Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.2.30 (PARP)
 13,611 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DNA strand breaks arise continuously as the result of intracellular metabolism and in response to a multitude of genotoxic agents. To overcome such challenges to genomic stability, cells have evolved genome surveillance pathways that detect and repair damaged DNA in a coordinated fashion. Here we identify the previously uncharacterized human protein Xip1 (C2orf13) as a novel component of the checkpoint response to DNA strand breaks. Green fluorescent protein-tagged Xip1 was rapidly recruited to sites of DNA breaks, and this accumulation was dependent on a novel type of zinc finger motif located in the C terminus of Xip1. The initial recruitment kinetics of Xip1 closely paralleled that of XRCC1, a central organizer of single strand break (SSB) repair, and its accumulation was both delayed and sustained when the detection of SSBs was abrogated by inhibition of PARP-1. Xip1 and XRCC1 stably interacted through recognition of CK2 phosphorylation sites in XRCC1 by the Forkhead-associated (FHA) domain of Xip1, and XRCC1 was required to maintain steady-state levels of Xip1. Moreover, Xip1 was phosphorylated on Ser-116 by ataxia telangiectasia-mutated in response to ionizing radiation, further underscoring the potential importance of Xip1 in the DNA damage response. Finally, depletion of Xip1 significantly decreased the clonogenic survival of cells exposed to DNA SSB- or double strand break-inducing agents. Collectively, these findings implicate Xip1 as a new regulator of genome maintenance pathways, which may function to organize DNA strand break repair complexes at sites of DNA damage.
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PMID:Human Xip1 (C2orf13) is a novel regulator of cellular responses to DNA strand breaks. 1750 82

Genome integrity is constantly threatened by DNA lesions arising from numerous exogenous and endogenous sources. Survival depends on immediate recognition of these lesions and rapid recruitment of repair factors. Using laser microirradiation and live cell microscopy we found that the DNA-damage dependent poly(ADP-ribose) polymerases (PARP) PARP-1 and PARP-2 are recruited to DNA damage sites, however, with different kinetics and roles. With specific PARP inhibitors and mutations, we could show that the initial recruitment of PARP-1 is mediated by the DNA-binding domain. PARP-1 activation and localized poly(ADP-ribose) synthesis then generates binding sites for a second wave of PARP-1 recruitment and for the rapid accumulation of the loading platform XRCC1 at repair sites. Further PARP-1 poly(ADP-ribosyl)ation eventually initiates the release of PARP-1. We conclude that feedback regulated recruitment of PARP-1 and concomitant local poly(ADP-ribosyl)ation at DNA lesions amplifies a signal for rapid recruitment of repair factors enabling efficient restoration of genome integrity.
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PMID:Feedback-regulated poly(ADP-ribosyl)ation by PARP-1 is required for rapid response to DNA damage in living cells. 1798 72

