scholarly journals Werner syndrome helicase activity is essential in maintaining fragile site stability

2008 ◽  
Vol 180 (2) ◽  
pp. 305-314 ◽  
Author(s):  
Livia Maria Pirzio ◽  
Pietro Pichierri ◽  
Margherita Bignami ◽  
Annapaola Franchitto
Keyword(s):  
Werner Syndrome ◽  
Fragile Site ◽  
Chromosome Breakage ◽  
Fragile Sites ◽  
Helicase Activity ◽  
Dna Helicases ◽  
Replication Checkpoint ◽  
Replicative Stress ◽  
Fork Stalling ◽  
The Stability

WRN is a member of the RecQ family of DNA helicases implicated in the resolution of DNA structures leading to the stall of replication forks. Fragile sites have been proposed to be DNA regions particularly sensitive to replicative stress. Here, we establish that WRN is a key regulator of fragile site stability. We demonstrate that in response to mild doses of aphidicolin, WRN is efficiently relocalized in nuclear foci in replicating cells and that WRN deficiency is associated with accumulation of gaps and breaks at common fragile sites even under unperturbed conditions. By expressing WRN isoforms impaired in either helicase or exonuclease activity in defective cells, we identified WRN helicase activity as the function required for maintaining the stability of fragile sites. Finally, we find that WRN stabilizes fragile sites acting in a common pathway with the ataxia telangiectasia and Rad3 related replication checkpoint. These findings provide the first evidence of a crucial role for a helicase in protecting cells against chromosome breakage at normally occurring replication fork stalling sites.

scholarly journals DNA synthesis by Pol η promotes fragile site stability by preventing under-replicated DNA in mitosis

2013 ◽  
Vol 201 (3) ◽  
pp. 395-408 ◽  
Author(s):  
Valérie Bergoglio ◽  
Anne-Sophie Boyer ◽  
Erin Walsh ◽  
Valeria Naim ◽  
Gaëlle Legube ◽  
...  
Keyword(s):  
Dna Synthesis ◽  
Dna Sequences ◽  
Molecular Mechanisms ◽  
Fragile Site ◽  
Fragile Sites ◽  
Nuclear Bodies ◽  
Replication Checkpoint ◽  
Genome Damage ◽  
Fork Stalling ◽  
The Stability

Human DNA polymerase η (Pol η) is best known for its role in responding to UV irradiation–induced genome damage. We have recently observed that Pol η is also required for the stability of common fragile sites (CFSs), whose rearrangements are considered a driving force of oncogenesis. Here, we explored the molecular mechanisms underlying this newly identified role. We demonstrated that Pol η accumulated at CFSs upon partial replication stress and could efficiently replicate non-B DNA sequences within CFSs. Pol η deficiency led to persistence of checkpoint-blind under-replicated CFS regions in mitosis, detectable as FANCD2-associated chromosomal sites that were transmitted to daughter cells in 53BP1-shielded nuclear bodies. Expression of a catalytically inactive mutant of Pol η increased replication fork stalling and activated the replication checkpoint. These data are consistent with the requirement of Pol η–dependent DNA synthesis during S phase at replication forks stalled in CFS regions to suppress CFS instability by preventing checkpoint-blind under-replicated DNA in mitosis.

Fragile Genes That Are Frequently Altered in Cancer: Players Not Passengers

2016 ◽  
Vol 150 (3-4) ◽  
pp. 208-216 ◽  
Author(s):  
Jenna R. Karras ◽  
Morgan S. Schrock ◽  
Bahadir Batar ◽  
Kay Huebner
Keyword(s):  
Genome Instability ◽  
Fragile Site ◽  
Replication Stress ◽  
Fragile Sites ◽  
Gap Formation ◽  
A Genome ◽  
Protein Functions ◽  
Fhit Protein ◽  
The Stability ◽  
Selection Of

