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Refaat AM, Nakata M, Husain A, Kosako H, Honjo T, Begum NA. HNRNPU facilitates antibody class-switch recombination through C-NHEJ promotion and R-loop suppression. Cell Rep 2023; 42:112284. [PMID: 36943867 DOI: 10.1016/j.celrep.2023.112284] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Revised: 10/23/2022] [Accepted: 03/03/2023] [Indexed: 03/22/2023] Open
Abstract
B cells generate functionally different classes of antibodies through class-switch recombination (CSR), which requires classical non-homologous end joining (C-NHEJ) to join the DNA breaks at the donor and acceptor switch (S) regions. We show that the RNA-binding protein HNRNPU promotes C-NHEJ-mediated S-S joining through the 53BP1-shieldin DNA-repair complex. Notably, HNRNPU binds to the S region RNA/DNA G-quadruplexes, contributing to regulating R-loop and single-stranded DNA (ssDNA) accumulation. HNRNPU is an intrinsically disordered protein that interacts with both C-NHEJ and R-loop complexes in an RNA-dependent manner. Strikingly, recruitment of HNRNPU and the C-NHEJ factors is highly sensitive to liquid-liquid phase separation inhibitors, suggestive of DNA-repair condensate formation. We propose that HNRNPU facilitates CSR by forming and stabilizing the C-NHEJ ribonucleoprotein complex and preventing excessive R-loop accumulation, which otherwise would cause persistent DNA breaks and aberrant DNA repair, leading to genomic instability.
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Affiliation(s)
- Ahmed M Refaat
- Department of Immunology and Genomic Medicine, Center for Cancer Immunotherapy and Immunobiology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan; Zoology Department, Faculty of Science, Minia University, El-Minia 61519, Egypt
| | - Mikiyo Nakata
- Department of Immunology and Genomic Medicine, Center for Cancer Immunotherapy and Immunobiology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan
| | - Afzal Husain
- Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, Aligarh, Uttar Pradesh 202002, India
| | - Hidetaka Kosako
- Division of Cell Signaling, Institute of Advanced Medical Sciences, University of Tokushima, Tokushima 770-8503, Japan
| | - Tasuku Honjo
- Department of Immunology and Genomic Medicine, Center for Cancer Immunotherapy and Immunobiology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan.
| | - Nasim A Begum
- Department of Immunology and Genomic Medicine, Center for Cancer Immunotherapy and Immunobiology, Kyoto University Graduate School of Medicine, Kyoto 606-8501, Japan
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2
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ASTE1 promotes shieldin-complex-mediated DNA repair by attenuating end resection. Nat Cell Biol 2021; 23:894-904. [PMID: 34354233 DOI: 10.1038/s41556-021-00723-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Accepted: 06/25/2021] [Indexed: 12/23/2022]
Abstract
The shieldin complex functions as the downstream effector of 53BP1-RIF1 to promote DNA double-strand break end-joining by restricting end resection. The SHLD2 subunit binds to single-stranded DNA ends and blocks end resection through OB-fold domains. Besides blocking end resection, it is unclear how the shieldin complex processes SHLD2-bound single-stranded DNA and promotes non-homologous end-joining. Here, we identify a downstream effector of the shieldin complex, ASTE1, as a structure-specific DNA endonuclease that specifically cleaves single-stranded DNA and 3' overhang DNA. ASTE1 localizes to DNA damage sites in a shieldin-dependent manner. Loss of ASTE1 impairs non-homologous end-joining, leads to hyper-resection and causes defective immunoglobulin class switch recombination. ASTE1 deficiency also causes resistance to poly(ADP-ribose) polymerase inhibitors in BRCA1-deficient cells owing to restoration of homologous recombination. These findings suggest that ASTE1-mediated 3' single-stranded DNA end cleavage contributes to the control of DSB repair choice by 53BP1, RIF1 and shieldin.
