Distress and DNA repair in human lymphocytes

This research assessed differences in DNA repair in lymphocytes from high-and low-distressed individuals. A median split on Minnesota Multiphasic Personality Inventory (MMPI) Scale 2 divided 28 newly admitted nonpsychotic psychiatric inpatients into high- and low-distress subgroups. The high-distress subgroup had significantly poorer DNA repair in lymphocytes exposed to X-irradiation than low-distress subjects. We also found that lymphocytes obtained from this psychiatric sample had significantly poorer DNA repair than lymphocytes from nonpsychiatric control subjects when compared 5 hr after X-irradiation. A high level of distress therefore appears to be associated with significant dysfunctional differences at the molecular level which may have important implications for health. These data provide evidence for a direct pathway through which distress could influence the incidence of cancer.This research was funded in part by General Molecular Applications, Inc., the Bremer Foundation, the Samuel J. Roessler Fund, and Comprehensive Cancer Center Core Grant CA-16068-09.     

XRCC1与DNA修复

XRCC1是影响细胞对电离辐射的敏感性的第一个哺乳类动物基因。XRCC1通过与PARP、DNA连接酶Ⅲ和DNA多聚酶β等作用,在DNA损伤时单链断裂修复中起重要作用。现就XRCC1的分子生物学特性及XRCC1在DNA修复可能机制进行综述。     

DNA修复与顺铂耐药

顺铂的主要药理机制是损伤细胞DNA，肿瘤细胞DNA修复能力增强则会导致其对顺铂耐药。目前研究发现，DNA修复途径中的核苷酸切除修复、错配修复、碱基切除修复均与顺铂耐药有关，核苷酸切除修复为其中最为重要的途径。     

DNA repair in aging rat neurons

This laboratory, using post-mitotic rat brain neurons as a model system, has been testing the hypothesis that the inherited DNA repair potential would have profound influence on the aging process of the individual. It has been found that both single and double strand breaks in DNA accumulate in neurons with age. Since base excision repair (BER) is the pathway to effect repair of the type of DNA damage that is likely to occur in neurons, model oligo duplexes were used to assess the BER pathway. Both extension of a primer and one or four nucleotide gap repair are markedly reduced in aging neurons as compared with the young. The extension activity could be restored by supplementing the neuronal extracts with pure DNA polymerase beta (pol beta) while the restoration of gap repair needed the addition of both pol beta and DNA ligase. It thus appears that both pol beta and DNA ligase are deficient in aging neurons. We have also established a system to study the non-homologous end joining (NHEJ) mode of DNA repair in neurons. The end joining of cohesive but not of blunt or non-matching ends, is reduced with age and attempts to identify the limiting factor(s) in this case have been unsuccessful so far. These results are reviewed vis-à-vis the existing literature.     

Fight to the bitter end: DNA repair and aging

DNA carries the genetic information that directs complex biological processes; thus, maintaining a stable genome is critical for individual growth and development and for human health. DNA repair is a fundamental and conserved mechanism responsible for mending damaged DNA and restoring genomic stability, while its deficiency is closely related to multiple human disorders. In recent years, remarkable progress has been made in the field of DNA repair and aging. Here, we will extensively discuss the relationship among DNA damage, DNA repair, aging and aging-associated diseases based on the latest research. In addition, the possible role of DNA repair in several potential rejuvenation strategies will be discussed. Finally, we will also review the emerging methods that may facilitate future research on DNA repair.     

糖尿病大鼠心肌DNA损伤及DNA修复酶表达的变化

目的探讨大鼠糖尿病心肌病变的心肌细胞DNA损伤及DNA修复酶OGG1和APE1表达的变化。方法提取糖尿病大鼠心肌组织中DNA、RNA及总蛋白。用Q-PCR检测心肌DNA损伤;用RT-q PCR和Western blot检测DNA修复酶OGG1和APE1表达的变化。用ELISA检测DNA内8羟基脱氧鸟苷(8-OHd G)的含量变化。结果糖尿病大鼠心肌mt DNA出现明显损伤(P0.05),n DNA无明显损伤,DNA内8-OHd G的含量增加(P0.05),OGG1和APE1的表达增加(P0.01)。结论糖尿病大鼠心肌组织内出现mt DNA损伤,虽然OGG1和APE1的表达是增加的,但可能并不足以修复mt DNA的损伤,导致mt DNA的损伤累积,引起心脏功能的损伤。     

