New DNA polymorphisms of human MMH/OGG1 gene: prevalence of one polymorphism among lung-adenocarcinoma patients in Japanese

Oxidatively induced DNA damage and its repair in cancer

Oxidatively induced DNA damage is caused in living organisms by endogenous and exogenous reactive species. DNA lesions resulting from this type of damage are mutagenic and cytotoxic and, if not repaired, can cause genetic instability that may lead to disease processes including carcinogenesis. Living organisms possess DNA repair mechanisms that include a variety of pathways to repair multiple DNA lesions. Mutations and polymorphisms also occur in DNA repair genes adversely affecting DNA repair systems. Cancer tissues overexpress DNA repair proteins and thus develop greater DNA repair capacity than normal tissues. Increased DNA repair in tumors that removes DNA lesions before they become toxic is a major mechanism for development of resistance to therapy, affecting patient survival. Accumulated evidence suggests that DNA repair capacity may be a predictive biomarker for patient response to therapy. Thus, knowledge of DNA protein expressions in normal and cancerous tissues may help predict and guide development of treatments and yield the best therapeutic response. DNA repair proteins constitute targets for inhibitors to overcome the resistance of tumors to therapy. Inhibitors of DNA repair for combination therapy or as single agents for monotherapy may help selectively kill tumors, potentially leading to personalized therapy. Numerous inhibitors have been developed and are being tested in clinical trials. The efficacy of some inhibitors in therapy has been demonstrated in patients. Further development of inhibitors of DNA repair proteins is globally underway to help eradicate cancer.

Impaired 8-hydroxyguanine repair activity of MUTYH variant p.Arg109Trp found in a Japanese patient with early-onset colorectal cancer

PURPOSE

The biallelic inactivation of the 8-hydroxyguanine repair gene MUTYH leads to MUTYH-associated polyposis (MAP), which is characterized by colorectal multiple polyps and carcinoma(s). However, only limited information regarding MAP in the Japanese population is presently available. Since early-onset colorectal cancer (CRC) is a characteristic of MAP and might be caused by the inactivation of another 8-hydroxyguanine repair gene, OGG1, we investigated whether germline MUTYH and OGG1 mutations are involved in early-onset CRC in Japanese patients.

METHODS

Thirty-four Japanese patients with early-onset CRC were examined for germline MUTYH and OGG1 mutations using sequencing.

RESULTS

Biallelic pathogenic mutations were not found in any of the patients; however, a heterozygous p.Arg19∗  MUTYH variant and a heterozygous p.Arg109Trp MUTYH variant were detected in one patient each. The p.Arg19∗ and p.Arg109Trp corresponded to p.Arg5∗ and p.Arg81Trp, respectively, in the type 2 nuclear-form protein. The defective DNA repair activity of p.Arg5∗ is apparent, while that of p.Arg81Trp has been demonstrated using DNA cleavage and supF forward mutation assays.

CONCLUSION

These results suggest that biallelic MUTYH or OGG1 pathogenic mutations are rare in Japanese patients with early-onset CRC; however, the p.Arg19∗ and p.Arg109Trp MUTYH variants are associated with functional impairments.

hOGG1 Ser326Cys polymorphism and lung cancer susceptibility: a meta-analysis

The Ser326Cys polymorphism in the human 8-oxogunaine glycosylase (hOGG1) gene with lung cancer susceptibility had been investigated by the approaches of PCR-RFLP, PCR-SSCP and ASA. Due to limited specimen and different approaches the conclusion was drawn toughly. To evaluate this correlation comprehensively, a meta-analysis was performed based on 30 case-control studies, including 10,327 cases and 12,148 controls. The random-effects model was used to estimate the odds ratios and 95 % confidence interval for various contrasts of this polymorphism. The combined results suggested that the hOGG1 Ser326Cys polymorphism was not associated with lung cancer susceptibility in different genetic models. Similarly, in the stratified analyses by ethnicity and source of control, no risk was observed between all the genetic models and lung cancer risk. Our meta-analysis revealed that there was little correlation between the hOGG1 Ser326Cys polymorphism and the risk of lung cancer.

Could 8-oxoguanine DNA glycosylase 1 Ser326Cys polymorphism be a biomarker of susceptibility in cancer?

Biomarkers are key molecular or cellular events that give an indication whether there is a threat for disease, whether a disease already exists, or how such disease may develop in an individual case. The discovery of polymorphisms in genes that function in the metabolism of chemicals and in DNA repair has demonstrated the importance of understanding the phenomenon of genetic susceptibility in a population. Polymorphisms in DNA repair genes as an important component of the individual susceptibility to the development of cancer and various hereditary diseases have been commonly studied, since these genes have critical roles in maintaining genome integrity. Furthermore, the evaluation of cancer risk depends on the level of exposure to carcinogenic factors as well as on the genetic codes of the individual. This approach is supported by studies that present positive association between these polymorphic genes and cancers. Although 8-oxoguanine DNA glycosylase 1 (OGG1) is one of the promising biomarker candidates of cancer susceptibility, there are also some controversial results. Epidemiological studies show that the OGG1 might be a biomarker of susceptibility for various cancers; however, the small sample size and difference in the eligibility criteria for inclusion of subjects and sources might limit the studies to demonstrate the association between the OGG1 Ser326Cys polymorphism and the risk of cancer. Thus, meta-analyses may provide more valuable and reliable data to demonstrate the potential of OGG1 Ser326Cys DNA repair enzyme polymorphisms that could be the biomarkers of susceptibility of cancer. Our aim in this review is to compile published studies, including some controversial results on the association between the OGG1 Ser326Cys polymorphism and the risk of cancer.

Oxidatively induced DNA damage: mechanisms, repair and disease

Endogenous and exogenous sources cause oxidatively induced DNA damage in living organisms by a variety of mechanisms. The resulting DNA lesions are mutagenic and, unless repaired, lead to a variety of mutations and consequently to genetic instability, which is a hallmark of cancer. Oxidatively induced DNA damage is repaired in living cells by different pathways that involve a large number of proteins. Unrepaired and accumulated DNA lesions may lead to disease processes including carcinogenesis. Mutations also occur in DNA repair genes, destabilizing the DNA repair system. A majority of cancer cell lines have somatic mutations in their DNA repair genes. In addition, polymorphisms in these genes constitute a risk factor for cancer. In general, defects in DNA repair are associated with cancer. Numerous DNA repair enzymes exist that possess different, but sometimes overlapping substrate specificities for removal of oxidatively induced DNA lesions. In addition to the role of DNA repair in carcinogenesis, recent evidence suggests that some types of tumors possess increased DNA repair capacity that may lead to therapy resistance. DNA repair pathways are drug targets to develop DNA repair inhibitors to increase the efficacy of cancer therapy. Oxidatively induced DNA lesions and DNA repair proteins may serve as potential biomarkers for early detection, cancer risk assessment, prognosis and for monitoring therapy. Taken together, a large body of accumulated evidence suggests that oxidatively induced DNA damage and its repair are important factors in the development of human cancers. Thus this field deserves more research to contribute to the development of cancer biomarkers, DNA repair inhibitors and treatment approaches to better understand and fight cancer.

