Endogenous Mutagens Research Articles

Colon Macrophages Polarized by Commensal Bacteria Cause Colitis and Cancer through the Bystander Effect

Intestinal commensal bacteria have recently been shown to trigger macrophages to produce diffusible clastogens (or chromosome-breaking factors) through a bystander effect (BSE) that mediates DNA damage and induces chromosomal instability in neighboring cells. Colon macrophages appear central to colon carcinogenesis and BSE through the expression of tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2). The former induces netrin-1, a regulator of intestinal epithelial cell apoptosis, and the latter generates trans-4-hydroxy-2-nonenal (4-HNE), an endogenous mutagen. To test whether colon macrophages are key effectors for BSE, we depleted these cells in interleukin-10 knockout mice colonized with Enterococcus faecalis using encapsulated liposomal clodronate (ELC), a bisphosphonate that causes macrophage apoptosis. We observed that E. faecalis polarizes colon macrophages to an M1 phenotype. In addition, depleting these cells suppressed COX-2 and TNF-α, blocked the formation of 4-HNE protein adducts, and inhibited up-regulation of netrin-1—all markers for BSE. Finally, treatment with ELC prevented colitis, β-catenin activation, and cancer formation. These results show that selected human commensals can polarize colon macrophages to the M1 phenotype and, when activated, serve as the key effector for bacterial-induced BSE. Our findings suggest that depleting M1-polarized macro-phages is a mechanism for the chemopreventive activity of bisphosphonates and that it represents a new strategy for preventing colon cancer induced by intestinal commensals.

DNA Damage Processing by Human 8-Oxoguanine-DNA Glycosylase Mutants with the Occluded Active Site

8-Oxoguanine-DNA glycosylase (OGG1) removes premutagenic lesion 8-oxoguanine (8-oxo-G) from DNA and then nicks the nascent abasic (apurinic/apyrimidinic) site by β-elimination. Although the structure of OGG1 bound to damaged DNA is known, the dynamic aspects of 8-oxo-G recognition are not well understood. To comprehend the mechanisms of substrate recognition and processing, we have constructed OGG1 mutants with the active site occluded by replacement of Cys-253, which forms a wall of the base-binding pocket, with bulky leucine or isoleucine. The conformational dynamics of OGG1 mutants were characterized by single-turnover kinetics and stopped-flow kinetics with fluorescent detection. Additionally, the conformational mobility of wild type and the mutant OGG1 substrate complex was assessed using molecular dynamics simulations. Although pocket occlusion distorted the active site and greatly decreased the catalytic activity of OGG1, it did not fully prevent processing of 8-oxo-G and apurinic/apyrimidinic sites. Both mutants were notably stimulated in the presence of free 8-bromoguanine, indicating that this base can bind to the distorted OGG1 and facilitate β-elimination. The results agree with the concept of enzyme plasticity, suggesting that the active site of OGG1 is flexible enough to compensate partially for distortions caused by mutation.

In Vitro Screening for Compounds That Enhance Human L1 Mobilization

The Long interspersed element 1 (LINE1 or L1) retrotransposon constitutes 17% of the human genome. There are currently 80–100 human L1 elements that are thought to be active in any diploid human genome. These elements can mobilize into new locations of the genome, resulting in changes in genomic information. Active L1s are thus considered to be a type of endogenous mutagen, and L1 insertions can cause disease. Certain stresses, such as gamma radiation, oxidative stress, and treatment with some agents, can induce transcription and/or mobilization of retrotransposons. In this study, we used a reporter gene assay in HepG2 cells to screen compounds for the potential to enhance the transcription of human L1. We assessed 95 compounds including genotoxic agents, substances that induce cellular stress, and commercially available drugs. Treatment with 15 compounds increased the L1 promoter activity by >1.5-fold (p<0.05) after 6 or 24 hours of treatment. In particular, genotoxic agents (benzo[a]pyrene, camptothecin, cytochalasin D, merbarone, and vinblastine), PPARα agonists (bezafibrate and fenofibrate), and non-steroidal anti-inflammatory drugs (diflunisal, flufenamic acid, salicylamide, and sulindac) induced L1 promoter activity. To examine their effects on L1 retrotransposition, we developed a high-throughput real-time retrotransposition assay using a novel secreted Gaussia luciferase reporter cassette. Three compounds (etomoxir, WY-14643, and salicylamide) produced a significant enhancement in L1 retrotransposition. This is the first study to report the effects of a wide variety of compounds on L1 transcription and retrotransposition. These results suggest that certain chemical- and drug-induced stresses might have the potential to cause genomic mutations by inducing L1 mobilization. Thus, the risk of induced L1 transcription and retrotransposition should be considered during drug safety evaluation and environmental risk assessments of chemicals.

