Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.1.30.2 (endonuclease)
18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this study, we investigated the mechanism of apoptosis by 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) in cocultures of parenchymal and nonparenchymal liver cells, since the liver consists of various cell types and they cooperatively respond to chemicals. It was found that cocultures were more susceptible to cell death by Trp-P-1 than culture of each cell type alone. In cocultures, Trp-P-1 induced DNA fragmentation accompanied by the activation of 18-kDa endonuclease. Trp-P-1 (30 microM) caused a rapid increase in Bid protein level in mitochondria and the leakage of cytochrome c from mitochondria into the cytosol 15 min after treatment. On the other hand, an increase in Bax protein and a decrease in Bcl-2 protein were detected in the mitochondrial fraction 2 h after treatment following the increases in p53 protein level and DNA binding activity of NF-kappa B. Caspase-8 was activated within 30 min followed by the activation of downstream caspases as measured using the corresponding peptide substrates. The activation of caspases was also confirmed by cleavage of caspase-3, poly(ADP-ribose)polymerase, and protein kinase C-delta as analyzed by Western blotting. A peptide inhibitor of caspase-8 diminished DNA ladder formation and the activation of downstream caspases, but a caspase-9 inhibitor and pyrrolidinedithiocarbamate as an inhibitor of NF-kappa B showed only partial inhibition, suggesting that caspase-8 is the apical caspase in the cascade. These results led to the conclusion that Trp-P-1 mainly drives the caspase-8-mediated pathway that involves Bid, accompanied by a delay in the p53/NF-kappa B-mediated side pathway that involves Bax, Bcl-2, and caspase-9.
...
PMID:The heterocyclic amine, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole induces apoptosis in cocultures of rat parenchymal and nonparenchymal liver cells. 1170 1

Hydroxyurea is a chemotherapeutic agent used for the treatment of myeloproliferative disorders (MPD) and solid tumors. The mutagenic and carcinogenic potential of hydroxyurea has not been established, although hydroxyurea has been associated with an increased risk of leukemia in MPD patients. To clarify whether hydroxyurea has potential carcinogenicity, we examined site-specific DNA damage induced by hydroxyurea using (32)P-5'-end-labeled DNA fragments obtained from the human p53 and p16 tumor suppressor genes and the c-Ha-ras-1 protooncogene. Hydroxyurea caused Cu(II)-mediated DNA damage especially at thymine and cytosine residues. NADH efficiently enhanced hydroxyurea-induced DNA damage. The DNA damage was almost entirely inhibited by catalase and bathocuproine, a Cu(I)-specific chelator, suggesting the involvement of hydrogen peroxide (H(2)O(2)) and Cu(I). Typical free hydroxyl radical scavengers did not inhibit DNA damage by hydroxyurea, but methional did. These results suggest that crypto-hydroxyl radicals such as Cu(I)-hydroperoxo complex (Cu(I)-OOH) cause DNA damage. Formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) was induced by hydroxyurea in the presence of Cu(II). An electron spin resonance spectroscopic study using N-(dithiocarboxy)sarcosine as a nitric oxide (NO)-trapping reagent demonstrated that NO was generated from hydroxyurea in the presence and absence of catalase. In addition, the generation of formamide was detected by both gas chromatography-mass spectrometry (GC-MS) and time-of-flight-mass spectrometry (TOF-MS). A high concentration of hydroxyurea induced depurination at DNA bases in an H(2)O(2)-independent manner, and endonuclease IV treatment led to chain cleavages. These results suggest that hydroxyurea could induce base oxidation as the major pathway of DNA modification and depurination as a minor pathway. Therefore, it is considered that DNA damage by hydroxyurea participates in not only anti-cancer activity, but also carcinogenesis.
...
PMID:Hydroxyurea induces site-specific DNA damage via formation of hydrogen peroxide and nitric oxide. 1171 40

