SEARCH · PubMed Health

Results for “DNA Repair Enzymes”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1979

Induction of the DNA repair enzyme uracil-DNA glycosylase in stimulated human lymphocytes.

The capacity of human cells to modulate the synthesis of DNA repair enzymes has been investigated by measuring the induction of the uracil-DNA glycosylase during lymphocyte stimulation. Treatment of peripheral lymphocytes with phytohemagglutinin increased glycosylase activity 10-fold. Glycosylase stimulation was coordinate with the activation of DNA synthesis and DNA polymerase activity. Two chromatographically distinct species of the glycosylase have been resolved; only one species is induced during phytohemagglutinin stimulation. The effect of actinomycin D and cycloheximide on glycosylase induction was determined. Treatment with either inhibitor at 96 hr after phytohemagglutinin addition (maximal induction) decreased glycosylase activity after an appreciable lag period. This suggested that induction of the uracil-DNA glycosylase requires transcription and translation although the enzyme may be quite stable once induced.

Cycloheximide↗

PubMed1977

DNA repair enzymes in ataxia telangiectasia and Bloom's syndrome fibroblasts.

Ataxia telangiectasia, Bloom's syndrome and normal fibroblasts were compared as to the capacity of their cellular extracts to enhance the priming activity of gamma-irradiated colicin E1 DNA for purified DNA polymerase. It was found that an ataxia strain had substantially lower, and a Bloom's syndrome strain had slightly lower capacity than a normal strain; while the activities of apurinic site specific endonuclease in these extracts were comparable.

Ataxia Telangiectasia↗

PubMed1979

DNA polymerase beta from brain neurons is a repair enzyme.

DNA polymerase beta was isolated from rat cortex neurons and characterised. Its properties were strikingly similar to those of other mammalian beta-polymerases. In adult rats, this was the major DNA polymerase occurring in neuronal nuclei, which contained no alpha-polymerase, 99.2% beta-polymerase and only 0.8% gamma-polymerase. Isolated neuronal nuclei of this developmental stage were shown to perform ultraviolet-induced repair DNA synthesis in vitro. Since beta-polymerase was virtually the exclusive DNA polymerase in these nuclei it was concluded that the beta enzyme was responsible for the observed DNA repair. This was further substantiated by demonstrating a virtually complete suppression of DNA repair in irradiated nuclei by 2',3'-dideoxyribosylthymine 5'-triphosphate (d2TTP), a potent beta-polymerase inhibitor. However, the presence of minute amounts of gamma-polymerase in neuronal nuclei and its susceptibility to d2TTP did not allow one to rule out an ancillary role of DNA polymerase gamma in DNA repair. In view of the similarity of the neuronal DNA polymerase beta with all other mammalian beta-polymerases it may be speculated that the ability to perform repair DNA synthesis is not unique to the neuronal enzyme but is a general function of all beta-polymerases.

Animals↗

PubMed2022

Preparation of Nucleosome Core Particles Complexed with DNA Repair Factors for Cryo-Electron Microscopy Structural Determination.

DNA repair in the context of chromatin is poorly understood. Biochemical studies using nucleosome core particles, the fundamental repeating unit of chromatin, show most DNA repair enzymes remove DNA damage at reduced rates as compared to free DNA. The molecular details on how base excision repair (BER) enzymes recognize and remove DNA damage in nucleosomes have not been elucidated. However, biochemical BER data of nucleosomal substrates suggest the nucleosome presents different structural barriers dependent on the location of the DNA lesion and the enzyme. This indicates the mechanisms employed by these enzymes to remove DNA damage in free DNA may be different than those employed in nucleosomes. Given that the majority of genomic DNA is assembled into nucleosomes, structural information of these complexes is needed. To date, the scientific community lacks detailed protocols to perform technically feasible structural studies of these complexes. Here, we provide two methods to prepare a complex of two genetically fused BER enzymes (Polymerase β and AP Endonuclease1) bound to a single-nucleotide gap near the entry-exit of the nucleosome for cryo-electron microscopy (cryo-EM) structural determination. Both methods of sample preparation are compatible for vitrifying quality grids via plunge freezing. This protocol can be used as a starting point to prepare other nucleosomal complexes with different BER factors, pioneer transcription factors, and chromatin-modifying enzymes.

Chromatin↗

PubMed1977

Regulation of ribonucleoside diphosphate reductase synthesis in Escherichia coli: increased enzyme synthesis as a result of inhibition of deoxyribonucleic acid synthesis.