[Mutational analysis of hOGG1 gene promoter in patients with non-small cell lung cancer]

背景与目的

8-羟基鸟嘌呤DNA糖苷酶（8-hydroxygumine DNA glycosylase 1, OGG1）是一种DNA修复酶，可以从DNA切除修复8-羟基鸟嘌呤（8-dihydro-8-oxoguanine, 8-OH-G）。人类OGG1基因（hOGG1）的多态性可能会改变酶的活性而影响个体修复损伤DNA的能力，促进癌变。然而，hOGG1基因启动子区域的突变与非小细胞肺癌（non-small cell lung cancer, NSCLC）的关系尚不明晰。我们拟探讨hOGG1基因启动子区域的突变与NSCLC发生发展的潜在关系。

方法

选取苏州大学附属第一医院2003年1月-2005年12月新鲜手术切除的40例NSCLC组织标本，采用PCR-SSCP和直接测序的方法检测NSCLC及其对应的癌旁组织中hOGG1基因启动子区域的突变。

结果

在40例NSCLC患者中未发现hOGG1基因启动子区域的异常突变，但发现单核苷酸多态位点rs159153与TNM分期明显相关（P=0.008）；同时发现吸烟者中淋巴结转移率明显较低（P=0.034）。

结论

单核苷酸多态位点rs159153和吸烟史可能对NSCLC的侵袭和转移潜在性提供预测。

Association of genetic polymorphisms in DNA repair pathway genes with non-small cell lung cancer risk

DNA repair function is believed to play an important role in cancer development and to be affected by genetic polymorphisms. Numerous epidemiological studies have examined the associations between single nucleotide polymorphisms (SNPs) in the DNA repair genes and lung cancer risk, but the results are inconsistent. The aim of this study was to investigate the associations of several SNPs in the DNA repair pathways and risk of non-small cell lung cancer (NSCLC) in a Chinese population. The study included 581 NSCLC cases and 603 healthy controls. The polymorphisms studied include XRCC1 (rs25487), hOGG1 (rs1052133), MUTYH (rs3219489) in the base excision repair (BER) pathway, XPA (rs1800975), ERCC2 (rs1799793 and rs13181) in the nucleotide excision repair (NER) pathway and XRCC3 (rs861539) in the double strand break repair (DSB) pathway. The associations between lung cancer risk and genetic polymorphisms were evaluated using the logistic regression models and subgroup analyses. Meta-analyses were conducted for the SNPs shown to be significantly associated with lung cancer risk in our study. Our findings showed that XPA -4G>A (rs1800975) had a significant association with lung cancer (OR=1.64; 95% CI: 1.03-2.60), and the association was more evident in squamous cell carcinoma (OR=1.69; 95% CI: 1.00-2.84). Three BER polymorphisms showed no independent effects on the risk of lung cancer. The stratified analysis showed higher lung cancer risk among the smokers carrying the variant XPA allele (OR=1.75; 95% CI: 1.15-2.65) and among the non-smokers carrying the variant ERCC2 allele of 312Asn (OR=2.10; 95% CI: 1.22-3.64). Meta-analysis showed that individuals with the variant AA genotype of XPA (-4G>A) had higher risk of lung cancer compared to those with the 'G' wild allele (OR=1.28; 95% CI: 1.12-1.47); and those with variant alleles of ERCC2 312Asn had higher risk compared to those with wild 312Asp alleles among nonsmokers (OR=1.58; 95% CI: 1.20-2.08). Although smoking is the dominant risk factor of lung cancer, XPA -4G>A (rs1800975) is also associated with the risk of NSCLC, especially for squamous cell carcinoma, among Asian young smokers. ERCC2 Asp/Asn (rs1799793) polymorphism may also affect lung cancer risk among nonsmokers. The NER pathway seems to have more strong influences on lung cancer than the BER pathway.

Two functional variations in 5'-UTR of hoGG1 gene associated with the risk of breast cancer in Chinese

8-Hydroxy-2'-deoxyguanine (8-OHdG) is produced by the oxidative stress-induced damage in DNA, which could pair with adenine (A) during DNA replication, leading to G-T transversion mutations. Glycosylase hOGG1 can recognize and excise oxidized guanines from duplex DNA. This work aims to investigate the relationship between the functional variations in 5-untranslated region (5'-UTR) of hOGG1 gene and the risk of breast cancer. Genotypes were analyzed in 518 sporadic breast cancer patients and 777 health controls. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression. Risk-stratified subgroup analysis was performed to reveal the associations between the detected variations and the risk of characteristic breast cancer. In addition, immunohistochemistry was carried out to assess the functional effect of these variations on hOGG1gene expression. Five variations in 5'-UTR of hOGG1 gene are found in this study. Three of them, c.-18G>T, c.-23A>G, and c.-53G>C, are known single nucleotide polymorphisms, the other two, c.-45G>A and c.-63G>C, are rare variations. The frequency of c.-18G/T and c.-53G/C was significantly higher in breast cancer patients than those in healthy controls (P = 0.03, OR 2.01, 95% CI 1.04-3.90; and P = 0.01, OR 2.43, 95% CI 1.17-5.04, respectively). Both variations were especially prevalent in premenopausal status, and in the triple (estrogen receptor, progesterone receptor, and human epidermal growth factor Receptor 2) negative subgroups, respectively. Moreover, the variation of c.-18G>T could cause a reduced expression of hOGG1 gene.

Functional polymorphism of hOGG1 gene is associated with type 2 diabetes mellitus in Chinese population

hOGG1 protein excises the 8-hydroxy-2'-deoxyguanine (8-OHdG) which is associated with type 2 diabetes mellitus (T2DM). Our aim of this work is to explore whether the polymorphisms of hOGG1 gene are associated with T2DM. We screened the polymorphisms in the 5'-UTR (c.-18G>T, c.-23A>G, c.-45G>A and c.-53G>C) and c.977C>G (Ser326Cys) in exon 7 of hOGG1 gene. A case-control study indicated that c.-23A/G heterozygote was markedly associated with diabetes (P=0.004, OR=2.648, 95%CI=1.355-5.176) and with an increased level of C-peptide (705.00 versus 545.91 pmol/L, P=0.044). Furthermore, a significantly increased risk of T2DM was observed in the subjects carrying heterozygous variant of c.-23A>G and homozygous mutation of Ser326Cys (OR=3.684, 95%CI=1.400-9.697). The promoter activity of the variant allele c.-23G decreased 30-40% in Hela and HEK293 cell lines. In conclusion, the variant c.-23A>G of hOGG1 gene could decrease the gene promoter activity and was a risk factor for T2DM.

Chemopreventive effects of gefitinib on nonsmoking-related lung tumorigenesis in activating epidermal growth factor receptor transgenic mice

Twenty-five percent of all lung cancer cases are not attributable to smoking. Epidermal growth factor receptor (EGFR) mutations, which are involved in approximately 50% of nonsmoker lung cancer, are positively correlated with responsiveness to gefitinib, and inversely correlated with smoking history. Activating EGFR mutations play a critical role in the carcinogenesis of nonsmoking-related lung cancer. To investigate the chemopreventive effects of gefitinib on nonsmoking-related lung cancer, we generated transgenic mice expressing EGFR L858R in type II pneumocytes constitutively using the surfactant protein-C promoter. The transgenic mice invariably developed atypical adenomatous hyperplasia at age 4 weeks and multifocal adenocarcinoma of varying sizes at age 7 weeks. Notably, the expression levels of phosphorylated and total ErbB2, ErbB3, and thyroid transcription factor-1 were elevated in the transgenic mice compared with wild-type controls at age 3 weeks. Administration of gefitinib to 3-week-old transgenic mice for 1 week before carcinogenesis reduced the amount of phosphorylated EGFR in the lungs of the mice to the baseline level. Gefitinib (5 mg/kg/d; n = 5, 5, and 15) or vehicle (n = 5, 5, and 15) was administered to transgenic mice from age 3 to 8, 13, and 18 weeks, respectively. The numbers of lung tumors in the control and gefitinib-treated groups were 1.75, 5.8, 10.2, and 0 (P < 0.05), respectively. No fatal toxic events occurred in either group, and gefitinib inhibited tumorigenesis completely in this mouse model. These results suggest the utility of molecular targeted chemoprevention against nonsmoking-related lung cancer.

Comet assay-based methods for measuring DNA repair in vitro; estimates of inter- and intra-individual variation

DNA repair is one of the important determinants of susceptibility to cancer. It is therefore useful to be able to measure DNA repair capacity in samples from population studies. Our aim was, first, to develop a simple comet-based in vitro assay for nucleotide excision repair (NER), similar to that already in use for base excision repair (BER), and then to apply these in vitro assays to lymphocyte samples collected on several occasions from healthy subjects, to gain an impression of the degree of intra- and inter-individual variability. The in vitro assay consists of an incubation of lymphocyte extract with substrate nucleoid DNA from cells pretreated with specific damaging agent; either photosensitiser plus light to induce 8-oxoguanine, for BER, or short wavelength ultraviolet light irradiation for NER. In the new NER assay, which requires magnesium but not adenosine triphosphate, there was significant accumulation of UV-dependent incisions during a 30-min incubation of extract with DNA. We found significant correlations between individual repair rates from samples taken on different occasions; i.e. individuals have a characteristic repair capacity. There was also significant variation between individuals, to the extent of about fourfold for BER and tenfold for NER. There was no correlation between BER and NER rates. The BER and NER assays are simple to perform and can provide valuable information in molecular epidemiological studies in which DNA instability is an endpoint.