Cancer development requires the accumulation of numerous genetic changes, which are believed to initiate through the presence of unrepaired lesions in the genome. In the absence of proficient repair, genotoxic agents can lead to crucial mutations of vital cellular genes via replication of damaged DNA. Many cell cycle regulatory proteins are known to modulate the repair capacity and consequently the fate of cells. We and others have recently shown that p53 tumor suppressor gene product is required for efficient global genomic repair (GGR) but not the transcription coupled repair (TCR) of the nucleotide excision repair (NER) sub-pathways. In order to discern the nature of the p53 modulation to be direct or indirect through a downstream mediator, we have investigated the processing of UV radiation induced lesions in human colon carcinoma, HCT116 cells expressing wild-type p53 but having different p21(waf1cip1) (hereafter p21) genotypes (p21+/+, p21+/-, p21-/-). Following 20 J/m(2) UV, all the three cell lines showed rapid increase in p53 protein but the accompanying increase in the expression of its downstream target protein p21 could only be seen in p21+/+ and p21+/- cells and not in p21-/- cells. Nevertheless, an absence of detectable p21 protein in deficient cells had no demonstrable effect on DNA repair response to UV irradiation, as measured by an immunoassay to detect removal of UV photoproducts from genomic DNA (GGR) and by individual strand specific removal of endonuclease-sensitive CPD from a target gene fragment (TCR). Introduction of cytomegalovirus (CMV)-driven luciferase reporter plasmid, UV damaged in vitro, into the un-irradiated cells of varying p21 background, revealed a relatively small but statistically significant decrease in the reporter expression in the host p21-/- as compared with p21+/+ and p21+/- HCT116 cells. Super-expression of p21 protein upon reintroduction of p21 expression construct, showed an enhanced recovery of UV damaged reporter activity that was not greatly different from a similar enhancement observed with undamaged plasmid reporter DNA. Taken together, the results indicate that (i) the p21 protein does not have a significant role in the repair of genomic DNA at chromosomal level; (ii) the well-established p53 dependent modulation of NER is distinct and independent of its cell cycle checkpoint function; and (iii) the reproducible enhancing effect of p21 expression observed through host cell reactivation (HCR) of extrachromosomal DNA is mainly attributable to an effect exerted on transcription rather than repair.
...
PMID:Human cells deficient in p53 regulated p21(waf1/cip1) expression exhibit normal nucleotide excision repair of UV-induced DNA damage. 1189 54

Heteroduplex joints represent intermediates of Rad51-dependent recombination processes, which are recognized by p53 with extremely high affinities, in a manner independent of the DNA sequence content. To determine the structural elements required for complex formation, we monitored DNA-binding by protection against restriction endonuclease cleavage. We show that wild-type (wt) p53 interacts with heteroduplex joints in the proximity of the flexible junction. Association of p53 within this junction region was also observed with preformed Rad51-heteroduplex complexes, whereas SSB counteracted p53 binding. At a distance of 31 bp from the junction p53 established very few contacts with the heteroduplex, despite the presence of an A-G mismatch. Consistently, p53-dependent exonucleolytic degradation decreased when we raised the distance between the junction and the heteroduplex terminus by 27 bp. Different from the cancer-related mutant p53(273H), which did not recognize the junction, tetramerization defective p53-1262 was protection competent but displayed reduced complex stability in gel shifts. Moreover, p53-1262 performed exonucleolytic activities towards ssDNA like wtp53, but reduced degradation of heteroduplex joints. These results suggest that during recombination wild-type p53, as a tetramer, stably binds to strand transfer regions, enabling the protein to exonucleolytically correct heteroduplex intermediates early after strand invasion.
...
PMID:p53 and recombination intermediates: role of tetramerization at DNA junctions in complex formation and exonucleolytic degradation. 1194 96

Background p21 (WAF1/CIP1) is a downstream protein from p53 and can arrest the cell cycle at the G1/S phase in response to signal from p53. The most frequently seen polymorphic site is at codon 31, where a base change from AGC to AGA causes an amino acid change from serine to arginine. Tumor necrosis factor-alpha (TNF-alpha) is a cytokine that is secreted from macrophages, and is related to a sequence of events in the response to inflammation and cancer formation. The TNF-alpha gene promoter -308 G/A polymorphism has been reported to be associated with some cancers. In this study, these polymorphisms were proposed to be a candidate genetic marker of nasopharyngeal carcinoma (NPC). The distribution was analyzed in 47 NPC patients and a control group of 119 healthy people. The association of the p21 codon 31 polymorphism with NPC was detected by polymerase chain reaction (PCR) and restriction analysis by Blp I endonuclease, and calculated by the chi-square test. The TNF-alpha gene promoter -308 G/A polymorphism was identified by Nco I endonuclease. The distribution of the gene p21 codon 31 polymorphisms showed no significant difference between the two groups. The serine form of p21 codon 31 was more prominent in smokers than nonsmokers among the NPC patients (P < 0.05). There was no significant difference in the distribution of TNF-alpha gene promoter -308 G/A polymorphism between control and cancer patients. The results indicate that the gene p21 codon 31 polymorphism and TNF-alpha promoter -308 polymorphism are not correlated with NPC. However, the difference between smokers and nonsmokers suggests that an environmental factor may be involved in association with the p21 gene in the formation of NPC.
...
PMID:Correlation of p21 gene codon 31 polymorphism and TNF-alpha gene polymorphism with nasopharyngeal carcinoma. 1196 52

