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

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

Human breast carcinoma (MCF7-MLNr) cells resistant to the bifunctional drugs L-phenylalanine mustard (L-PAM, 5-fold resistance), mechlorethamine (9-fold), cisplatin (3-fold), and BCNU (3-fold) were used to investigate the role of DNA repair in the development of resistance to alkylating agents. We have previously shown that neither L-PAM transport and metabolism nor glutathione-associated enzymes were altered in MCF7-MLNr cells, compared to the sensitive cells MCF7-WT. This study shows that treatment of pRSV-CAT plasmid with L-PAM at concentrations up to 1 microM proportionally inhibit the expression of chloramphenicol acetyl transferase (CAT) activity, while higher concentrations abolished CAT activity. pRSV-CAT reactivation was significantly increased when plasmid was transfected into MCF7-MLNr cells, compared to MCF7-WT cells. This indicates that resistant cells have more efficient capacity to recognize and repair L-PAM induced DNA damage. The mRNA expression of DNA nucleotide excision repair genes ERCC1, XPD (ERCC2), XPB (ERCC3), and polymerase beta was found to be similar in both the MCF7-WT and MCF7-MLNr cells. Western blot analysis also reveals no difference in the expression of ERCC1, AP endonuclease, poly (ADP-ribose) polymerase, and alkyl-N-purine-DNA glycosylase proteins. The lack of correlation between enhanced host cell reactivation capacity in resistant cells, and the expression of these specific DNA repair genes suggests that proteins encoded by these genes are not rate limiting steps for resistance to bi-functional alkylating drugs in human breast cancer cells.
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PMID:Enhanced host cell reactivation capacity and expression of DNA repair genes in human breast cancer cells resistant to bi-functional alkylating agents. 749 Nov 21

A human apurinic/apyrimidinic endonuclease activity, called AP endonuclease I, is missing from or altered specifically in cells cultured from Xeroderma pigmentosum group-D individuals (XP-D cells) (Kuhnlein, U., Lee, B., Penhoet, E. E., and Linn, S. (1978) Nucleic Acids Res. 5,951-960). We have now observed that another nuclease activity, UV endonuclease III, is similarly not detected in XP-D cells and is inseparable from the AP endonuclease I activity. This activity preferentially cleaves the phosphodiester backbone of heavily ultraviolet-irradiated DNA at unknown lesions as well as at one of the phosphodiester bonds within a cyclobutane pyrimidine dimer. The nuclease activities have been purified from mouse cells to yield a peptide of M(r) = 32,000, whose sequence indicates identity with ribosomal protein S3. The nuclease activities all cross-react with immunopurified antibody directed against authentic rat ribosomal protein S3, and, upon expression in Escherichia coli of a cloned rat cDNA for ribosomal protein S3, each of the activities was recovered and was indistinguishable from those of the mammalian UV endonuclease III. Moreover, the protein expressed in E. coli and its activities cross-react with the rat protein antibody. Ribosomal protein S3 contains a potential nuclear localization signal, and the protein isolated as a nuclease also has a glycosylation pattern consistent with a nuclear localization as determined by lectin binding. The unexpected role of a ribosomal protein in DNA damage processing and the unexplained inability to detect the nuclease activities in extracts from XP-D cells are discussed.
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PMID:Implication of mammalian ribosomal protein S3 in the processing of DNA damage. 777 13