Gene prophylaxis by a DNA repair function

Gene therapy, the treatment of disorders or pathophysiologic states on the basis of the transfer of genetic information, has been thoroughly investigated for the treatment of lung illnesses, e.g. cystic fibrosis, alpha1-antitrypsin deficiency-related emphysema and cancer. Transfer of genetic information may be further used to elevate the level of protection of normal lung tissues in at risk individuals, with preventing purposes. This concept can be described by the term "gene prophylaxis". Lying at the gas-exchange interface, lung epithelia may be at risk of oxidation-induced mutagenesis. Further, inflammation processes possibly consequent on smoking liberate reactive oxygen species (ROS) that multiply the carcinogenic effects of tobacco. Some studies report in lung cancer patients an high frequency of variations of the 8-oxoguanine DNA glycosylase (hOGG1) gene that encodes a sluggish glycosylase for oxidized purines. Unlike dietary interventions with antioxidant drugs that only allow temporary oxy-radical scavenging, reinforcing the DNA repair capacity in lung epithelia may afford long-term, steady protection from ROS-generated mutagenesis and carcinogenesis. In this regard, the Escherichia coli formamidopyrimidine DNA glycosylase (FPG) is a possible tool. FPG is 80-fold faster than hOGG1 in repairing oxidized purines and has broader substrate specificity. Cell culture studies have shown that FPG can be expressed in mammalian cells where it accelerates DNA repair and abates mutagenicity of a wide range of DNA damaging agents. Spontaneous mutagenesis drops too. Prophylaxis of oxidative DNA damage and mutation could be achieved in lung epithelia and other tissues of at-risk individuals by FPG expression. Currently available vehicles for this peculiar type of gene therapy are briefly surveyed.

Repair and mutagenesis at oxidized DNA lesions in the developing brain of wild-type and Ogg1-/- mice

OGG1 (8-oxoguanine DNA glycosylase-1) is one of the main DNA glycosylases present in mammalian cells. The enzyme removes 7,8-dihydro-8-oxoguanine (8-oxoG) lesions, believed to be the most important oxidized lesions due to their relatively high incidence and their miscoding properties. This study shows that in prenatal mice brains the repair capacity for 8-oxoG is 5-10-fold higher than in adult mice brains. Western blot analysis and repair activity in extracts from Ogg1(-/-) mice revealed that OGG1 was responsible for the efficient 8-oxoG removal from prenatal mice. To investigate how OGG1 protects against oxidative stress-induced mutagenesis, pregnant Big Blue/wild-type and Big Blue/Ogg1(-/-) mice were exposed to nontoxic doses of gamma radiation. A 2.5-fold increase in the mutation frequency in Ogg1(-/-) mouse brains was obtained by exposure to 3.5 Gy at day 19 postfertilization. This was largely due to GC to TA transversions, believed to originate from 8-oxoG mispairing with A during replication. Furthermore, rapid cell divisions seemed to be required for fixation of mutations, as a similar dose of radiation did not increase the mutation frequency, or the frequency of GC to TA transversion, in the adult brain.

8-Hydroxyguanine: From its discovery in 1983 to the present status

8-Hydroxyguanine (8-OH-G) was discovered in 1983 in our laboratory at the National Cancer Center Research Institute, Tokyo. Since it could be formed in DNA not only in vitro but also in vivo by oxygen radical forming agents, we immediately hypothesized the importance of this discovery in connection with its biological consequence. Further intensive efforts by us from 1983 to 1990 confirmed that 8-OH-G is a highly significant oxidated DNA lesion involved in mutation and/or carcinogenesis in mammals, including humans. With the subsequent entry of many investigators to this research field the number of publications on 8-OH-G increased exponentially, reaching more than several thousands by the end of 2005. In this article, a summary is given of the important works carried out in the early days, and further notable contributions by many investigators are reviewed, focusing on 8-OH-G in the mammalian system. A special emphasis is given to research on knockout mice that are deficient in genes involved in the repair systems of the 8-OH-G lesion. Lastly, our own recent work is summarized involving a one-year carcinogenesis study of Ogg1 (the gene for 8-OH-G specific glycosylase/AP lyase) knockout mice that have been exposed to oxidative stress.

Polymorphisms of DNA repair genes XRCC1 and XRCC3, interaction with environmental exposure and risk of chronic gastritis and gastric cancer

AIM

To evaluate the association between polymorphisms XRCC1 Arg194Trp and Arg399Gln and XRCC3 Thr241Met and the risk for chronic gastritis and gastric cancer, in a Southeastern Brazilian population.

METHODS

Genotyping by PCR-RFLP was carried out on 202 patients with chronic gastritis (CG) and 160 patients with gastric cancer (GC), matched to 202 (C1) and 150 (C2) controls, respectively.

RESULTS

No differences were observed among the studied groups with regard to the genotype distribution of XRCC1 codons 194 and 399 and of XRCC3 codon 241. However, the combined analyses of the three variant alleles (194Trp, 399Gln and 241Met) showed an increased risk for chronic gastritis when compared to the GC group. Moreover, an interaction between the polymorphic alleles and demographic and environmental factors was observed in the CG and GC groups. XRCC1 194Trp was associated with smoking in the CG group, while the variant alleles XRCC1 399Gln and XRCC3 241Met were related with gender, smoking, drinking and H pylori infection in the CG and GC groups.

CONCLUSION

Our results showed no evidence of a relationship between the polymorphisms XRCC1 Arg194Trp and Arg399Gln and XRCC3 Thr241Met and the risk of chronic gastritis and gastric cancer in the Brazilian population, but the combined effect of these variants may interact to increase the risk for chronic gastritis, considered a premalignant lesion. Our data also indicate a gene-environment interaction in the susceptibility to chronic gastritis and gastric cancer.

Expression of human 8-oxoguanine DNA glycosylase (hOGG1) in follicular lymphoma

The human homologue of the yeast DNA repair enzyme 8-oxoguanine DNA glycosylase (hOGG1) repairs oxidatively damaged guanosine nucleotides in DNA. This enzyme is highly expressed in reactive germinal centers, where lymphoid cells are under oxidative stress, and has been thought to protect lymphocytes from mutation. As a first step to investigate the role of hOGG1 in lymphomagenesis, we evaluated hOGG1 expression in follicular lymphoma. Immunohistochemistry was performed on formalin-fixed paraffin-embedded tissue of 28 follicular lymphoma cases (16 grade 1, seven grade 2, and five grade 3) to evaluate the expression of hOGG1 in neoplastic follicles. Reactive germinal centers of non-neoplastic tonsil and lymph node tissue were also examined. Fluorescent-in-situ hybridization (FISH) was performed using a DNA probe from BAC clone RP11-266J6 corresponding to 3p25, where the hOGG1 gene resides, to evaluate for the presence or absence of a deletion. In reactive germinal centers, the majority of centroblasts and centrocytes were positive for hOGG1. In contrast, the majority (21 of 28 or 75%) of follicular lymphoma cases showed absent/minimal expression of hOGG1. Only four of 28 (14%) follicular lymphoma cases revealed the same levels of hOGG1 expression as reactive germinal centers. There was no correlation between hOGG1 expression and histologic grade. None of the 16 cases evaluated by FISH showed a deletion of hOGG1. Furthermore, absent/minimal hOGG1 expression was observed in four of six Bcl-2-negative follicular lymphoma cases. Our findings suggest that absent/minimal hOGG1 expression occurs in the majority of follicular lymphomas. The downregulation of hOGG1 does not appear to be due to a deletion of the hOGG1 locus. Additionally, finding absent/minimal hOGG1 expression in a subset of Bcl-2-negative follicular lymphomas suggests that hOGG1 may have utility in diagnosing Bcl-2-negative follicular lymphomas.