BRCA1 is critical for the maintenance of genomic stability, in part through its interaction with the Rad50.Mre11.Nbs1 complex, which occupies a central role in DNA double strand break repair mediated by nonhomologous end joining (NHEJ) and homologous recombination. BRCA1 has been shown to be required for homology-directed recombination repair. However, the role of BRCA1 in NHEJ, a critical pathway for the repair of double strand breaks and genome stability in mammalian cells, remains elusive. Here, we established a pair of mouse embryonic fibroblasts (MEFs) derived from 9.5-day-old embryos with genotypes Brca1(+/+):p53(-/-) or Brca1(-/-):p53(-/-). The Brca1(-/-):p53(-/-) MEFs appear to be extremely sensitive to ionizing radiation. The contribution of BRCA1 in NHEJ was evaluated in these cells using three different assay systems. First, transfection of a linearized plasmid in which expression of the reporter gene required precise end joining indicated that Brca1(-/-) MEFs display a moderate deficiency when compared with Brca1(+/+) cells. Second, using a retrovirus infection assay dependent on NHEJ, a 5-10-fold reduction in retroviral integration efficiency was observed in Brca1(-/-) MEFs when compared with the Brca1(+/+) MEFs. Third, Brca1(-/-) MEFs exhibited a 50-100-fold deficiency in microhomology-mediated end-joining activity of a defined chromosomal DNA double strand break introduced by a rare cutting endonuclease I-SceI. These results provide evidence that Brca1 has an essential role in microhomology-mediated end joining and suggest a novel molecular basis for its caretaker role in the maintenance of genome integrity.
...
PMID:BRCA1 facilitates microhomology-mediated end joining of DNA double strand breaks. 1203 51

Due to its minor groove selectivity, Me-lex preferentially generates N3-methyladenine (3-MeA) adducts in double-stranded DNA. We undertook a genetic approach in yeast to establish the influence of base excision repair (BER) defects on the processing of Me-lex lesions on plasmid DNA that harbors the p53 cDNA as target. We constructed a panel of isogenic strains containing a reporter gene to test p53 function and the following gene deletions: deltamag1, deltaapn1apn2, and deltaapn1apn2mag1. When compared with the wild-type strain, a decrease in survival was observed in deltamag1, deltaapn1apn2, and deltaapn1apn2mag1. The Me-lex-induced mutation frequency increased in the following order: wild type < deltamag1< deltaapn1apn2 = deltaapn1apn2mag1. A total of 77 mutants (23 in wild type, 31 in deltamag1, and 23 in deltaapn1apn2) were sequenced. Eighty-one independent mutations (24 in wild type, 34 in deltamag1, and 23 in deltaapn1apn2) were detected. The majority of base pair substitutions were AT-targeted in all strains (14/23, 61% in wild type; 20/34, 59%, in deltamag1; and 14/23, 61%, in deltaapn1apn2). The Mag1 deletion was associated with a significant decrease of GC > AT transitions when compared with both the wild-type and the AP endonuclease mutants. This is the first time that the impact of Mag1 and/or AP endonuclease defects on the mutational spectra caused by 3-MeA has been determined. The results suggest that 3-MeA is critical for Me-lex cytotoxicity and that its mutagenicity is slightly elevated in the absence of Mag1 glycosylase activity but significantly higher in the absence of AP endonuclease activity.
...
PMID:Influences of base excision repair defects on the lethality and mutagenicity induced by Me-lex, a sequence-selective N3-adenine methylating agent. 1204 10

Numerous investigators have reported that irradiation of cells with a low dose of ionizing radiation (IR) can induce a condition of enhanced radioresistance, i.e. a radioadaptive response. In this report, we investigated the hypothesis that a radioadaptive bystander effect may be induced in unirradiated cells by a transmissible factor(s) present in the supernatants of cells exposed to low dose gamma-rays. Normal human lung fibroblasts (HFL-1) were irradiated with a 1 cGy dose of gamma-rays and their supernatants were transferred to unirradiated HFL-1 as a bystander cell model. Compared with the directly irradiated cells, such treatment resulted in increased clonogenic survival following subsequent gamma-irradiation with 2 and 4 Gy. This radioadaptive bystander effect was found to be preceded by early decreases in cellular levels of TP53 protein, increase in intracellular ROS, and increase in the redox and DNA repair protein AP-endonuclease (APE). The demonstration that radioadaptation can occur in unirradiated cells via a fluid-phase, transferable factor(s) adds to the complexity of the current understanding of mechanisms by which radioadaptive responses can be induced by low dose, low-LET IR.
...
PMID:Low dose, low-LET ionizing radiation-induced radioadaptation and associated early responses in unirradiated cells. 1205 98