Human cells from patients suffering with xeroderma pigmentosum (XP) characterized by extreme sensitivity to UV light and a high incidence of skin tumors fall into seven complementation groups, XPA to XPG, and are lacking a functional helicase, endonuclease, or lesion-recognizing protein involved in the initial steps during nucleotide excision repair (NER); a number of proteins involved in DNA repair are termed XPA to XPG depending on which one is defective in a particular complementation group of XP and include: (i) proteins involved in the recognition of (6-4) photoproducts (XPE) and of a broad range of lesions such as pyrimidine dimers (XPA); (ii) proteins that are DNA helicases and integral parts of the general transcription factor TFIIH functioning in both transcription and repair (XPB, XPD); (iii) endonucleases that perform the two incisions, the XPG incising six nucleotides (nt) to the 3' side from a photodimer and the ERCC1-XPF protein complex incising 22 nt to the 5' side of the lesion; and (iv) single-strand DNA-binding proteins (XPC). The ERCC6 helicase is largely responsible for coupling transcription to repair whereas XPC seems to be responsible for the repair of the inactive parts of the genome as well as for the repair of the nontranscribed strand in active genes. p53 recognizes insertion/deletion mismatches as well as free ends of DNA produced by ionizing radiation to arrest the cell cycle. Most of the human DNA repair proteins have their counterparts in both budding and fission yeasts and some of them also in E. coli evoking an evolutionary conservation of DNA repair pathways. Accumulation of mutations within repair genes in single cells followed by their escape from the immune surveillance and in clonal expansion may greatly contribute to the appearance and development of human cancers.
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PMID:Xeroderma pigmentosum and molecular cloning of DNA repair genes. 868 16

The repair-deficient mutant rodent cell lines UV20 and UV41, which are defective in the ERCC1/ERCC4[XPF]-mediated 5'-endonuclease activity, are unusually sensitive to gamma-irradiation under hypoxic (but not oxic) conditions. Because this 5'-endonuclease appears to be involved in two distinct (but overlapping) DNA-repair pathways-the nucleotide excision repair pathway and the recombination-dependent pathway for the removal of DNA interstrand cross-links-it is unclear which of these defective activities is responsible for the hypoxic radiosensitivity of UV20 and UV41 cells. Accordingly, we have extended these measurements to the UV5 and UV24 lines which carry mutations in the ERCC2[XPD] and ERCC3[XPB] genes, respectively; both of these genes encode DNA helicases. These two mutants display a sensitivity to ultraviolet light that is similar to that of UV20 and UV41 cells, reflecting their defect in the incision step of the nucleotide excision repair pathway. However, neither UV5 nor UV24 cells are especially cross-sensitive to agents that produce DNA interstrand cross-links, suggesting that the ERCC2 and ERCC3 activities are not crucial for the repair of these lesions. We show that neither UV5 nor UV24 cells exhibit the unusual hypoxic radiosensitivity that characterizes UV20 and UV41 cells. Based on these data and on a comparison of the patterns of cross-sensitivity of these various mutants to other DNA-damaging agents, we conclude that the increased hypoxic radiosensitivity observed in the UV20 and UV41 mutants is due to a defect in the ERCC1/ERCC4-dependent pathway for the repair of DNA cross-links and not in the nucleotide excision repair pathway. The evidence suggests that this sensitivity may be mediated by some type of radiation-induced cross-links, possibly DNA-protein cross-links.
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PMID:The importance of the ERCC1/ERCC4[XPF] complex for hypoxic-cell radioresistance does not appear to derive from its participation in the nucleotide excision repair pathway. 896 Jan 33

The multisubunit basal transcription factor IIH (TFIIH) has a dual involvement in nucleotide excision repair (NER) of a variety of DNA lesions, including UV-induced photoproducts, and RNA polymerase II transcription. In both processes, TFIIH is implicated with local DNA unwinding, which is attributed to its helicase subunits XPB and XPD. To further define the role of TFIIH in NER, functional interactions between TFIIH and other DNA repair proteins were analyzed. We show that the TFIIH-associated ATPase activity is stimulated by both XPA and the XPC-HR23B complex. However, while XPA promotes the ATPase activity specifically in the presence of damaged DNA, stimulation by XPC-HR23B is lesion independent. Furthermore, we reveal that TFIIH inhibits the structure-specific endonuclease activities of both XPG and ERCC1-XPF, responsible for the 3' and 5' incision in NER, respectively. The inhibition occurs in the absence of ATP and is reversed upon addition of ATP. These results point toward additional roles for TFIIH and ATP during NER distinct from a requirement for DNA unwinding in the regulation of the endonuclease activities of XPG and ERCC1-XPF.
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PMID:Novel functional interactions between nucleotide excision DNA repair proteins influencing the enzymatic activities of TFIIH, XPG, and ERCC1-XPF. 1114 Oct 66

