Small-molecule inhibitor of OGG1 suppresses proinflammatory gene expression and inflammation

Unprocessed genomic uracil as a source of DNA replication stress in cancer cells

Alterations of bases in DNA constitute a major source of genomic instability. It is believed that base alterations trigger base excision repair (BER), generating DNA repair intermediates interfering with DNA replication. Here, we show that genomic uracil, a common type of base alteration, induces DNA replication stress (RS) without being processed by BER. In the absence of uracil DNA glycosylase (UNG), genomic uracil accumulates to high levels, DNA replication forks slow down, and PrimPol-mediated repriming is enhanced, generating single-stranded gaps in nascent DNA. ATR inhibition in UNG-deficient cells blocks the repair of uracil-induced gaps, increasing replication fork collapse and cell death. Notably, a subset of cancer cells upregulates UNG2 to suppress genomic uracil and limit RS, and these cancer cells are hypersensitive to co-treatment with ATR inhibitors and drugs increasing genomic uracil. These results reveal unprocessed genomic uracil as an unexpected source of RS and a targetable vulnerability of cancer cells.

BER genes expression in oral and pre-oral cancer: Combinatorial approach to propose potential biomarker

OBJECTIVE

DNA repair genes and their variants have been found to alter the risk of oral cancer.

METHOD

The level of expression of XRCC3, NBS1, and OGG1 genes among 20 cases of oral cancer, 6 pre-oral cancer, and 50 healthy control subjects was measured with RT-PCR. All the subjects were also genotyped for XRCC3 rs861539 C>T, NBS1 rs1805794 C>G, and OGG1 rs1052133 C>G polymorphisms by the PCR-RFLP method; their genotypes were correlated with their level of expression. Further, a localized fold structure analysis of the mRNA sequence surrounding the studied SNPs was performed with RNAfold.

RESULTS

Results showed increased expression of XRCC3, NBS1, and OGG1 transcripts among oral cancer (4.49 fold, 3.45 fold, and 3.27 fold) as well as pre-oral cancer (3.04 fold, 5.32 fold, and 1.74 fold) as compared to control subjects. The transcript level of OGG1 was found to be significantly increased (6.68 fold, p-value 0.009) with the GG genotype compared to the CC genotype. The C>T polymorphism of XRCC3 and the C>G polymorphism of OGG1 result in an apparent change in its mRNA secondary structure. Folding energy with the C allele for XRCC3 C>T polymorphism was lower than that of the T allele (MFE C vs T: -50.20 kcal/mol vs -48.70 kcal/mol). In the case of OGG1 C>G polymorphism MFE for the C allele was higher (-23.30 kcal/mole) than with the G allele (-24.80 kcal/mol).

CONCLUSION

Our results showed elevated levels of XRCC3, NBS1, and OGG1 both in oral cancer and pre-oral cancer conditions, which indicates their role as prospective biomarkers of oral cancer and pre-cancerous lesions. SNPs in these genes alter their level of expression, possibly by altering the secondary structure of their transcript. However, due to the small sample size our study can only provide a suggestive conclusion and warned future study with large sample size to verify our findings.

The role of DNA and RNA guanosine oxidation in cardiovascular diseases

Cardiovascular diseases (CVD) persist as a prominent cause of mortality worldwide, with oxidative stress constituting a pivotal contributory element. The oxidative modification of guanosine, specifically 8-oxoguanine, has emerged as a crucial biomarker for oxidative stress, providing novel insights into the molecular underpinnings of CVD. 8-Oxoguanine can be directly generated at the DNA (8-oxo-dG) and RNA (8-oxo-G) levels, as well as at the free nucleotide level (8-oxo-dGTP or 8-oxo-GTP), which are produced and can be integrated through DNA replication or RNA transcription. When exposed to oxidative stress, guanine is more readily produced in RNA than in DNA. A burgeoning body of research surrounds 8-oxoguanine, exhibits its accumulation playing a pivotal role in the development of CVD. Therapeutic approaches targeting oxidative 8-Oxoguanine damage to DNA and RNA, encompassing the modulation of repair enzymes and the development of small molecule inhibitors, are anticipated to enhance CVD management. In conclusion, we explore the noteworthy elevation of 8-oxoguanine levels in patients with various cardiac conditions and deliberate upon the formation and regulation of 8-oxo-dG and 8-oxo-G under oxidative stress, as well as their function in CVD.

The potential for OGG1 inhibition to be a therapeutic strategy for pulmonary diseases

INTRODUCTION

Pulmonary diseases impose a daunting burden on healthcare systems and societies. Current treatment approaches primarily address symptoms, underscoring the urgency for the development of innovative pharmaceutical solutions. A noteworthy focus lies in targeting enzymes recognizing oxidatively modified DNA bases within gene regulatory elements, given their pivotal role in governing gene expression.

AREAS COVERED

This review delves into the intricate interplay between the substrate-specific binding of 8-oxoguanine DNA glycosylase 1 (OGG1) and epigenetic regulation, with a focal point on elucidating the molecular underpinnings and their biological implications. The absence of OGG1 distinctly attenuates the binding of transcription factors to cis elements, thereby modulating pro-inflammatory or pro-fibrotic transcriptional activity. Through a synergy of experimental insights gained from cell culture studies and murine models, utilizing prototype OGG1 inhibitors (O8, TH5487, and SU0268), a promising panorama emerges. These investigations underscore the absence of cytotoxicity and the establishment of a favorable tolerance profile for these OGG1 inhibitors.

EXPERT OPINION

Thus, the strategic targeting of the active site pocket of OGG1 through the application of small molecules introduces an innovative trajectory for advancing redox medicine. This approach holds particular significance in the context of pulmonary diseases, offering a refined avenue for their management.

Cellular Repair of Synthetic Analogs of Oxidative DNA Damage Reveals a Key Structure-Activity Relationship of the Cancer-Associated MUTYH DNA Repair Glycosylase

The base excision repair glycosylase MUTYH prevents mutations associated with the oxidatively damaged base, 8-oxo-7,8-dihydroguanine (OG), by removing undamaged misincorporated adenines from OG:A mispairs. Defects in OG:A repair in individuals with inherited MUTYH variants are correlated with the colorectal cancer predisposition syndrome known as MUTYH-associated polyposis (MAP). Herein, we reveal key structural features of OG required for efficient repair by human MUTYH using structure-activity relationships (SAR). We developed a GFP-based plasmid reporter assay to define SAR with synthetically generated OG analogs in human cell lines. Cellular repair results were compared with kinetic parameters measured by adenine glycosylase assays in vitro. Our results show substrates lacking the 2-amino group of OG, such as 8OI:A (8OI = 8-oxoinosine), are not repaired in cells, despite being excellent substrates in in vitro adenine glycosylase assays, new evidence that the search and detection steps are critical factors in cellular MUTYH repair functionality. Surprisingly, modification of the O8/N7H of OG, which is the distinguishing feature of OG relative to G, was tolerated in both MUTYH-mediated cellular repair and in vitro adenine glycosylase activity. The lack of sensitivity to alterations at the O8/N7H in the SAR of MUTYH substrates is distinct from previous work with bacterial MutY, indicating that the human enzyme is much less stringent in its lesion verification. Our results imply that the human protein relies almost exclusively on detection of the unique major groove position of the 2-amino group of OG within OGsyn:Aanti mispairs to select contextually incorrect adenines for excision and thereby thwart mutagenesis. These results predict that MUTYH variants that exhibit deficiencies in OG:A detection will be severely compromised in a cellular setting. Moreover, the reliance of MUTYH on the interaction with the OG 2-amino group suggests that disrupting this interaction with small molecules may provide a strategy to develop potent and selective MUTYH inhibitors.

Leveraging CRISPR/Cas12 signal amplifier to sensitive detection of apurinic/apyrimidinic endonuclease 1 and high-throughput inhibitor screening

As an essential protein in DNA repair, apurinic/apyrimidinic endonuclease 1 (APE1) plays multiple critical functions in maintaining homeostasis, making it a significant biomarker and therapeutic target for many disorders. Here, we describe a simple method to detect APE1 based on the Releasing-Extension-Signal amplification Test (REST) strategy that leverages the dsDNA as the activator to fully unlock the trans-cleavage activity of CRISPR/Cas12a. This assay provides a rapid and specific APE1 detection with a detection limit down to 1.05 × 10-5 U/mL. We also combined this method with an automated pipetting platform and a microplate reader for high-throughput screening of potential inhibitors of APE1. Besides, by changing the modification on the probe, the REST strategy was easily repurposed to detect various DNA glycosylases. Taken together, the simplicity and robustness of the method offer a new choice for APE1 detection and inhibitor screening, showing great potential in practical use. Furthermore, the REST strategy devised in this study provides a new example of applying CRISPR/Cas12a signal amplifier to non-nucleic acid biosensing and inhibitor screening, which broadens the CRISPR-Dx toolbox.

