoplasms/diagnosis , Mutation , Deoxyribonuclease (Pyrimidine Dimer)/geneticsABSTRACT
Therapeutic oligonucleotides have emerged as a powerful drug modality with the potential to treat a wide range of diseases; however, the rising number of therapies poses a manufacturing challenge. Existing synthetic methods use stepwise extension of sequences immobilized on solid supports and are limited by their scalability and sustainability. We report a biocatalytic approach to efficiently produce oligonucleotides in a single operation where polymerases and endonucleases work in synergy to amplify complementary sequences embedded within catalytic self-priming templates. This approach uses unprotected building blocks and aqueous conditions. We demonstrate the versatility of this methodology through the synthesis of clinically relevant oligonucleotide sequences containing diverse modifications.
Subject(s)
Biocatalysis , Oligonucleotides , Oligonucleotides/biosynthesis , DNA-Directed DNA Polymerase/chemistry , Deoxyribonuclease (Pyrimidine Dimer)/chemistryABSTRACT
Parkinson's disease (PD) is a common movement disorder caused by a characteristic loss of dopaminergic neurons in the substantia nigra and degeneration of dopamine terminals in the dorsal striatum. Previous studies have suggested that oxidative stress-induced DNA damage may be involved in PD pathogenesis, as steady-state levels of several types of oxidized nucleobases were shown to be elevated in PD brain tissues. These DNA lesions are normally removed from the genome by base excision repair, which is initiated by DNA glycosylase enzymes such as endonuclease VIII-like 1 (Neil1). In this study, we show that Neil1 plays an important role in limiting oxidative stress-induced degeneration of dopaminergic neurons. In particular, Neil1-deficient male mice exhibited enhanced sensitivity to nigrostriatal degeneration after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration, and Neil1-deficient animals had higher levels of γH2AX-marked DNA damage than wild-type (WT) controls, regardless of treatment status. Moreover, MPTP-treated Neil1-/- male mice had slightly elevated expression of genes related to the nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent antioxidant pathway. Treatment with the Nrf2 activator, monomethyl fumarate, reduced PD-like behaviors and pathology in Neil1-/- male mice, suggesting that Neil1 is an important defense molecule in an oxidative cellular environment. Taken together, these results suggest that Neil1 DNA glycosylase may play an important role in limiting oxidative stress-mediated PD pathogenesis.
Subject(s)
DNA Glycosylases , Parkinson Disease , Male , Mice , Animals , Parkinson Disease/metabolism , 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine/metabolism , 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine/pharmacology , Deoxyribonuclease (Pyrimidine Dimer)/metabolism , Dopaminergic Neurons/metabolism , NF-E2-Related Factor 2/genetics , NF-E2-Related Factor 2/metabolism , Substantia Nigra/pathology , DNA Glycosylases/genetics , DNA Glycosylases/metabolism , Mice, Inbred C57BL , Disease Models, Animal , Corpus Striatum/metabolismABSTRACT
Endonuclease V (EndoV), which is widespread in bacteria, eukarya and Archaea, can cleave hypoxanthine (Hx)-containing DNA or RNA strand, and play an essential role in Hx repair. However, our understanding on archaeal EndoV's function remains incomplete. The model archaeon Sulfolobus islandicus REY15A encodes a putative EndoV protein (Sis-EndoV). Herein, we probed the biochemical characteristics of Sis-EndoV and dissected the roles of its seven conserved residues. Our biochemical data demonstrate that Sis-EndoV displays maximum cleavage efficiency at above 60 °C and at pH 7.0-9.0, and the enzyme activity is dependent on a divalent metal ion, among which Mg2+ is optimal. Importantly, we first measured the activation energy for cleaving Hx-containing ssDNA by Sis-EndoV to be 9.6 ± 0.8 kcal/mol by kinetic analyses, suggesting that chemical catalysis might be a rate-limiting step for catalysis. Mutational analyses show that residue D38 in Sis-EndoV is essential for catalysis, but has no role in DNA binding. Furthermore, we first revealed that residues Y41 and D189 in Sis-EndoV are involved in both DNA cleavage and DNA binding, but residues F77, H103, K156 and F161 are only responsible for DNA binding.
