title: Analysis of human syndromes with disordered chromatin reveals the impact of heterochromatin on the efficacy of ATM-dependent G2/M checkpoint arrest.
abstract: Heterochromatin (HC) poses a barrier to γH2AX focus expansion and DNA double-strand break (DSB) repair, the latter being relieved by ATM-dependent KAP-1 phosphorylation. Using high-resolution imaging, we show here that the HC superstructure markedly restricts ATM signaling to cell cycle checkpoint proteins. The impact of HC is greater than anticipated from the percentage of HC-DNA and, in distinction to DSB repair, ATM only partly overcomes the constraints posed by HC. Importantly, we examine ATM signaling in human syndromes with disordered HC. After depletion of MeCP2 and DNMT3B, proteins defective in the Rett and immunodeficiency with centromere instability and facial anomalies (ICF) syndromes, respectively, we demonstrate enhanced γH2AX signal expansion at HC-chromocenters in mouse NIH 3T3 cells, which have visible HC-chromocenters. Previous studies have shown that the G(2)/M checkpoint is inefficient requiring multiple DSBs to initiate arrest. MeCP2 and DNMT3B depletion leads to hypersensitive radiation-induced G(2)/M checkpoint arrest despite normal DSB repair. Cell lines from Rett, ICF, and Hutchinson-Guildford progeria syndrome patients similarly showed hyperactivated ATM signaling and hypersensitive and prolonged G(2)/M checkpoint arrest. Collectively, these findings reveal that heterochromatin contributes to the previously described inefficient G(2)/M checkpoint arrest and demonstrate how the signaling response can be uncoupled from DSB repair.
authors.affiliation: Genome Damage and Stability Centre, University of Sussex, East Sussex BN1 9RQ, United Kingdom.
authors.forename: Holly
authors.initials: H
authors.lastname: Brunton
authors.forename: Aaron A
authors.initials: AA
authors.lastname: Goodarzi
authors.forename: Angela T
authors.initials: AT
authors.lastname: Noon
authors.forename: Amruta
authors.initials: A
authors.lastname: Shrikhande
authors.forename: R Scott
authors.initials: RS
authors.lastname: Hansen
authors.forename: Penny A
authors.initials: PA
authors.lastname: Jeggo
authors.forename: Atsushi
authors.initials: A
authors.lastname: Shibata
mesh_terms: D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D059565:G2 Phase Cell Cycle Checkpoints / Q000502:physiology*; D030342:Genetic Diseases, Inborn / Q000235:genetics*; D006570:Heterochromatin / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure*; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051783:Methyl-CpG-Binding Protein 2 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015518:Rett Syndrome / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics*; D013577:Syndrome; D000076183:Tripartite Motif-Containing Protein 28; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D000097584:DNA Methyltransferase 3B
chemical_list: D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D004248:DNA (Cytosine-5-)-Methyltransferases; D004268:DNA-Binding Proteins; D006570:Heterochromatin; D006657:Histones; D051783:Methyl-CpG-Binding Protein 2; D017346:Protein Serine-Threonine Kinases; D012097:Repressor Proteins; D000076183:Tripartite Motif-Containing Protein 28; D025521:Tumor Suppressor Proteins; D000097584:DNA Methyltransferase 3B; C468783:H2AX protein, human; C497392:MECP2 protein, human; C101116:TRIM28 protein, human; C576324:ATM protein, human; C576325:Atm protein, mouse