Targeting OGG1 and PARG radiosensitises head and neck cancer cells to high-LET protons through complex DNA damage persistence

Complex DNA damage (CDD), containing two or more DNA lesions within one or two DNA helical turns, is a signature of ionising radiation (IR) and contributes significantly to the therapeutic effect through cell killing. The levels and complexity of CDD increases with linear energy transfer (LET), however, the specific cellular response to this type of DNA damage and the critical proteins essential for repair of CDD is currently unclear. We performed an siRNA screen of ~240 DNA damage response proteins to identify those specifically involved in controlling cell survival in response to high-LET protons at the Bragg peak, compared to low-LET entrance dose protons which differ in the amount of CDD produced. From this, we subsequently validated that depletion of 8-oxoguanine DNA glycosylase (OGG1) and poly(ADP-ribose) glycohydrolase (PARG) in HeLa and head and neck cancer cells leads to significantly increased cellular radiosensitivity specifically following high-LET protons, whilst no effect was observed after low-LET protons and X-rays. We subsequently confirmed that OGG1 and PARG are both required for efficient CDD repair post-irradiation with high-LET protons. Importantly, these results were also recapitulated using specific inhibitors for OGG1 (TH5487) and PARG (PDD00017273). Our results suggest OGG1 and PARG play a fundamental role in the cellular response to CDD and indicate that targeting these enzymes could represent a promising therapeutic strategy for the treatment of head and neck cancers following high-LET radiation.

Label-free fluorescence detection of human 8-oxoguanine DNA glycosylase activity amplified by target-induced rolling circle amplification

BACKGROUND

Human 8-oxoG DNA glycosylase 1 (hOGG1) is one of the important members of DNA glycosylase for Base excision repair (BER), the abnormal activity of which can lead to the failure of BER and the appearance of various diseases, such as breast cancer, bladder cancer, Parkinson's disease and lung cancer. Therefore, it is important to detect the activity of hOGG1. However, traditional detection methods suffer from time consuming, complicated operation, high false positive results and low sensitivity. Thus, it remains a challenge to develop simple and sensitive hOGG1 analysis strategies to facilitate early diagnosis and treatment of the relative disease.

RESULTS

A target-induced rolling circle amplification (TIRCA) strategy for label-free fluorescence detection of hOGG1 activity was proposed with high sensitivity and specificity. The TIRCA strategy was constructed by a hairpin probe (HP) containing 8-oxoG site and a primer probe (PP). In the presence of hOGG1, the HP transformed into dumbbell DNA probe (DDP) after the 8-oxoG site of which was removed. Then the DDP formed closed circular dumbbell probe (CCDP) by ligase. CCDP could be used as amplification template of RCA to trigger RCA. The RCA products containing repeated G4 sequences could combine with ThT to produce enhanced fluorescence, achieving label-free fluorescence sensing of hOGG1. Given the high amplification efficiency of RCA and the high fluorescence quantum yield of the G4/ThT, the proposed TIRCA achieved highly sensitive measurement of hOGG1 activity with a detection limit of 0.00143 U/mL. The TIRCA strategy also exhibited excellent specificity for hOGG1 analysis over other interference enzymes.

SIGNIFICANCE

This novel TIRCA strategy demonstrates high sensitivity and high specificity for the detection of hOGG1, which has also been successfully used for the screening of inhibitors and the analysis of hOGG1 in real samples. We believe that this TIRCA strategy provides new insight into the use of the isothermal nucleic acid amplification as a useful tool for hOGG1 detection and will play an important role in disease early diagnosis and treatment.

Investigation of APE1 and OGG1 expression in chronic hemodialysis patients

BACKGROUND

The role of DNA repair mechanisms is of significant importance in diseases characterized by elevated oxidative DNA damage, such as chronic kidney disease. It is imperative to thoroughly understand the functions of molecules associated with DNA repair mechanisms, not only for assessing susceptibility to diseases but also for monitoring disease progression. In this research, we investigated the APE1 and OGG1 gene expression levels, both of which are involved in the base excision repair (BER) mechanism in chronic hemodialysis patients with malignancy (HPM; n = 8) and without malignancy (HP; n = 36) in pre- and post-dialysis period and 37 healty persons. We also assessed how these values correlate with the clinical profiles of the patients.

METHODS AND RESULTS

We conducted gene expression analysis using real-time polymerase chain reaction (qRT-PCR). No significant differences in APE1 gene expression levels were observed in pre-dialysis when comparing the HP and HPM groups to the control group. The expression levels of the OGG1 gene were significantly lower in both the HP and HPM groups in pre- and post-dialysis periods compared to the control group. Dialysis procedures led to a reduction in APE1 and OGG1 gene expression levels in both HP and HPM groups.

CONCLUSIONS

The findings of our study elucidate the impact of alterations in the base excision repair (BER) mechanism, including the hemodialysis process, in end-stage renal disease (ESRD).

Repair-driven DNA tetrahedral nanomachine combined with DNAzyme for 8-oxo guanine DNA glycosylase activity assay, drug screening and intracellular imaging

8-oxo guanine DNA glycosylase (8-oxoG DNA glycosylase), a crucial DNA repair enzyme, is essential for maintaining genome integrity and preventing diseases caused by DNA oxidative damage. Imaging 8-oxoG DNA glycosylase in living cells requires a dependable technique. In this study, we designed a DNAzyme-modified DNA tetrahedral nanomachine (DTDN) powered by 8-oxoG restoration. Incorporating a molecular beacon probe (MB), the constructed platform was used for amplified in situ monitoring of 8-oxoG DNA glycosylase. Under normal conditions, duplexing with a complementary strand modified with two 8-oxoG sites inhibited the activity of DNAzyme. The restoration of DNAzyme activity by the repair of intracellular 8-oxoG DNA glycosylase on 8-oxoG bases can initiate a signal amplification reaction. This detection system can detect 8-oxoG DNA glycosylase activity linearly between 0 and 20 U mL-1, with a detection limit as low as 0.52 U mL-1. Using this method, we were able to screen 14 natural compounds and identify 6 of them as 8-oxoG DNA glycosylase inhibitors. In addition, a novel approach was utilized to assess the activity of 8-oxoG DNA glycosylase in living cells. In conclusion, this method provides a universal tool for monitoring the activity of 8-oxoG DNA glycosylase in vitro and in living cells, which holds great promise for elucidating the enzyme's functionality and facilitating drug screening endeavors.

Induction of binding sites for RecA aptamers by differentiated-competition capillary Electrophoresis-SELEX

The binding site-oriented SELEX strategy is an effective way to promote the functional evolution of aptamers. Here we report a novel aptamer screening strategy (Differentiated-competition Capillary Electrophoresis-SELEX), which enables candidate aptamers to be directionally induced to bind to different active sites of RecA. In this strategy, we introduce two competing binding factors into the "binding - dissociation" dynamic equilibrium system of RecA and ssDNA libraries. Due to the completely different binding mechanism of the competitive factor and the ssDNA library, it exerts different interference on the binding of RecA and the ssDNA library, which directed the binding site of aptamer candidates during the SELEX process. Multifunctional aptamers with high affinity and specificity were found to inhibit RecA activity by binding to different active sites. In conclusion, the SELEX method developed in our current study have identified a variety of biologically functional aptamers with relatively well-defined binding sites that regulate RecA protein activity, which has potential applications and future prospects for accurate screening of biological functional aptamers.

OGG1 promoted lung fibrosis by activating fibroblasts via interacting with Snail1

One of abundant DNA lesions induced by reactive oxygen species is 8-oxoguanine (8-oxoG), which compromises genetic instability. 8-oxoG is recognized by the DNA repair protein 8-oxoguanine DNA glycosylase-1 (OGG1) that not only participates in base excision repair but also involves in transcriptional regulation.OGG1 has an important role inIdiopathic Pulmonary Fibrosis (IPF) processing and targeting fibroblasts is a major strategy for the treatment of pulmonary fibrosis, but whether OGG1 activate fibroblast is not clear. In this study, we show that OGG1 expression level is increased at the fibroblast activation stage in mouse lungs induced by bleomycin (BLM) treatment. OGG1 promoted the expression level of fibroblast activation markers (CTGF, fibronectin, and collagen 1) in a pro-fibrotic gene transcriptional regulation pathway via interacting with Snail1, which dependent on 8-oxoG recognition. Global inhibition of OGG1 at the middle stage of lung fibrosis also relieved BLM-induced lung fibrosis in mice. Our results suggest that OGG1 is a target for inhibiting fibroblast activation and a potential therapeutic target for IPF.

