Genotype-phenotype analysis of S326C OGG1 polymorphism: a risk factor for oxidative pathologies

A Low-Activity Polymorphic Variant of Human NEIL2 DNA Glycosylase

Human NEIL2 DNA glycosylase (hNEIL2) is a base excision repair protein that removes oxidative lesions from DNA. A distinctive feature of hNEIL2 is its preference for the lesions in bubbles and other non-canonical DNA structures. Although a number of associations of polymorphisms in the hNEIL2 gene were reported, there is little data on the functionality of the encoded protein variants, as follows: only hNEIL2 R103Q was described as unaffected, and R257L, as less proficient in supporting the repair in a reconstituted system. Here, we report the biochemical characterization of two hNEIL2 variants found as polymorphisms in the general population, R103W and P304T. Arg103 is located in a long disordered segment within the N-terminal domain of hNEIL2, while Pro304 occupies a position in the β-turn of the DNA-binding zinc finger motif. Similar to the wild-type protein, both of the variants could catalyze base excision and nick DNA by β-elimination but demonstrated a lower affinity for DNA. Steady-state kinetics indicates that the P304T variant has its catalytic efficiency (in terms of k_cat/K_M) reduced ~5-fold compared with the wild-type hNEIL2, whereas the R103W enzyme is much less affected. The P304T variant was also less proficient than the wild-type, or R103W hNEIL2, in the removal of damaged bases from single-stranded and bubble-containing DNA. Overall, hNEIL2 P304T could be worthy of a detailed epidemiological analysis as a possible cancer risk modifier.

The Role of Oxidative Stress and the Importance of miRNAs as Potential Biomarkers in the Development of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the primary cause of blindness in developed countries. With the progressive aging of the population, AMD is a significant ophthalmological problem in the population over 50 years of age. The etiology of AMD is known to be based on various biochemical, immunological and molecular pathways and to be influenced by a range of genetic and environmental elements. This review provides an overview of the pathophysiological role of oxidative stress and free radicals in the retina with a special focus on the DNA repair efficiency and enzymatic antioxidant defense. It also presents a correlation between miRNA profile and AMD, and indicates their involvement in inflammation, angiogenesis, increased oxidation of cellular components, enzymatic antioxidant capacity and DNA repair efficiency, which play particularly important roles in AMD pathogenesis. Gene silencing by miRNAs can induce changes in antioxidant enzymes, leading to a complex interplay between redox imbalance by free radicals and miRNAs in modulating cellular redox homeostasis.

Focus on DNA Glycosylases-A Set of Tightly Regulated Enzymes with a High Potential as Anticancer Drug Targets

Cancer is the second leading cause of death with tens of millions of people diagnosed with cancer every year around the world. Most radio- and chemotherapies aim to eliminate cancer cells, notably by causing severe damage to the DNA. However, efficient repair of such damage represents a common mechanism of resistance to initially effective cytotoxic agents. Thus, development of new generation anticancer drugs that target DNA repair pathways, and more particularly the base excision repair (BER) pathway that is responsible for removal of damaged bases, is of growing interest. The BER pathway is initiated by a set of enzymes known as DNA glycosylases. Unlike several downstream BER enzymes, DNA glycosylases have so far received little attention and the development of specific inhibitors of these enzymes has been lagging. Yet, dysregulation of DNA glycosylases is also known to play a central role in numerous cancers and at different stages of the disease, and thus inhibiting DNA glycosylases is now considered a valid strategy to eliminate cancer cells. This review provides a detailed overview of the activities of DNA glycosylases in normal and cancer cells, their modes of regulation, and their potential as anticancer drug targets.

Genetic polymorphism of hOGG1 ser326cys and its association with breast cancer in Jammu and Kashmir

Background

8-Oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxodG) is a potent DNA damage marker that leads to cellular oxidative stress. It is a DNA-repair enzyme that participates in "8-oxodG" DNA adducts removal. Previous studies show weak associations of rs1052133 (hOGG1) in breast cancer patients of Northern India. We performed this study to explore the variant rs1052133 (hOGG1) with breast in the population of Jammu and Kashmir (J and K).