Inhibition of deoxyribonucleic acid (DNA) synthesis in Escherichia coli by chemical inhibitors or by shifting cultures of temperature-sensitive elongation (dnaE and dnaB) or initiation (dnaA) mutants to nonpermissive conditions led to greatly increased synthesis of the enzyme ribonucleoside diphosphate reductase, which catalyzes the first reaction unique to the pathway leading to DNA replication. In contrast to the Gudas and Pardee proposed model for control of the synthesis of DNA repair enzymes, in which both DNA inhibition and DNA degradation are involved, DNA synthesis inhibition in recA, recB, recC, or lex strains results in increased synthesis of ribonucleotide reductase, which suggests that DNA degradation is not required. We propose that inhibition of DNA synthesis causes a cell to accumulate an unknown compound that stimulates the initiation of a new round of DNA replication, and that this same signal is used to induce ribonucleotide reductase synthesis.

Bacterial Proteins↗

PubMed2025

Circadian variation in MGMT promoter methylation and expression predicts sensitivity to temozolomide in glioblastoma.

PURPOSE: Recent studies show that glioblastoma (GBM) is more sensitive to temozolomide (TMZ) in the morning. In cells, inhibiting O6-Methylguanine-DNA-Methyltransferase (MGMT) abolished time-dependent TMZ efficacy, suggesting that circadian regulation of this DNA repair enzyme underlies daily TMZ sensitivity. Here, we tested the hypotheses that MGMT promoter methylation and protein abundance vary with time-of-day in GBM, resulting in daily rhythms in TMZ efficacy. METHODS: We assessed daily rhythms in MGMT promoter methylation in GBM in vitro and retrospectively analyzed MGMT methylation status in human GBM biopsies collected at different times of day. Next, we measured MGMT and BMAL1 protein abundances in GBM cells collected at four-hour intervals. To understand the therapeutic implications of circadian variations in MGMT, we incorporated its daily rhythms into an in vitro mathematical model capturing interactions between MGMT, TMZ, and GBM DNA. RESULTS: We found daily rhythms in MGMT promoter methylation and protein levels in GBM in vitro, and in patient biopsies peaking at midday. Further, MGMT protein levels peaked at CT4, corresponding to the time of maximal TMZ efficacy in vitro. When we incorporated cell-intrinsic circadian rhythms in MGMT protein into a mathematical model for GBM chemotherapy, we found that dosing when daily MGMT levels peaked and began to decline produced maximum DNA damage. CONCLUSION: Our findings suggest that the likelihood of diagnosis of MGMT promoter methylation may vary with time of biopsy in GBM. Furthermore, theoretical modeling predicts that efforts to deliver TMZ after the daily peak of MGMT activity, with exact time being dose-dependent, may significantly enhance its therapeutic efficacy.

Humans↗

PubMed1978

Environmental carcinogenesis: an integrative model.

An integrative theory is proposed in which environmental carcinogenesis is viewed as a process by which the genetic control of cell division and differentiation is altered by carcinogens. In this theory, carcinogens include physical, chemical, and viral "mutagens," as well as chemical and viral gene modulators. Existing explanations of carcinogenesis can be considered either as somatic mutation theories or as epigenetic theories. Evidence seems to support the hypothesis that both mutations and epigenetic processes are components of carcinogenesis. The mutational basis of cancer is supported by the clonal nature of tumors, the mutagenicity of most carcinogens, high mutation frequencies in cells of cancer-prone human fibroblasts lacking DNA repair enzymes, the correlation of in vitro DNA damage and in vitro mutation and transformation frequencies with in vivo tumorigenesis, age-related incidences of various hereditary tumors, and the correlation between photoreactivation of DNA damage and the biological amelioration of UV-induced neoplasms. Since both mutagens and gene modulators can be carcinogenic it may be that carcinogens affect genes which control cell division. An integration of the mutation and epigenetic theories of cancer with the "two-stage" theory and Comings's general theory of carcinogenesis is proposed. This integrative theory postulates that carcinogens can affect regulatory genes which control a series of "transforming genes." A general hypothesis is advanced that involves a common mechanism of somatic mutagenesis via error-prone repair of DNA damage which links carcinogenesis, teratogenesis, atherosclerosis and aging. Various concepts are presented to provide a framework for evaluating the scientific, medical, and social implications of cancer.

Aging↗

PubMed2026

Vitamin D Supplementation Modulates Base Excision Repair (BER) Machinery in Systemic Sclerosis: A Prospective Longitudinal Study.