Thermococcus kodakarensis TK0353 is a novel AP lyase with a new fold

Hyperthermophilic organisms thrive in extreme environments prone to high levels of DNA damage. Growth at high temperature stimulates DNA base hydrolysis resulting in apurinic/apyrimidinic (AP) sites that destabilize the genome. Organisms across all domains have evolved enzymes to recognize and repair AP sites to maintain genome stability. The hyperthermophilic archaeon Thermococcus kodakarensis encodes several enzymes to repair AP site damage including the essential AP endonuclease TK endonuclease IV. Recently, using functional genomic screening, we discovered a new family of AP lyases typified by TK0353. Here, using biochemistry, structural analysis, and genetic deletion, we have characterized the TK0353 structure and function. TK0353 lacks glycosylase activity on a variety of damaged bases and is therefore either a monofunctional AP lyase or may be a glycosylase-lyase on a yet unidentified substrate. The crystal structure of TK0353 revealed a novel fold, which does not resemble other known DNA repair enzymes. The TK0353 gene is not essential for T. kodakarensis viability presumably because of redundant base excision repair enzymes involved in AP site processing. In summary, TK0353 is a novel AP lyase unique to hyperthermophiles that provides redundant repair activity necessary for genome maintenance.

OGG1 as an Epigenetic Reader Affects NFκB: What This Means for Cancer

8-oxoguanine glycosylase 1 (OGG1), which was initially identified as the enzyme that catalyzes the first step in the DNA base excision repair pathway, is now also recognized as a modulator of gene expression. What is important for cancer is that OGG1 acts as a modulator of NFκB-driven gene expression. Specifically, oxidant stress in the cell transiently halts enzymatic activity of substrate-bound OGG1. The stalled OGG1 facilitates DNA binding of transactivators, such as NFκB to their cognate sites, enabling the expression of cytokines and chemokines, with ensuing recruitment of inflammatory cells. Recently, we highlighted chief aspects of OGG1 involvement in regulation of gene expression, which hold significance in lung cancer development. However, OGG1 has also been implicated in the molecular underpinning of acute myeloid leukemia. This review analyzes and discusses how these cells adapt through redox-modulated intricate connections, via interaction of OGG1 with NFκB, which provides malignant cells with alternative molecular pathways to transform their microenvironment, enabling adjustment, promoting cell proliferation, metastasis, and evading killing by therapeutic agents.

Small molecule inhibitor binds to NLRP3 and prevents inflammasome activation

Despite recent advances in the mechanism of oxidized DNA activating NLRP3, the molecular mechanism and consequence of oxidized DNA associating with NLRP3 remains unknown. Cytosolic NLRP3 binds oxidized DNA which has been released from the mitochondria, which subsequently triggers inflammasome activation. Human glycosylase (hOGG1) repairs oxidized DNA damage which inhibits inflammasome activation. The fold of NLRP3 pyrin domain contains amino acids and a protein fold similar to hOGG1. Amino acids that enable hOGG1 to bind and cleave oxidized DNA are conserved in NLRP3. We found NLRP3 could bind and cleave oxidized guanine within mitochondrial DNA. The binding of oxidized DNA to NLRP3 was prevented by small molecule drugs which also inhibit hOGG1. These same drugs also inhibited inflammasome activation. Elucidating this mechanism will enable design of drug memetics that treat inflammasome pathologies, illustrated herein by NLRP3 pyrin domain inhibitors which suppressed interleukin-1β (IL-1β) production in macrophages.

One-Sentence Summary

NLRP3 cleaves oxidized DNA and small molecule drug binding inhibits inflammasome activation.

8-Oxoguanine DNA glycosylase 1 selectively modulates ROS-responsive NF-κB targets through recruitment of MSK1 and phosphorylation of RelA/p65 at Ser276

Nuclear factor kappa B (NF-κB) activity is regulated by various posttranslational modifications, of which Ser276 phosphorylation of RelA/p65 is particularly impacted by reactive oxygen species (ROS). This modification is responsible for selective upregulation of a subset of NF-κB targets; however, the precise mechanism remains elusive. ROS have the ability to modify cellular molecules including DNA. One of the most common oxidation products is 8-oxo-7,8-dihydroguanine (8-oxoGua), which is repaired by the 8-oxoguanine DNA glycosylase1 (OGG1)-initiated base excision repair pathway. Recently, a new function of OGG1 has been uncovered. OGG1 binds to 8-oxoGua, facilitating the occupancy of NF-κB at promoters and enhancing transcription of pro-inflammatory cytokines and chemokines. In the present study, we demonstrated that an interaction between DNA-bound OGG1 and mitogen-and stress-activated kinase 1 is crucial for RelA/p65 Ser276 phosphorylation. ROS scavenging or OGG1 depletion/inhibition hindered the interaction between mitogen-and stress-activated kinase 1 and RelA/p65, thereby decreasing the level of phospho-Ser276 and leading to significantly lowered expression of ROS-responsive cytokine/chemokine genes, but not that of Nfkbis. Blockade of OGG1 binding to DNA also prevented promoter recruitment of RelA/p65, Pol II, and p-RNAP II in a gene-specific manner. Collectively, the data presented offer new insights into how ROS signaling dictates NF-κB phosphorylation codes and how the promoter-situated substrate-bound OGG1 is exploited by aerobic mammalian cells for timely transcriptional activation of ROS-responsive genes.

NEIL3 promoter G-quadruplex with oxidatively modified bases shows magnesium-dependent folding that stalls polymerase bypass

Oxidative stress unleashes reactive species capable of oxidizing 2'-deoxyguanosine (G) nucleotides in G-rich sequences of the genome, such as the potential G-quadruplex forming sequencing (PQS) in the NEIL3 gene promoter. Oxidative modification of G yields 8-oxo-7,8-dihydro-2'-deoxyguanosine (OG) that can be further oxidized to hydantoin products. Herein, OG was synthesized into the NEIL3 PQS that was allowed to fold to a G-quadruplex (G4) in K+ ion solutions with varying amounts of Mg2+ in the physiological range. The Mg2+ dependency in the oxidatively modified NEIL3 G4 to stall a replicative DNA polymerase was evaluated. The polymerase was found to stall at the G4 or OG, as well as continue to full-length extension with dependency on the location of the modification and the concentration of Mg2+. To provide some clarity on these findings, OG or the hydantoins were synthesized in model NEIL3 G4 folding sequences at the positions of the polymerase study. The model G4 sequences were allowed to fold in K+ ion solutions with varying levels of Mg2+ to identify how the presence of the divalent metal impacted G4 folding depending on the location of the modification. The presence of Mg2+ either caused the transition of the NEIL3 G4 folds from an antiparallel to parallel orientation of the strands or had no impact. Structural models are proposed to understand the findings using the literature as a guide. The biological significance of the results is discussed.

Base Excision Repair: Mechanisms and Impact in Biology, Disease, and Medicine

Base excision repair (BER) corrects forms of oxidative, deamination, alkylation, and abasic single-base damage that appear to have minimal effects on the helix. Since its discovery in 1974, the field has grown in several facets: mechanisms, biology and physiology, understanding deficiencies and human disease, and using BER genes as potential inhibitory targets to develop therapeutics. Within its segregation of short nucleotide (SN-) and long patch (LP-), there are currently six known global mechanisms, with emerging work in transcription- and replication-associated BER. Knockouts (KOs) of BER genes in mouse models showed that single glycosylase knockout had minimal phenotypic impact, but the effects were clearly seen in double knockouts. However, KOs of downstream enzymes showed critical impact on the health and survival of mice. BER gene deficiency contributes to cancer, inflammation, aging, and neurodegenerative disorders. Medicinal targets are being developed for single or combinatorial therapies, but only PARP and APE1 have yet to reach the clinical stage.

Spatio-temporal dynamics of the DNA glycosylase OGG1 in finding and processing 8-oxoguanine

OGG1 is the DNA glycosylase responsible for the removal of the oxidative lesion 8-oxoguanine (8-oxoG) from DNA. The recognition of this lesion by OGG1 is a complex process that involves scanning the DNA for the presence of 8-oxoG, followed by recognition and lesion removal. Structural data have shown that OGG1 evolves through different stages of conformation onto the DNA, corresponding to elementary steps of the 8-oxoG recognition and extrusion from the double helix. Single-molecule studies of OGG1 on naked DNA have shown that OGG1 slides in persistent contact with the DNA, displaying different binding states probably corresponding to the different conformation stages. However, in cells, the DNA is not naked and OGG1 has to navigate into a complex and highly crowded environment within the nucleus. To ensure rapid detection of 8-oxoG, OGG1 alternates between 3D diffusion and sliding along the DNA. This process is regulated by the local chromatin state but also by protein co-factors that could facilitate the detection of oxidized lesions. We will review here the different methods that have been used over the last years to better understand how OGG1 detects and process 8-oxoG lesions.