Method

A polymerase chain reaction-restriction fragment length polymorphism -based single-nucleotide polymorphism (SNP) genotypic study was carried out in peripheral blood samples of 165 breast cancer patients and 200 healthy controls, using specific primers. Sanger sequencing verified the results.

Results

hOGG1-Ser326Cys polymorphism occurred frequently in cases as compared with controls. Data were evaluated by SPSS V.13 software, following Hardy-Weinberg equilibrium (P = 0.002 at OR 2.57; 95% CI [1.68-3.93]), which showed that the SNP rs1052133 had a significant association with increased risk of breast cancer.

Conclusion

Overall, the results of this analysis show that the hOGG1-Ser326Cys polymorphism may be associated with an increased risk for breast cancer in the J and K population.

Oxidative DNA Damage Accelerates Skin Inflammation in Pristane-Induced Lupus Model

Systemic Lupus Erythematosus (SLE) is a chronic inflammatory autoimmune disease in which type I interferons (IFN) play a key role. The IFN response can be triggered when oxidized DNA engages the cytosolic DNA sensing platform cGAS-STING, but the repair mechanisms that modulate this process and govern disease progression are unclear. To gain insight into this biology, we interrogated the role of oxyguanine glycosylase 1 (OGG1), which repairs oxidized guanine 8-Oxo-2'-deoxyguanosine (8-OH-dG), in the pristane-induced mouse model of SLE. Ogg1 ^-/- mice showed increased influx of Ly6C^hi monocytes into the peritoneal cavity and enhanced IFN-driven gene expression in response to short-term exposure to pristane. Loss of Ogg1 was associated with increased auto-antibodies (anti-dsDNA and anti-RNP), higher total IgG, and expression of interferon stimulated genes (ISG) to longer exposure to pristane, accompanied by aggravated skin pathology such as hair loss, thicker epidermis, and increased deposition of IgG in skin lesions. Supporting a role for type I IFNs in this model, skin lesions of Ogg1 ^-/- mice had significantly higher expression of type I IFN genes (Isg15, Irf9, and Ifnb). In keeping with loss of Ogg1 resulting in dysregulated IFN responses, enhanced basal and cGAMP-dependent Ifnb expression was observed in BMDMs from Ogg1 ^-/- mice. Use of the STING inhibitor, H151, reduced both basal and cGAMP-driven increases, indicating that OGG1 regulates Ifnb expression through the cGAS-STING pathway. Finally, in support for a role for OGG1 in the pathology of cutaneous disease, reduced OGG1 expression in monocytes associated with skin involvement in SLE patients and the expression of OGG1 was significantly lower in lesional skin compared with non-lesional skin in patients with Discoid Lupus. Taken together, these data support an important role for OGG1 in protecting against IFN production and SLE skin disease.

Oxidative stress and DNA damage in the mechanism of fetal alcohol spectrum disorders

This review covers molecular mechanisms involving oxidative stress and DNA damage that may contribute to morphological and functional developmental disorders in animal models resulting from exposure to alcohol (ethanol, EtOH) in utero or in embryo culture. Components covered include: (a) a brief overview of EtOH metabolism and embryopathic mechanisms other than oxidative stress; (b) mechanisms within the embryo and fetal brain by which EtOH increases the formation of reactive oxygen species (ROS); (c) critical embryonic/fetal antioxidative enzymes and substrates that detoxify ROS; (d) mechanisms by which ROS can alter development, including ROS-mediated signal transduction and oxidative DNA damage, the latter of which leads to pathogenic genetic (mutations) and epigenetic changes; (e) pathways of DNA repair that mitigate the pathogenic effects of DNA damage; (f) related indirect mechanisms by which EtOH enhances risk, for example by enhancing the degradation of some DNA repair proteins; and, (g) embryonic/fetal pathways like NRF2 that regulate the levels of many of the above components. Particular attention is paid to studies in which chemical and/or genetic manipulation of the above mechanisms has been shown to alter the ability of EtOH to adversely affect development. Alterations in the above components are also discussed in terms of: (a) individual embryonic and fetal determinants of risk and (b) potential risk biomarkers and mitigating strategies. FASD risk is likely increased in progeny which/who are biochemically predisposed via genetic and/or environmental mechanisms, including enhanced pathways for ROS formation and/or deficient pathways for ROS detoxification or DNA repair.