Global cerebral ischemia induces increased expression of multiple retrotransposons

Retrotransposons (RTs) account for ∼45% of the mammalian genome. They are capable of inserting into new genomic locations, which can result in deleterious outcomes. We examined the response of nine RTs to global cerebral ischemia (GCI) and explored the DNA methylation status of the two significantly altered RTs. Seven of the nine RTs were significantly increased at 24h post-insult in ischemic hippocampus. GCI also led to a significant decrease in the DNA methylation status of intracisternal A-particle (IAP) RT, but had no marked effect upon DNA methylation of long interspersed nucleotide element 1 (L1) RT. In summary, GCI produced marked increases in RT RNA expression and had a differential effect on the DNA methylation status of two RTs in vulnerable hippocampal neurons destined to die. These data suggest that RTs may play an active role in ischemic brain pathology and that these endogenous mutagens and their regulatory elements could be targeted as potential therapeutic targets in this devastating condition.

Mammalian Base Excision Repair: the Forgotten Archangel

Base excision repair (BER) is a frontline repair system that is responsible for maintaining genome integrity and thus preventing premature aging, cancer and many other human diseases by repairing thousands of DNA lesions and strand breaks continuously caused by endogenous and exogenous mutagens. This fundamental and essential function of BER not only necessitates tight control of the continuous availability of basic components for fast and accurate repair, but also requires temporal and spatial coordination of BER and cell cycle progression to prevent replication of damaged DNA. The major goal of this review is to critically examine controversial and newly emerging questions about mammalian BER pathways, mechanisms regulating BER capacity, BER responses to DNA damage and their links to checkpoint control of DNA replication.

Molecular epidemiology of DNA repair gene polymorphisms and head and neck cancer

Although tobacco and alcohol consumption are two common risk factors of head and neck cancer (HNC), other specific etiologic causes, such as viral infection and genetic susceptibility factors, remain to be understood. Human DNA is often damaged by numerous endogenous and exogenous mutagens or carcinogens, and genetic variants in interaction with environmental exposure to these agents may explain interindividual differences in HNC risk. Single nucleotide polymorphisms (SNPs) in genes involved in the DNA damage-repair response are reported to be risk factors for various cancer types, including HNC. Here, we reviewed epidemiological studies that have assessed the associations between HNC risk and SNPs in DNA repair genes involved in base-excision repair, nucleotide-excision repair, mismatch repair, double-strand break repair and direct reversion repair pathways. We found, however, that only a few SNPs in DNA repair genes were found to be associated with significantly increased or decreased risk of HNC, and, in most cases, the effects were moderate, depending upon locus-locus interactions among the risk SNPs in the pathways. We believe that, in the presence of exposure, additional pathway-based analyses of DNA repair genes derived from genome-wide association studies (GWASs) in HNC are needed.

Detection of Polymorphisms of DNA Repair Genes (XRCC1 and XPC) in Prostate Cancer