The roles of non-productive complexes of DNA repair proteins with DNA lesions

A multitude of different types of lesions is continuously introduced into the DNA inside our cells, and their rapid and efficient repair is fundamentally important for the maintenance of genomic stability and cellular viability. This is achieved by a number of DNA repair systems that each involve different protein factors and employ versatile strategies to target different types of DNA lesions. Intriguingly, specialized DNA repair proteins have also evolved to form non-functional complexes with their target lesions. These proteins allow the marking of innocuous lesions to render them visible for DNA repair systems and can serve to directly recruit DNA repair cascades. Moreover, they also provide links between different DNA repair mechanisms or even between DNA lesions and transcription regulation. I will focus here in particular on recent findings from single molecule analyses on the alkyltransferase-like protein ATL, which is believed to initiate nucleotide excision repair (NER) of non-native NER target lesions, and the base excision repair (BER) enzyme hOGG1, which recruits the oncogene transcription factor Myc to gene promoters under oxidative stress.

Substrate-specific binding of 8-oxoguanine DNA glycosylase 1 (OGG1) reprograms mucosal adaptations to chronic airway injury

Recent advances have uncovered the non-random distribution of 7, 8-dihydro-8-oxoguanine (8-oxoGua) induced by reactive oxygen species, which is believed to have epigenetic effects. Its cognate repair protein, 8-oxoguanine DNA glycosylase 1 (OGG1), reads oxidative substrates and participates in transcriptional initiation. When redox signaling is activated in small airway epithelial cells, the DNA repair function of OGG1 is repurposed to transmit acute inflammatory signals accompanied by cell state transitions and modification of the extracellular matrix. Epithelial-mesenchymal and epithelial-immune interactions act cooperatively to establish a local niche that instructs the mucosal immune landscape. If the transitional cell state governed by OGG1 remains responsive to inflammatory mediators instead of differentiation, the collateral damage provides positive feedback to inflammation, ascribing inflammatory remodeling to one of the drivers in chronic pathologies. In this review, we discuss the substrate-specific read through OGG1 has evolved in regulating the innate immune response, controlling adaptations of the airway to environmental and inflammatory injury, with a focus on the reader function of OGG1 in initiation and progression of epithelial to mesenchymal transitions in chronic pulmonary disease.

Epigenetic control of type III interferon expression by 8-oxoguanine and its reader 8-oxoguanine DNA glycosylase1

Interferons (IFNs) are secreted cytokines with the ability to activate expression of IFN stimulated genes that increase resistance of cells to virus infections. Activated transcription factors in conjunction with chromatin remodelers induce epigenetic changes that reprogram IFN responses. Unexpectedly, 8-oxoguanine DNA glycosylase1 (Ogg1) knockout mice show enhanced stimuli-driven IFN expression that confers increased resistance to viral and bacterial infections and allergen challenges. Here, we tested the hypothesis that the DNA repair protein OGG1 recognizes 8-oxoguanine (8-oxoGua) in promoters modulating IFN expression. We found that functional inhibition, genetic ablation, and inactivation by post-translational modification of OGG1 significantly augment IFN-λ expression in epithelial cells infected by human respiratory syncytial virus (RSV). Mechanistically, OGG1 bound to 8-oxoGua in proximity to interferon response elements, which inhibits the IRF3/IRF7 and NF-κB/RelA DNA occupancy, while promoting the suppressor NF-κB1/p50-p50 homodimer binding to the IFN-λ2/3 promoter. In a mouse model of bronchiolitis induced by RSV infection, functional ablation of OGG1 by a small molecule inhibitor (TH5487) enhances IFN-λ production, decreases immunopathology, neutrophilia, and confers antiviral protection. These findings suggest that the ROS-generated epigenetic mark 8-oxoGua via its reader OGG1 serves as a homeostatic thresholding factor in IFN-λ expression. Pharmaceutical targeting of OGG1 activity may have clinical utility in modulating antiviral response.

The DNA Damage Response and Inflammation in Cancer

Genomic stability in normal cells is crucial to avoid oncogenesis. Accordingly, multiple components of the DNA damage response (DDR) operate as bona fide tumor suppressor proteins by preserving genomic stability, eliciting the demise of cells with unrepairable DNA lesions, and engaging cell-extrinsic oncosuppression via immunosurveillance. That said, DDR sig-naling can also favor tumor progression and resistance to therapy. Indeed, DDR signaling in cancer cells has been consistently linked to the inhibition of tumor-targeting immune responses. Here, we discuss the complex interactions between the DDR and inflammation in the context of oncogenesis, tumor progression, and response to therapy.

SIGNIFICANCE

Accumulating preclinical and clinical evidence indicates that DDR is intimately connected to the emission of immunomodulatory signals by normal and malignant cells, as part of a cell-extrinsic program to preserve organismal homeostasis. DDR-driven inflammation, however, can have diametrically opposed effects on tumor-targeting immunity. Understanding the links between the DDR and inflammation in normal and malignant cells may unlock novel immunotherapeutic paradigms to treat cancer.

Mitochondrial OGG1 expression reduces age-associated neuroinflammation by regulating cytosolic mitochondrial DNA

Aging is accompanied by a decline in DNA repair efficiency, which leads to the accumulation of different types of DNA damage. Age-associated chronic inflammation and generation of reactive oxygen species exacerbate the aging process and age-related chronic disorders. These inflammatory processes establish conditions that favor accumulation of DNA base damage, especially 8-oxo-7,8 di-hydroguanine (8-oxoG), which in turn contributes to various age associated diseases. 8-oxoG is repaired by 8-oxoG glycosylase1 (OGG1) through the base excision repair (BER) pathway. OGG1 is present in both the cell nucleus and in mitochondria. Mitochondrial OGG1 has been implicated in mitochondrial DNA repair and increased mitochondrial function. Using transgenic mouse models and cell lines that have been engineered to have enhanced expression of mitochondria-targeted OGG1 (mtOGG1), we show that elevated levels of mtOGG1 in mitochondria can reverse aging-associated inflammation and improve functions. Old male mtOGG1Tg mice show decreased inflammation response, decreased TNFα levels and multiple pro-inflammatory cytokines. Moreover, we observe that male mtOGG1Tg mice show resistance to STING activation. Interestingly, female mtOGG1Tg mice did not respond to mtOGG1 overexpression. Further, HMC3 cells expressing mtOGG1 display decreased release of mtDNA into the cytoplasm after lipopolysacchride induction and regulate inflammation through the pSTING pathway. Also, increased mtOGG1 expression reduced LPS-induced loss of mitochondrial functions. These results suggest that mtOGG1 regulates age-associated inflammation by controlling release of mtDNA into the cytoplasm.

Lactobacillus sp. Facilitate the Repair of DNA Damage Caused by Bile-Induced Reactive Oxygen Species in Experimental Models of Gastroesophageal Reflux Disease

Gastroesophageal reflux disease (GERD) leads to the accumulation of bile-induced reactive oxygen species and oxidative stress in esophageal tissues, causing inflammation and DNA damage. The progression sequence from healthy esophagus to GERD and eventually cancer is associated with a microbiome shift. Lactobacillus species are commensal organisms known for their probiotic and antioxidant characteristics in the healthy esophagus. This prompted us to investigate how Lactobacilli survive in a bile-rich environment during GERD, and to identify their interaction with the bile-injured esophageal cells. To model human reflux conditions, we exposed three Lactobacillus species (L. acidophilus, L. plantarum, and L. fermentum) to bile. All species were tolerant to bile possibly enabling them to colonize the esophageal epithelium under GERD conditions. Next, we assessed the antioxidant potential of Lactobacilli and role in bile injury repair: we measured bile-induced DNA damage using the ROS marker 8-oxo guanine and COMET assay. Lactobacillus addition after bile injury accelerated repair of bile-induced DNA damage through recruitment of pH2AX/RAD51 and reduced NFκB-associated inflammation in esophageal cells. This study demonstrated anti-genotoxic and anti-inflammatory effects of Lactobacilli, making them of significant interest in the prevention of Barrett's esophagus and esophageal adenocarcinoma in patients with GERD.

Effect of 8-Hydroxyguanine DNA Glycosylase 1 on the Function of Immune Cells

Excess reactive oxygen species (ROS) can cause an imbalance between oxidation and anti-oxidation, leading to the occurrence of oxidative stress in the body. The most common product of ROS-induced base damage is 8-hydroxyguanine (8-oxoG). Failure to promptly remove 8-oxoG often causes mutations during DNA replication. 8-oxoG is cleared from cells by the 8-oxoG DNA glycosylase 1 (OGG1)-mediated oxidative damage base excision repair pathway so as to prevent cells from suffering dysfunction due to oxidative stress. Physiological immune homeostasis and, in particular, immune cell function are vulnerable to oxidative stress. Evidence suggests that inflammation, aging, cancer, and other diseases are related to an imbalance in immune homeostasis caused by oxidative stress. However, the role of the OGG1-mediated oxidative damage repair pathway in the activation and maintenance of immune cell function is unknown. This review summarizes the current understanding of the effect of OGG1 on immune cell function.