Effects of the Ser326Cys Polymorphism in the DNA Repair OGG1 Gene on Cancer, Cardiovascular, and All-Cause Mortality in the PREDIMED Study: Modulation by Diet

BACKGROUND

Oxidatively induced DNA damage, an important factor in cancer etiology, is repaired by oxyguanine glycosylase 1 (OGG1). The lower repair capacity genotype (homozygote Cys326Cys) in the OGG1-rs1052133 (Ser326Cys) polymorphism has been associated with cancer risk. However, no information is available in relation to cancer mortality, other causes of death, and modulation by diet.

OBJECTIVE

Our aim was to evaluate the association of the OGG1-rs1052133 with total, cancer, and cardiovascular disease (CVD) mortality and to analyze its modulation by the Mediterranean diet, focusing especially on total vegetable intake as one of the main characteristics of this diet.

DESIGN

Secondary analysis in the PREDIMED (Prevención con Dieta Mediterránea) trial is a randomized, controlled trial conducted in Spain from 2003 to 2010.

PARTICIPANTS/SETTING

Study participants (n=7,170) were at high risk for CVD and were aged 55 to 80 years.

INTERVENTION

Participants were randomly allocated to two groups with a Mediterranean diet intervention or a control diet. Vegetable intake was measured at baseline.

MAIN OUTCOME MEASURES

Main outcomes were all-cause, cancer, and CVD mortality after a median follow-up of 4.8 years.

STATISTICAL ANALYSES

Multivariable-adjusted Cox regression models were fitted.

RESULTS

Three hundred eighteen deaths were detected (cancer, n=127; CVD, n=81; and other, n=110). Cys326Cys individuals (prevalence 4.2%) presented higher total mortality rates than Ser326-carriers (P=0.009). The multivariable-adjusted hazard ratio for Cys326Cys vs Ser326-carriers was 1.69 (95% CI 1.09 to 2.62; P=0.018). This association was greater for CVD mortality (P=0.001). No relationship was detected for cancer mortality in the whole population (hazard ratio 1.07; 95% CI 0.47 to 2.45; P=0.867), but a significant age interaction (P=0.048) was observed, as Cys326Cys was associated with cancer mortality in participants <66.5 years (P=0.029). Recessive effects limited our ability to investigate Cys326Cys×diet interactions for cancer mortality. No statistically significant interactions for total or CVD mortality were found for the Mediterranean diet intervention. However, significant protective interactions for CVD mortality were found for vegetable intake (hazard ratio interaction per standard deviation 0.42; 95% CI 0.18 to 0.98; P=0.046).

CONCLUSIONS

In this population, the Cys326Cys-OGG1 genotype was associated with all-cause mortality, mainly CVD instead of cancer mortality. Additional studies are needed to provide further evidence on its dietary modulation.

Fetal oxidative stress mechanisms of neurodevelopmental deficits and exacerbation by ethanol and methamphetamine

In utero exposure of mouse progeny to alcohol (ethanol, EtOH) and methamphetamine (METH) causes substantial postnatal neurodevelopmental deficits. One emerging pathogenic mechanism underlying these deficits involves fetal brain production of reactive oxygen species (ROS) that alter signal transduction, and/or oxidatively damage cellular macromolecules like lipids, proteins, and DNA, the latter leading to altered gene expression, likely via non-mutagenic mechanisms. Even physiological levels of fetal ROS production can be pathogenic in biochemically predisposed progeny, and ROS formation can be enhanced by drugs like EtOH and METH, via activation/induction of ROS-producing NADPH oxidases (NOX), drug bioactivation to free radical intermediates by prostaglandin H synthases (PHS), and other mechanisms. Antioxidative enzymes, like catalase in the fetal brain, while low, provide critical protection. Oxidatively damaged DNA is normally rapidly repaired, and fetal deficiencies in several DNA repair proteins, including oxoguanine glycosylase 1 (OGG1) and breast cancer protein 1 (BRCA1), enhance the risk of drug-initiated postnatal neurodevelopmental deficits, and in some cases deficits in untreated progeny, the latter of which may be relevant to conditions like autism spectrum disorders (ASD). Risk is further regulated by fetal nuclear factor erythroid 2-related factor 2 (Nrf2), a ROS-sensing protein that upregulates an array of proteins, including antioxidative enzymes and DNA repair proteins. Imbalances between conceptal pathways for ROS formation, versus those for ROS detoxification and DNA repair, are important determinants of risk. Birth Defects Research (Part C) 108:108-130, 2016. © 2016 Wiley Periodicals, Inc.

