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DNA Repair Pathways (dna + repair_pathway)
Selected AbstractsAnalysis of Saccharomyces cerevisiae null allele strains identifies a larger role for DNA damage versus oxidative stress pathways in growth inhibition by seleniumMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 11 2008Eden Seitomer Abstract Selenium toxicity is a growing environmental concern due to widespread availability of high-dose selenium supplements and the development of high-selenium agricultural drainage basins. To begin to analyze the effects of selenium toxicity at the genetic level, we have systematically determined which genes are involved in responding to high environmental selenium using a collection of viable haploid null allele strains of Saccharomyces cerevisiae representing three major stress pathways: the RAD9 -dependent DNA repair pathway, the RAD6/RAD18 DNA damage tolerance pathway, and the oxidative stress pathway. A total of 53 null allele strains were tested for growth defects in the presence of a range of sodium selenite and selenomethionine (SeMet) concentrations. Our results show that ,64,72% of the strains lacking RAD9 -dependent DNA repair or RAD6/RAD18 DNA damage tolerance pathway genes show reduced growth in sodium selenite versus ,28,36% in SeMet. Interestingly both compounds reduced growth in ,21,25% of the strains lacking oxidative stress genes. These data suggest that both selenite and SeMet are likely inducing DNA damage by generating reactive species. The anticipated effects of loss of components of the oxidative stress pathway were not observed, likely due to apparent redundancies in these gene products that may keep the damaging effects in check. [source] Induction of Persistent Double Strand Breaks Following Multiphoton Irradiation of Cycling and G1 -arrested Mammalian Cells,Replication-induced Double Strand BreaksPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 6 2008Jane V. Harper DNA double strand breaks (DSBs) are amongst the most deleterious lesions induced within the cell following exposure to ionizing radiation. Mammalian cells repair these breaks predominantly via the nonhomologous end joining pathway which is active throughout the cell cycle and is error prone. The alternative pathway for repair of DSBs is homologous recombination (HR) which is error free and active during S- and G2/M-phases of the cell cycle. We have utilized near-infrared laser radiation to induce DNA damage in individual mammalian cells through multiphoton excitation processes to investigate the dynamics of single cell DNA damage processing. We have used immunofluorescent imaging of ,-H2AX (a marker for DSBs) in mammalian cells and investigated the colocalization of this protein with ATM, p53 binding protein 1 and RAD51, an integral protein of the HR DNA repair pathway. We have observed persistent DSBs at later times postlaser irradiation which are indicative of DSBs arising at replication, presumably from UV photoproducts or clustered damage containing single strand breaks. Cell cycle studies have shown that in G1 cells, a significant fraction of multiphoton laser-induced prompt DSBs persists for >4 h in addition to those induced at replication. [source] Mutagenicity of non-homologous end joining DNA repair in a resistant subset of human chronic lymphocytic leukaemia B cellsBRITISH JOURNAL OF HAEMATOLOGY, Issue 5 2006Ludovic Deriano Summary Non-homologous end joining (NHEJ) is an important determinant of genomic stability in mammalian cells. This DNA repair pathway is upregulated in a subset of B-cell chronic lymphocytic leukaemia (B-CLL) cells resistant to DNA damage-induced apoptosis. Using an in vitro assay for double-strand breaks (DSB) end ligation, we studied the fidelity of DSB repair in B-CLL cells which were resistant or sensitive to in vitro DSB-induced apoptosis with concomitant patients' resistance or sensitivity to chemotherapy, respectively. The fidelity of DNA repair was determined by DNA sequencing of polymerase chain reaction products cloned in pGEM-T vector. Sequence analysis of DNA end junctions showed that the frequency of accurate ligation was higher in sensitive B-CLL cells and control cell lines, than in resistant cells where end joining was associated with extended deletions. Upregulated and error-prone NHEJ in resistant cells could be a quite possible mechanism underlying both genomic instability and poor clinical outcome. [source] Formaldehyde and leukemia: Epidemiology, potential mechanisms, and implications for risk assessment,ENVIRONMENTAL AND MOLECULAR MUTAGENESIS, Issue 3 2010Luoping Zhang Abstract Formaldehyde is widely used in the United States and other countries. Occupational and environmental exposures to formaldehyde may be associated with an increased risk of