The severe xeroderma pigmentosum/Cockayne syndrome (XP/CS) syndrome is caused by mutations in the XPB, XPD and XPG genes that encode the helicase subunits of TFIIH and the 3' endonuclease of nucleotide excision repair (NER). Because XPB and XPD have been implicated in p53-mediated apoptosis, we examined the possible involvement of XPG in this process. After ultraviolet light (UV) irradiation, primary fibroblasts of XP complementation group G (XP-G) individuals with CS enter apoptosis more readily than other NER-deficient cells, but this is unlinked to unrepaired damage. These XP-G/CS cells accumulate p53 post-UV but they fail to accumulate the 90/92 kDa isoforms of Mdm2 and their cellular distribution of Mdm2 is impaired. Apoptosis levels revert to wild type, Mdm2 90/92 kDa isoforms accumulate, and Mdm2 regains its normal post-UV nuclear location in transduced XP-G/CS cells expressing wild-type XPG, but not an XPG catalytic site mutant. These results suggest that XPG suppresses UV-induced apoptosis and that this suppression, most simply, requires its endonuclease function.
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PMID:Suppression of UV-induced apoptosis by the human DNA repair protein XPG. 1616 68

There are more than 50 subtypes of soft tissue sarcomas, among which 30% are associated with specific genetic alterations, including translocations. Several studies have reported associations between cancer risk and polymorphisms of DNA repair genes from the nucleotide excision repair (NER) pathway. NER involves more than 20 proteins whose inactivation leads to xeroderma pigmentosum (XP) or cockayne syndrome (CS), among which XPD, a helicase allowing DNA strand excision by the endonuclease XPG. DNA from 93 patients with synovial sarcomas, myxoid liposarcomas, dermatofibrosarcomas protuberans (DFSP), malignant fibrous histiocytomas and leiomyosarcomas were genotyped for both XPD Lys751Gln and XPG Asp1104His polymorphisms. Departure from Hardy-Weinberg was highly significant for the XPG polymorphism with an excess of heterozygotes in synovial sarcomas (p = 1.5 x 10(-5)), myxoid liposarcomas (p = 1.5 x 10(-4)) and to a lesser extent in DFSP (p = 0.028). In the case of XPD, a significant deviation was observed in synovial sarcomas (p = 3 x 10(-6)) and DFSP (p = 0.0014). When tumors were pooled according to their genetic alterations, the proportion of carriers of the variant XPG allele was significantly increased in sarcomas with specific translocations as compared to sarcomas with complex genetics (p < 10(-9)). No difference was found for XPD. Genotyping of the tumor samples in synovial sarcomas and myxoid liposarcomas revealed frequent loss of heterozygosity for XPG, mostly due to the loss of the frequent allele. For XPD, both alleles were lost with a similar frequency. Our results raise the potential implication of the XPG Asp1104His polymorphism in the occurrence of chromosomal translocations associated with specific subtypes of sarcomas.
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PMID:Genetic polymorphisms of the XPG and XPD nucleotide excision repair genes in sarcoma patients. 1664 69

XPB is a superfamily 2 helicase with a 3'-5' polarity. In eukaryotes, XPB is an integral subunit of the transcription factor TFIIH, which plays a dual role in DNA opening at RNA polymerase II promoters and in establishing the repair bubble around a DNA lesion in nucleotide excision repair. Eukaryotic XPB has only very limited helicase activity in vitro and may function as a DNA-dependent molecular switch to catalyse local distortion of DNA in transcription and repair. Most archaea have one or two homologues of the XPB protein with a presumed role in DNA repair, but only one other subunit of the TFIIH complex, the 5'-3' helicase XPD, has been identified in archaea. Here we report the biochemical characterisation of the two homologous XPB proteins from the crenarchaeon Sulfolobus solfataricus. Although both proteins are single-stranded-DNA-stimulated ATPases, neither displays any helicase activity in vitro, consistent with recent studies of eukaryotic XPB. In almost all archaeal genomes, the xpb gene lies adjacent to a conserved partner gene, and we demonstrate that these two gene products form a physical interaction in vitro. We propose the name Bax1 (Binds archaeal XPB) for this protein, which has a predicted endonuclease domain. XPB and Bax1 may collaborate in processing nucleic acid in an archaeal-specific DNA repair pathway.
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PMID:The archaeal XPB protein is a ssDNA-dependent ATPase with a novel partner. 1817 90