Single nucleotide polymorphisms in DNA glycosylases: From function to disease

Oxidative stress is associated with a growing number of diseases that span from cancer to neurodegeneration. Most oxidatively induced DNA base lesions are repaired by the base excision repair (BER) pathway which involves the action of various DNA glycosylases. There are numerous genome wide studies attempting to associate single-nucleotide polymorphisms (SNPs) with predispositions to various types of disease; often, these common variants do not have significant alterations in their biochemical function and do not exhibit a convincing phenotype. Nevertheless several lines of evidence indicate that SNPs in DNA repair genes may modulate DNA repair capacity and contribute to risk of disease. This overview provides a convincing picture that SNPs of DNA glycosylases that remove oxidatively generated DNA lesions are susceptibility factors for a wide disease spectrum that includes besides cancer (particularly lung, breast and gastrointestinal tract), cochlear/ocular disorders, myocardial infarction and neurodegenerative disorders which can be all grouped under the umbrella of oxidative stress-related pathologies.

The hOGG1 Ser326Cys Gene Polymorphism and Breast Cancer Risk in Saudi Population

The purpose of this study was to test the association between human 8-oxoguanine glycosylase 1 (hOGG1) gene polymorphisms and susceptibility to breast cancer in Saudi population. We have also aimed to screen the hOGG1 Ser326Cys polymorphism effect on structural and functional properties of the hOGG1 protein using in silico tools. We have analyzed four SNPs of hOGG1 gene among Saudi breast cancer patients along with healthy controls. Genotypes were screened using TaqMan SNP genotype analysis method. Experimental data was analyzed using Chi-square, t test and logistic regression analysis using SPSS software (v.16). In silco analysis was conducted using discovery studio and HOPE program. Genotypic analysis showed that hOGG1 rs1052133 (Ser326Cys) is significantly associated with breast cancer samples in Saudi population, however rs293795 (T >C), rs2072668 (C>G) and rs2075747 (G >A) did not show any association with breast cancer. The hOGG1 SNP rs1052133 (Ser326Cys) minor allele T showed a significant association with breast cancer samples (OR = 1.78, χ2 = 7.86, p = 0.02024). In silico structural analysis was carried out to compare the wild type (Ser326) and mutant (Cys326) protein structures. The structural prediction studies revealed that Ser326Cys variant may destabilize the protein structure and it may disturb the hOGG1 function. Taken together this is the first In silico study report to confirm Ser326Cys variant effect on structural and functional properties of hOGG1 gene and Ser326Cys role in breast cancer susceptibility in Saudi population.

Association between polymorphisms of OGG1, EPHA2 and age-related cataract risk: a meta-analysis

Background

Evidences have identified the correlation of 8-oxoguanine DNA glycosylase-1 (OGG1) and eph-receptor tyrosine kinase-type A2 (EPHA2) polymorphisms in age-related cataract (ARC) risk. However, the results were not consistent. The objective of this study was to examine the role of these two gene polymorphisms in ARC susceptibility.

Methods

Eligible case–control studies published between January 2000 and 2015 were searched and retrieved in the electronic databases. The odds ratio with 95 % confidence interval (CI) was employed to calculate the strength of the relationship.