Identification of key residues of the DNA glycosylase OGG1 controlling efficient DNA sampling and recruitment to oxidized bases in living cells

The DNA-glycosylase OGG1 oversees the detection and clearance of the 7,8-dihydro-8-oxoguanine (8-oxoG), which is the most frequent form of oxidized base in the genome. This lesion is deeply buried within the double-helix and its detection requires careful inspection of the bases by OGG1 via a mechanism that remains only partially understood. By analyzing OGG1 dynamics in the nucleus of living human cells, we demonstrate that the glycosylase constantly samples the DNA by rapidly alternating between diffusion within the nucleoplasm and short transits on the DNA. This sampling process, that we find to be tightly regulated by the conserved residue G245, is crucial for the rapid recruitment of OGG1 at oxidative lesions induced by laser micro-irradiation. Furthermore, we show that residues Y203, N149 and N150, while being all involved in early stages of 8-oxoG probing by OGG1 based on previous structural data, differentially regulate the sampling of the DNA and recruitment to oxidative lesions.

Distinctive Formation of a DNA-Protein Cross-Link during the Repair of DNA Oxidative Damage: Insights into Human Disease from MD Simulations and QM/MM Calculations

Reactive oxygen species damage DNA and result in health issues. The major damage product, 8-oxo-7,8-dihydroguanine (8oG), is repaired by human adenine DNA glycosylase homologue (MUTYH). Although MUTYH misfunction is associated with a genetic disorder called MUTYH-associated polyposis (MAP) and MUTYH is a potential target for cancer drugs, the catalytic mechanism required to develop disease treatments is debated in the literature. This study uses molecular dynamics simulations and quantum mechanics/molecular mechanics techniques initiated from DNA-protein complexes that represent different stages of the repair pathway to map the catalytic mechanism of the wild-type MUTYH bacterial homologue (MutY). This multipronged computational approach characterizes a DNA-protein cross-linking mechanism that is consistent with all previous experimental data and is a distinct pathway across the broad class of monofunctional glycosylase repair enzymes. In addition to clarifying how the cross-link is formed, accommodated by the enzyme, and hydrolyzed for product release, our calculations rationalize why cross-link formation is favored over immediate glycosidic bond hydrolysis, the accepted mechanism for all other monofunctional DNA glycosylases to date. Calculations on the Y126F mutant MutY highlight critical roles for active site residues throughout the reaction, while investigation of the N146S mutant rationalizes the connection between the analogous N224S MUTYH mutation and MAP. In addition to furthering our knowledge of the chemistry associated with a devastating disorder, the structural information gained about the distinctive MutY mechanism compared to other repair enzymes represents an important step for the development of specific and potent small-molecule inhibitors as cancer therapeutics.

A ratiometric SERS aptasensor array for human DNA glycosylaseat single-cell sensitivity/resolution

Human 8-oxoguanine DNA glycosylase (hOGG1) is involved in the cellular genomic 8-oxoguanine (8-oxoG) excision repair to maintain genome stability. Accurate detection of hOGG1 activity is essential for clinical diagnosis and treatment of various human pathology. Yet, the quantitative detection of hOGG1 remains challenging for existing methods due to poor reproducibility and portability. Herein, we propose a ratiometric array-based SERS point-of-care testing method for hOGG1 activity. A kind of reproducible, uniform and stable plasmonic multi-microarray reaction cells was constructed by assembling AuNPs on the substrate modified by aminosilane and segmented by silica gel gasket, which greatly improved the sensitivity, portability and repeatability of SERS measurement. Based on this, the ratiometric method is further used to effectively overcome the instability of single SERS signal intensity, which allows signal rationing and provides built-in correction for environment effects. In specific, we designed two different Raman-labeled probes for the detection of hOGG1, a thiol- and Cy3-labeled aptamer as an internal standard and a Rox-labeled 8-oxoG-modified complementary aptamer as a signal probe. The ratio value between Cy3 and Rox SERS intensity is well linear with the hOGG1 activity on logarithmic scales in the range from 5 × 10^-5 to 5 × 10^-3 U/mL, and the limit of detection reaches 3.3 × 10^-5 U/mL. Moreover, this strategy can be applied for the screening of inhibitors and the monitoring of cellular hOGG1 activity fluctuation at single-cell levels, providing a flexible and adaptive tool for clinical diagnosis, biochemical processes and drug discovery.

OGG1 and MUTYH repair activities promote telomeric 8-oxoguanine induced cellular senescence

Telomeres are prone to formation of the common oxidative lesion 8-oxoguanine (8oxoG), and the acute production of 8oxoG damage at telomeres is sufficient to drive rapid cellular senescence. OGG1 and MUTYH glycosylases initiate base excision repair (BER) at 8oxoG sites to remove the lesion or prevent mutation. Here, we show OGG1 loss or inhibition, or MUTYH loss, partially rescues telomeric 8oxoG-induced senescence, and loss of both glycosylases results in a near complete rescue. Loss of these glycosylases also suppresses 8oxoG-induced telomere fragility and dysfunction, indicating that single-stranded break (SSB) intermediates arising downstream of glycosylase activity impair telomere replication. The failure to initiate BER in glycosylase-deficient cells suppresses PARylation at SSB intermediates and confers resistance to the synergistic effects of PARP inhibitors on damage-induced senescence. Our studies reveal that inefficient completion of 8oxoG BER at telomeres triggers cellular senescence via SSB intermediates which impair telomere replication and stability.

8-Oxoguanine targeted by 8-oxoguanine DNA glycosylase 1 (OGG1) is central to fibrogenic gene activation upon lung injury

Reactive oxygen species (ROS) are implicated in epithelial cell-state transition and deposition of extracellular matrix upon airway injury. Of the many cellular targets of ROS, oxidative DNA modification is a major driving signal. However, the role of oxidative DNA damage in modulation profibrotic processes has not been fully delineated. Herein, we report that oxidative DNA base lesions, 8-oxoG, complexed with 8-oxoguanine DNA glycosylase 1 (OGG1) functions as a pioneer factor, contributing to transcriptional reprogramming within airway epithelial cells. We show that TGFβ1-induced ROS increased 8-oxoG levels in open chromatin, dynamically reconfigure the chromatin state. OGG1 complexed with 8-oxoG recruits transcription factors, including phosphorylated SMAD3, to pro-fibrotic gene promoters thereby facilitating gene activation. Moreover, 8-oxoG levels are elevated in lungs of mice subjected to TGFβ1-induced injury. Pharmacologic targeting of OGG1 with the selective small molecule inhibitor of 8-oxoG binding, TH5487, abrogates fibrotic gene expression and remodeling in this model. Collectively, our study implicates that 8-oxoG substrate-specific binding by OGG1 is a central modulator of transcriptional regulation in response to tissue repair.

Characterization of a Novel Thermostable DNA Lyase Used To Prepare DNA for Next-Generation Sequencing

Recently, we constructed a hybrid thymine DNA glycosylase (hyTDG) by linking a 29-amino acid sequence from the human thymine DNA glycosylase with the catalytic domain of DNA mismatch glycosylase (MIG) from M. thermoautotrophicum, increasing the overall activity of the glycosylase. Previously, it was shown that a tyrosine to lysine (Y126K) mutation in the catalytic site of MIG could convert the glycosylase activity to a lyase activity. We made the corresponding mutation to our hyTDG to create a hyTDG-lyase (Y163K). Here, we report that the hybrid mutant has robust lyase activity, has activity over a broad temperature range, and is active under multiple buffer conditions. The hyTDG-lyase cleaves an abasic site similar to endonuclease III (Endo III). In the presence of β-mercaptoethanol (β-ME), the abasic site unsaturated aldehyde forms a β-ME adduct. The hyTDG-lyase maintains its preference for cleaving opposite G, as with the hyTDG glycosylase, and the hyTDG-lyase and hyTDG glycosylase can function in tandem to cleave T:G mismatches. The hyTDG-lyase described here should be a valuable tool in studies examining DNA damage and repair. Future studies will utilize these enzymes to quantify T:G mispairs in cells, tissues, and genomic DNA using next-generation sequencing.