The cytosine nucleoside analogue 2'-C-cyano-2'-deoxy-1-beta-d-arabino-pentofuranosylcytosine (CNDAC) causes DNA single-strand breaks after its incorporation into DNA. This investigation sought to determine if DNA excision repair pathways were activated to repair this damage. Neither the base excision repair nor the mismatch repair pathway seemed to be involved. Cells deficient in the CSB protein, which initiates transcription-coupled nucleotide excision repair (NER) pathway (TC-NER), exhibited increased clonogenic sensitivity to CNDAC, whereas cells deficient in XPC, which initiates global genome NER, were slightly resistant relative to wild-type cells. The cells lacking either helicase XPB, which unwinds 5' of the lesion, or endonuclease XPF, which incises 5' to a lesion, exhibited increased clonogenic sensitivity to CNDAC, as did cells lacking the XPF partner protein ERCC1. This sensitization was independent of p53 function. Repletion of XPF restored sensitivity comparable with the wild type. In contrast, cells lacking either XPD, the 3'-helicase, or the 3'-endonuclease XPG were equally as sensitive as wild-type cells. In comparison, cells deficient in XPF were not sensitized to other cytosine nucleoside analogues, troxacitabine and cytarabine. Thus, the single-strand nick caused by CNDAC is recognized and, in part, repaired by the TC-NER pathway. NER proteins that function in the 5' direction relative to the UV-induced lesion also participate in the repair of the CNDAC-induced nick, in contrast to proteins that process on the 3' side of the lesion.
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PMID:Repair of 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine-induced DNA single-strand breaks by transcription-coupled nucleotide excision repair. 1848 73

PR-104 is a dinitrobenzamide mustard currently in clinical trial as a hypoxia-activated prodrug. Its major metabolite, PR-104A, is metabolized to the corresponding hydroxylamine (PR-104H) and amine (PR-104M), resulting in activation of the nitrogen mustard moiety. We characterize DNA damage responsible for cytotoxicity of PR-104A by comparing sensitivity of repair-defective hamster Chinese hamster ovary cell lines with their repair-competent counterparts. PR-104H showed a repair profile similar to the reference DNA cross-linking agents chlorambucil and mitomycin C, with marked hypersensitivity of XPF(-/-), ERCC1(-/-), and Rad51D(-/-) cells but not of XPD(-/-) or DNA-PK(CS)(-/-) cells. This pattern confirmed the expected dependence on the ERCC1-XPF endonuclease, implicated in unhooking DNA interstrand cross-links at blocked replication forks, and homologous recombination repair (HRR) in restarting collapsed forks. However, even under anoxia, the hypersensitivity of XPF(-/-), ERCC1(-/-), and Rad51D(-/-) cells to PR-104A itself was lower than for chlorambucil. To test whether this reflects inefficient PR-104A reduction, a soluble form of human NADPH:cytochrome P450 oxidoreductase was stably expressed in Rad51D(-/-) cells and their HRR-restored counterpart. This expression increased hypoxic metabolism of PR-104A to PR-104H and PR-104M as well as hypoxia-selective cytotoxicity of PR-104A and its dependence on HRR. We conclude that PR-104A cytotoxicity is primarily due to DNA interstrand cross-linking by its reduced metabolites, although under conditions of inefficient PR-104A reduction (low reductase expression or aerobic cells), a second mechanism contributes to cell killing. This study shows that hypoxia, reductase activity, and DNA interstrand cross-link repair proficiency are key variables that interact to determine PR-104A sensitivity.
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PMID:Roles of DNA repair and reductase activity in the cytotoxicity of the hypoxia-activated dinitrobenzamide mustard PR-104A. 1950 45


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