Results

We totally screened out six articles, including 5971 cataract patients and 4189 matched controls. Three variants were contained (OGG1 rs1052133; EPHA2 rs7543472 and rs11260867). For OGG1 rs1052133, we detected a significant correlation between OGG1 polymorphism and ARC risk under the heterogenous model (CG vs. CC: OR = 1.34, 95 % CI = 1.06–1.70, P = 0.01) and dominant model (GG+CG vs. CC: OR = 1.45, 95 % CI = 1.16–1.81, P = 0.001), especially in patients with cortical cataract of subgroup analysis by phenotypes (P < 0.05). For EPHA2 rs7543472 and rs11260867, we did not find a positive association between these two mutations and ARC susceptibility in total cases. Subgroup analysis by phenotypes of cataract showed that only in cortical cataract, genotypes of rs7543472 under the allele model, homogenous model and recessive model; genotypes of rs11260867 under the heterogenous model and dominant model were associated with ARC risk.

Conclusions

OGG1 rs1052133 (CG and CG+GG genotypes) might be risk factor for ARC, particularly in cortical cataract risk. EPHA2 rs7543472 (T allele and TT genotype) and rs11260867 (CG and GG+CG genotypes) might be associated with cortical cataract.

The response to oxidative stress and metallomics analysis in a twin study: The role of the environment

Inefficient response to oxidative stress has been associated with ageing and health risk. Metals are known to inhibit DNA repair and may modify the antioxidant response. How genetic variability and lifestyle factors modulate the response to oxidative stress is poorly explored. Our study aims to disentangle the contribution of genetics and environmental exposures to oxidative stress response using data from twin pairs. The non-enzymatic antioxidant capacity (NEAC), the repair capacity of 8-oxo-7,8-dihydroguanine (OGG activity) and the levels of 12 metals were measured in blood of 64 monozygotic and 31 dizygotic twin pairs. The contributions of genetic and environmental effects were assessed using standard univariate twin modelling. NEAC and OGG activity significantly decreased with age. Gender-, age- and body mass index-associated differences were identified for some metals. Principal Component Analysis identified two groups of metals whose levels in blood were highly correlated: As, Hg, Pb, Se, Zn and Al, Co, Cr, Mn, Ni. The environmental influence was predominant on OGG activity and NEAC variance whereas for most metals the best-fitting model incorporated additive genetic and unique environmental sources of variance. NEAC and OGG activity were both inversely correlated with blood levels of various metals. The inhibition of OGG activity by Cd was largely explained by smoking. Our data show a substantial role of environmental factors in NEAC and OGG activity variance that is not explained by twins' age. Exogenous environmental factors such as metals contribute to oxidative stress by decreasing NEAC and inhibiting repair of oxidatively-induced DNA damage.

Impact of ribonucleotide incorporation by DNA polymerases β and λ on oxidative base excision repair

Oxidative stress is a very frequent source of DNA damage. Many cellular DNA polymerases (Pols) can incorporate ribonucleotides (rNMPs) during DNA synthesis. However, whether oxidative stress-triggered DNA repair synthesis contributes to genomic rNMPs incorporation is so far not fully understood. Human specialized Pols β and λ are the important enzymes involved in the oxidative stress tolerance, acting both in base excision repair and in translesion synthesis past the very frequent oxidative lesion 7,8-dihydro-8-oxoguanine (8-oxo-G). We found that Pol β, to a greater extent than Pol λ can incorporate rNMPs opposite normal bases or 8-oxo-G, and with a different fidelity. Further, the incorporation of rNMPs opposite 8-oxo-G delays repair by DNA glycosylases. Studies in Pol β- and λ-deficient cell extracts suggest that Pol β levels can greatly affect rNMP incorporation opposite oxidative DNA lesions.

Oxidative stress is a common source of DNA damage and is repaired by the base excision repair machinery, including polymerase beta. Here the authors find that polymerase beta, and to a lesser extent lambda, can mistakenly incorporate ribonucleotides during synthesis.