Subject(s)
Deoxyribonuclease (Pyrimidine Dimer) , Sulfolobus , Deoxyribonuclease (Pyrimidine Dimer)/chemistry , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Deoxyribonuclease (Pyrimidine Dimer)/metabolism , Sulfolobus/genetics , Sulfolobus/metabolism , DNA Repair , DNA Damage , DNAABSTRACT
BACKGROUND/AIM: Several cases of concurrent reduction of expression of polycystin 1 (PKD1) and Tuberous Sclerosis Complex 2 (TSC2) that are contiguous in chromosome 16p13 have been previously reported. This study newly addresses the concurrent reduction of expression of PKD1, TSC2 and NTHL1, which is adjacent to TSC2 and is a tumor suppressor gene. MATERIALS AND METHODS: We investigated the mRNA expression levels of PKD1, TSC2, PKD2, TSC1 and NTHL1 in blood and renal cell carcinoma (RCC) tissues in a proband with autosomal dominant polycystic kidney disease (ADPKD), tuberous sclerosis complex (TSC) and multiple pathologically diverse RCCs, including clear cell, papillary and chromophobe types. Additionally, we investigated germline variants in blood using whole exome sequencing (WES) in the proband and her four siblings. RESULTS: mRNA expression levels of PKD1, TSC2 and NTHL1 were reduced in the proband's blood and RCCs, compared with control groups. WES identified one novel variant with amino acid changes in the PKD1 exon in the three subjects with ADPKD, including the proband. Moreover, two variants in the TSC2 intron specific to the proband were also identified. CONCLUSION: In this study, we report a novel pathogenic variant in the PKD1 exon which likely led to ADPKD, and two variants in the TSC2 intron, which might have led to reduction in the expression of both TSC2 and NTHL1, consequently leading to TSC and multiple pathologically diverse RCCs.
Subject(s)
Carcinoma, Renal Cell , Deoxyribonuclease (Pyrimidine Dimer) , Kidney Neoplasms , Polycystic Kidney, Autosomal Dominant , TRPP Cation Channels , Tuberous Sclerosis Complex 2 Protein , Female , Humans , Carcinoma, Renal Cell/genetics , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Kidney Neoplasms/genetics , Polycystic Kidney, Autosomal Dominant/genetics , RNA, Messenger/genetics , Tuberous Sclerosis Complex 2 Protein/genetics , Tumor Suppressor Proteins/genetics , TRPP Cation Channels/geneticsABSTRACT
Nei Like DNA Glycosylase 1 (NEIL1) is a DNA glycosylase, which specifically processes oxidative DNA damage by initiating base excision repair. NEIL1 recognizes and removes bases, primarily oxidized pyrimidines, which have been damaged by endogenous oxidation or exogenous mutagenic agents. NEIL1 functions through a combined glycosylase/AP (apurinic/apyrimidinic)-lyase activity, whereby it cleaves the N-glycosylic bond between the DNA backbone and the damaged base via its glycosylase activity and hydrolysis of the DNA backbone through beta-delta elimination due to its AP-lyase activity. In our study we investigated our hypothesis proposing that the cancer resistance of the bowhead whale can be associated with a better DNA repair with NEIL1 being upregulated or more active. Here, we report the molecular cloning and characterization of three transcript variants of bowhead whale NEIL1 of which two were homologous to human transcripts. In addition, a novel NEIL1 transcript variant was found. A differential expression of NEIL mRNA was detected in bowhead eye, liver, kidney, and muscle. The A-to-I editing of NEIL1 mRNA was shown to be conserved in the bowhead and two adenosines in the 242Lys codon were subjected to editing. A mass spectroscopy analysis of liver and eye tissue failed to demonstrate the existence of a NEIL1 isoform originating from RNA editing. Recombinant bowhead and human NEIL1 were expressed in E. coli and assayed for enzymatic activity. Both bowhead and human recombinant NEIL1 catalyzed, with similar efficiency, the removal of a 5-hydroxyuracil lesion in a DNA bubble structure. Hence, these results do not support our hypothesis but do not refute the hypothesis either.
Subject(s)
Bowhead Whale , DNA Glycosylases , Escherichia coli Proteins , Lyases , Animals , Humans , Bowhead Whale/genetics , Bowhead Whale/metabolism , Escherichia coli/genetics , Escherichia coli/metabolism , DNA Repair , DNA Glycosylases/genetics , DNA Glycosylases/chemistry , DNA Glycosylases/metabolism , Cloning, Molecular , DNA , RNA, Messenger , Lyases/metabolism , Escherichia coli Proteins/genetics , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Deoxyribonuclease (Pyrimidine Dimer)/metabolismABSTRACT
NTHL1-associated tumor syndrome (NATS) is an autosomal recessive condition characterized by an increased risk for colorectal polyposis and colorectal cancer (CRC). Only 46 case reports have been previously published. In a retrospective review, we analyzed the clinical histories of six patients found to have NATS after genetic counseling and testing. NATS appears to be associated with an increased risk for colorectal polyposis, CRC, female breast cancer, meningiomas, and endometrial cancer. Although research is limited, prior publications have reported a multi-tumor predisposition for individuals with biallelic pathogenic or likely pathogenic variants in NTHL1. Additional data are necessary to further define the cancer risks so affected individuals can be appropriately managed.