Small-molecule-mediated OGG1 inhibition attenuates pulmonary inflammation and lung fibrosis in a murine lung fibrosis model

Interstitial lung diseases such as idiopathic pulmonary fibrosis (IPF) are caused by persistent micro-injuries to alveolar epithelial tissues accompanied by aberrant repair processes. IPF is currently treated with pirfenidone and nintedanib, compounds which slow the rate of disease progression but fail to target underlying pathophysiological mechanisms. The DNA repair protein 8-oxoguanine DNA glycosylase-1 (OGG1) has significant roles in the modulation of inflammation and metabolic syndromes. Currently, no pharmaceutical solutions targeting OGG1 have been utilized in the treatment of IPF. In this study we show Ogg1-targeting siRNA mitigates bleomycin-induced pulmonary fibrosis in male mice, highlighting OGG1 as a tractable target in lung fibrosis. The small molecule OGG1 inhibitor, TH5487, decreases myofibroblast transition and associated pro-fibrotic gene expressions in fibroblast cells. In addition, TH5487 decreases levels of pro-inflammatory mediators, inflammatory cell infiltration, and lung remodeling in a murine model of bleomycin-induced pulmonary fibrosis conducted in male C57BL6/J mice. OGG1 and SMAD7 interact to induce fibroblast proliferation and differentiation and display roles in fibrotic murine and IPF patient lung tissue. Taken together, these data suggest that TH5487 is a potentially clinically relevant treatment for IPF but further study in human trials is required.

OGG1 competitive inhibitors show important off-target effects by directly inhibiting efflux pumps and disturbing mitotic progression

One of the most abundant DNA lesions induced by Reactive oxygen species (ROS) is 8-oxoG, a highly mutagenic lesion that compromises genetic instability when not efficiently repaired. 8-oxoG is specifically recognized by the DNA-glycosylase OGG1 that excises the base and initiates the Base Excision Repair pathway (BER). Furthermore, OGG1 has not only a major role in DNA repair but it is also involved in transcriptional regulation. Cancer cells are particularly exposed to ROS, thus challenging their capacity to process oxidative DNA damage has been proposed as a promising therapeutic strategy for cancer treatment. Two competitive inhibitors of OGG1 (OGG1i) have been identified, TH5487 and SU0268, which bind to the OGG1 catalytic pocket preventing its fixation to the DNA. Early studies with these inhibitors show an enhanced cellular sensitivity to cytotoxic drugs and a reduction in the inflammatory response. Our study uncovers two unreported off-targets effects of these OGG1i that are independent of OGG1. In vitro and in cellulo approaches have unveiled that OGG1i TH5487 and SU0268, despite an unrelated molecular structure, are able to inhibit some members of the ABC family transporters, in particular ABC B1 (MDR1) and ABC G2 (BCRP). The inhibition of these efflux pumps by OGG1 inhibitors results in a higher intra-cellular accumulation of various fluorescent probes and drugs, and largely contributes to the enhanced cytotoxicity observed when the inhibitors are combined with cytotoxic agents. Furthermore, we found that SU0268 has an OGG1-independent anti-mitotic activity-by interfering with metaphase completion-resulting in a high cellular toxicity. These two off-target activities are observed at concentrations of OGG1i that are normally used for in vivo studies. It is thus critical to consider these previously unreported non-specific effects when interpreting studies using TH5487 and SU0268 in the context of OGG1 inhibition. Additionally, our work highlights the persistent need for new specific inhibitors of the enzymatic activity of OGG1.

OGG1 inhibition suppresses African swine fever virus replication

African swine fever virus (ASFV) is an important pathogen that causes a highly contagious and lethal disease in swine, for which neither a vaccine nor treatment is available. The DNA repair enzyme 8-oxoguanine DNA glycosylase 1 (OGG1), which excises the oxidative base lesion 8-oxo-7,8-dihydroguanine (8-oxoG), has been linked to the pathogenesis of different diseases associated with viral infections. However, the role of OGG1-base excision repair (BER) in ASFV infection has been poorly investigated. Our study aimed to characterize the alteration of host reactive oxygen species (ROS) and OGG1 and to analyse the role of OGG1 in ASFV infection. We found that ASFV infection induced high levels and dynamic changes in ROS and 8-oxoG and consistently increased the expression of OGG1. Viral yield, transcription level, and protein synthesis were reduced in ASFV-infected primary alveolar macrophages (PAMs) treated by TH5487 or SU0268 inhibiting OGG1. The expression of BER pathway associated proteins of ASFV was also suppressed in OGG1-inhibited PAMs. Furthermore, OGG1 was found to negatively regulate interferon β (IFN-β) production during ASFV infection and IFN-β could be activated by OGG1 inhibition with TH5487 and SU0268, which blocked OGG1 binding to 8-oxoG. Additionally, the interaction of OGG1 with viral MGF360-14-L protein could disturb IFN-β production to further affect ASFV replication. These results suggest that OGG1 plays the crucial role in successful viral infection and OGG1 inhibitors SU0268 or TH5487 could be used as antiviral agents for ASFV infection.

Optimization of N-Piperidinyl-Benzimidazolone Derivatives as Potent and Selective Inhibitors of 8-Oxo-Guanine DNA Glycosylase 1

8-oxo Guanine DNA Glycosylase 1 is the initiating enzyme within base excision repair and removes oxidized guanines from damaged DNA. Since unrepaired 8-oxoG could lead to G : C→T : A transversion, base removal is of utmost importance for cells to ensure genomic integrity. For cells with elevated levels of reactive oxygen species this dependency is further increased. In the past we and others have validated OGG1 as a target for inhibitors to treat cancer and inflammation. Here, we present the optimization campaign that led to the broadly used tool compound TH5487. Based on results from a small molecule screening campaign, we performed hit to lead expansion and arrived at potent and selective substituted N-piperidinyl-benzimidazolones. Using X-ray crystallography data, we describe the surprising binding mode of the most potent member of the class, TH8535. Here, the N-Piperidinyl-linker adopts a chair instead of a boat conformation which was found for weaker analogues. We further demonstrate cellular target engagement and efficacy of TH8535 against a number of cancer cell lines.

Deregulated DNA damage response network in Behcet's disease

Behcet's disease (BD) is a chronic, relapsing systemic vasculitis of unknown etiology. Since the DNA repair enzyme NEIL1 has been identified as one of the two genetic risk factors for BD by whole exome study, we examined the potential involvement of the DNA damage response (DDR) network in BD. Peripheral blood mononuclear cells from 26 patients and 26 age-/sex-matched healthy controls were studied. Endogenous DNA damage levels were increased in active BD patients compared to controls or patients in remission. In parallel, BD patients had defective nucleotide excision repair capacity. RNA-sequencing revealed reduced expression of NEIL1 that negatively correlated with DNA damage accumulation. On the other hand, expression of genes involved in senescence and senescence-associated secretory phenotype positively correlated with individual endogenous DNA damage levels. We conclude that deregulated DDR contributes to the proinflammatory environment in BD.

OGG1 in the Kidney: Beyond Base Excision Repair

8-Oxoguanine DNA glycosylase (OGG1) is a repair protein for 8-oxoguanine (8-oxoG) in eukaryotic atopic DNA. Through the initial base excision repair (BER) pathway, 8-oxoG is recognized and excised, and subsequently, other proteins are recruited to complete the repair. OGG1 is primarily located in the cytoplasm and can enter the nucleus and mitochondria to repair damaged DNA or to exert epigenetic regulation of gene transcription. OGG1 is involved in a wide range of physiological processes, such as DNA repair, oxidative stress, inflammation, fibrosis, and autophagy. In recent years, studies have found that OGG1 plays an important role in the progression of kidney diseases through repairing DNA, inducing inflammation, regulating autophagy and other transcriptional regulation, and governing protein interactions and functions during disease and injury. In particular, the epigenetic effects of OGG1 in kidney disease have gradually attracted widespread attention. This study reviews the structure and biological functions of OGG1 and the regulatory mechanism of OGG1 in kidney disease. In addition, the possibility of OGG1 as a potential therapeutic target in kidney disease is discussed.

Pan-Cancer Landscape of NEIL3 in Tumor Microenvironment: A Promising Predictor for Chemotherapy and Immunotherapy

With the aim of enhancing the understanding of NEIL3 in prognosis prediction and therapy administration, we conducted a pan-cancer landscape analysis on NEIL3. The mutation characteristics, survival patterns, and immune features of NEIL3 across cancers were analyzed. Western blotting, qPCR, and immunohistochemistry were conducted to validate the bioinformatics results. The correlation between NEIL3 and chemotherapeutic drugs, as well as immunotherapies, was estimated. NEIL3 was identified as an oncogene with prognostic value in predicting clinical outcomes in multiple cancers. Combined with the neoantigen, tumor mutational burden (TMB), and microsatellite instability (MSI) results, a strong relationship between NEIL3 and the TME was observed. NEIL3 was demonstrated to be closely associated with multiple immune parameters, including infiltrating immunocytes and pro-inflammatory chemokines, which was verified by experiments. More importantly, patients with a higher expression of NEIL3 were revealed to be more sensitive to chemotherapeutic regimens and immune checkpoint inhibitors in selected cancers, implying that NEIL3 may be an indicator for therapeutic administration. Our study indicated NEIL3 has a strong association with the immune microenvironment and phenotypic changes in certain types of cancers, which facilitated the improved understanding of NEIL3 across cancers and highlighted the potential for clinical application of NEIL3 in precision medical stratification.