Polymorphic variation in hOGG1 and risk of cancer: a review of the functional and epidemiologic literature

The gene encoding human 8-oxoguanine glycosylase 1 (hOGG1) is involved in DNA base excision repair. The encoded DNA glycosylase excises 7,8-dihydro-8-oxoguanine (8-OHdG), a highly mutagenic base produced in DNA as a result of exposure to reactive oxygen species (ROS). Polymorphisms in this gene may alter glycosylase function and an individual's ability to repair damaged DNA, possibly resulting in genetic instability that can foster carcinogenesis. In order to elucidate the possible impact of polymorphisms in hOGG1, we performed a literature review of both functional and epidemiologic studies that assessed the effects of these polymorphisms on repair function, levels of oxidative DNA damage, or associations with cancer risk. Fourteen functional studies and 19 epidemiologic studies of breast, colon, esophageal, head and neck, lung, nasopharyngeal, orolaryngeal, prostate, squamous cell carcinoma of the head and neck (SCCHN), and stomach cancers were identified. Although the larger functional studies suggest reduced repair function with variant alleles in hOGG1, the evidence is generally inconclusive. There is some epidemiologic evidence that risk for esophageal, lung, nasopharyngeal, orolaryngeal, and prostate is related to hOGG1 genotype, whereas risk of breast cancer does not appear related. In studies that explored potential interactions with environmental factors, cancer risk for hOGG1 genotypes differed depending on exposure, especially for colon cancer. In summary, there is limited evidence that polymorphisms in hOGG1 affect repair function and carcinogenesis. Larger, well-designed functional and epidemiologic studies are needed to clarify these relationships, especially with respect to interactions with other DNA repair enzymes and interactions with environmental factors that increase carcinogenic load.

hOGG1 Ser326Cys polymorphism and G:C-to-T:A mutations: no evidence for a role in tobacco-related non small cell lung cancer

Human 8-oxoguanine DNA glycosylase 1 (hOGG1) plays a major role in the repair of 8-hydroxyguanine, one of the major forms of DNA damage generated by reactive oxygen species in tobacco smoke. If left unrepaired by hOGG1, 8-hydroxyguanine can produce G:C-to-T:A transversions. Recent studies have suggested that the hOGG1 Ser326Cys polymorphism is associated with both a decrease in enzyme activity and an increased risk of lung cancer. To define the interaction between tobacco carcinogens, hOGG1-mediated DNA repair and DNA damage, we examined the role of the hOGG1 Ser326Cys polymorphism in mutation of the p53 gene in non small cell lung cancer (NSCLC). Tumor and nonneoplastic DNA were collected from 141 cigarette smokers with NSCLC. p53 mutations were detected by direct dideoxy sequencing and/or the GeneChip p53 assay in 74 of the 141 (52%) tumors. hOGG1 codon 326 polymorphisms were identified by polymerase chain reaction-restriction fragment length polymorphism analysis. The distribution of hOGG1 codon 326 genotypes was Ser/Ser, 90 of 141 (64%); Ser/Cys, 45 of 141 (32%); and Cys/Cys, 6 of 141 (4%). p53 mutations were significantly (p = 0.04) less common in NSCLC from patients with codon 326 Ser/Cys or Cys/Cys genotypes (21 of 51; 41%) than in NSCLC from Ser/Ser homozygotes (53 of 90; 59%). The decrease in p53 mutation frequency among carriers of the Cys allele was more evident in lung squamous cell cancer [7 of 17 (41%) for Cys/Cys and Ser/Cys vs. 27 of 38 (71%) for Ser/Ser; p = 0.04] than in nonbronchoalveolar adenocarcinoma [11 of 26 (42%) for Cys/Cys and Ser/Cys vs. 20 of 35 (57%) for Ser/Ser; p = 0.25]. The prevalence of G:C-to-T:A transversions was similar among hOGG1 codon 326 genotypes. In summary, the hOGG1 codon 326 Cys allele was associated with a decrease in p53 mutations and no effect on G:C-to-T:A transversions in NSCLC. This decrease in p53 mutations in vivo is not consistent with a decrease in the repair of 8-hydroxyguanine among carriers of the hOGG1 codon 326 Cys allele in vitro.

Commentary: DNA base excision repair defects in human pathologies

DNA base excision repair (BER) is the main pathway for repair of endogenous damage in human cells. It was expected that a number of degenerative diseases could derive from BER defects. On the contrary, the link between BER defects and human pathology is elusive and the literature is full of conflicting results. The fact that most studies have investigated DNA variations but not their functional consequences has probably contributed to this confusing picture. From a functional point of view, it is likely that gross BER defects are simply not compatible with life and only limited reductions can be observed. Notwithstanding those limits, the pathological consequences of partial BER defects might be widespread and significant at the population level. This starts to emerge in particular for colorectal and lung cancer.

Contribution of hMTH1 to the maintenance of 8-oxoguanine levels in lung DNA of non-small-cell lung cancer patients

BACKGROUND

The level of 8-oxoguanine (8-oxoG), a general marker of oxidative DNA damage, in DNA is the result of both an equilibrium between the rates of its formation and removal from DNA by DNA repair enzymes and the removal of 8-oxodGTP from the cellular nucleotide pool by hydrolysis to 8-oxodGMP, preventing its incorporation into DNA. To determine the contribution of each component to the level of 8-oxoG in DNA, we compared 8-oxoG-excising activity (encoded by hOGG1), 8-oxodGTPase activity (encoded by hMTH1), and 8-oxoG levels in DNA from tumors and surrounding normal lung tissues from non-small-cell lung cancer patients.

METHODS

We measured the level of 8-oxoG in DNA of 47 patients by high-performance liquid chromatography/electrochemical detection (HPLC/ECD), hOGG1 activity in tissue extracts of 56 patients by the nicking assay using an oligodeoxynucleotide containing a single 8-oxoG, and hMTH1 activity in tissue extracts of 33 patients by HPLC/UV detection. All statistical tests were two-sided.

RESULTS

The 8-oxoG level was lower in tumor DNA than in DNA from normal lung tissue (geometric mean: 5.81 versus 10.18 8-oxoG/10(6) G, geometric mean of difference = 1.75; P<.001). The hOGG1 activity was also lower in tumor than in normal lung tissue (geometric mean: 8.76 versus 20.91 pmol/h/mg protein, geometric mean of difference = 2.39; P<.001), whereas the hMTH1 activity was higher in tumor than in normal lung tissue (geometric mean: 28.79 versus 8.94 nmol/h/mg protein, geometric mean of difference = 0.31; P<.001). The activity of hMTH1 was three orders of magnitude higher than that of hOGG1 (nanomoles versus picomoles per hour per milligram of protein, respectively).

CONCLUSIONS

Several different components contribute to the maintenance of 8-oxoG levels in human DNA, with the greatest contributor being the removal of 8-oxodGTP from the cellular nucleotide pool by hMTH1.

Repair of oxidative damage of thymine by HeLa whole-cell extracts: simultaneous analysis using a microsupport and comparison with traditional PAGE analysis

In mammalian cells, the base excision repair (BER) pathway allows the remove of small DNA base lesions such as oxidized bases. It is initiated by glycosylases that removed the modified base leaving an abasic site that is subsequently processed by AP endonuclease activities. Measurement of BER activities in cell extracts is time consuming and hazardous when radioactive material is used. We report in this study, the parallelized fluorescent analysis of excision of several oxidation products of thymine by cell extracts. To conduct the study, 5-(hydroxymethyl)uracil, 5-formyluracil, 5-carboxyuracil and formylamine together with uracil and the control thymine, were incorporated into oligonucleotides of identical sequences and paired either with adenine or with guanine containing DNA fragments. The oligonucleotides were fixed by sandwich hybridization in wells of a microplate (OLISA technology). Excision by HeLa extracts of the six different DNA base lesions could be followed simultaneously in the same well. Our results showed that the extent of excision of the lesions was the same on support and in solution using classical PAGE analysis approach with modified (32)P-labeled oligonucleotides. We demonstrated that the simultaneous analysis on support is a successful approach to facilitate high-throughput screening of BER activities present in cell extracts. Moreover, extended study of 5-carboxyuracil revealed that this lesion displays similar biological properties as 5-formyluracil.