Prostate cancer is a common disease with a multifactorial and complex etiology. It is the most common male malignancy and the second leading cause of death in many countries. The widespread use of PSA testing has increased the detection of this cancer at earlier stages, although this diagnostic method has proved to be insufficient to identify the disease. DNA in most cells is regularly damaged by endogenous and exogenous mutagens. At least four main partially overlapping damage repair pathways operate in mammals. Common polymorphisms in DNA repair genes may alter protein function and an individual’s capacity to repair damaged DNA; deficits in repair capacity may lead to genetic instability and carcinogenesis. In the present study, we investigated the genotypic distribution of XRCC1 and XPC polymorphisms and its association with prostate cancer risk, pathological staging and Gleason’s scoring. The present study was conducted in the departments of Clinical Pathology, Pathology, and Urology Faculty of Medicine, Alexandria University-Egypt. A total number of 50 patients with pathologically confirmed prostate cancer and 50 age-matched control subjects were enrolled in this study. The diagnosis was made on the basis of histopathological findings, following radical prostatectomy or transurethral resection of the prostate (TURP). Genomic DNA was extracted from peripheral blood using QIAamp blood DNA isolation kits. PCR followed by enzymatic digestion of the PCR products for (XRCC1, XPC) was used for the genotyping of these polymorphisms. Statistical analyses were performed using SPSS statistics version 20. The genotype frequencies of the studied polymorphisms in all the samples (n = 100), PC patients (n = 50) and healthy controls (n = 50) were consistent with the Hardy-Weinberg equilibrium distribution (p-value > 0.05). There was no statistical difference in the genotypes of the XRCC1 Arg399Gln and XPC Lys939Gln between cases and controls. The “Gln” allele frequency of XPC Lys939Gln as well as the “Gln” allele frequency of XRCC1 Arg399Gln tended to be lower in controls than in PC patients. Yet, these decreases were not statistically significant. We also examined the combined effect of XPC and XRCC1 and we found a decreased PC risk when XPC 939 Lys/Lys + Lys/Gln and XRCC1 399 Arg/Arg + Arg/Gln are combined (OR = 0.370, 95% CI = 0.142 - 0.962).

Role of Operon aaoSo-mutT in Antioxidant Defense in Streptococcus oligofermentans

Previously, we have found that an insertional inactivation of aaoSo, a gene encoding L-amino acid oxidase (LAAO), causes marked repression of the growth of Streptococcus oligofermentans. Here, we found that aaoSo and mutT, a homolog of pyrophosphohydrolase gene of Escherichia coli, constituted an operon. Deletion of either gene did not impair the growth of S. oligofermentans, but double deletion of both aaoSo and mutT was lethal. Quantitative PCR showed that the transcript abundance of mutT was reduced for 13-fold in the aaoSo insertional mutant, indicating that gene polarity derived from the inactivation of aaoSo attenuated the expression of mutT. Enzymatic assays were conducted to determine the biochemical functions of LAAO and MutT of S. oligofermentans. The results indicated that LAAO functioned as an aminoacetone oxidase [47.75 nmol H2O2 (min·mg protein)–1]; and MutT showed the pyrophosphohydrolase activity, which removed mutagens such as 8-oxo-dGTP. Like paraquat, aaoSo mutations increased the expression of SOD, and addition of aminoacetone (final concentration, 5 mM) decreased the mutant’s growth by 11%, indicating that the aaoSo mutants are under ROS stress. HPLC did reveal elevated levels of cytoplasmic aminoacetone in both the deletion and insertional gene mutants of aaoSo. Electron spin resonance spectroscopy showed increased hydroxyl radicals in both types of aaoSo mutant. This demonstrated that inactivation of aaoSo caused the elevation of the prooxidant aminoacetone, resulting the cellular ROS stress. Our study indicates that the presence of both LAAO and MutT can prevent endogenous metabolites-generated ROS and mutagens. In this way, we were able to determine the role of the aaoSo-mutT operon in antioxidant defense in S. oligofermentans.