Nuclear factor Nrf2 promotes glycosidase OGG1 expression by activating the AKT pathway to enhance leukemia cell resistance to cytarabine

Chemotherapy resistance is the dominant challenge in the treatment of acute myeloid leukemia (AML). Nuclear factor E2-related factor 2 (Nrf2) exerts a vital function in drug resistance of many tumors. Nevertheless, the potential molecular mechanism of Nrf2 regulating the base excision repair pathway that mediates AML chemotherapy resistance remains unclear. Here, in clinical samples, we found that the high expression of Nrf2 and base excision repair pathway gene encoding 8-hydroxyguanine DNA glycosidase (OGG1) was associated with AML disease progression. In vitro, Nrf2 and OGG1 were highly expressed in drug-resistant leukemia cells. Upregulation of Nrf2 in leukemia cells by lentivirus transfection could decrease the sensitivity of leukemia cells to cytarabine, whereas downregulation of Nrf2 in drug-resistant cells could enhance leukemia cell chemosensitivity. Meanwhile, we found that Nrf2 could positively regulate OGG1 expression in leukemia cells. Our chromatin immunoprecipitation assay revealed that Nrf2 could bind to the promoter of OGG1. Furthermore, the use of OGG1 inhibitor TH5487 could partially reverse the inhibitory effect of upregulated Nrf2 on leukemia cell apoptosis. In vivo, downregulation of Nrf2 could increase the sensitivity of leukemia cell to cytarabine and decrease OGG1 expression. Mechanistically, Nrf2-OGG1 axis-mediated AML resistance might be achieved by activating the AKT signaling pathway to regulate downstream apoptotic proteins. Thus, this study reveals a novel mechanism of Nrf2-promoting drug resistance in leukemia, which may provide a potential therapeutic target for the treatment of drug-resistant/refractory leukemia.

Chemical Tools for the Study of DNA Repair

DNA repair enzymes continuously provide surveillance throughout our cells, protecting the enclosed DNA from the damage that is constantly arising from oxidation, alkylating species, and radiation. Members of this enzyme class are intimately linked to pathways controlling cancer and inflammation and are promising targets for diagnostics and future therapies. Their study is benefiting widely from the development of new tools and methods aimed at measuring their activities. Here, we provide an Account of our laboratory's work on developing chemical tools to study DNA repair processes in vitro, as well as in cells and tissues, and what we have learned by applying them.We first outline early work probing how DNA repair enzymes recognize specific forms of damage by use of chemical analogs of the damage with altered shapes and H-bonding abilities. One outcome of this was the development of an unnatural DNA base that is incorporated selectively by polymerase enzymes opposite sites of missing bases (abasic sites) in DNA, a very common form of damage.We then describe strategies for design of fluorescent probes targeted to base excision repair (BER) enzymes; these were built from small synthetic DNAs incorporating fluorescent moieties to engender light-up signals as the enzymatic reaction proceeds. Examples of targets for these DNA probes include UDG, SMUG1, Fpg, OGG1, MutYH, ALKBH2, ALKBH3, MTH1, and NTH1. Several such strategies were successful and were applied both in vitro and in cellular settings; moreover, some were used to discover small-molecule modulators of specific repair enzymes. One of these is the compound SU0268, a potent OGG1 inhibitor that is under investigation in animal models for inhibiting hyperinflammatory responses.To investigate cellular nucleotide sanitation pathways, we designed a series of "two-headed" nucleotides containing a damaged DNA nucleotide at one end and ATP at the other; these were applied to studying the three human sanitation enzymes MTH1, dUTPase, and dITPase, some of which are therapeutic targets. The MTH1 probe (ARGO) was used in collaboration with oncologists to measure the enzyme in tumors as a disease marker and also to develop the first small-molecule activators of the enzyme.We proceed to discuss the development of a "universal" probe of base excision repair processes (UBER), which reacts covalently with abasic site intermediates of base excision repair. UBER probes light up in real time as the reaction occurs, enabling the observation of base excision repair as it occurs in live cells and tissues. UBER probes can also be used in efficient and simple methods for fluorescent labeling of DNA. Finally, we suggest interesting directions for the future of this field in biomedicine and human health.

The Role of 8-oxoG Repair Systems in Tumorigenesis and Cancer Therapy

Tumorigenesis is highly correlated with the accumulation of mutations. The abundant and extensive DNA oxidation product, 8-Oxoguanine (8-oxoG), can cause mutations if it is not repaired by 8-oxoG repair systems. Therefore, the accumulation of 8-oxoG plays an essential role in tumorigenesis. To avoid the accumulation of 8-oxoG in the genome, base excision repair (BER), initiated by 8-oxoguanine DNA glycosylase1 (OGG1), is responsible for the removal of genomic 8-oxoG. It has been proven that 8-oxoG levels are significantly elevated in cancer cells compared with cells of normal tissues, and the induction of DNA damage by some antitumor drugs involves direct or indirect interference with BER, especially through inducing the production and accumulation of reactive oxygen species (ROS), which can lead to tumor cell death. In addition, the absence of the core components of BER can result in embryonic or early post-natal lethality in mice. Therefore, targeting 8-oxoG repair systems with inhibitors is a promising avenue for tumor therapy. In this study, we summarize the impact of 8-oxoG accumulation on tumorigenesis and the current status of cancer therapy approaches exploiting 8-oxoG repair enzyme targeting, as well as possible synergistic lethality strategies involving exogenous ROS-inducing agents.

Pharmacological OGG1 inhibition decreases murine allergic airway inflammation

Background and aim: Allergic asthma is a complex inflammatory disease involving type 2 innate lymphoid cells, type 2 T helper cells, macrophages, and eosinophils. The disease is characterized by wheezing, dyspnea, coughing, chest tightness and variable airflow limitation for which there is no cure and is symptomatically treated with inhaled corticosteroids and β2-agonists. Molecular mechanisms underlying its complex pathogenesis are not fully understood. However, 8-oxoguanine DNA glycosylase-1 (OGG1), a DNA repair protein may play a central role, as OGG1 deficiency decreases both innate and allergic inflammation.

Methods: Using a murine ovalbumin (OVA) model of allergic airway inflammation we assessed the utility of an inhibitor of OGG1 (TH5487) in this disease context. Cytokines and chemokines, promoting immune cell recruitment were measured using a 23-multiplex assay and Western blotting. Additionally, immune cell recruitment to bronchi was measured using flow cytometry. Histological analyses and immunofluorescent staining were used to confirm immune cell influx and goblet cell hyperplasia of the airways. A PCR array was used to assess asthma-related genes in murine lung tissue following TH5487 treatment. Finally, airway hyperresponsiveness was determined using in vivo lung function measurement.

Results: In this study, administration of TH5487 to mice with OVA-induced allergic airway inflammation significantly decreased goblet cell hyperplasia and mucus production. TH5487 treatment also decreased levels of activated NF-κB and expression of proinflammatory cytokines and chemokines resulting in significantly lower recruitment of eosinophils and other immune cells to the lungs. Gene expression profiling of asthma and allergy-related proteins after TH5487 treatment revealed differences in several important regulators, including down regulation of Tnfrsf4, Arg1, Ccl12 and Ccl11, and upregulation of the negative regulator of type 2 inflammation, Bcl6. Furthermore, the gene Clca1 was upregulated following TH5487 treatment, which should be explored further due to its ambiguous role in allergic asthma. In addition, the OVA-induced airway hyperresponsiveness was significantly reduced by TH5487 treatment.

Conclusion: Taken together, the data presented in this study suggest OGG1 as a clinically relevant pharmacological target for the treatment of allergic inflammation.