Subject(s)
Adenomatous Polyposis Coli , Colorectal Neoplasms , Deoxyribonuclease (Pyrimidine Dimer) , Female , Humans , Adenomatous Polyposis Coli/diagnosis , Adenomatous Polyposis Coli/genetics , Colorectal Neoplasms/diagnosis , Colorectal Neoplasms/genetics , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Genetic Predisposition to Disease , Breast Neoplasms/genetics , Meningioma/genetics , Endometrial Neoplasms/geneticsABSTRACT
Human Endonuclease III (EndoIII), hNTH1, is an FeS containing enzyme which repairs oxidation damaged bases in DNA. We report here the first comparative biophysical study of full-length and an N-terminally truncated hNTH1, with a domain architecture homologous to bacterial EndoIII. Vibrational spectroscopy, spectroelectrochemistry and SAXS experiments reveal distinct properties of the two enzyme forms, and indicate that the N-terminal domain is important for DNA binding at the onset of damage recognition.
Subject(s)
DNA Repair , Deoxyribonuclease (Pyrimidine Dimer) , Iron-Sulfur Proteins , Humans , DNA , Endonucleases/genetics , Iron-Sulfur Proteins/chemistry , Scattering, Small Angle , X-Ray Diffraction , Deoxyribonuclease (Pyrimidine Dimer)/chemistryABSTRACT
Proteins that recognize specific DNA sequences or structural elements often find their cognate DNA lesions in a processive mode, in which an enzyme binds DNA non-specifically and then slides along the DNA contour by one-dimensional diffusion. Opposite to the processive mechanism is distributive search, when an enzyme binds, samples and releases DNA without significant lateral movement. Many DNA glycosylases, the repair enzymes that excise damaged bases from DNA, use processive search to find their cognate lesions. Here, using a method based on correlated cleavage of multiply damaged oligonucleotide substrates we investigate the mechanism of lesion search by three structurally related DNA glycosylases-bacterial endonuclease VIII (Nei) and its mammalian homologs NEIL1 and NEIL2. Similarly to another homologous enzyme, bacterial formamidopyrimidine-DNA glycosylase, NEIL1 seems to use a processive mode to locate its targets. However, the processivity of Nei was notably lower, and NEIL2 exhibited almost fully distributive action on all types of substrates. Although one-dimensional diffusion is often regarded as a universal search mechanism, our results indicate that even proteins sharing a common fold may be quite different in the ways they locate their targets in DNA.
Subject(s)
DNA Glycosylases , Deoxyribonuclease (Pyrimidine Dimer) , Animals , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Deoxyribonuclease (Pyrimidine Dimer)/metabolism , DNA-Formamidopyrimidine Glycosylase/genetics , DNA-Formamidopyrimidine Glycosylase/metabolism , DNA Repair , DNA Glycosylases/genetics , DNA/metabolism , Oligonucleotides , Mammals/metabolismABSTRACT
Oxidative DNA base lesions in DNA are repaired through the base excision repair (BER) pathway, which consequently plays a vital role in the maintenance of genome integrity and in suppressing mutagenesis. 8-oxoguanine DNA glycosylase (OGG1), endonuclease III-like protein 1 (NTH1), and the endonuclease VIII-like proteins 1-3 (NEIL1-3) are the key enzymes that initiate repair through the excision of the oxidized base. We have previously identified that the E3 ubiquitin ligase tripartite motif 26 (TRIM26) controls the cellular response to oxidative stress through regulating both NEIL1 and NTH1, although its potential, broader role in BER is unclear. We now show that TRIM26 is a central player in determining the response to different forms of oxidative stress. Using siRNA-mediated knockdowns, we demonstrate that the resistance of cells to X-ray radiation and hydrogen peroxide generated as a consequence of trim26 depletion can be reversed through suppression of selective DNA glycosylases. In particular, a knockdown of neil1 or ogg1 can enhance sensitivity and DNA repair rates in response to X-rays, whereas a knockdown of neil1 or neil3 can produce the same effect in response to hydrogen peroxide. Our study, therefore, highlights the importance of TRIM26 in balancing cellular DNA glycosylase levels required for an efficient BER response.
