Claude Niedergang

Bio: Claude Niedergang is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Poly ADP ribose polymerase & Polymerase. The author has an hindex of 24, co-authored 46 publications receiving 5749 citations. Previous affiliations of Claude Niedergang include École Normale Supérieure & French Alternative Energies and Atomic Energy Commission.

Requirement of poly(ADP-ribose) polymerase in recovery from DNA damage in mice and in cells

Abstract: Poly(ADP-ribose) polymerase [PARP; NAD+ ADP-ribosyltransferase; NAD+: poly(adenosine-diphosphate-d-ribosyl)-acceptor ADP-d-ribosyltransferase, EC 2.4.2.30] is a zinc-finger DNA-binding protein that detects specifically DNA strand breaks generated by genotoxic agents. To determine its biological function, we have inactivated both alleles by gene targeting in mice. Treatment of PARP−/− mice either by the alkylating agent N-methyl-N-nitrosourea (MNU) or by γ-irradiation revealed an extreme sensitivity and a high genomic instability to both agents. Following whole body γ-irradiation (8 Gy) mutant mice died rapidly from acute radiation toxicity to the small intestine. Mice-derived PARP−/− cells displayed a high sensitivity to MNU exposure: a G2/M arrest in mouse embryonic fibroblasts and a rapid apoptotic response and a p53 accumulation were observed in splenocytes. Altogether these results demonstrate that PARP is a survival factor playing an essential and positive role during DNA damage recovery.

XRCC1 Is Specifically Associated with Poly(ADP-Ribose) Polymerase and Negatively Regulates Its Activity following DNA Damage

Abstract: The genomic integrity of cells is controlled by a network of protein factors that assess the status of the genome and either cause progression of proliferation or induce a halt in the cell cycle. In eukaryotes, DNA strand breaks, introduced either directly by ionizing radiation or indirectly following enzymatic incision of a DNA lesion, trigger the synthesis of poly(ADP-ribose) by the enzyme poly(ADP-ribose) polymerase (PARP) (1, 13, 39). At the site of breakage, PARP catalyzes the transfer of the ADP-ribose moiety from its substrate, NAD+, to a limited number of protein acceptors involved in chromatin architecture and DNA metabolism, including the enzyme itself. These modified proteins, which carry long chains of negatively charged ADP-ribose polymers, lose their affinity for DNA and are thus inactivated. The short half-life of the polymer is attributed to the high activity of poly(ADP-ribose) glycohydrolase, which cleaves the ribose-ribose bond (28, 30). Therefore, poly(ADP-ribosylation) is an immediate but transient postranslational modification of nuclear proteins, induced by DNA-damaging agents. The physiological role of PARP has been much debated in the last decade, but recent molecular and genetic approaches, including expression of either a dominant-negative mutant (26, 36, 44) or antisense oligonucleotides (14), have clearly implicated PARP in the base excision repair (BER) pathway. A more definitive assessment of PARP function was recently provided by the generation of PARP-deficient mice by homologous recombination (35, 53). We found that PARP−/− mice are hypersensitive to monofunctional alkylating agents and γ-irradiation and display a marked genomic instability (sister chromatid exchanges and chromatid and chromosome breaks) following DNA damage (35). Interestingly, γ-irradiation of these mice causes acute toxicity of the epithelia of their small intestines (35), as has been observed with other DNA damage and signalling and repair enzyme deficiencies (2, 3), thus emphasizing the crucial function of DNA surveillance programs of rapidly dividing cells. Similar results indicating that PARP is important for the maintenance of genomic stability following environmental or experimental stress were recently obtained (54). In this work, we have used the two-hybrid system to identify genes encoding proteins that putatively interact with PARP and are involved in its biological function. The human PARP cDNA fused to the LexA-encoding DNA-binding domain (DBD) was used as bait to screen a HeLa cDNA library fused with the activation domain of Gal4. This screening resulted in the identification of the BER pathway protein XRCC1 (X-ray repair cross-complementing 1) as a factor that associates with PARP. This interaction was further confirmed by in vivo experiments with glutathione S-transferase (GST)-tagged fusion proteins expressed in Cos-7 and HeLa cells. XRCC1 and PARP were found to interact via their respective BRCT (BRCA1 C terminus) modules (4, 9) and via an additional site located in the N-terminal zinc-finger domain of PARP. This association dramatically decreased the catalytic activity of PARP without modifying its nick sensor function. Therefore, the association of PARP with XRCC1, a partner of DNA ligase III (7, 8) and DNA polymerase β (25), is suggestive of a role in the detection and protection of a DNA strand break and the subsequent targeting of a BER complex to the damaged site.

Functional interaction between PARP-1 and PARP-2 in chromosome stability and embryonic development in mouse

Abstract: The DNA damage-dependent poly(ADP-ribose) polymerases, PARP-1 and PARP-2, homo- and heterodimerize and are both involved in the base excision repair (BER) pathway. Here, we report that mice carrying a targeted disruption of the PARP-2 gene are sensitive to ionizing radiation. Following alkylating agent treatment, parp-2(-/-)-derived mouse embryonic fibroblasts exhibit increased post-replicative genomic instability, G(2)/M accumulation and chromosome mis-segregation accompanying kinetochore defects. Moreover, parp-1(-/-)parp-2(-/-) double mutant mice are not viable and die at the onset of gastrulation, demonstrating that the expression of both PARP-1 and PARP-2 and/or DNA-dependent poly(ADP-ribosyl) ation is essential during early embryogenesis. Interestingly, specific female embryonic lethality is observed in parp-1(+/-)parp-2(-/-) mutants at E9.5. Meta phase analyses of E8.5 embryonic fibroblasts highlight a specific instability of the X chromosome in those females, but not in males. Together, these results support the notion that PARP-1 and PARP-2 possess both overlapping and non-redundant functions in the maintenance of genomic stability.