Genetic polymorphism of hOGG1 and risk of pterygium in Chinese

PURPOSE

Ultraviolet irradiation is known to cause oxidative DNA damage and is thought to be a major factor implicated in the pathogenesis of pterygium. The highly mutagenic 8-hydroxy-2'-deoxyguanosine, a marker for the evaluation of photo-oxidative DNA damage, can be repaired by human 8-oxoguanine glycosylase I (hOGG1). A transition of C to G at nucleotide position 1245 in exon 7 of the hOGG1 gene is associated with the substitution of cysteine for serine at codon 326. In this study, we investigated the association of the hOGG1 Ser326Cys polymorphism with pterygium in a Chinese population.

METHODS

In all, 70 patients and 86 controls were enrolled in this study. The Ser326Cys polymorphism was determined by the polymerase chain reaction-restriction fragment-length polymorphism analysis. The association between this genetic polymorphism and risk of pterygium was examined by chi(2)-test and logistic regression.

RESULTS

The allelic frequencies for the Ser and Cys variants of hOGG1 gene were not significantly different between the two groups. However, when compared with Ser/Ser and Ser/Cys genotypes combined, we found that the homozygous Cys/Cys genotype was more prevalent in pterygium patients than controls (P=0.024) with the odds ratio being 2.2 (95% CI: 1.1-4.5). In the pterygium group, the mean age of patients with the Cys/Cys genotype was younger than those with the other two genotypes (P=0.025).

CONCLUSIONS

Our findings suggest that the 1245C --> G transition in exon 7 of the hOGG1 gene, which results in Ser326Cys substitution of the enzyme, might play a role in the susceptibility of humans to pterygium.

Oxidative DNA damage and disease: induction, repair and significance

The generation of reactive oxygen species may be both beneficial to cells, performing a function in inter- and intracellular signalling, and detrimental, modifying cellular biomolecules, accumulation of which has been associated with numerous diseases. Of the molecules subject to oxidative modification, DNA has received the greatest attention, with biomarkers of exposure and effect closest to validation. Despite nearly a quarter of a century of study, and a large number of base- and sugar-derived DNA lesions having been identified, the majority of studies have focussed upon the guanine modification, 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-OH-dG). For the most part, the biological significance of other lesions has not, as yet, been investigated. In contrast, the description and characterisation of enzyme systems responsible for repairing oxidative DNA base damage is growing rapidly, being the subject of intense study. However, there remain notable gaps in our knowledge of which repair proteins remove which lesions, plus, as more lesions identified, new processes/substrates need to be determined. There are many reports describing elevated levels of oxidatively modified DNA lesions, in various biological matrices, in a plethora of diseases; however, for the majority of these the association could merely be coincidental, and more detailed studies are required. Nevertheless, even based simply upon reports of studies investigating the potential role of 8-OH-dG in disease, the weight of evidence strongly suggests a link between such damage and the pathogenesis of disease. However, exact roles remain to be elucidated.

Identification of critical residues required for the mutation avoidance function of human MutY (hMYH) and implications in colorectal cancer

Mutations found in human tumors often include transversions of GC to TA that may result from the mis-pairing of 8-oxoG with adenine during DNA replication. The human MutY (hMYH) enzyme, an adenine-specific DNA glycosylase, initiates repair at this mismatch. It has recently been demonstrated that inherited variants of hMYH may predispose individuals to multiple colorectal adenomas and carcinoma [Nat. Genet. 30 (2002) 227]. In this study, we demonstrate that two of these cancer-associated hMYH mutants, Y165C and G382D, are devoid of glycosylase activity directed towards 8-oxoG:A mispairs. These findings implicate a total loss of hMYH function associated with colorectal cancers.

Impact of Types of Lymphocyte Chromosomal Aberrations on Human Cancer Risk

The frequency of cells with structural chromosomal aberrations (CAs) in peripheral blood lymphocytes is the first genotoxicity biomarker that has shown an association with cancer risk. CAs are usually divided into chromosome-type (CSAs) and chromatid-type aberrations (CTAs), with different mechanisms of formation. From a mechanistic point of view, it is of interest to clarify whether the cancer predictivity of CAs is different with respect to CSAs and CTAs. We report here cancer risk for cytogenetically tested, healthy subjects with respect to frequency of CAs, CSAs, and CTAs in peripheral blood lymphocytes, using Nordic (1981 subjects with CA data, 1871 subjects with CSA/CTA data) and Italian (1573 subjects with CA data, 877 subjects with CTA/CSA data) cohorts, with a median follow-up of 17 years. High levels of CAs at test were clearly associated with increased total cancer incidence in the Nordic cohorts and increased total cancer mortality in the Italian cohort. In the Nordic cohorts, significantly elevated cancer risks were observed for subjects with both high CSAs and high CTAs at test, and these variables showed equally strong cancer predictivity. The results of the Italian cohort did not indicate any clear-cut difference in cancer predictivity between the CSA and CTA biomarkers. There was no significant effect modification by age at test, gender, country, or time since test. The results suggest that both DNA double-strand breaks and other initial DNA lesions responsible for CSAs and CTAs are associated with cancer risk.

Transcription Factors NF-YA Regulate the Induction of Human OGG1 Following DNA-alkylating Agent Methylmethane Sulfonate (MMS) Treatment

A human 8-oxoguanine-DNA glycosylase (hOGG1) is the main enzyme that repairs 8-oxoG, which is a critical mutagenic lesion. There is a great deal of interest in the up- or down-regulation of OGG1 expression after DNA damage. In this study, we investigated the effect of a DNA-alkylating agent, methylmethane sulfonate (MMS), on hOGG1 expression level and found that MMS treatment resulted in an increase in the functional hOGG1 expression in HCT116 cells. A region between -121 and -61 of the hOGG1 promoter was found to be crucial for this induction by MMS. Site-directed mutations of the two inverted CCAAT motifs substantially abrogated the induction of the hOGG1 promoter as a result of MMS treatment. In addition, the NF-YA protein (binding to the inverted CCAAT box) was induced after exposing cells to MMS. Moreover, gel shift and supershift analyses with the nuclear extracts prepared from HCT116 cells identified NF-YA as the transcription factor interacting with the inverted CCAAT box. Mutations of the inverted CCAAT box either prevented the binding of this factor or abolished its activation as a result of MMS treatment. Finally, this study showed that hOGG1-expressing HCT116 cells exhibited increased hOGG1 repair activity and resistance to MMS. Overall, these results demonstrate that MMS can up-regulate hOGG1 expression through the induction of the transcription factor, NF-YA, and increased transcription level of the hOGG1 gene correlates with an increase in enzyme activity providing functional protection from MMS.

Polymorphisms in DNA repair and environmental interactions

The repair of damage to DNA is critical to the survival of a cell. However, not all organisms nor all individuals express a similar response to challenges to their genetic material. Numerous polymorphisms in genes involved in DNA repair have been found in individuals with DNA repair-related disease as well as in the general population. Studies of these variants are critical in understanding the response of the cell to DNA damage. In some cases, these changes predispose the carrier to a greatly increased risk of cancer. In other cases, the effects are subtler and depend on interactions between the alleles of several genes, or with environmental factors. Consequently, the health effects of exposure to genotoxic or carcinogenic compounds or agents can depend on the variations in these genes. This review will highlight some of the effects that variants, found in many of the genes involved in human DNA repair pathways, have on the response to damage, and their role in susceptibility of the cell and organism to environmental genotoxins. This review will concentrate on the mismatch repair, nucleotide repair, base excision repair, strand break repair, and direct alkyl repair pathways.