Effects of physical exercise training in DNA damage and repair activity in humans with different genetic polymorphisms of hOGG1 (Ser326Cys)

The main purpose of this pilot study was to investigate the possible influence of genetic polymorphisms of the hOGG1 (Ser326Cys) gene in DNA damage and repair activity by 8-oxoguanine DNA glycosylase 1 (OGG1 enzyme) in response to 16 weeks of combined physical exercise training. Thirty-two healthy Caucasian men (40-74 years old) were enrolled in this study. All the subjects were submitted to a training of 16 weeks of combined physical exercise. The subjects with Ser/Ser genotype were considered as wild-type group (WTG), and Ser/Cys and Cys/Cys genotype were analysed together as mutant group (MG). We used comet assay in conjunction with formamidopyrimidine DNA glycoslyase (FPG) to analyse both strand breaks and FPG-sensitive sites. DNA repair activity were also analysed with the comet assay technique. Our results showed no differences between DNA damage (both strand breaks and FPG-sensitive sites) and repair activity (OGG1) between genotype groups (in the pre-training condition). Regarding the possible influence of genotype in the response to 16 weeks of physical exercise training, the results revealed a decrease in DNA strand breaks in both groups, a decrease in FPG-sensitive sites and an increase in total antioxidant capacity in the WTG, but no changes were found in MG. No significant changes in DNA repair activity was observed in both genotype groups with physical exercise training. This preliminary study suggests the possibility of different responses in DNA damage to the physical exercise training, considering the hOGG1 Ser326Cys polymorphism.

Polymorphisms of human 8-oxoguanine DNA glycosylase 1 and 8-hydroxydeoxyguanosine increase susceptibility to arsenic methylation capacity-related urothelial carcinoma

Arsenic causes oxidative stress in cultured animal and human cells, and it is a well-documented human carcinogen. We conducted a hospital-based case-control study including 167 cases of urothelial carcinoma (UC) and 334 age- and gender-matched healthy controls to evaluate the relationships between urinary arsenic profiles, urinary 8-hydroxydeoxyguanosine (8-OHdG) levels, and human 8-oxoguanine DNA glycosylase (hOGG1) genotypes and UC. The urinary arsenic species were analyzed by high-performance liquid chromatography and hydride generator-atomic absorption spectrometry. Genotyping for hOGG1 (Ser326Cys) and hOGG1 (-15C>G) was performed using the Sequenom MassARRAY platform with iPLEX Gold chemistry. Urinary 8-OHdG was measured with high-sensitivity enzyme-linked immunosorbent assay kits. The results indicated that the hOGG1 326 Cys/Cys genotype and the hOGG1 -15C>G G/G genotype were associated with an increased risk of UC (OR [95 % CI] 1.57 [1.04-2.35] and 1.57 [1.04-2.35], respectively). Participants with high urinary total arsenic, regardless of the haplotype of hOGG1 Ser326Cys and the -15C>G polymorphism, had significantly higher urinary 8-OHdG compared to participants with low urinary total arsenic. This is the first study to investigate the joint effects of high urinary total arsenic or inefficient arsenic methylation capacity indices, and the high-risk G-G haplotype of hOGG1 on the risk of UC. The findings are especially meaningful for participants with risk factors such as high urinary total arsenic, inefficient arsenic methylation indices, high urinary 8-OHdG, and the high-risk G-G haplotype of hOGG1 which are all associated with an increased UC risk.

Inactivation of a common OGG1 variant by TNF-alpha in mammalian cells

Reactive oxygen species threaten genomic integrity by inducing oxidative DNA damage. One common form of oxidative DNA damage is the mutagenic lesion 8-oxoguanine (8-oxodG). One driver of oxidative stress that can induce 8-oxodG is inflammation, which can be initiated by the cytokine tumor necrosis factor alpha (TNF-α). Oxidative DNA damage is primarily repaired by the base excision repair pathway, initiated by glycosylases targeting specific DNA lesions. 8-oxodG is excised by 8-oxoguanine glycosylase 1 (OGG1). A common Ogg1 allelic variant is S326C-Ogg1, prevalent in Asian and Caucasian populations. S326C-Ogg1 is associated with various forms of cancer, and is inactivated by oxidation. However, whether oxidative stress caused by inflammatory cytokines compromises OGG1 variant repair activity remains unknown. We addressed whether TNF-α causes oxidative stress that both induces DNA damage and inactivates S326C-OGG1 via cysteine 326 oxidation. In mouse embryonic fibroblasts, we found that S326C-OGG1 was inactivated only after exposure to H2O2 or TNF-α. Treatment with the antioxidant N-acetylcysteine prior to oxidative stress rescued S326C-OGG1 activity, demonstrated by in vitro and cellular repair assays. In contrast, S326C-OGG1 activity was unaffected by potassium bromate, which induces oxidative DNA damage without causing oxidative stress, and presumably cysteine oxidation. This study reveals that Cys326 is vulnerable to oxidation that inactivates S326C-OGG1. Physiologically relevant levels of TNF-α simultaneously induce 8-oxodG and inactivate S326C-OGG1. These results suggest a mechanism that could contribute to increased risk of cancer among S326C-Ogg1 homozygous individuals.