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Vítor AC, Huertas P, Legube G, de Almeida SF. Studying DNA Double-Strand Break Repair: An Ever-Growing Toolbox. Front Mol Biosci 2020; 7:24. [PMID: 32154266 PMCID: PMC7047327 DOI: 10.3389/fmolb.2020.00024] [Citation(s) in RCA: 87] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Accepted: 02/04/2020] [Indexed: 12/29/2022] Open
Abstract
To ward off against the catastrophic consequences of persistent DNA double-strand breaks (DSBs), eukaryotic cells have developed a set of complex signaling networks that detect these DNA lesions, orchestrate cell cycle checkpoints and ultimately lead to their repair. Collectively, these signaling networks comprise the DNA damage response (DDR). The current knowledge of the molecular determinants and mechanistic details of the DDR owes greatly to the continuous development of ground-breaking experimental tools that couple the controlled induction of DSBs at distinct genomic positions with assays and reporters to investigate DNA repair pathways, their impact on other DNA-templated processes and the specific contribution of the chromatin environment. In this review, we present these tools, discuss their pros and cons and illustrate their contribution to our current understanding of the DDR.
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Affiliation(s)
- Alexandra C Vítor
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
| | - Pablo Huertas
- Department of Genetics, University of Seville, Seville, Spain.,Centro Andaluz de Biología Molecular y Medicina Regenerativa-CABIMER, Universidad de Sevilla-CSIC-Universidad Pablo de Olavide, Seville, Spain
| | - Gaëlle Legube
- LBCMCP, Centre de Biologie Integrative (CBI), CNRS, Université de Toulouse, Toulouse, France
| | - Sérgio F de Almeida
- Instituto de Medicina Molecular João Lobo Antunes, Faculdade de Medicina da Universidade de Lisboa, Lisbon, Portugal
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Barnum KJ, Nguyen YT, O'Connell MJ. XPG-related nucleases are hierarchically recruited for double-stranded rDNA break resection. J Biol Chem 2019; 294:7632-7643. [PMID: 30885940 DOI: 10.1074/jbc.ra118.005415] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 03/11/2019] [Indexed: 12/11/2022] Open
Abstract
dsDNA breaks (DSBs) are resected in a 5'→3' direction, generating single-stranded DNA (ssDNA). This promotes DNA repair by homologous recombination and also assembly of signaling complexes that activate the DNA damage checkpoint effector kinase Chk1. In fission yeast (Schizosaccharomyces pombe), genetic screens have previously uncovered a family of three xeroderma pigmentosum G (XPG)-related nucleases (XRNs), known as Ast1, Exo1, and Rad2. Collectively, these XRNs are recruited to a euchromatic DSB and are required for ssDNA production and end resection across the genome. Here, we studied why there are three related but distinct XRN enzymes that are all conserved across a range of species, including humans, whereas all other DSB response proteins are present as single species. Using S. pombe as a model, ChIP and DSB resection analysis assays, and highly efficient I-PpoI-induced DSBs in the 28S rDNA gene, we observed a hierarchy of recruitment for each XRN, with a progressive compensatory recruitment of the other XRNs as the responding enzymes are deleted. Importantly, we found that this hierarchy reflects the requirement for different XRNs to effect efficient DSB resection in the rDNA, demonstrating that the presence of three XRN enzymes is not a simple division of labor. Furthermore, we uncovered a specificity of XRN function with regard to the direction of transcription. We conclude that the DSB-resection machinery is complex, is nonuniform across the genome, and has built-in fail-safe mechanisms, features that are in keeping with the highly pathological nature of DSB lesions.
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Affiliation(s)
- Kevin J Barnum
- From the Department of Oncological Sciences and.,Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029
| | - Y Tram Nguyen
- From the Department of Oncological Sciences and.,Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029
| | - Matthew J O'Connell
- From the Department of Oncological Sciences and .,Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029
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5
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Liu D, Frederiksen JH, Liberti SE, Lützen A, Keijzers G, Pena-Diaz J, Rasmussen LJ. Human DNA polymerase delta double-mutant D316A;E318A interferes with DNA mismatch repair in vitro. Nucleic Acids Res 2017; 45:9427-9440. [PMID: 28934474 PMCID: PMC5766205 DOI: 10.1093/nar/gkx611] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2016] [Accepted: 07/05/2017] [Indexed: 12/11/2022] Open
Abstract
DNA mismatch repair (MMR) is a highly-conserved DNA repair mechanism, whose primary role is to remove DNA replication errors preventing them from manifesting as mutations, thereby increasing the overall genome stability. Defects in MMR are associated with increased cancer risk in humans and other organisms. Here, we characterize the interaction between MMR and a proofreading-deficient allele of the human replicative DNA polymerase delta, PolδD316A;E318A, which has a higher capacity for strand displacement DNA synthesis than wild type Polδ. Human cell lines overexpressing PolδD316A;E318A display a mild mutator phenotype, while nuclear extracts of these cells exhibit reduced MMR activity in vitro, and these defects are complemented by overexpression or addition of exogenous human Exonuclease 1 (EXO1). By contrast, another proofreading-deficient mutant, PolδD515V, which has a weaker strand displacement activity, does not decrease the MMR activity as significantly as PolδD316A;E318A. In addition, PolδD515V does not increase the mutation frequency in MMR-proficient cells. Based on our findings, we propose that the proofreading activity restricts the strand displacement activity of Polδ in MMR. This contributes to maintain the nicks required for EXO1 entry, and in this manner ensures the dominance of the EXO1-dependent MMR pathway.