Recently, we reported that among Singapore Chinese, cigarette smoking and alcohol drinking were independent risk factors for colorectal cancer. Both tobacco smoking and alcohol use are plausible colorectal cancer risk factors, partly due to their ability to induce mutations in the colorectal lumen. In the present study, we investigated the role in colorectal cancer of single-nucleotide polymorphisms in five DNA repair genes: XRCC1 (Arg(194)Trp and Arg(399)Gln), PARP (Val(762)Ala, Lys(940)Arg), XPD (Asp(312)Asn, Lys(751)Gln), OGG1 (Ser(326)Cys), and MGMT (Leu(84)Phe). We conducted this study within the Singapore Chinese Health Study, a population-based cohort of 63,257 middle-aged and older Singapore Chinese men and women enrolled between 1993 and 1998. Our study included 1,176 controls and 310 cases (180 colon and 130 rectum cancer). We observed a positive association between the PARP codon 940 Lys/Arg and Arg/Arg genotypes and colorectal cancer risk [odds ratio (OR), 1.8; 95% confidence interval (95% CI), 1.1-3.1], and an inverse association between the MGMT codon 84 Leu/Phe or Phe/Phe genotypes and colon cancer risk (OR, 0.6; 95% CI, 0.3-0.9), but not rectal cancer (test of heterogeneity by tumor site, P=0.027). We observed evidence that XRCC1 may modify the effects of smoking (interaction P=0.012). The effect of smoking among carriers of the Arg(194)-Gln(399) haplotype was OR=0.7 (95% CI, 0.4-1.1), whereas, among carriers of the Trp(194)-Arg(399) haplotype, it was OR=1.6 (95% CI, 1.1-2.5). We also observed a nonstatistically significant modification of XRCC1 on the effects of alcohol (P=0.245). Whereas alcohol had no effect among carriers of the codon 194 Arg/Arg (OR, 1.0; 95% CI, 0.6-1.7) or Arg/Trp genotypes (OR, 1.1; 95% CI, 0.6-1.9), there was a positive association among carriers of the Trp/Trp genotype (OR, 2.8; 95% CI, 1.0-8.1). Our results support a role for reactive oxygen species as relevant genotoxins that may account for the effects of both smoking and alcohol on colorectal cancer risk.
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PMID:DNA repair single-nucleotide polymorphisms in colorectal cancer and their role as modifiers of the effect of cigarette smoking and alcohol in the Singapore Chinese Health Study. 1800 25

Efficient repair of DNA double-strand breaks (DSBs) is critical for the maintenance of genomic integrity. In mammalian cells, DSBs are preferentially repaired by non-homologous end-joining (NHEJ). We have previously described a new DSBs microhomology end-joining pathway depending on PARP-1 and the XRCC1/DNA ligase III complex. In this study we analysed, with recombinant proteins and protein extracts, the effect of DSB end sequences: (i) on the DSB synapsis activity; (ii) on the end-joining activity. We report that PARP-1 DSB synapsis activity is independent of the DSB sequence and could be detected with non-complementary DSBs. We demonstrate also that the efficiency of DSBs repair by PARP-1 NHEJ is strongly dependent on the presence of G:C base pairs at microhomology termini. These results highlight a new role of the PARP-1 protein on the synapsis of DSBs and could explain why the PARP-1 NHEJ pathway is strongly dependent on the DSBs microhomology sequence.
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PMID:Effect of double-strand break DNA sequence on the PARP-1 NHEJ pathway. 1805 77

Single-strand breaks (SSBs) can occur in cells either directly, or indirectly following initiation of base excision repair (BER). SSBs generally have blocked termini lacking the conventional 5'-phosphate and 3'-hydroxyl groups and require further processing prior to DNA synthesis and ligation. XRCC1 is devoid of any known enzymatic activity, but it can physically interact with other proteins involved in all stages of the overlapping SSB repair and BER pathways, including those that conduct the rate-limiting end-tailoring, and in many cases can stimulate their enzymatic activities. XRCC1(-/-) mouse fibroblasts are most hypersensitive to agents that produce DNA lesions repaired by monofunctional glycosylase-initiated BER and that result in formation of indirect SSBs. A requirement for the deoxyribose phosphate lyase activity of DNA polymerase beta (pol beta) is specific to this pathway, whereas pol beta is implicated in gap-filling during repair of many types of SSBs. Elevated levels of strand breaks, and diminished repair, have been demonstrated in MMS-treated XRCC1(-/-), and to a lesser extent in pol beta(-/-) cell lines, compared with wild-type cells. Thus a strong correlation is observed between cellular sensitivity to MMS and the ability of cells to repair MMS-induced damage. Exposure of wild-type and pol beta(-/-) cells to an inhibitor of PARP activity dramatically potentiates MMS-induced cytotoxicity. XRCC1(-/-) cells are also sensitized by PARP inhibition demonstrating that PARP-mediated poly(ADP-ribosyl)ation plays a role in modulation of cytotoxicity beyond recruitment of XRCC1 to sites of DNA damage.
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PMID:XRCC1 and DNA polymerase beta in cellular protection against cytotoxic DNA single-strand breaks. 1816 76