Subject(s)
DNA Glycosylases , Deoxyribonuclease (Pyrimidine Dimer) , Cell Survival/genetics , DNA/metabolism , DNA Damage , DNA Glycosylases/metabolism , DNA Repair , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Deoxyribonuclease (Pyrimidine Dimer)/metabolism , Endonucleases/metabolism , Hydrogen Peroxide/pharmacology , Oxidative Stress , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolism , Ubiquitin-Protein Ligases/metabolismABSTRACT
Deoxyinosine (dI) is a highly mutagenic lesion that preferentially pairs with deoxycytidine during replication, which may induce A to G transition and ultimately contribute to carcinogenesis. Therefore, finding the site of dI modification in DNA is of great value for both basic research and clinical applications. Herein, we developed a novel method to sequence the dI modification site in DNA, which utilizes endonuclease V (EndoV)-dependent deamination repair to specifically label the modification site with biotin-14-dATP that allows the affinity enrichment of dI-bearing DNA for sequencing. We have achieved efficient determination of the location of the modified nucleotide in dI-bearing plasmid DNA with the assistance of EndoV-dependent deamination repair. We have also successfully applied this approach to locate the dI modification sites in the mitochondrial DNA of human cells. Our method should be generally applicable for genome-wide sequencing analysis of dI modifications in living organisms.
Subject(s)
DNA , Deoxyribonuclease (Pyrimidine Dimer) , DNA/genetics , DNA Repair , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Deoxyribonuclease (Pyrimidine Dimer)/metabolism , Humans , Inosine/analogs & derivativesABSTRACT
A common approach to estimate the strength and direction of selection acting on protein coding sequences is to calculate the dN/dS ratio. The method to calculate dN/dS has been widely used by many researchers and many critical reviews have been made on its application after the proposition by Nei and Gojobori in 1986. However, the method is still evolving considering the non-uniform substitution rates and pretermination codons. In our study of SNPs in 586 genes across 156 Escherichia coli strains, synonymous polymorphism in 2-fold degenerate codons were higher in comparison to that in 4-fold degenerate codons, which could be attributed to the difference between transition (Ti) and transversion (Tv) substitution rates where the average rate of a transition is four times more than that of a transversion in general. We considered both the Ti/Tv ratio, and nonsense mutation in pretermination codons, to improve estimates of synonymous (S) and non-synonymous (NS) sites. The accuracy of estimating dN/dS has been improved by considering the Ti/Tv ratio and nonsense substitutions in pretermination codons. We showed that applying the modified approach based on Ti/Tv ratio and pretermination codons results in higher values of dN/dS in 29 common genes of equal reading-frames between E. coli and Salmonella enterica. This study emphasizes the robustness of amino acid composition with varying codon degeneracy, as well as the pretermination codons when calculating dN/dS values.
Subject(s)
Escherichia coli Proteins , Selection, Genetic , Codon , Codon, Nonsense , Deoxyribonuclease (Pyrimidine Dimer)/genetics , Escherichia coli/genetics , Evolution, Molecular , Models, GeneticABSTRACT
Base excision repair is the major pathway for the repair of oxidatively-induced DNA damage, with DNA glycosylases removing modified bases in the first step. Human NTHL1 is specific for excision of several pyrimidine- and purine-derived lesions from DNA, with loss of function NTHL1 showing a predisposition to carcinogenesis. A rare single nucleotide polymorphism of the Nthl1 gene leading to the substitution of Asp239 with Tyr within the active site, occurs within global populations. In this work, we overexpressed and purified the variant NTHL1-Asp239Tyr (NTHL1-D239Y) and determined the substrate specificity of this variant relative to wild-type NTHL1 using gas chromatography-tandem mass spectrometry with isotope-dilution, and oxidatively-damaged genomic DNA containing multiple pyrimidine- and purine-derived lesions. Wild-type NTHL1 excised seven DNA base lesions with different efficiencies, whereas NTHL1-D239Y exhibited no glycosylase activity for any of these lesions. We also measured the activities of human glycosylases OGG1 and NEIL1, and E. coli glycosylases Nth and Fpg under identical experimental conditions. Different substrate specificities among these DNA glycosylases were observed. When mixed with NTHL1-D239Y, the activity of NTHL1 was not reduced, indicating no substrate binding competition. These results and the inactivity of the variant D239Y toward the major oxidatively-induced DNA lesions points to the importance of the understanding of this variant's role in carcinogenesis and the potential of individual susceptibility to cancer in individuals carrying this variant.