Cyclooxygenase and Prostaglandin in Cancer

See Article on Page 253-258 Inflammation, especially longstanding abnormal inflammation, seems to contribute to neoplastic transformation to some extent. We cannot help thinking of cyclooxygenase (Cox) and prostaglandin (PG) whenever we mention it. Three isoenzymes of Cox have been identified so far: Cox-1, Cox-2, and Cox-3, but Cox-3, recently identified, is a variant of Cox-1 and is also called Cox-1v. It is formed from a frame shift of the original Cox-1 gene, but it seems not to play usual Cox physiologic roles as in inflammation and fever, and it is still being studied [1, 2]. Although Cox-1 and Cox-2 enzymes basically work in the same way, they are expressed in different ways and at different levels in various organs and tissues. That is the reason side effects are different from selective inhibition against each enzyme. Cox-1, as a constitutional enzyme, is expressed from most cells in homeostatic processes and is inhibited in feedback. On the other hand, Cox-2 is mostly an enzyme that is induced under certain conditions such as inflammation or neoplastic process, but is rarely inhibited. Therefore, Cox-2 selective inhibitors effectively play their roles, especially at inflammatory sites, and do not damage the mucosa protection of gastric tissue without prohibiting the secretion of Cox-1, which is easily blocked by nonsteroidal antiinflammatory drugs (NSAIDs) in general. However, the selectivity of Cox-2 inhibitors does not seem to relieve other side effects of NSAIDs. Recently, increased risks of heart attack, cerebral stroke and renal failure have been reported with Cox-2 selective inhibitors, which seems to result from the reduced level of prostacyclin caused by Cox-2 inhibition. Prostacyclin has an important role in preventing platelets aggregation and blood clotting [3, 4]. As we know, Cox converts arachidonic acid in the cell membrane to prostaglandin H2, the precursor of the final series-2 prostanoids such as PGE2, PGD2, PGF2, PGI2, and thromboxane A2. PGE2, one of the final products, is well known for its activities, such as softening the cervix, uterine contraction, inducing abortion, etc., in obstetric field [5]. However, the important thing is that PGE2 has recently been shown to have a strong relation with tumorigenesis in that it increases cell proliferation, angiogenesis and metastatic potential, and inhibits apoptosis and cellular immunity, which seem to be due to the increased expression of PGE2 by Cox-2 because excessive levels of PGE2 and Cox-2 are implicated in mediating several kinds of malignancies. However, we must also consider the Cox-2 activity in tumor tissue on its own without mediating prostaglandins. It can behave directly for tumorigenesis with activities similar to those mentioned above. For example, Cox-2 directly increases the intranuclear nuclear factor-κB, which is the main stimulus for gene activation and replication, and forms endogenous mutagen, malondialdehyde, from arachidonic acid, which can cause a mutation of p53, and stimulates vascular endothelial growth factor for angiogenesis [6, 7]. 15-hydroxyprostaglandin dehydrogenase (15-PGDH) is supposed to degrade PGE2 selectively, and decreased expression of 15-PGDH might also be related with cancer as previously reported [8, 9]. As the author has mentioned, selective PGE2 inhibitors would work for the prevention or treatment of cancer if it developed. However, considering the direct effects of Cox-2 on carcinogenesis, cancer is unfortunately not that simple to get over. Therefore, selective PGE2 inhibitors will continue to be just one of many ordinary agents, but one that has a slight benefit in treating cancer. However numerous, these sorts of studies should form a basis for the future conquest of cancer.

Abstract LB-193: APOBEC3 catalyzed genomic mutations in breast cancer

Abstract In this work, we present evidence that an endogenous DNA mutating protein, APOBEC3, is massively overexpressed in a high proportion of breast cancers and that this overexpression may be responsible for the genetic variability seen in these cancers. Multiple driver mutations are required for cancer development and recent genome-wide approaches have revealed that many cancers, including breast, harbor staggering numbers of mutations, both point mutations as well as gross chromosomal rearrangements. The molecular origins of most of these somatic aberrations remain unclear. In this work, we test the hypothesis that APOBEC3, an endogenous DNA mutator, is a causative factor driving these mutations. One clue derives from the fact that C/G-to-T/A transition mutations, both within and outside of methyl-C-p-G dinucleotide motifs, predominate in subsets of many tumor types, including breast cancer. We demonstrate that APOBEC3, a DNA cytosine deaminase, is a likely endogenous source of mutation in breast cancer. We show, using quantitative reverse transcriptase PCR (qRT-PCR), that APOBEC3 is overexpressed in a majority of commonly available breast cancer cell lines (34/44) when compared to MCF-10A and hTERT-HMEC control lines. This overexpression phenotype persists when examining primary breast tumors (24/37) using patient-matched normal tissues as controls. APOBEC3 is predominantly localized to the nuclear compartment when overexpressed, as seen using fluorescently tagged APOBEC3. Additionally, its catalytic DNA cytosine to uracil deamination activity is dramatically elevated in this compartment in multiple breast cancer cell lines, as quantified using a FRET-based DNA oligonucleotide cleavage assay. This presentation will discuss the potential impact of this potent endogenous mutagen on the breast cancer genome and the implications for tumor evolution and therapy resistance. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-193. doi:10.1158/1538-7445.AM2011-LB-193