Systemic sclerosis (SSc) is a chronic, autoimmune, fibrotic disorder involving immune dysregulation, vascular abnormalities and progressive fibrosis. Although oxidative stress and defective DNA repair have been implicated in its pathogenesis, the impact of vitamin D on DNA repair pathways remains unclear. This study aimed to investigate the expression of DNA repair enzymes in SSc, explore their relationship with vitamin D status and assess the effects of vitamin D supplementation on the transcriptional expression of these enzymes. Peripheral blood samples were collected from 52 female patients with SSc and 31 age-matched healthy controls (HCs). Gene expression levels of base excision repair (BER) enzymes (APE1 and OGG1) and nucleotide excision repair (NER) enzymes (XPA and XPC) were analyzed. Serum vitamin D levels were measured and correlated with disease activity scores. In a prospective arm of the study, patients received six months of vitamin D supplementation and their DNA repair capacity was evaluated pre- and post-intervention. Baseline expression of APE1 and OGG1 was significantly lower in SSc patients than in HCs, whereas expression of the NER genes remained unchanged, indicating selective impairment of the BER pathway. Vitamin D deficiency was prevalent in SSc and inversely correlated with disease severity. Supplementation significantly increased serum vitamin D levels and up-regulated APE1 and OGG1 expression; while NER genes remained unaffected. These findings are consistent with evidence of elevated oxidative DNA lesions in SSc and support a mechanistic link between BER activity and the repair of oxidative DNA damage. SSc patients exhibit reduced transcription of BER-specific enzymes associated with vitamin D deficiency andrestoration of vitamin D levels partially rescues BER enzyme expression. These findingshighlight a potentially modifiable axis linking micronutrient status, genomic stability and disease activity and provide a rationale for investigating vitamin D optimization as an adjunctive strategy to enhance DNA repair and potentially attenuate inflammatory and fibrotic processes in SSc.

Humans↗

PubMed1975

Sister chromatid exchange in xeroderma pigmentosum cells that are defective in DNA excision repair or post-replication repair.

The formation of sister chromatid exchanges has been postulated to depend upon the action of DNA repair enzymes. Our experiments with various human cell lines show that the yield of sister chromatid exchanges is within normal limits in both excision-repair-defective and post-replication-repair-defective cells from the autosomal recessive disease, xeroderma pigmentosum. These results indicate that hypotheses invoking known DNA repair processes to acconnt for the recombination of sister chromatids are inadequate and that the exact enzymatic processes are as yet unknown.

Cell Line↗

PubMed2024

The Ercc1-/Δ mouse model of XFE progeroid syndrome undergoes accelerated retinal degeneration.

Age-related macular degeneration (AMD) is a major cause of vision loss in older adults. AMD is caused by degeneration in the macula of the retina. The retina is the highest oxygen consuming tissue in our body and is prone to oxidative damage. DNA damage is one hallmark of aging implicated in loss of organ function. Genome instability has been associated with several disorders that result in premature vision loss. We hypothesized that endogenous DNA damage plays a causal role in age-related retinal changes. To address this, we used a genetic model of systemic depletion of expression of the DNA repair enzyme ERCC1-XPF. The neural retina and retinal pigment epithelium (RPE) from Ercc1-/Δ mice, which models a human progeroid syndrome, were compared to age-matched wild-type (WT) and old WT mice. By 3-months-of age, Ercc1-/Δ mice presented abnormal optokinetic and electroretinogram responses consistent with photoreceptor dysfunction and visual impairment. Ercc1-/Δ mice shared many ocular characteristics with old WT mice including morphological changes, elevated DNA damage markers (γ-H2AX and 53BP1), and increased cellular senescence in the neural retinal and RPE, as well as pathological angiogenesis. The RPE is essential for the metabolic health of photoreceptors. The RPE from Ercc1-/Δ mice displayed mitochondrial dysfunction causing a compensatory glycolytic shift, a characteristic feature of aging RPE. Hence, our study suggests spontaneous endogenous DNA damage promotes the hallmarks of age-related retinal degeneration.

Animals↗

PubMed1979

Comparison of aflatoxin B1 and aflatoxin G1 binding to cellular macromolecules in vitro, in vivo and after peracid oxidation; characterisation of the major nucleic acid adducts.