We used a recently developed method to produce mutant alleles of five endogenous Drosophila genes, including the homolog of the p53 tumor suppressor. Transgenic expression of the FLP site-specific recombinase and the I-SceI endonuclease generates extrachromosomal linear DNA molecules in vivo. These molecules undergo homologous recombination with the corresponding chromosomal locus to generate targeted alterations of the host genome. The results address several questions about the general utility of this technique. We show that genes not near telomeres can be efficiently targeted; that no knowledge of the mutant phenotype is needed for targeting; and that insertional mutations and allelic substitutions can be easily produced.
...
PMID:Targeted mutagenesis by homologous recombination in D. melanogaster. 1208 94

The mutagenicity of a prominent tobacco carcinogen, benzo[a]pyrene (B[a]P), is believed to result from chemical reactions between its diol epoxide metabolite, (+)-anti-7r,8t-dihydroxy-c9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE), and DNA, producing promutagenic lesions, e.g., (+)-trans-anti-7R,8S,9S-trihydroxy-10S-(N(2)-deoxyguanosyl)-7,8,9,10-tetrahydrobenzo[a]pyrene (N(2)-BPDE-dG). Previous studies used the DNA repair enzyme UvrABC endonuclease in combination with ligation-mediated PCR (LMPCR) to demonstrate an increased reactivity of BPDE toward guanine nucleobases within codons 157, 248, and 273 of the p53 tumor suppressor gene (Denissenko, M. F., Pao, A., Tang, M., and Pfeifer, G. P. Science 274, 430-432). These sites are also "hot spots" for mutations observed in lung tumors of smokers, suggesting an involvement of B[a]P in the initiation of lung cancer. However, the LMPCR approach relies on the ability of the repair enzyme to excise BPDE-induced lesions, and thus the slowly repaired lesions may escape detection. Furthermore, BPDE-DNA adduct structure and stereochemistry cannot be determined. In the present work, we performed a direct quantitative analysis of N(2)-BPDE-dG originating from specific guanine nucleobases within p53- and K-ras-derived DNA sequences by using a stable isotope labeling-mass spectrometry approach recently developed in our laboratory. (15)N-labeled dG was placed at defined positions within DNA sequences derived from the K-ras proto-oncogene and p53 tumor suppressor gene, the two genes most frequently mutated in smoking-induced lung cancer. (15)N-labeled DNA was annealed to the complementary strands, followed by BPDE treatment and liquid chromatography-electrospray ionization tandem mass spectrometry analysis (HPLC-ESI-MS/MS) of N(2)-BPDE-dG lesions. The extent of adduct formation at (15)N-labeled guanine was determined directly from the HPLC-ESI-MS/MS peak area ratios of (15)N-N(2)-BPDE-dG and N(2)-BPDE-dG. BPDE-induced guanine adducts were produced nonrandomly along K-ras and p53 gene-derived DNA sequences, with over 5-fold differences in adduct formation depending on sequence context. N(2)-BPDE-dG yield was enhanced by the presence of 5-Me substituent at the cytosine base-paired with the target guanine nucleobase, an endogenous DNA modification characteristic for CpG dinucleotides within the p53 gene. In the K-ras-derived DNA sequence, the majority of N(2)-BPDE-dG adducts originated from the first position of the codon 12 (GGT), consistent with the large number of G --> T transversions observed at this nucleotide in smoking-induced lung cancer. On the contrary, the pattern of N(2)-BPDE-dG formation within the p53 exon 5 sequences did not correlate with the mutational spectrum in lung cancer, suggesting that factors other than N(2)-BPDE-dG formation are responsible for these mutations. The stable isotope labeling HPLC-ESI-MS/MS approach described in this work is universally applicable to studies of modifications to isolated DNA by other carcinogens and alkylating drugs.
...
PMID:Formation of benzo[a]pyrene diol epoxide-DNA adducts at specific guanines within K-ras and p53 gene sequences: stable isotope-labeling mass spectrometry approach. 1213 76


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---