leukemia in exposed individuals. However, risk assessment of formaldehyde and leukemia has been challenging due to inconsistencies in human and animal studies and the lack of a known mechanism for leukemia induction. Here, we provide a summary of the symposium at the Environmental Mutagen Society Meeting in 2008, which focused on the epidemiology of formaldehyde and leukemia, potential mechanisms, and implication for risk assessment, with emphasis on future directions in multidisciplinary formaldehyde research. Updated results of two of the three largest industrial cohort studies of formaldehyde-exposed workers have shown positive associations with leukemia, particularly myeloid leukemia, and a recent meta-analysis of studies to date supports this association. Recent mechanistic studies have shown the formation of formaldehyde-induced DNA adducts and characterized the essential DNA repair pathways that mitigate formaldehyde toxicity. The implications of the updated findings for the design of future studies to more effectively assess the risk of leukemia arising from formaldehyde exposure were discussed and specific recommendations were made. A toxicogenomic approach in experimental models and human exposure studies, together with the measurement of biomarkers of internal exposure, such as formaldehyde-DNA and protein adducts, should prove fruitful. It was recognized that increased communication among scientists who perform epidemiology, toxicology, biology, and risk assessment could enhance the design of future studies, which could ultimately reduce uncertainty in the risk assessment of formaldehyde and leukemia. Environ. Mol. Mutagen., 2010. Published 2009 Wiley-Liss, Inc. [source] DNA repair pathways involved in anaphase bridge formationGENES, CHROMOSOMES AND CANCER, Issue 6 2007Ceyda Acilan Cancer cells frequently exhibit gross chromosomal alterations such as translocations, deletions, or gene amplifications an important source of chromosomal instability in malignant cells. One of the better-documented examples is the formation of anaphase bridges,chromosomes pulled in opposite directions by the spindle apparatus. Anaphase bridges are associated with DNA double strand breaks (DSBs). While the majority of DSBs are repaired correctly, to restore the original chromosome structure, incorrect fusion events also occur leading to bridging. To identify the cellular repair pathways used to form these aberrant structures, we tested a requirement for either of the two major DSB repair pathways in mammalian cells: homologous recombination (HR) and nonhomologous end joining (NHEJ). Our observations show that neither pathway is essential, but NHEJ helps prevent bridges. When NHEJ is compromised, the cell appears to use HR to repair the break, resulting in increased anaphase bridge formation. Moreover, intrinsic NHEJ activity of different cell lines appears to have a positive trend with induction of bridges from DNA damage. © 2007 Wiley-Liss, Inc. [source] Atypical Response of Xeroderma Pigmentosum to 5-Fluorouracil: A Histopathological Image Analysis Study Reveals New Insight into EtiopathogenesisJOURNAL OF CUTANEOUS PATHOLOGY, Issue 1 2005S.A. Centurion Xeroderma pigmentosum (XP) is a recessively inherited genodermatosis associated with extreme sun sensitivity, defective repair of several types of sunlight induced adducts in cellular DNA, and numerous, early-onset skin cancers. The dry, rough skin corresponds to progressive cytologic atypia and loss of polarity in the underlying epidermis. Associated with these changes are immune deficiencies against ultraviolet radiation-induced skin cancer. 5-Fluorouracil (5-FU) is a DNA synthesis antimetabolite used against several types of cancers. Applied topically in normal subjects it is associated with moderate to severe inflammation in areas where actinic keratoses have arisen followed by ablation of the actinic keratoses which is dependent on the inflammation. We applied 5-FU to the sun-exposed skin of two patients with XP, a 14 year-old light complected black male and a 14 year-old Caucasian female. No inflammation was observed, but marked improvement in the clinical presentation of the skin was seen, as well as an absence of new malignancies. This change was confirmed histopathologically and correlated with normalization of polarity and cytologic changes in the epidermal cells. These histologic findings were quantitated using computerized image analysis. These results may be due to activation of alternative DNA repair pathways in these nucleotide excision repair deficient cells. [source] Xeroderma pigmentosum , bridging a gap between clinic and laboratoryPHOTODERMATOLOGY, PHOTOIMMUNOLOGY & PHOTOMEDICINE, Issue 2 2001Shin-Ichi Moriwaki Xeroderma pigmentosum (XP) is an autosomal recessive photosensitive disorder