Polymorphisms of the DNA repair gene XPD and risk of lung cancer in a Chinese population

Previous studies suggested that suboptimal DNA repair capacity is associated with cancer risk and that the Asp312Asn and Lys751Gln polymorphisms in the xeroderma pigmentosum complementary group D (XPD) gene may influence DNA repair capacity. We therefore tested the hypothesis that these two XPD polymorphisms are associated with susceptibility to lung cancer in a hospital-based, case-control study in a Chinese population. Genotypes were determined by polymerase chain reaction-based restriction fragment length polymorphism methods in 383 healthy controls and 351 patients with lung cancer. We found that those who carried at least one 312Asn variant allele had an increased risk of squamous cell carcinoma (SCC) of the lung compared with those with the 312Asp/Asp genotype (adjusted odds ratio (OR), 1.80; 95% confidence interval (CI), 1.10-2.96). Compared with those having the 751Lys/Lys genotype, subjects carrying at least one variant 751 Gln allele were at a borderline increased risk of SCC of the lung (adjusted OR, 1.52; 95% CI, 0.94-2.46). Furthermore, stratified analysis suggested a multiplicative interaction between tobacco smoking and the Asp312Asn polymorphism on risk of SCC of the lung. The adjusted ORs of SCC of the lung for the variant XPD 312Asn genotype alone, for smoking > or = 29 pack-years alone, and for both the factors combined were 1.04 (95% CI, 0.37-2.94), 4.74 (95% CI, 2.88-9.49), and 14.32 (95% CI, 5.80-35.2), respectively. Similar results were evident for the Lys751Gln polymorphism that was in the linkage disequilibrium with the variant 312Asn allele. These data suggest that the two polymorphisms in the XPD gene may influence risk of smoking-related SCC of the lung.

Incision of AP sites in lung cancer patients: a pilot study

DNA base excision repair (BER) removes frequent DNA lesions of either endogenous or exogenous origin. Some indications point to BER defects in lung cancer patients. We have investigated the ability of ten lung cancer patients to repair natural AP sites, the most frequent genetic lesion, using an in vitro assay in which peripheral blood lymphocytes (PBL) extracts incise randomly depurinated plasmid DNA. The median value of repair activity in patients was lower than that of matched controls but the difference did not reach significance. Unlike other BER enzymatic steps, marked defects in incision of AP sites may not be associated with lung carcinogenesis.

DNA adducts, genetic polymorphisms, and K-ras mutation in human pancreatic cancer

To test the hypothesis that carcinogen exposure and oxidative stress are involved in pancreatic carcinogenesis in susceptible individuals, aromatic DNA adducts and 8-hydroxyguanosine (8-OH-dG) were measured by (32)P-postlabeling and HPLC-EC, respectively, in 31 pancreatic tumors and 13 normal tissues adjacent to the tumor from patients with pancreatic cancer. Normal pancreatic tissues from 24 organ donors, from six patients with non-pancreatic cancers, and from five patients with chronic pancreatitis served as controls. It was found that tissue samples from patients with pancreatic cancer had significantly higher levels of both aromatic DNA adducts and 8-OH-dG compared with control samples. The mean (+/-S.D.) levels of aromatic DNA adducts were 101.8+/-74.6, 26.9+/-26.6, and 11.2+/-6.6 per 10(9) nucleotides in adjacent tissues, tumors, and controls, respectively. The mean (+/-S.D.) levels of 8-OH-dG were 11.9+/-9.6, 10.8+/-10.6, and 6.7+/-4.6 per 10(5) nucleotides in adjacent tissues, tumors, and controls, respectively. Polymorphisms of the CYP1A1, CYP2E1, NAT1, NAT2, GSTM1, MnSOD, and hOGG1 genes were determined in these patients. The level of aromatic DNA adducts was significantly associated with polymorphism of the CYP1A1 gene. No significant correlation was found between the level of 8-OH-dG and the MnSOD, GSTM1, and hOGG1 polymorphisms. However, one novel polymorphism/mutation of the hOGG1 gene was found in a pancreatic tumor. Mutation at codon 12 of the K-ras gene was found in 25 (81%) of 31 pancreatic tumors, including three G-to-A transitions and 22 G-to-T transversions. Patients with the G-to-T mutation had a significantly higher level of aromatic DNA adducts than those with G-to-A or wild-type codon (P=0.02). On the other hand, the K-ras mutation profile was not related to the level of 8-OH-dG. Given the limitation of sample size, these preliminary data lend further support the hypothesis that carcinogen exposure and oxidative stress are involved in pancreatic carcinogenesis.

Expression of Kin17 and 8-OxoG DNA glycosylase in cells of rodent and quail central nervous system

Kin17 and 8-Oxoguanine DNA glycosylase (Ogg1) are proteins, respectively, involved in illegitimate recombination and DNA repair in eukaryotic cells. To characterize the expression of these proteins in cell types of rodent and avian brains, we combined immunocytochemistry for either Kin17 or Ogg1 proteins with glial fibrillary acidic protein (GFAP, an astrocyte marker) immunodetection on the same tissue section. Both Kin17 and Ogg1 proteins were localized in cell nuclei and were extensively distributed in neuronal populations of quail and rodent brains. However, GFAP-immunoreactive cells were never labeled by Kin17 protein. This was observed in nerve fiber tracts, in the cerebral cortex, the hippocampal formation, the hypothalamic region, and the periventricular regions of the brain of both species studied. These results were confirmed by combining in situ hybridization of kin17 mRNA and GFAP immunodetection. On the contrary, GFAP-immunoreactive cells were often labeled by the Ogg1 protein in brain structures such as fiber tracts, the cortical surface, the cerebellum, and the ependymal surface of both quail and mouse brains. Our results suggest that the expression of the Kin17 protein (observed in neurons) and that of the Ogg1 protein (observed in neurons and glial cells) is conserved in brain phylogeny.

hOGG1 exon7 polymorphism and gastric cancer in case-control studies of Japanese Brazilians and non-Japanese Brazilians

Polymorphism of hOGG1 may be capable of serving as a genetic marker for individual susceptibility to various cancers because of its role in the repair of oxyradical DNA damage. We examined the distribution of the hOGG1 Ser326Cys polymorphism and its presumed correlation with gastric cancer risk in two case-control studies of different ethnic groups in São Paulo, Brazil. Potentially eligible Japanese (JB) and non-Japanese Brazilian (NJB) case subjects were defined as patients with newly diagnosed malignant neoplasms of the stomach in 13 hospitals in São Paulo. Ninety-six JBs and 236 NJBs were adopted as subjects. Two controls were matched for each JB case, and one control for each NJB case. The subjects were interviewed using a questionnaire and their blood samples were collected. A significant difference in the distribution of this polymorphism between the two ethnic groups was observed (chi(2)=58.3, P<0.01). The mutant type (Ser/Cys or Cys/Cys) was predominant (approximately 65%) in the JBs, but was only present in approximately 40% of the NJBs. Logistic regression analysis showed no significant increased risk for either the Ser/Cys or Cys/Cys type in either group. The odds ratios of the Cys allele for gastric cancer were 1.01 (95% confidence interval (CI): 0.52-1.93) in the JBs and 0.85 (95% CI: 0.57-1.26) in the NJBs. In the NJBs, a significant increased risk of smoking was shown only in the Ser/Ser type, and no increased risk was shown in the genotypes with the Cys allele. However, no statistically significant interactions were observed with smoking or other possible confounding factors. No statistically significant difference in the distribution of the polymorphism was observed between the intestinal type and diffuse type of gastric cancer in either the JBs or the NJBs. The ethnic difference in hOGG1 Ser326Cys polymorphism was much greater than the case-control difference, and this polymorphism is unlikely to be associated with gastric cancer.

DNA repair activity of 8-oxoguanine DNA glycosylase 1 (OGG1) in human lymphocytes is not dependent on genetic polymorphism Ser326/Cys326

8-oxoguanine DNA glycosylase 1 (OGG1) is a DNA repair enzyme that excises 7,8-dihydro-8-oxoguanine (8oxoG) from DNA. Since 8oxoG is a highly mispairing lesion, decreased OGG1 expression level could lead to a higher background mutation frequency and could possibly increase the cancer risk of an individual under oxidative stress. In order to analyse the natural variation of OGG1, we measured the DNA repair activity in human lymphocytes of healthy individuals by means of an 8oxoG-containing oligonucleotide assay. The data obtained revealed a two fold interindividual variation of OGG1 activity in lymphocytes. There was no difference in OGG1 activity due to gender and smoking behaviour. Transcriptional analyses of OGG1 showed the expression of two isoforms, 1a and b, in lymphocytes. Structural analysis of the human OGG1 (hOGG1) gene revealed a Ser326/Cys326 polymorphism in the Caucasian population with allele frequencies of 75% for Ser326 and 25% for Cys326. This polymorphism was not associated with altered OGG1 activity. The described routine test system for measuring OGG1 activity in cryopreserved lymphocytes provided highly reproducible results and is a useful tool for risk assessment associated with alterations in the repair of oxidative DNA damage.