OGG1 Inhibition Reduces Acinar Cell Injury in a Mouse Model of Acute Pancreatitis

Acute pancreatitis (AP) is a potentially life-threatening gastrointestinal disease with a complex pathology including oxidative stress. Oxidative stress triggers oxidative DNA lesions such as formation of 7,8-dihydro-8-oxo-2′-oxoguanine (8-oxoG) and also causes DNA strand breaks. DNA breaks can activate the nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP1) which contributes to AP pathology. 8-oxoG is recognized by 8-oxoG glycosylase 1 (OGG1) resulting in the removal of 8-oxoG from DNA as an initial step of base excision repair. Since OGG1 also possesses a DNA nicking activity, OGG1 activation may also trigger PARP1 activation. In the present study we investigated the role played by OGG1 in AP. We found that the OGG1 inhibitor compound TH5487 reduced edema formation, inflammatory cell migration and necrosis in a cerulein-induced AP model in mice. Moreover, TH5487 caused 8-oxoG accumulation and reduced tissue poly(ADP-ribose) levels. Consistent with the indirect PARP inhibitory effect, TH5487 shifted necrotic cell death (LDH release and Sytox green uptake) towards apoptosis (caspase activity) in isolated pancreatic acinar cells. In the in vivo AP model, TH5487 treatment suppressed the expression of various cytokine and chemokine mRNAs such as those of TNF, IL-1β, IL1ra, IL6, IL16, IL23, CSF, CCL2, CCL4, CCL12, IL10 and TREM as measured with a cytokine array and verified by RT-qPCR. As a potential mechanism underlying the transcriptional inhibitory effect of the OGG1 inhibitor we showed that while 8-oxoG accumulation in the DNA facilitates NF-κB binding to its consensus sequence, when OGG1 is inhibited, target site occupancy of NF-κB is impaired. In summary, OGG1 inhibition provides protection from tissue injury in AP and these effects are likely due to interference with the PARP1 and NF-κB activation pathways.

Direct hOGG1-Myc interactions inhibit hOGG1 catalytic activity and recruit Myc to its promoters under oxidative stress

The base excision repair (BER) glycosylase hOGG1 (human oxoguanine glycosylase 1) is responsible for repairing oxidative lesions in the genome, in particular oxidised guanine bases (oxoG). In addition, a role of hOGG1 in transcription regulation by recruitment of various transcription factors has been reported. Here, we demonstrate direct interactions between hOGG1 and the medically important oncogene transcription factor Myc that is involved in transcription initiation of a large number of genes including inflammatory genes. Using single molecule atomic force microscopy (AFM), we reveal recruitment of Myc to its E-box promoter recognition sequence by hOGG1 specifically under oxidative stress conditions, and conformational changes in hOGG1-Myc complexes at oxoG lesions that suggest loading of Myc at oxoG lesions by hOGG1. Importantly, our data show suppression of hOGG1 catalytic activity in oxoG repair by Myc. Furthermore, mutational analyses implicate the C28 residue in hOGG1 in oxidation induced protein dimerisation and suggest a role of hOGG1 dimerisation under oxidising conditions in hOGG1-Myc interactions. From our data we develop a mechanistic model for Myc recruitment by hOGG1 under oxidising, inflammatory conditions, which may be responsible for the observed enhanced gene expression of Myc target genes.

Lung recovery from DNA damage induced by graphene oxide is dependent on size, dose and inflammation profile

BACKGROUND

A key aspect of any new material safety assessment is the evaluation of their in vivo genotoxicity. Graphene oxide (GO) has been studied for many promising applications, but there are remaining concerns about its safety profile, especially after inhalation. Herein we tested whether GO lateral dimension, comparing micrometric (LGO) and nanometric (USGO) GO sheets, has a role in the formation of DNA double strand breaks in mouse lungs. We used spatial resolution and differential cell type analysis to measure DNA damages in both epithelial and immune cells, after either single or repeated exposure.

RESULTS

GO induced DNA damages were size and dose dependent, in both exposure scenario. After single exposure to a high dose, both USGO and LGO induced significant DNA damage in the lung parenchyma, but only during the acute phase response (p < 0.05 for USGO; p < 0.01 for LGO). This was followed by a fast lung recovery at day 7 and 28 for both GOs. When evaluating the chronic impact of GO after repeated exposure, only a high dose of LGO induced long-term DNA damages in lung alveolar epithelia (at 84 days, p < 0.05). Regardless of size, low dose GO did not induce any significant DNA damage after repeated exposure. A multiparametric correlation analysis of our repeated exposure data revealed that transient or persistent inflammation and oxidative stress were associated to either recovery or persistent DNA damages. For USGO, recovery from DNA damage was correlated to efficient recovery from acute inflammation (i.e., significant secretion of SAA3, p < 0.001; infiltration of neutrophils, p < 0.01). In contrast, the persistence of LGO in lungs was associated to a long-lasting presence of multinucleated macrophages (up to 84 days, p < 0.05), an underlying inflammation (IL-1α secretion up to 28 days, p < 0.05) and the presence of persistent DNA damages at 84 days.

CONCLUSIONS

Overall these results highlight the importance of the exposure scenario used. We showed that LGO was more genotoxic after repeated exposure than single exposure due to persistent lung inflammation. These findings are important in the context of human health risk assessment and toward establishing recommendations for a safe use of graphene based materials in the workplace.

A mechanism for oxidative damage repair at gene regulatory elements

Oxidative genome damage is an unavoidable consequence of cellular metabolism. It arises at gene regulatory elements by epigenetic demethylation during transcriptional activation^1,2. Here we show that promoters are protected from oxidative damage via a process mediated by the nuclear mitotic apparatus protein NuMA (also known as NUMA1). NuMA exhibits genomic occupancy approximately 100 bp around transcription start sites. It binds the initiating form of RNA polymerase II, pause-release factors and single-strand break repair (SSBR) components such as TDP1. The binding is increased on chromatin following oxidative damage, and TDP1 enrichment at damaged chromatin is facilitated by NuMA. Depletion of NuMA increases oxidative damage at promoters. NuMA promotes transcription by limiting the polyADP-ribosylation of RNA polymerase II, increasing its availability and release from pausing at promoters. Metabolic labelling of nascent RNA identifies genes that depend on NuMA for transcription including immediate-early response genes. Complementation of NuMA-deficient cells with a mutant that mediates binding to SSBR, or a mitotic separation-of-function mutant, restores SSBR defects. These findings underscore the importance of oxidative DNA damage repair at gene regulatory elements and describe a process that fulfils this function.

Inhibition of 8-oxoguanine DNA glycosylase (OGG1) expression suppresses polycystic ovarian syndrome via the NF-κB signaling pathway

It has been reported that oxidative stress and chronic inflammation may be involved in the pathogenesis of polycystic ovary syndrome (PCOS). 8-oxoguanine DNA glycosylase (OGG1) is the main glycosylase that catalyzes the excision of DNA oxidation products. In this study, we investigated the role and potential mechanisms of OGG1 in the development of PCOS. We first analyzed OGG1 levels in serum and follicular fluid (FF) of PCOS patients, and significantly elevated OGG1 levels were noted in PCOS patients. We similarly observed a significant upregulation of OGG1 expression levels in ovarian tissue of the dehydroepiandrosterone (DHEA)-induced PCOS rat model. In addition, increased apoptosis and increased production of reactive oxygen species (ROS) were observed after the addition of OGG1-specific inhibitor (TH5487) in human granulosa-like tumor cell line (KGN) cells following a concentration gradient, along with a significant decrease in mRNA levels of inflammatory factors such as CXCL2, IL-6, MCP1, IL-1β, and IL-18. Significant decreases in protein phosphorylation levels of P65 and IκBα were also observed in cells. In addition, we found a significant positive correlation between OGG1 and IL-6 expression levels in human and DHEA-induced PCOS rat models. In conclusion, our results suggest that OGG1 might be involved in the pathogenesis of PCOS by regulating the secretion of IL-6 through NF-κB signaling pathway, and there might be a balance between the inhibition of oxidative stress and the promotion of chronic inflammation by OGG1 on KGN cells.

Small molecule-mediated allosteric activation of the base excision repair enzyme 8-oxoguanine DNA glycosylase and its impact on mitochondrial function

8-Oxoguanine DNA glycosylase (OGG1) initiates base excision repair of the oxidative DNA damage product 8-oxoguanine. OGG1 is bifunctional; catalyzing glycosyl bond cleavage, followed by phosphodiester backbone incision via a β-elimination apurinic lyase reaction. The product from the glycosylase reaction, 8-oxoguanine, and its analogues, 8-bromoguanine and 8-aminoguanine, trigger the rate-limiting AP lyase reaction. The precise activation mechanism remains unclear. The product-assisted catalysis hypothesis suggests that 8-oxoguanine and analogues bind at the product recognition (PR) pocket to enhance strand cleavage as catalytic bases. Alternatively, they may allosterically activate OGG1 by binding outside of the PR pocket to induce an active-site conformational change to accelerate apurinic lyase. Herein, steady-state kinetic analyses demonstrated random binding of substrate and activator. 9-Deazaguanine, which can't function as a substrate-competent base, activated OGG1, albeit with a lower E_max value than 8-bromoguanine and 8-aminoguanine. Random compound screening identified small molecules with E_max values similar to 8-bromoguanine. Paraquat-induced mitochondrial dysfunction was attenuated by several small molecule OGG1 activators; benefits included enhanced mitochondrial membrane and DNA integrity, less cytochrome c translocation, ATP preservation, and mitochondrial membrane dynamics. Our results support an allosteric mechanism of OGG1 and not product-assisted catalysis. OGG1 small molecule activators may improve mitochondrial function in oxidative stress-related diseases.