Distinct patterns of somatic alterations in a lymphoblastoid and a tumor genome derived from the same individual

Although patterns of somatic alterations have been reported for tumor genomes, little is known on how they compare with alterations present in non-tumor genomes. A comparison of the two would be crucial to better characterize the genetic alterations driving tumorigenesis. We sequenced the genomes of a lymphoblastoid (HCC1954BL) and a breast tumor (HCC1954) cell line derived from the same patient and compared the somatic alterations present in both. The lymphoblastoid genome presents a comparable number and similar spectrum of nucleotide substitutions to that found in the tumor genome. However, a significant difference in the ratio of non-synonymous to synonymous substitutions was observed between both genomes (P = 0.031). Protein–protein interaction analysis revealed that mutations in the tumor genome preferentially affect hub-genes (P = 0.0017) and are co-selected to present synergistic functions (P < 0.0001). KEGG analysis showed that in the tumor genome most mutated genes were organized into signaling pathways related to tumorigenesis. No such organization or synergy was observed in the lymphoblastoid genome. Our results indicate that endogenous mutagens and replication errors can generate the overall number of mutations required to drive tumorigenesis and that it is the combination rather than the frequency of mutations that is crucial to complete tumorigenic transformation.

USP47 Is a Deubiquitylating Enzyme that Regulates Base Excision Repair by Controlling Steady-State Levels of DNA Polymerase β

DNA base excision repair (BER) is an essential cellular process required for genome stability, and misregulation of BER is linked to premature aging, increased rate of mutagenesis, and cancer. We have now identified the cytoplasmic ubiquitin-specific protease USP47 as the major enzyme involved in deubiquitylation of the key BER DNA polymerase (Pol β) and demonstrate that USP47 is required for stability of newly synthesized cytoplasmic Pol β that is used as a source for nuclear Pol β involved in DNA repair. We further show that knockdown of USP47 causes an increased level of ubiquitylated Pol β, decreased levels of Pol β, and a subsequent deficiency in BER, leading to accumulation of DNA strand breaks and decreased cell viability in response to DNA damage. Taken together, these data demonstrate an important role for USP47 in regulating DNA repair and maintaining genome integrity.

Regulation of DNA repair by ubiquitylation

Cellular DNA repair is a frontline system that is responsible for maintaining genome integrity and thus preventing premature aging and cancer by repairing DNA lesions and strand breaks caused by endogenous and exogenous mutagens. However, it is also the principal cellular system in cancer cells that counteracts the killing effect of the major cancer treatments, e.g. chemotherapy and ionizing radiation. Although it is clear that an individual's DNA repair capacity varies, the mechanisms involved in the regulation of repair systems that are responsible for such variations are only just emerging. This knowledge gap is impeding the finding of new cancer therapy targets and the development of novel treatment strategies. In recent years the vital role of post-translational modifications of DNA repair proteins, including ubiquitylation and phosphorylation, has been uncovered. This review will cover recent progress in our understanding of the role of ubiquitylation in the regulation of DNA repair.

Mechanisms in cadmium-induced carcinogenicity: recent insights

Cadmium is an environmental pollutant,with relevant exposures at workplaces and in the general population. The carcinogenicity has been long established, most evident for tumors in the lung and kidney, but with increasing evidence also for other tumor locations. While direct interactions with DNA appear to be of minor importance, the interference with the cellular response to DNA damage, the deregulation of cell growth as well as resistance to apoptosis have been demonstrated in diverse experimental systems. With respect to DNA repair processes,cadmium has been shown to disturb nucleotide excision repair, base excision repair and mismatch repair; consequences are increased susceptibility towards other DNA damaging agents and endogenous mutagens. Furthermore, cadmium induces cell proliferation, inactivates negative growth stimuli, such as the tumor suppressor protein p53, and provokes resistance towards apoptosis. Particularly the combination of these multiple mechanisms may give rise to a high degree of genomic instability in cadmium-adapted cells, relevant not only for tumor initiation, but also for later steps in tumor development. Future research needs to clarify the relevance of these interactions for low exposure conditions in humans.