Polymorphism of DNA repair genes OGG1, XRCC1, XPD and ERCC6 in bladder cancer in Belarus

CONTEXT

The study of DNA base and nucleotide excision repair gene polymorphisms in bladder cancer seems to have a predictive value because of the evident relationship between the DNA damage response induced by environmental mutagens and cancer predisposition.

OBJECTIVE

The objective was to determine OGG1 Ser326Cys, XRCC1 Arg399Gln, XPD Asp312Asn, and ERCC6 Met1097Val polymorphisms in bladder cancer patients as compared to controls.

METHODS

Both groups were predominantly represented by Belarusians and Eastern Slavs. DNA samples from 336 patients and 370 controls were genotyped using a PCR-RFLP method.

RESULTS

The genotype distributions were in agreement with the Hardy-Weinberg equilibrium. The minor allele frequencies in the control population were in the range of those in Caucasians in contrast to Asians. The OGG1 326 Ser/Cys and XPD 312 Asp/Asn heterozygous genotypes were inversely associated with cancer risk (OR [95% CI] = 0.69 [0.50-0.95] and 1.35 [1.0-1.82], respectively). The contrasting effects of these genotypes were potentiated due to their interactions with smoking habit or age.

CONCLUSIONS

Among four DNA repair gene polymorphisms, the OGG1 326 Ser/Cys and XPD 312 Asp/Asn heterozygous genotypes might be recognized as potential genetic markers modifying susceptibility to bladder cancer in Belarus.

Cellular accumulation of Cys326-OGG1 protein complexes under conditions of oxidative stress

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Novel use of BiFC to study a component of base excision repair pathway.

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First time that OGG1 complex formation has been observed inside of cells.

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Complexes restricted to the Cys326 variant and conditions of oxidative stress.

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Evidence supports role of OGG1 dimer formation in reduced repair capacity.

The common Ser326Cys polymorphism in the base excision repair protein 8-oxoguanine glycosylase 1 is associated with a reduced capacity to repair oxidative DNA damage particularly under conditions of intracellular oxidative stress and there is evidence that Cys326-OGG1 homozygous individuals have increased susceptibility to specific cancer types. Indirect biochemical studies have shown that reduced repair capacity is related to OGG1 redox modification and also possibly OGG1 dimer formation. In the current study we have used bimolecular fluorescence complementation to study for the first time a component of the base excision repair pathway and applied it to visualise accumulation of Cys326-OGG1 protein complexes in the native cellular environment. Fluorescence was observed both within and around the cell nucleus, was shown to be specific to cells expressing Cys326-OGG1 and only occurred in cells under conditions of cellular oxidative stress following depletion of intracellular glutathione levels by treatment with buthionine sulphoximine. Furthermore, OGG1 complex formation was inhibited by incubation of cells with the thiol reducing agents β-mercaptoethanol and dithiothreitol and the antioxidant dimethylsulfoxide indicating a causative role for oxidative stress in the formation of OGG1 cellular complexes.

In conclusion, this study has provided for the first time evidence of redox sensitive Cys326-OGG1 protein accumulation in cells under conditions of intracellular oxidative stress that may be related to the previously reported reduced repair capacity of Cys326-OGG1 specifically under conditions of oxidative stress.