Many predictive factors of tumor radiosensitivity have been described. Number of clonogenic cells, proliferation rate, hypoxia and intrinsic radiosensitivity are usually considered as the main parameters of tumor control. Intrinsic radiosensitivity is correlated in a first approach to the ability of the cell to detect and repair DNA damages, and so integrity of the different pathways involved in this function: PARP-1, XRCC1, ATM, p53, MRN complex or BRCA1... Genetic polymorphisms of some of these genes, found in normal lymphocytes, have been correlated to late toxicity of normal tissues. But, in tumors, because of the difficulty to obtain samplings and heterogeneity, accurate molecular analysis is not possible in many cases, and no valuable test of radiosensitivity exist at this moment. For example, TP53 gene has been evaluated in many studies and results regarding its potential as a predictive factor of tumor sensitivity are conflicting. Surviving fraction at 2Gy (SF2) allowed a global evaluation of sensitivity, but the obtention of this parameter often takes a long time and failed in 20 to 40%. Evaluation of double-strand break repair capacity by immunochemistry quantification of phosphorylated forms of ATM, H2AX or MRE11 is an interesting topic. However, discovery of tumor stem cells in a number of epithelial tumors could revolutionize the understanding of radiosensitivity. Combination of genomic and functional techniques are probably essential to better predict this parameter.
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PMID:[Determinants and predictive factors of tumour radiosensitivity]. 1818 56

DNA double-strand breaks (DSBs) induced in the genome of higher eukaryotes by ionizing radiation (IR) are predominantly removed by two pathways of non-homologous end-joining (NHEJ) termed D-NHEJ and B-NHEJ. While D-NHEJ depends on the activities of the DNA-dependent protein kinase (DNA-PK) and DNA ligase IV/XRCC4/XLF, B-NHEJ utilizes, at least partly, DNA ligase III/XRCC1 and PARP-1. Using in vitro end-joining assays and protein fractionation protocols similar to those previously applied for the characterization of DNA ligase III as an end-joining factor, we identify here histone H1 as an additional putative NHEJ factor. H1 strongly enhances DNA-end joining and shifts the product spectrum from circles to multimers. While H1 enhances the DNA-end-joining activities of both DNA Ligase IV and DNA Ligase III, the effect on ligase III is significantly stronger. Histone H1 also enhances the activity of PARP-1. Since histone H1 has been shown to counteract D-NHEJ, these observations and the known functions of the protein identify it as a putative alignment factor operating preferentially within B-NHEJ.
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PMID:Histone H1 functions as a stimulatory factor in backup pathways of NHEJ. 1825 87

Ionizing radiation induces a variety of different DNA lesions; in addition to the most critical DNA damage, the DSB, numerous base alterations, SSBs and other modifications of the DNA double-helix are formed. When several non-DSB lesions are clustered within a short distance along DNA, or close to a DSB, they may interfere with the repair of DSBs and affect the measurement of DSB induction and repair. We have shown previously that a substantial fraction of DSBs measured by pulsed-field gel electrophoresis (PFGE) are in fact due to heat-labile sites within clustered lesions, thus reflecting an artifact of preparation of genomic DNA at elevated temperature. To further characterize the influence of heat-labile sites on DSB induction and repair, cells of four human cell lines (GM5758, GM7166, M059K, U-1810) with apparently normal DSB rejoining were tested for biphasic rejoining after gamma irradiation. When heat-released DSBs were excluded from the measurements, the fraction of fast rejoining decreased to less than 50% of the total. However, the half-times of the fast (t(1/2) = 7-8 min) and slow (t(1/2) = 2.5 h) DSB rejoining were not changed significantly. At t = 0, the heat-released DSBs accounted for almost 40% of the DSBs, corresponding to 10 extra DSBs per cell per Gy in the initial DSB yield. These heat-released DSBs were repaired within 60-90 min in all cells tested, including M059K cells treated with wortmannin and DNA-PKcs-defective M059J cells. Furthermore, cells lacking XRCC1 or poly(ADP-ribose) polymerase 1 (PARP1) rejoined both total DSBs and heat-released DSBs similarly to normal cells. In summary, the presence of heat-labile sites has a substantial impact on DSB induction and DSB rejoining rates measured by pulsed-field gel electrophoresis, and heat-labile sites repair is independent of DNA-PKcs, XRCC1 and PARP.
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PMID:Repair of radiation-induced heat-labile sites is independent of DNA-PKcs, XRCC1 and PARP. 1843 38