Oxidative DNA damage and 8-hydroxy-2-deoxyguanosine DNA glycosylase/apurinic lyase in human breast cancer

To test the hypothesis that oxidative stress is involved in breast cancer, we compared the levels of 8-hydroxy-2-deoxyguanosine (8-oxo-dG), an oxidized DNA base common in cells undergoing oxidative stress, in normal breast tissues from women with or without breast cancer. We found that breast cancer patients (N = 76) had a significantly higher level of 8-oxo-dG than control subjects (N = 49). The mean ( +/- SD) values of 8-oxo-dG/10(5) dG, as measured by high-performance liquid chromatography electrochemical detection, were 10.7 +/- 15.5 and 6.3 +/- 6.8 for cases and controls, respectively (P = 0.035). This difference also was found by immunohistochemistry with double-fluorescence labeling and laser-scanning cytometry. The average ratios (x10(6)) of the signal intensity of antibody staining to that of DNA content were 3.9 +/- 7.2 and 1.1 +/- 1.4 for cases (N = 57) and controls (N = 34), respectively (P = 0.008). There was no correlation between the ages of the study subjects and the levels of 8-oxo-dG. Cases also had a significantly higher level of 8-hydroxy-2-deoxyguanosine DNA glycosylase/apurinic lyase (hOGG1) protein expression in normal breast tissues than controls (P = 0.008). There was no significant correlation between hOGG1 expression and 8-oxo-dG. Polymorphism of the hOGG1 gene was very rare in this study population. The previously reported exon 1 polymorphism and two novel mutations of the hOGG1 gene were found in three of 168 cases and two of 55 controls. In conclusion, normal breast tissues from cancer patients had a significantly higher level of oxidative DNA damage. The elevated level of 8-oxo-dG in cancer patients was not related to age or to deficiency of the hOGG1 repair gene.

Expression of hepatocyte growth factor, transforming growth factor alpha, apoptosis related proteins Bax and Bcl-2, and gastrin in human gastric cancer

BACKGROUND

Gastric cancer is one of the most frequent neoplasms and a leading cause of the death world-wide. In recent years, epidemiological and animal studies demonstrated a link between gastric cancer and chronic infection with H. pylori. The exact mechanism responsible for the development of gastric cancer in H. pylori-infected patients still remains unclear. There is evidence that the up-regulation of certain growth factors could play an important role in the promotion of the gastric carcinogenesis.

AIMS

The present study was designed to determine the gene expression of major known growth factors such as transforming growth factor alpha (TGFalpha), hepatocyte growth factor (HGF) and gastrin in the gastric cancer tissue, the surrounding mucosa and, for comparison, in the normal gastric mucosa. Furthermore, the luminal and plasma levels of gastrin in patients with gastric cancer were determined. In addition, the gene and protein expressions of apoptosis-related proteins such as Bax and Bcl-2 were investigated by reverse transcription-polymerase chain reaction and Western blot. Twenty-five gastric cancer patients and 40 age- and gender-matched control subjects hospitalized with non-ulcer dyspepsia were included into this study.

RESULTS

An overall H. pylori-seropositivity among gastric cancer patients was about 72% and was significantly higher than in the controls (56%). The prevalence of CagA-positive strains was also significantly higher among gastric cancer patients than in controls (56% vs. 32%). The gene expression of HGF and TGFalpha was detected more frequently in gastric cancer tissue samples than in normal gastric mucosa (52% vs. 12% for HGF and 48% vs. 24% for TGFalpha). The extent of protein expression in Western blotting analysis for HGF and TGFalpha correlated with the mRNA expression of these factors. Gene expression of gastrin was detected in the antrum of all tested patients and in the majority (84%) of gastric cancer patients. The median plasma and luminal concentrations of gastrin in gastric cancer patients were significantly higher than in controls. The gene expression of bcl-2 was detected in all (100%) and that of proapoptotic bax only in 56% of gastric cancer samples. In comparison to the surrounding non-tumorous tisssue, the gene expression of bax was significantly down-regulated and the gene expression of bcl-2 was up-regulated in gastric cancer tissue. At the protein level, Bax was not detectable and Bcl-2 was seen in 80% of gastric cancer samples.

CONCLUSIONS

It is concluded that the patients infected with H. pylori, especially with CagA-positive strains, are at a higher risk of developing a gastric cancer. An increased production and release of gastrin, as well as an over-expression of growth factors such as HGF and TGFalpha, might contribute to the gastric carcinogenesis. In addition, a dysregulation of the Bax/Bcl-2 system with significant up-regulation of Bcl-2 is observed in gastric cancer.

Ser326Cys polymorphism in hOGG1 gene and risk of esophageal cancer in a Chinese population

Ser326Cys polymorphism in the hOGG1 gene, which is involved in the repair of 8-hydroxyguanine in oxidatively damaged DNA, has been identified and the variant genotype appears to be related to susceptibility to certain cancers. We investigated the association between Ser326Cys polymorphism and squamous-cell carcinoma of the esophagus among a Chinese population. hOGG1 gene polymorphism was detected by PCR-based single-strand conformation polymorphism and DNA sequencing among 201 normal controls and 196 patients with esophageal cancer from Linxian, China, a high-risk area for the disease. The association between this genetic polymorphism and risk of the cancer was examined by a multivariate analysis. We found that the distribution of hOGG1 Ser326Cys genotypes among controls (Ser/Ser, 33.8%; Ser/Cys, 52.8%; and Cys/Cys, 13.4%) was significantly different from that among esophageal cancer cases (39.8%, 38.8% and 21.4%, respectively) (p < 0.05). Homozygosity for the Cys/Cys genotype significantly increased the risk of developing esophageal squamous-cell carcinoma, with the odds ratio (OR) adjusted for age, sex and smoking being 1.9 (95% confidence interval [CI] = 1.3-2.6). Although smoking alone also significantly increased esophageal cancer risk in this case-control study (adjusted OR = 2.6; 95% CI = 1.7-3.9), no significant interaction between smoking and the Cys/Cys genotype was observed in terms of risk. Our results suggest that the hOGG1 326Cys allele might play a role in the carcinogenesis of the esophagus.

Spontaneous loss-of-function mutations of the 8-oxoguanine DNA glycosylase gene in mice and exploration of the possible implication of the gene in senescence

8-Oxoguanine is one of the major premutagenic oxidative base legions in vivo and is suspected to play a crucial role in various pathophysiological processes, such as cancer and aging. Mammalian 8-oxoguanine DNA glycosylase (OGG1) is thought to play a major role in the removal of 8-oxoguanine adducts in vivo. We have identified several inbred mouse strains with a spontaneous mutation, OGG1-R336H or double mutations, OGG1-R304W/R336H. R304W mutation caused a complete loss of OGG1 activity, while the R336H mutation led to disruption of nuclear localization of the enzyme although the activity remained normal. Among the double mutants was SAMP1, which exhibits accelerated senescence and short lifespan. We assessed the possible implication of the mutant OGG1 and 8-oxoguanine in aging utilizing SAMP1 mice. SAMP1 retained 1.5- to 1.9-fold increase in 8-oxoguanine level of hepatic nuclear DNA as compared with normal mice, until at least 12 months of age. A genetic association study, however, indicated that the mutant Ogg1 gene per se is not responsible for the accelerated senescence and short lifespan of SAMP1. Mutant OGG1 may be associated with pathologic conditions in other mouse strains.