Polymorphisms of the homologous recombination gene RAD51 in keratoconus and Fuchs endothelial corneal dystrophy

PURPOSE

We investigated the association between genotypes and haplotypes of the c.-61G>T (rs 1801320) and c.-98G>C (rs 1801321) polymorphisms of the RAD51 gene and the occurrence of keratoconus (KC) and Fuchs endothelial corneal dystrophy (FECD) in dependence on some environmental factors.

METHODS

The polymorphisms were genotyped in peripheral blood lymphocytes of 100 KC and 100 FECD patients as well as 150 controls with PCR-RFLP.

RESULTS

The G/T genotype of the c.-61G>T polymorphism was associated with significantly increased frequency occurrence of KC (crude OR 2.99, 95% CI 1.75-5.13). On the other hand, the G/G genotype of this polymorphism was positively correlated with a decreased occurrence of this disease (crude OR 0.52, 95% CI 0.31-0.88). We did not find any correlation between genotypes/alleles of the c.-98G>C polymorphism and the occurrence of KC. We also found that the G/G genotype and G allele of the c.-98G>C polymorphism had a protective effect against FECD (crude OR 0.51, 95% CI 0.28-0.92; crude OR 0.53, 95% CI 0.30-0.92, resp.), while the G/C genotype and the C allele increased FECD occurrence (crude OR 1.85, 95% CI 1.01-3.36; crude OR 1.90, 95% CI 1.09-3.29, resp.).

CONCLUSIONS

The c.-61T/T and c.-98G>C polymorphisms of the RAD51 gene may have a role in the KC and FECD pathogenesis and can be considered as markers in these diseases.

Effect of blood storage conditions on DNA repair capacity measurements in peripheral blood mononuclear cells

Due to the great number of genes involved in DNA repair and the interactions among the pathways responsible for the repair of different types of DNA damage, there is an increasing need for simple and reliable approaches to phenotypically assess DNA repair capacity (DRC). The use of peripheral blood mononuclear cells (PBMCs) in DRC assays is particularly useful for human monitoring studies. However, in such studies it is not always possible to collect and process samples on the same day as the blood is taken. We performed a genotype-phenotype correlation study on DRC on 225 healthy subjects. Due to the large number of blood samples to be processed, PBMCs were either isolated and cryopreserved on the same day of blood collection (day 1) or on the following day after 24h blood storage at room temperature (day 2-RT). Samples processed in different days showed a significant difference in the DRC evaluated as 8-oxoguanine glycosylase activity (OGG assay) in cell extracts (p<0.0001) and as benzo[a]pyrene diol epoxide (BPDE)-induced damage repair by the comet assay (p=0.05). No apparent effect of the blood storage conditions on the outcome of γ-ray induced H2AX phosphorylation assay was reported. These results prompted us to further analyze the effects of blood storage conditions by performing a validation study. Three blood samples were simultaneously taken from ten healthy donors, PBMCs were isolated and cryopreserved as follows: immediately after blood collection (day 1); on the following day, after blood storage at RT (day 2-RT); or after blood storage at 4°C (day 2-4°C). DRC was then evaluated using phenotypic assays. The γ-ray induced H2AX phosphorylation assay has been confirmed as the only assay that showed good reproducibility independently of the blood storage conditions. The measurement of OGG assay was most affected by the blood storage conditions.

Excision of 8-oxoguanine from methylated CpG dinucleotides by human 8-oxoguanine DNA glycosylase

CpG dinucleotides are targets for epigenetic methylation, many of them bearing 5-methylcytosine (mCyt) in the human genome. Guanine in this context can be easily oxidized to 8-oxoguanine (oxoGua), which is repaired by 8-oxoguanine-DNA glycosylase (OGG1). We have studied how methylation affects the efficiency of oxoGua excision from damaged CpG dinucleotides. Methylation of the adjacent cytosine moderately decreased the oxoGua excision rate while methylation opposite oxoGua lowered the rate of product release. Cytosine methylation abolished stimulation of OGG1 by repair endonuclease APEX1. The OGG1 S326C polymorphic variant associated with lung cancer showed poorer base excision and lost sensitivity to the opposite-base methylation. The overall repair in the system reconstituted from purified proteins decreased for CpG with mCyt in the damaged strand.