Somatic expression of LINE-1 elements in human tissues

LINE-1 expression damages host DNA via insertions and endonuclease-dependent DNA double-strand breaks (DSBs) that are highly toxic and mutagenic. The predominant tissue of LINE-1 expression has been considered to be the germ line. We show that both full-length and processed L1 transcripts are widespread in human somatic tissues and transformed cells, with significant variation in both L1 expression and L1 mRNA processing. This is the first demonstration that RNA processing is a major regulator of L1 activity. Many tissues also produce translatable spliced transcript (SpORF2). An Alu retrotransposition assay, COMET assays and 53BP1 foci staining show that the SpORF2 product can support functional ORF2 protein expression and can induce DNA damage in normal cells. Tests of the senescence-associated β-galactosidase expression suggest that expression of exogenous full-length L1, or the SpORF2 mRNA alone in human fibroblasts and adult stem cells triggers a senescence-like phenotype, which is one of the reported responses to DNA damage. In contrast to previous assumptions that L1 expression is germ line specific, the increased spectrum of tissues exposed to L1-associated damage suggests a role for L1 as an endogenous mutagen in somatic tissues. These findings have potential consequences for the whole organism in the form of cancer and mammalian aging.

A novel Escherichia coli‐derived mutation detected with the Big Blue® cII mutant selectable assay

Transgenic mouse mutation detection systems allow investigation of the origins and mechanisms of mutation associated with exogenous and endogenous mutagen exposures in individual tissues and cell types. In the past, selection assays for transgenic mutants have been contaminated with nonmurine-derived mutations and assay validation is critical to ensure murine in vivo origins of mutations. This is critical in studies of spontaneous mutations and extrapolation to endogenous mammalian genes. Herein, we provide one measure of the contribution of Escherichia coli (E. coli)-derived mutations to the Big Blue(R) cII transgene mutant selection assay. We report the first direct evidence of an E. coli-derived cII mutation identified among mutations recovered in the cII selective assay. An E. coli transposable 5 (Tn5) element IS50R inverted repeat (1,534 bp) was identified at base pair 414 in the cII transgene and the insertion generated a 9 bp target site duplication typical of this type of transposition. The bacterial transposition occurred only once in the assay of 25 x 10(6) plaque forming units and sequencing of 1,177 cII mutants. The observed frequency of this type of mutation is 4 x 10(-8) in retrieved lambda phage and 8.5 x 10(-4) in harvested cII mutants and thus a very rare occurrence in typical analyses of spontaneous in vivo mutations. Given that the frequency of transposition is equal to, or an order of magnitude higher, than the frequency of point mutations in E. coli, this article provides excellent validation for the murine origins of mutations detected using the cII mutant selection assay.

Nucleotides function as endogenous chemical sensors for oxidative stress signaling

Oxidized and nitrated nucleotides including 8-oxogunanine and 8-nitroguanine derivatives such as 8-nitroguanosine 3',5'-cyclic monophosphate were generated by reactive nitrogen oxides and reactive oxygen species in cultured cells and in tissues. 8-oxoguanine and 8-nitroguanine in DNA and RNA are potentially mutagenic, and the former also induces cell death. Some derivative, 8-nitroguanosine 3',5'-cyclic monophosphate a major nitrated guanine nucleotide, was identified as a novel second messenger. Surprisingly, the amount of 8-nitroguanosine 3',5'-cyclic monophosphate generated was found to be higher than that of guanosine 3',5'-cyclic monophosphate in cells expressing inducible nitric oxide synthase. More important, 8-nitroguanosine 3',5'-cyclic monophosphate is electrophilic and reacted efficiently with sulfhydryls of proteins to produce a novel posttranslational modification (named S-guanylation) via guanosine 3',5'-cyclic monophosphate adduction. For example, 8-nitroguanosine 3',5'-cyclic monophosphate-induced S-guanylation of Kelch-like ECH-associated protein 1 led to NF-E2-related factor activation and induction of antioxidant enzymes. 8-nitroguanosine 3',5'-cyclic monophosphate may thus protect cells against oxidative stress-related cytotoxicity. Therefore, although chemically modified nucleotides produced via oxidative and nitrative stress are regarded simply as endogenous mutagens, the endogenous nucleotides stored in cells per se may serve functionally as a sensing mechanism for reactive nitrogen oxides and oxygen species to induce cellular adaptive responses to oxidative stress.