with an extremely high incidence of UV-related skin cancers associated with impaired ability to repair UV-induced DNA damage. There are seven nucleotide excision repair (NER) complementation groups (A through G) and an NER proficient form (XP variant). XPA, B, D and G patients may also develop XP neurological disease. The laboratory diagnosis of XP can be performed by autoradiography. Recently, the isolation and characterization of the genes responsible for XP have made it possible to use molecular biological techniques to diagnose XP patients, for carrier detection and for prenatal diagnosis, especially in Japanese XPA patients. These techniques include polymerase chain reaction (PCR) and plasmid host cell reactivation assays with cloned XP genes. DNA damage is not repaired by the NER system equally throughout the genome. There are two DNA repair pathways: 1) transcription-coupled repair, and 2) global genome repair. Many factors involved in these pathways are related to the pathogenesis of XP and a related photosensitive disease, Cockayne syndrome. Clinical management consists of early diagnosis followed by a rigorous program of sun protection including avoidance of unnecessary UV exposure, wearing UV blocking clothing, and use of sunblocks on the skin. Although there is no cure for XP, the efficacy of oral retinoids for the prevention of new skin cancers, local injection of interferon, and the external use of a prokaryotic DNA repair enzyme have been reported. [source] Folate deficiency followed by ionizing radiation perturbs hepatic dihydrofolate reducatse activityBIOFACTORS, Issue 4 2008Vipen Batra Abstract There is lot of interest in the folate metabolism because of the essential role of folate coenzymes in nucleic acid synthesis. Gamma (,) radiation is well known for inducing damage in the DNA. To counteract these damage, a variety of DNA repair pathways have evolved that require regular supply of DNA bases whose biosynthesis in turn depends on sufficient pools of folate dependent enzymes like dihydrofolate reductase (DHFR). In the present study, we examined the ionizing radiation mediated perturbation of DHFR activity in folate deficient and folate sufficient conditions. In folate deficient animals a potent inhibition of liver DHFR activity was observed. Our results showed that combination of folate starvation and ionizing radiation might adversely affect the DHFR activity, compared to their individual treatments. Measurement of apurinic/apyrimidinic sites (AP sites), a major type of DNA damage generated by radiation induced loss of purine and/or pyrimidine base, indicated a dose dependent DNA damage in folate deficient animals. In conclusion our data suggest an interactive role of folate deficiency and radiation injury in inhibiting DHFR activity. [source] Polymorphisms in ERCC2, MSH2, and OGG1 DNA repair genes and gallbladder cancer risk in a population of Northern IndiaCANCER, Issue 13 2010Kshitij Srivastava MSc Abstract BACKGROUND: Genetic variants of DNA repair enzymes may lead to genetic instability and contribute to gallbladder (GB) carcinogenesis. METHODS: A case-control study (230 GB carcinogenesis patients and 230 controls) was undertaken to evaluate whether genetic variations in 3 DNA repair genes ERCC2 (Asp312Asn [rs1799793] and Lys751Gln [rs13181]), MSH2 (,118T>C [rs2303425] and IVS1 + 9G>C [rs2303426]), and OGG1 (Ser326Cys [rs1052133] and 748-15C>G [rs2072668]) are associated with GB carcinogenesis risk in a North Indian population. RESULTS: The authors found that the ERCC2 Asp312Asn AA, MSH2 IVS1 + 9G>C CC, OGG1 Ser326Cys GG and CG + GG, and OGG1 748-15C>G GG and CG + GG genotypes were significantly associated with an increased risk of GB carcinogenesis (odds ratio [OR], 2.1, 1.8, 2.5, 1.8, 2.0, and 1.6, respectively). In contrast, ERCC2 Lys751Gln, and MSH2 ,118T>C markers showed no significant associations with GB carcinogenesis risk, although because of the small sample size their effects cannot be ruled out. Female GB carcinogenesis patients with the OGG1 748-15C>G GG, OGG1 Ser326Cys GG, and ERCC2 Asp312Asn genotypes had a greater risk for developing the disease (OR, 3.6, 7.7, and 2.7, respectively). There was a significant interaction between MSH2 IVS1 + 9G>C and OGG1 748-15C>G polymorphisms (P = .001). Furthermore, individuals with >6 variant alleles of the studied polymorphisms were at 4-fold increased risk for developing GB carcinogenesis. Classification and Regression Tree analysis revealed potential higher-order gene-gene interactions and categorized a few higher-risk subgroups for GB carcinogenesis. CONCLUSIONS: These results suggest that genetic variants in the DNA repair pathways may be involved in GB carcinogenesis etiology. Cancer 2010. © 2010 American Cancer Society. [source] | ||||||||||||||||||||||