Common polymorphisms and somatic mutations in human base excision repair genes in ovarian and endometrial cancers

The purpose of this study was to determine whether the human APEX and OGG1 genes, encoding proteins important in base excision repair (BER) of DNA, contain nucleotide sequence polymorphisms or are mutated somatically in tumors from women diagnosed with ovarian or endometrial cancer. Based upon the analysis of germline DNA from 83 individuals, 63 with ovarian cancer and 20 with endometrial cancer, we found two missense polymorphisms in APEX (Q51H and D 148E) and two missense (A3P and S326C) and one intronic (Exon 5-15 bp) polymorphism in OGG1. The frequencies of the various alleles (in the ovarian and endometrial cancer patients combined) were 4.8% for 51-His and 56.2% for 148-Glu in APEX, and 1.0% for 3-Pro and 20.0% for 326-Cys in OGG1. Somatic mutations in APEX (P112L, W188X and R237C) were identified in three of 20 endometrial tumors, but no mutations were identified in APEX in 43 ovarian tumors, or in OGG1 at either tumor site. Given the crucial role of the APEX and OGG1 proteins in BER of oxidative DNA damage, the identified polymorphisms are good candidates for genetic epidemiologic studies of cancer susceptibility, while the finding that three of 20 (15%) endometrial tumors have somatic mutations in APEX suggests that inactivation of the BER pathway is important for the development of endometrial cancer in at least a subset of cases.

Human DNA repair genes

DNA repair systems are essential for the maintenance of genome integrity. Consequently, the disregulation of repair genes can be expected to be associated with significant, detrimental health effects, which can include an increased prevalence of birth defects, an enhancement of cancer risk, and an accelerated rate of aging. Although original insights into DNA repair and the genes responsible were largely derived from studies in bacteria and yeast, well over 125 genes directly involved in DNA repair have now been identified in humans, and their cDNA sequence established. These genes function in a diverse set of pathways that involve the recognition and removal of DNA lesions, tolerance to DNA damage, and protection from errors of incorporation made during DNA replication or DNA repair. Additional genes indirectly affect DNA repair, by regulating the cell cycle, ostensibly to provide an opportunity for repair or to direct the cell to apoptosis. For about 70 of the DNA repair genes listed in Table I, both the genomic DNA sequence and the cDNA sequence and chromosomal location have been elucidated. In 45 cases single-nucleotide polymorphisms have been identified and, in some cases, genetic variants have been associated with specific disorders. With the accelerating rate of gene discovery, the number of identified DNA repair genes and sequence variants is quickly rising. This report tabulates the current status of what is known about these genes. The report is limited to genes whose function is directly related to DNA repair.

hOGG1 polymorphism and loss of heterozygosity (LOH): significance for lung cancer susceptibility in a caucasian population

Oxidative damage is implicated in several chronic diseases including cancer. 8-Hydroxyguanine (8-oxoG) is one of the major promutagenic DNA lesions, which is produced by reactive oxygen species, causes G:C to T:A transversions and is excised by OGG1, an 8-oxoG specific DNA glycosylase/AP-Lyase. In a nested case-control study, gDNA from 105 Caucasian primary non-small cell lung cancer cases and 105 matched controls was screened for 6 possible new polymorphic sites in the human OGG1 gene, detected previously mainly in tumour tissue. The previously described Ser(326)Cys polymorphism was found to be common (allele frequency 0.22) in Caucasians. However, no major difference in Ser(326)Cys genotype distribution could be detected between cases and controls. Two 5;-end polymorphisms previously found in Japanese as well as Arg(131)Gln could not be detected in this population. An Ala(85)Ser polymorphism was found in 2 controls, whereas Arg(46)Gln was detected in only 1 case. As the hOGG1 gene is mapped (3p26.2) to a region frequently lost in primary lung tumours, the frequency of loss of heterozygosity (LOH) was investigated. Forty-three percent of the studied lung tumours exhibited loss of one of the hOGG1 alleles. The wt Ser(326) allele was not predominantly lost in our sample set, which suggests a minor role of this polymorphism in tumourgenesis. Our results show that LOH at the hOGG1 gene locus is a very common occurrence in lung tumourgenesis, possibly leading to increased mutational damage due to ROS in smokers. However, the hOGG1 polymorphisms studied are probably not major contributors to individual lung cancer susceptibility in Caucasians.

Detection of 8-oxoG DNA glycosylase activity and OGG1 transcripts in the rat CNS

The oxoguanine DNA glycosylase (Ogg1) is a DNA repair enzyme that excises 7,8-dihydro-8-oxoguanine present in DNA damaged by oxidative stress. We have investigated the expression of the OGG1 gene in different regions of the rat CNS. Biochemical studies on brain homogenates of adult rats have shown that Ogg1 nicking activity is present at relatively similar levels in the cerebral cortex, the hypothalamus, the pons and the cerebellum. Following in situ hybridization with radiolabeled OGG1 cDNA or specific antisense oligonucleotides, OGG1 transcripts showed a widespread but heterogeneous distribution pattern among distinct brain regions of adult rats: high levels of this transcript were detected in the CA1-CA3 layers and the gyrus dentate of the hippocampal formation, the piriform cortex, the supraoptic nuclei, the olivary complex as well as in the pyramidal cells of layer V of the cortex and the Purkinje cells of the cerebellum. In peripheral organs such as the lungs, the stomach and the spleen, OGG1 transcript is however expressed in specific subpopulations of cells. Using a semi-quantitative reverse transcription - polymerase chain reaction assay on total mRNA from the frontal cortex, OGG1 mRNA was determined to be expressed with relatively the same levels in 1-day-old and 7-day-old rats as well as in adult rats. These results provide evidence for the widespread expression of the OGG1 gene in developing and adult brains.

Effect of single mutations in the OGG1 gene found in human tumors on the substrate specificity of the Ogg1 protein

We have investigated the effect of single amino acid substitutions of conserved arginines on the catalytic activities of the human Ogg1 protein (alpha-hOgg1-Ser(326)) (wild-type alpha-hOgg1). Mutant forms of hOgg1 with mutations Arg(46)-->Gln (alpha-hOgg1-Gln(46)) and Arg(154)-->His (alpha-hOgg1-His(154)) have previously been identified in human tumors. The mutant proteins alpha-hOgg1-Gln(46) and alpha-hOgg1-His(154) were expressed in Escherichia coli and purified to homogeneity. The substrate specificities of these proteins and wild-type alpha-hOgg1 were investigated using gamma-irradiated DNA and the technique of gas chromatography/isotope-dilution mass spectrometry. All three enzymes excised 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) and 8-hydroxyguanine (8-OH-Gua) from gamma-irradiated DNA containing a multiplicity of base lesions. Michaelis-Menten kinetics of excision were measured. Significant differences between excision kinetics of these three enzymes were observed. Excision of FapyGua and 8-OH-Gua by wild-type alpha-hOgg1 was greater than that by alpha-hOgg1-Gln(46) and alpha-hOgg1-His(154). The latter mutant protein was less active than the former. The diminished activity of the mutant proteins was more pronounced for 8-OH-Gua than for FapyGua. Cleavage assays were also performed using (32)P-labeled 34mer oligonucleotide duplexes containing a single 8-OH-Gua paired to each of the four DNA bases. The results obtained with the oligonucleotide containing the 8-OH-Gua/Cyt pair were in good agreement with those observed with gamma-irradiated DNA. Wild-type alpha-hOgg1 and its mutants repaired the three mismatches less efficiently than the 8-OH-Gua/Cyt pair. The substitution of Arg(154), in addition to diminishing the activity on 8-OH-Gua, relaxes the selectivity found in the wild-type alpha-hOgg1 for the base opposite 8-OH-Gua. Taken together the results show that the mutant forms alpha-hOgg1-Gln(46) and alpha-hOgg1-His(154) found in human tumors are defective in their catalytic capacities.

Structure and chromosome location of human OGG1

OGG1 (alias MMH) encodes an 8-hydroxyguanine glycosylase, functionally homologous to bacterial mutM. Here, we report its genomic structure and fine chromosome location. The human OGG1 gene corresponding to the isoform 1 transcripts, consists of seven exons, spanning 7,421 bps, while an alternative additional exon, utilized for isoform 2, is located approximately 9 kb downstream. TATA-like sequence was not found in the 5'-upstream region, common in so-called "housekeeping" genes. The last 55 bases of the 3' untranslated region in exon 7 were unexpectedly conserved among species, presumably because the 3' end of the CAMK1 gene, which is transcribed convergently on the opposite strand, is overlapped at the 3' end. By radiation hybrid panel mapping, OGG1 was localized between WI-4179 and AFMA216ZG1 at 3p26, proximal to the VHL gene.