DNA错配修复蛋白多功能性的研究进展

DNA错配修复(mismatch repair,MMR)系统是DNA损伤修复的多种途径之一,存在于从细菌、酵母到人体的所有生物体,由一组高保守性酶蛋白组成.其通过校正DNA复制及重组中产生的碱基错配与插入/缺失环,维持所有生物基因组稳定性的功能已研究比较清楚.越来越多的研究还揭示了错配修复蛋白的其他功能:参与调控DNA损伤应答,同源重组,减数分裂的染色体配对和分离,抗体多样性产生及三核苷酸重复序列扩增等过程.本文将对错配修复蛋白多功能性的研究进展作一综述.     

Roles of DNA repair methyltransferase in mutagenesis and carcinogenesis

Summary Alkylation of DNA at theO ⁶-position of guanine is one of the most critical events leading to induction of mutation as well as cancer. An enzyme,O ⁶-methylguanine-DNA methyltransferase, is present in various organisms, from bacteria to human cells, and appears to be responsible for preventing the occurrence of such mutations. The enzyme transfers methyl groups fromO ⁶-methylguanine and other methylated moieties of the DNA to its own molecule, thereby repairing DNA lesions in a single-step reaction. To elucidate the role of methyltransferase in preventing cancer, animal models with altered levels of enzyme activity were generated. Transgenic mice carrying extra copies of the foreign methyltransferase gene showed a decreased susceptibility to alkylating carcinogens, with regard to tumor formation. By means of gene targeting, mouse lines defective in both alleles of the methyltransferase gene were established. Administration of methylnitrosourea to these gene-targeted mice led to early death while normal mice treated in the same manner showed no untoward effects. Numerous tumors were formed in the gene-defective mice exposed to a low dose of methylnitrosourea, while none or only few tumors were induced in the methyltransferase-proficient mice. It seems apparent that the DNA repair methyltransferase plays an important role in lowering a risk of occurrence of cancer in organisms.     

Mutational specificity of alkylating agents and the influence of DNA repair

Alkylating treatments predominantly induce G: C = greater than A:T transitions, consistent with the predicted significance of the miscoding potential of the O6-alG lesion. However, the frequency and distribution of these events induced by any one compound may be diagnostic. SN1 agents that act via an alkyldiazonium cation, such as the N-nitroso compounds, preferentially generate G: C = greater than A:T transitions at 5'-RG-3' sites, while the more SN2 alkylsulfates and alkylalkane-sulfonates do not. The precise nature of this site bias and the possibility of strand bias are target dependent. The extent of this site bias and the contribution of other base substitutions are substituent size dependent. A similar 5'-RT-3' effect is seen for A:T = greater than G:C transitions, presumably directed by O4-alT lesions. The 5'-RG-3' effect, at least, likely reflects a deposition specificity arising from some aspect of helix geometry, although it may be further exaggerated by alkylation-specific repair. Excision repair appears to preferentially reduce the occurrence of ethylation-induced G:C = greater than A:T and A:T = greater than G:C transitions at sites flanked by A:T base pairs. This may be due to an enhancement of the helical distortion imposed by damage at such positions. A similar effect is not seen for methylation-induced mutations and in the case of propyl adducts, the influence of excision repair on the ultimate distribution of mutation cannot be as easily defined with respect to neighbouring sequence.     

A correlation between aging and DNA repair in human epidermal cells

Ultraviolet-induced unscheduled DNA synthesis (i.e. repair synthesis) in human epidermal cells was measured as a function of age. Normal mammary skin specimens were obtained at surgery from 36 female patients, ranging in age from 17 to 77 years. The enzymatically isolated epidermal cells were analyzed for two parameters: (1) the number and percentage of cells carrying out repair synthesis, and (2) the rate of ultraviolet-induced unscheduled thymidine incorporation in individual cells. The results show that the percentage of epidermal cells capable of DNA excision repair synthesis does not decrease significantly with age, but that the rate of unscheduled DNA synthesis in individual cells decreases to a highly significant degree with advancing age.     