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Affiliation(s)
- Dekang Liu
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Jane H Frederiksen
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Sascha E Liberti
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Anne Lützen
- Department of Science, Systems and Models, Roskilde University, Denmark
| | - Guido Keijzers
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Javier Pena-Diaz
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
| | - Lene Juel Rasmussen
- Center for Healthy Aging, University of Copenhagen, Denmark.,Department of Cellular and Molecular Medicine, University of Copenhagen, Denmark
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Barnum KJ, O'Connell MJ. Molecular mechanisms involved in initiation of the DNA damage response. Mol Cell Oncol 2015; 2:e970065. [PMID: 27308403 PMCID: PMC4905235 DOI: 10.4161/23723548.2014.970065] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Revised: 09/04/2014] [Accepted: 09/06/2014] [Indexed: 11/19/2022]
Abstract
DNA is subject to a wide variety of damage. In order to maintain genomic integrity, cells must respond to this damage by activating repair and cell cycle checkpoint pathways. The initiating events in the DNA damage response entail recognition of the lesion and the assembly of DNA damage response complexes at the DNA. Here, we review what is known about these processes for various DNA damage pathways.
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Affiliation(s)
- Kevin J Barnum
- Department of Oncological Sciences and the Graduate School of Biomedical Sciences; Icahn School of Medicine at Mount Sinai ; New York, NY USA
| | - Matthew J O'Connell
- Department of Oncological Sciences and the Graduate School of Biomedical Sciences; Icahn School of Medicine at Mount Sinai ; New York, NY USA
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Budd ME, Campbell JL. Dna2 is involved in CA strand resection and nascent lagging strand completion at native yeast telomeres. J Biol Chem 2013; 288:29414-29. [PMID: 23963457 DOI: 10.1074/jbc.m113.472456] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Post-replicational telomere end processing involves both extension by telomerase and resection to produce 3'-GT-overhangs that extend beyond the complementary 5'-CA-rich strand. Resection must be carefully controlled to maintain telomere length. At short de novo telomeres generated artificially by HO endonuclease in the G2 phase, we show that dna2-defective strains are impaired in both telomere elongation and sequential 5'-CA resection. At native telomeres in dna2 mutants, GT-overhangs do clearly elongate during late S phase but are shorter than in wild type, suggesting a role for Dna2 in 5'-CA resection but also indicating significant redundancy with other nucleases. Surprisingly, elimination of Mre11 nuclease or Exo1, which are complementary to Dna2 in resection of internal double strand breaks, does not lead to further shortening of GT-overhangs in dna2 mutants. A second step in end processing involves filling in of the CA-strand to maintain appropriate telomere length. We show that Dna2 is required for normal telomeric CA-strand fill-in. Yeast dna2 mutants, like mutants in DNA ligase 1 (cdc9), accumulate low molecular weight, nascent lagging strand DNA replication intermediates at telomeres. Based on this and other results, we propose that FEN1 is not sufficient and that either Dna2 or Exo1 is required to supplement FEN1 in maturing lagging strands at telomeres. Telomeres may be among the subset of genomic locations where Dna2 helicase/nuclease is essential for the two-nuclease pathway of primer processing on lagging strands.
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Affiliation(s)
- Martin E Budd
- From Braun Laboratories, California Institute of Technology, Pasadena, California 91125
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