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      Parp1 facilitates alternative NHEJ, whereas Parp2 suppresses IgH/c-myc translocations during immunoglobulin class switch recombination

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          Immunoglobulin class switch recombination (CSR) is initiated by DNA breaks triggered by activation-induced cytidine deaminase (AID). These breaks activate DNA damage response proteins to promote appropriate repair and long-range recombination. Aberrant processing of these breaks, however, results in decreased CSR and/or increased frequency of illegitimate recombination between the immunoglobulin heavy chain locus and oncogenes like c-myc. Here, we have examined the contribution of the DNA damage sensors Parp1 and Parp2 in the resolution of AID-induced DNA breaks during CSR. We find that although Parp enzymatic activity is induced in an AID-dependent manner during CSR, neither Parp1 nor Parp2 are required for CSR. We find however, that Parp1 favors repair of switch regions through a microhomology-mediated pathway and that Parp2 actively suppresses IgH/c-myc translocations. Thus, we define Parp1 as facilitating alternative end-joining and Parp2 as a novel translocation suppressor during CSR.

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          Most cited references 56

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

          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.
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            Class switch recombination and hypermutation require activation-induced cytidine deaminase (AID), a potential RNA editing enzyme.

            Induced overexpression of AID in CH12F3-2 B lymphoma cells augmented class switching from IgM to IgA without cytokine stimulation. AID deficiency caused a complete defect in class switching and showed a hyper-IgM phenotype with enlarged germinal centers containing strongly activated B cells before or after immunization. AID-/- spleen cells stimulated in vitro with LPS and cytokines failed to undergo class switch recombination although they expressed germline transcripts. Immunization of AID-/- chimera with 4-hydroxy-3-nitrophenylacetyl (NP) chicken gamma-globulin induced neither accumulation of mutations in the NP-specific variable region gene nor class switching. These results suggest that AID may be involved in regulation or catalysis of the DNA modification step of both class switching and somatic hypermutation.
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              Poly(ADP-ribose): novel functions for an old molecule.

              The addition to proteins of the negatively charged polymer of ADP-ribose (PAR), which is synthesized by PAR polymerases (PARPs) from NAD(+), is a unique post-translational modification. It regulates not only cell survival and cell-death programmes, but also an increasing number of other biological functions with which novel members of the PARP family have been associated. These functions include transcriptional regulation, telomere cohesion and mitotic spindle formation during cell division, intracellular trafficking and energy metabolism.

                Author and article information

                J Exp Med
                J. Exp. Med
                The Journal of Experimental Medicine
                The Rockefeller University Press
                11 May 2009
                : 206
                : 5
                : 1047-1056
                [1 ]Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Department of Cancer Biology. Institut National de la Santé et de la Recherche Médicale U964-Centre National de la Recherche Scientifique UMR7104, Université de Strasbourg, 67404 Illkirch, France
                [2 ]Poly(ADP-ribosyl)ation et Intégrité du Génome, IREBS-FRE3211 Centre National de la Recherche Scientifique, Université de Strasbourg, Ecole Supérieure de Biotechnologie de Strasbourg, 67412 Illkirch, France
                Author notes
                CORRESPONDENCE Bernardo Reina-San-Martin: reinab@
                © 2009 Robert et al.

                This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at




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