Psychogenic carcinogenesis: Carcinogenesis is without exogenic carcinogens

The history of researches of a problem of cancer has cleared a number of key cellular-molecular-genetic mechanisms of carcinogenesis, however process of carcinogenesis, is still out of control and a world forecast is unfavorable despite the advanced pathogenetically focused medication and excellent results of cancer treatment in vivo. Numerous researches have shown that chronic psycho-emotional stress by means of stressful hormones and endogenous mutagens (reactive oxygen and nitrogen species) are capable to damage cells DNA and to compromise immune system. Actually, chronic psycho-emotional stress is capable to activate the key mechanisms of carcinogenesis. It specifies an opportunity of existence psychogenic carcinogenesis--"carcinogenesis is without carcinogens" which can function as independent and in a combination with physical, chemical and biological carcinogens, strengthening their carcinogenic effect. At cancer patients with psychogenically induced carcinogenesis use only the somatically focused therapy of a cancer (surgery, radiotherapy, chemotherapy, immunotherapy), apparently, is not enough for achievement of steady remission. At psychogenically induced carcinogenesis creation of effective anticarcinogenic medicines is also apparently problematic. The presented hypothesis allows to hope for search in the future of diagnostic criteria of revealing of persons with psychogenic also and development of new strategy of the second prophylactic, treatments and rehabilitations such cancer patients. The hypothesis psychogenic carcinogenesis expands existing representations about pathogenesis of malignant tumors and forms holistic approach to the decision of problems of a cancer at the person.

Haplotype analysis of XRCC1 (at codons 194 and 399) and breast cancer risk, a case–control study

DNA in most cells is regularly damaged by endogenous and exogenous mutagens. Among DNA repair systems, the base excision repair pathway is responsible for the repair of oxidative DNA damage and single-strand breaks. The X-ray repair cross-complementation group 1 (XRCC1) protein plays an important role in base excision repair. Several polymorphisms in the XRCC1 gene have been described, including Arg194Trp (db SNP rs. 1799782). Since it has been suggested that the XRCC1 codon 194 polymorphism might be associated with significant alterations in the DNA repair capacity, the present study was undertaken. Blood samples from 186 females with breast cancer and 187 age- and sex-matched healthy individuals were collected. The genotypes were determined using a polymerase chain reaction-restriction fragment length polymorphism method. Allele frequency of 194Trp was low in both cancer patients and controls (0.0968 and 0.0802, respectively) and exhibited a similar distribution within both groups (odd ratio = 1.22, 95% confidence interval: 0.74–2.04, P = 0.426). The association between Arg194Trp polymorphism and breast cancer risk was not significant neither in Trp/Trp (P = 1.0) nor Arg/Trp (P = 0.273) genotypes compared with the Arg/Arg genotype. The close physical proximity of the polymorphisms at codons 194 and 399 of XRCC1 place them in linkage disequilibrium (patients: D′ = 0.8386, P 0.05) was noted.

Crystal Structures of Two Archaeal 8-Oxoguanine DNA Glycosylases Provide Structural Insight into Guanine/8-Oxoguanine Distinction

Among the four DNA bases, guanine is particularly vulnerable to oxidative damage and the most common oxidative product, 7,8-dihydro-8-oxoguanine (8-oxoG), is the most prevalent lesion observed in DNA molecules. Fortunately, 8-oxoG is recognized and excised by the 8-oxoguanine DNA glycosylase (Ogg) of the base excision repair pathway. Ogg enzymes are divided into three separate families, namely, Ogg1, Ogg2, and archaeal GO glycosylase (AGOG). To date, structures of members of both Ogg1 and AGOG families are known but no structural information is available for members of Ogg2. Here we describe the first crystal structures of two archaeal Ogg2: Methanocaldococcus janischii Ogg and Sulfolobus solfataricus Ogg. A structural comparison with OGG1 and AGOG suggested that the C-terminal lysine of Ogg2 may play a key role in discriminating between guanine and 8-oxoG. This prediction was substantiated by measuring the glycosylase/lyase activity of a C-terminal deletion mutant of MjaOgg.