The consequences of PARP-1 disruption or inhibition on DNA single-strand break repair (SSBR) and radio-induced lethality were determined in synchronized, isogenic HeLa cells stably silenced or not for poly(ADP-ribose) polymerase-1 (PARP-1) (PARP-1(KD)) or XRCC1 (XRCC1(KD)). PARP-1 inhibition prevented XRCC1-YFP recruitment at sites of 405 nm laser micro irradiation, slowed SSBR 10-fold and triggered the accumulation of large persistent foci of GFP-PARP-1 and GFP-PCNA at photo damaged sites. These aggregates are presumed to hinder the recruitment of other effectors of the base excision repair (BER) pathway. PARP-1 silencing also prevented XRCC1-YFP recruitment but did not lengthen the lifetime of GFP-PCNA foci. Moreover, PARP-1(KD) and XRCC1(KD) cells in S phase completed SSBR as rapidly as controls, while SSBR was delayed in G1. Taken together, the data demonstrate that a PARP-1- and XRCC1-independent SSBR pathway operates when the short patch repair branch of the BER is deficient. Long patch repair is the likely mechanism, as GFP-PCNA recruitment at photo-damaged sites was normal in PARP-1(KD) cells. PARP-1 silencing elicited hyper-radiosensitivity, while radiosensitization by a PARP inhibitor reportedly occurs only in those cells treated in S phase. PARP-1 inhibition and deletion thus have different outcomes in terms of SSBR and radiosensitivity.
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PMID:PARP inhibition versus PARP-1 silencing: different outcomes in terms of single-strand break repair and radiation susceptibility. 1860 95

For many years, there has been uncertainty concerning the reason for Hsp70 translocation to the nucleus and nucleolus. Herein, we propose that Hsp70 translocates to the nucleus and nucleoli in order to participate in pathways related to the protection of the nucleoplasmic DNA or ribosomal DNA from single-strand breaks. The absence of Hsp70 in HeLa cells, via Hsp70 gene silencing (knockdown), indicated the essential role of Hsp70 in DNA integrity. Therefore, HeLa Hsp70 depleted cells were very sensitive in heat treatment and their DNA breaks were multiple compared to that of control HeLa cells. The molecular mechanism with which Hsp70 performs its role at the level of nucleus and nucleolus during stress was examined. Hsp70 co-localizes with PARP1 in the nucleus/nucleoli as was observed in confocal studies and binds to the BCRT domain of PARP1 as was revealed with protein-protein interaction assays. It was also found that Hsp70 binds simultaneously to XRCC1 and PARP-1, indicating that Hsp70 function takes place at the level of DNA repair and possibly at the base excision repair system. Making a hypothetical model, we have suggested that Hsp70 is the molecule that binds and interrelates with PARP1 creating the repair proteins simultaneously, such as XRCC1, at the single-strand DNA breaks. Our data partially clarify a previously unrecognized cellular response to heat stress. Finally, we can speculate that Hsp70 plays a role in the quality and integrity of DNA.
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PMID:Hsp70 translocates to the nuclei and nucleoli, binds to XRCC1 and PARP-1, and protects HeLa cells from single-strand DNA breaks. 1908 98


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