A comparison between [14C]aflatoxin B1 (AFB1) and [14C]aflatoxin G1 (AFG1) binding to rat liver and kidney cellular macromolecules has shown AFG1-DNA and-ribosomal RNA binding to be lower in both organs. For both mycotoxins more was bound to nucleic acids than to protein. Two hours after intraperitoneal injection (60 microgram/100 g) of [14C] AFB1, 40 ng, 151 ng/mg. Loss of radioactivity bound to liver DNA for both [14C]AFB1 and protein respectively and for [14C]AFG1 the respective figures were 10, 7 and 1 ng/mg. Loss of liver bound radioactivity to DNA for both [14C]AFG1 and [14C]AFG1 appeared to be biphasic indicating that an enzymic DNA repair process may be operating. In vitro binding studies also showed less AFG1 was bound to exogenous DNA after microsomal activation than AFB1. This difference was not a result of differences in the chemical reactivity of the "ultimate" electrophilic species, the respective expoxides, since chemical activation studies using 3-chloroperbenzoic acid showed similar amounts of AFG1 and AFB1 to be converted to the epoxides and to bind to DNA. Studies on the distribution coefficients of the two mycotoxins showed AFB1 to be more lipophilic than AFG1 and this may be an important factor in determining the weaker carcinogenicity of the latter compound. Characterisation of the major AFG1-DNA adduct formed in vitro, in vivo and after peracid oxidation showed it to have the structure trans-9,10-dihydro-9-(7-guanyl)-10-hydroxy-aflatoxin G1. This adduct is similar to that obtained from AFB1 by activation in vivo, in vitro and after peracid oxidation.

Aflatoxins↗

PubMed2026

Suppression of transcription-replication conflicts by sequence-coordinated actions of TRDMT1 and MutLα.

TRDMT1 is an RNA methyltransferase that catalyzes 5-methylcytosine (m5C) formation in R-loops to promote transcription-coupled homologous recombination (TC-HR). Although TRDMT1 inhibition selectively kills BRCA1-deficient cancer cells, broader cancer dependencies on TRDMT1 remain unclear. Here, a TRDMT1 inhibitor (TRDMT1i) sensitivity screen across a large panel of cancer cell lines identifies loss of MLH1 or PMS2, two components of the MutLα mismatch repair (MMR) complex frequently inactivated in tumors, as key determinants of TRDMT1 dependency. In contrast, MutLβ and MutSα/β are dispensable for TRDMT1i resistance, revealing a unique MMR-independent function of MutLα. Mechanistically, TRDMT1 and MutLα independently recognize DNA-RNA hybrids and cooperatively suppress co-transcriptional R-loops genome-wide in undamaged cells, with m5C directing pathway choice. Furthermore, MutLα suppresses R-loops through its ATPase and endonuclease activities and through recruitment of EXO1. Combined loss of TRDMT1 and MLH1 causes extensive R-loop accumulation and transcription replication conflicts (TRCs), impairing replication fork progression, inducing DNA damage, and driving apoptosis-mediated synthetic lethality. Importantly, TRDMT1i suppresses growth of MLH1-deficient tumors by inducing TRCs in vivo, suggesting a potential therapeutic strategy for targeting MutLα-deficient tumors. These studies not only expand our understanding of cancer dependency on TRDMT1, but also identify a promising strategy to exploit TRCs in cancer therapy.

Humans↗

PubMed2026

Biochemical, structural and mutational landscapes of base excision repair enzymes and cancer: from atomic resolution to tumor signatures.

PURPOSE: Base excision repair (BER) is the predominant pathway for repairing non‑bulky oxidized and alkylated DNA base lesions, and its fidelity depends on the coordinated action of lesion‑specific DNA glycosylases and downstream repair enzymes. This review aims to summarize recent structural, biochemical, and genomic insights into three base excision repair enzymes, MUTYH DNA glycosylase, NTHL1 DNA glycosylase, and DNA polymerase β. CONCLUSION: This review outlines how MUTYH, NTHL1 and DNA polymerase β protect the genome from mutagenesis, highlights major germline variants associated with disease, and synthesizes the current knowledge on the characteristic single base substitution (SBS) mutational signatures that occur when these repair enzymes are dysfunctional.

Base excision repair↗

PubMed1977

Simple isolation method and assay for T4 DNA ligase and characterization of the purified enzyme.

A method for the isolation of T4-amber-N82-induced DNA ligase is described which results in a nearly homogeneous enzyme preparation after two column chromatographic steps. The enzyme is detected during the purification by its ability to form a stable acid-precipitable enzyme-adenylate complex. Some properties of the assay, such as the effect of salt, temperature and incubation time, are presented. The isolated enzyme and its adenylate complex are characterized by acrylamide gel electrophoresis under native and denaturing conditions, as well as by isoelectric focusing. The purified enzyme exhibits a molecular weight of approximatel 60000. Isoelectric focusing yields at least 5 protein components, which are able to form an enzyme-adenylate complex. The main activity possesses a p1 of 6. The enzyme preparation is capable of repairing T5+ DNA known to contain about 4 or 5 single-strand breaks, to circularize lambda DNA and to join Hind111 and EcoR1 fragments.

Coliphages↗

PubMed2026

An IRAK1-snRNA axis activates ATM to promote accurate repair within transcriptionally active chromatin.