Hydrogen peroxide-induced DNA damage and DNA repair in lymphocytes from malnourished children

The aim of this study was to assess DNA repair capacity in lymphocytes of children with protein calorie malnutrition using the single-cell gel electrophoresis (comet) assay. Repair capacity was assessed by estimating the relative decrease of DNA migration length 5, 15, 30, and 60 min after hydrogen peroxide treatment, in three groups of children: well-nourished (WN), well-nourished infected (WN-I), and malnourished infected (MN-I). In addition, the DNA migration length was evaluated in all groups before and after peroxide treatment. Comparison of mean migration lengths observed in WN and WN-I children showed significant differences at all times tested; between WN-I and MN-I differences were also observed, except after hydrogen peroxide exposure. This implies that lymphocytes of WN-I and MN-I children were equally sensitive to hydrogen peroxide. Nevertheless, the MN-I group clearly shows the greatest overall percentage of damaged cells at all times tested. In relation to repair capacity, at 5 min it was approximately 30% in both groups of well-nourished children, but only 20% in MN-I; 15 min after exposure, repair capacity increased to 51% in well-nourished children but only to 31% in MN-I; and at 60 min this capacity increased to 82% in well-nourished but only to 55% in MN-I. These data indicate that lymphocytes of malnourished children show a decreased capacity to repair hydrogen peroxide-induced DNA damage compared to that of well-nourished controls. This reflects that only malnutrition is associated with decreased DNA repair capacity. Additionally, the data confirm that severe infection and malnutrition are two factors clearly associated with increased DNA damage.     

A comparison of DNA repair synthesis in primary hepatocytes from young and old rats

DNA repair synthesis has been compared in primary hepatocyte cultures obtained from 3-month-old and 16-20-month-old rats. Several morphological and metabolic characteristics were determined to assure cultures of comparable quality. DNA damage was induced by the addition of bleomycin or the exposure of the culture to UV irradiation. DNA repair (unscheduled DNA synthesis) was determined by measuring [3H]thymidine incorporation. After UV irradiation, there was almost twice as much [3H]thymidine incorporation in cells obtained from young rats as in those obtained from old rats. Equal amounts of bleomycin resulted in substantially greater damage to DNA in cells from old rats than from young rats. For equal amounts of DNA damage there was again diminished [3H]thymidine incorporation in cells obtained from old rats. Finally equal amounts of bleomycin resulted in equal damage to DNA when the bleomycin was added to isolated rat liver nuclei from young or old rats. Bleomycin treated nuclei from young rats incorporated substantially more [3H]thymidine triphosphate (TTP) than bleomycin treated nuclei from old rats. The results indicate that hepatocytes from old rats are much more susceptible to bleomycin than hepatocytes from young rats and that the capacity for DNA repair synthesis is impaired in hepatocytes from old rats.     

Methodologies for detecting environmentally induced DNA damage and repair

Environmental DNA damaging agents continuously challenge the integrity of the genome by introducing a variety of DNA lesions. The DNA damage caused by environmental factors will lead to mutagenesis and subsequent carcinogenesis if they are not removed efficiently by repair pathways. Methods for detection of DNA damage and repair can be applied to identify, visualize, and quantify the DNA damage formation and repair events, and they enable us to illustrate the molecular mechanisms of DNA damage formation, DNA repair pathways, mutagenesis, and carcinogenesis. Ever since the discovery of the double helical structure of DNA in 1953, a great number of methods have been developed to detect various types of DNA damage and repair. Rapid advances in sequencing technologies have facilitated the emergence of a variety of novel methods for detecting environmentally induced DNA damage and repair at the genome-wide scale during the last decade. In this review, we provide a historical overview of the development of various damage detection methods. We also highlight the current methodologies to detect DNA damage and repair, especially some next generation sequencing-based methods.