The Ubiquitin System

Abstract: The selective degradation of many short-lived proteins in eukaryotic cells is carried out by the ubiquitin system. In this pathway, proteins are targeted for degradation by covalent ligation to ubiquitin, a highly conserved small protein. Ubiquitin-mediated degradation of regulatory proteins plays important roles in the control of numerous processes, including cell-cycle progression, signal transduction, transcriptional regulation, receptor down-regulation, and endocytosis. The ubiquitin system has been implicated in the immune response, development, and programmed cell death. Abnormalities in ubiquitin-mediated processes have been shown to cause pathological conditions, including malignant transformation. In this review we discuss recent information on functions and mechanisms of the ubiquitin system. Since the selectivity of protein degradation is determined mainly at the stage of ligation to ubiquitin, special attention is focused on what we know, and would like to know, about the mode of action of ubiquitin-protein ligation systems and about signals in proteins recognized by these systems.

Targeting the DNA repair defect in BRCA mutant cells as a therapeutic strategy

Abstract: BRCA1 and BRCA2 are important for DNA double-strand break repair by homologous recombination, and mutations in these genes predispose to breast and other cancers. Poly(ADP-ribose) polymerase (PARP) is an enzyme involved in base excision repair, a key pathway in the repair of DNA single-strand breaks. We show here that BRCA1 or BRCA2 dysfunction unexpectedly and profoundly sensitizes cells to the inhibition of PARP enzymatic activity, resulting in chromosomal instability, cell cycle arrest and subsequent apoptosis. This seems to be because the inhibition of PARP leads to the persistence of DNA lesions normally repaired by homologous recombination. These results illustrate how different pathways cooperate to repair damage, and suggest that the targeted inhibition of particular DNA repair pathways may allow the design of specific and less toxic therapies for cancer.

Specific killing of BRCA2-deficient tumours with inhibitors of poly(ADP-ribose) polymerase

Abstract: Poly(ADP-ribose) polymerase (PARP1) facilitates DNA repair by binding to DNA breaks and attracting DNA repair proteins to the site of damage. Nevertheless, PARP1-/- mice are viable, fertile and do not develop early onset tumours. Here, we show that PARP inhibitors trigger gamma-H2AX and RAD51 foci formation. We propose that, in the absence of PARP1, spontaneous single-strand breaks collapse replication forks and trigger homologous recombination for repair. Furthermore, we show that BRCA2-deficient cells, as a result of their deficiency in homologous recombination, are acutely sensitive to PARP inhibitors, presumably because resultant collapsed replication forks are no longer repaired. Thus, PARP1 activity is essential in homologous recombination-deficient BRCA2 mutant cells. We exploit this requirement in order to kill BRCA2-deficient tumours by PARP inhibition alone. Treatment with PARP inhibitors is likely to be highly tumour specific, because only the tumours (which are BRCA2-/-) in BRCA2+/- patients are defective in homologous recombination. The use of an inhibitor of a DNA repair enzyme alone to selectively kill a tumour, in the absence of an exogenous DNA-damaging agent, represents a new concept in cancer treatment.

sources and effects of ionizing radiation

Abstract: NOTE The report of the Committee without its annexes appears as Official Records of the General Assembly, Sixty-third Session, Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The country names used in this document are, in most cases, those that were in use at the time the data were collected or the text prepared. In other cases, however, the names have been updated, where this was possible and appropriate, to reflect political changes. Scientific Annexes Annex A. Medical radiation exposures Annex B. Exposures of the public and workers from various sources of radiation INTROdUCTION 1. In the course of the research and development for and the application of atomic energy and nuclear technologies, a number of radiation accidents have occurred. Some of these accidents have resulted in significant health effects and occasionally in fatal outcomes. The application of technologies that make use of radiation is increasingly widespread around the world. Millions of people have occupations related to the use of radiation, and hundreds of millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilization of products, preservation of foodstuffs and gamma radiography require special care in the design and operation of equipment to avoid radiation injury to workers or to the public. Experience has shown that such technology is generally used safely, but on occasion controls have been circumvented and serious radiation accidents have ensued. 2. Reviews of radiation exposures from accidents have been presented in previous UNSCEAR reports. The last report containing an exclusive chapter on exposures from accidents was the UNSCEAR 1993 Report [U6]. 3. This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices. Its conclusions are to be seen in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation. 4. The Committee's evaluations of public, occupational and medical diagnostic exposures are mostly concerned with chronic exposures of …

Cleavage of poly(ADP-ribose) polymerase by a proteinase with properties like ICE

Abstract: Recent studies suggest that proteases of the interleukin 1-beta-converting enzyme (ICE)/ced-3 family are involved in initiating the active phase of apoptosis. Here we identify a novel protease resembling ICE (prICE) that is active in a cell-free system that reproduces the morphological and biochemical events of apoptosis. prICE cleaves the nuclear enzyme poly(ADP-ribose) polymerase (PARP) at a tetrapeptide sequence identical to one of two ICE sites in pro-interleukin-1-beta. However, prICE does not cleave purified pro-interleukin-1-beta, and purified ICE does not cleave PARP, indicating that the two activities are distinct. Inhibition of prICE abolishes all manifestations of apoptosis in the extracts including morphological changes, cleavage of PARP and production of an oligonucleosomal ladder. These studies suggest that prICE might be pivotal in initiating the active phase of apoptosis in vitro and in intact cells.