Genomic integrity in transcriptionally active regions is pivotal for suppressing oncogenic mutations, yet the mechanisms that govern precise homologous recombination (HR) repair within these regions remain elusive. Here, we report that the IRAK1-spliceosome axis operates with small nuclear RNA (snRNA) as a central hub, potently promoting accurate repair at DNA double-strand break (DSB) sites within active chromatin in human cancer cells. Mechanistically, IRAK1 phosphorylates spliceosomal serine/arginine (SR)-rich proteins to recruit snRNA to DSBs, inducing robust condensation of the MRE11-RAD50-NBS1 (MRN) complex near transcriptionally active regions to create an ATM activation platform. Collectively, our findings define a prevalent mechanism governing region-specific precise repair in transcriptionally active domains, where snRNA acts as a "transcription repair bridge" to link transcriptional processes to HR repair and ultimately preserves genomic stability. Inhibiting IRAK1 axis impairs HR repair in transcriptionally active regions, causing a marked increase in mutation rates specific to these regions and cancer-cell chemosensitivity.

Humans↗

PubMed2026

Yeast Rad55-Rad57-SHU paralog complex dynamically promotes Rad51 filament formation.

Homologous recombination (HR) is an important DNA repair pathway that safeguards genome integrity. During HR, the Rad51 nucleoprotein filaments catalyze strand invasion into a homologous duplex DNA. Filament formation requires a conserved family of Rad51 paralogs that act as tumor suppressors in humans. By capturing six distinct states using cryo-electron microscopy, we reveal that the Saccharomyces cerevisiae Rad51 paralog complex, composed of the Rad55-Rad57 heterodimer and the SHU (Psy3-Csm2-Shu1-Shu2) complex, selectively brings Rad51 to single-stranded DNA to seed filament formation. Rad51 itself is a transient yet integral component of this machinery which binds along the Rad57 subunit to complete a high-affinity DNA-binding site. We also uncover a dual-nucleotide regulatory mechanism: a structural ADP molecule stabilizes the complex, while a second, catalytic ATPase site at the Rad57-Rad51 interface promotes the release of the paralog complex. These structural and mechanistic features provide a blueprint for understanding the function of Rad51 paralogs across eukaryotes.

Saccharomyces cerevisiae Proteins↗

PubMed1975

Studies on DNA repair in Bacillus subtilis. II. Partial purification and mode of action of an enzyme enhancing the priming activity of gamma-irradiated DNA.

A cellular factor which makes T7 DNA irradiated with gamma-rays a better primer for Micrococcus DNA polymerase was partially purified by DEAE and phosphocellulose column chromatography and named "primer activating enzyme". Sucrose density gradient sedimentation analysis was carried out to examine actions of one major active fraction that appeared by phosphocellulose chromatography. It was shown that this factor introduced new nicks in T7 DNA in addition to those introduced directly by gamma-ray irradiation. This enzyme fraction also had an endonucleolytic activity towards DNA containing apurinic sites induced by heat treatment and had capacity to enhance the priming activity of heat- or methyl methansulfonate-treated DNA but affected very little that of ultraviolet-irradiated DNA. This enzyme had no effect on T7 DNA when it was not treated with the DNA-damaging agents. From these results we concluded that this enzyme may be analogous to the endonuclease II or apurinic site-specific enconuclease of Escherichia coli.

Bacillus subtilis↗

PubMed2024

The ARK2N-CK2 complex initiates transcription-coupled repair through enhancing the interaction of CSB with lesion-stalled RNAPII.

Transcription is extremely important for cellular processes but can be hindered by RNA polymerase II (RNAPII) pausing and stalling. Cockayne syndrome protein B (CSB) promotes the progression of paused RNAPII or initiates transcription-coupled nucleotide excision repair (TC-NER) to remove stalled RNAPII. However, the specific mechanism by which CSB initiates TC-NER upon damage remains unclear. In this study, we identified the indispensable role of the ARK2N-CK2 complex in the CSB-mediated initiation of TC-NER. The ARK2N-CK2 complex is recruited to damage sites through CSB and then phosphorylates CSB. Phosphorylation of CSB enhances its binding to stalled RNAPII, prolonging the association of CSB with chromatin and promoting CSA-mediated ubiquitination of stalled RNAPII. Consistent with this finding, Ark2n-/- mice exhibit a phenotype resembling Cockayne syndrome. These findings shed light on the pivotal role of the ARK2N-CK2 complex in governing the fate of RNAPII through CSB, bridging a critical gap necessary for initiating TC-NER.

DNA Repair Enzymes↗