FHIT, located at FRA3B, is one of the most commonly deleted genes in human cancers, and loss of FHIT protein is one of the earliest events in cancer initiation. However, location of FHIT at a chromosomal fragile site, a locus prone to breakage and gap formation under even mild replication stress, has encouraged claims that FHIT loss is a passenger event in cancers. We summarize accumulated evidence that FHIT protein functions as a genome “caretaker” required to protect the stability of genomes of normal cells of most tissues from agents causing intrinsic and extrinsic DNA damage. FHIT loss leads to intracellular replication stress and subsequent genome instability, which provides an opportunistic mutational landscape in preneoplasias for selection of a variety of other cancer-driving mutations. We also review evidence showing that FHIT loss leads to enhanced activation of other common fragile sites, including the FRA16D/WWOX locus, and creates optimal single-stranded DNA substrates for the hypermutator enzyme, APOBEC3B.

scholarly journals Deletion of a pseudogene within a fragile site triggers the oncogenic expression of the mitotic CCSER1 gene

2021 ◽  
Vol 4 (8) ◽  
pp. e202101019
Author(s):  
Benedetta M Santoliquido ◽  
Michela Frenquelli ◽  
Claudia Contadini ◽  
Stefano Bestetti ◽  
Marco Gaviraghi ◽  
...  
Keyword(s):  
Kinase Inhibitors ◽  
Fragile Site ◽  
Aurora Kinase ◽  
Fragile Sites ◽  
Immune Recognition ◽  
Cis Acting ◽  
Replicative Stress ◽  
Acting Mechanism ◽  
Focal Ablation ◽  
Tcga Dataset

The oncogenic role of common fragile sites (CFS), focal and pervasive gaps in the cancer genome arising from replicative stress, remains controversial. Exploiting the TCGA dataset, we found that in most CFS the genes residing within the associated focal deletions are down-regulated, including proteins involved in tumour immune recognition. In a subset of CFS, however, the residing genes are surprisingly overexpressed. Within the most frequent CFS in this group, FRA4F, which is deleted in up to 18% of cancer cases and harbours the CCSER1 gene, we identified a region which includes an intronic, antisense pseudogene, TMSB4XP8. TMSB4XP8 focal ablation or transcriptional silencing elicits the overexpression of CCSER1, through a cis-acting mechanism. CCSER1 overexpression increases proliferation and triggers centrosome amplifications, multinuclearity, and aberrant mitoses. Accordingly, FRA4F is associated in patient samples to mitotic genes deregulation and genomic instability. As a result, cells overexpressing CCSER1 become sensitive to the treatment with aurora kinase inhibitors. Our findings point to a novel tumourigenic mechanism where focal deletions increase the expression of a new class of “dormant” oncogenes.

Fragile Sites on Chromosomes

PEDIATRICS ◽  
1982 ◽  
Vol 69 (1) ◽  
pp. 121-123
Author(s):  
Frederick Hecht ◽  
Thomas W. Glover ◽  
Barbara Kaiser-Hecht
Keyword(s):  
Mental Retardation ◽  
X Chromosome ◽  
Fanconi Anemia ◽  
Ataxia Telangiectasia ◽  
Autosomal Recessive ◽  
Fragile Site ◽  
Chromosome Instability ◽  
Chromosome Complement ◽  
Fragile Sites ◽  
Chromosome Fragility

A fragile site on the X chromosome is associated with a common form of mental retardation in males and a proportion of females.1-3 This association was not fully appreciated when the fragile site on the X was first described in 1969,4 but it is crystal-clear today. Chromosome fragility can be random, as in Fanconi anemia, Bloom syndrome, and ataxia-telangiectasia, the chromosome instability syndromes.5 Breaks and rearrangements of chromosomes are seen in these disorders, all of which are autosomal recessive conditions predisposing to cancer. Fragile sites are special spots in the genome where gaps and breaks occur nonrandomly. The balance of the chromosome complement is normal.

Generation of a new adenovirus type 12-inducible fragile site by insertion of an artificial U2 locus in the human genome

1993 ◽  
Vol 13 (10) ◽  
pp. 6064-6070
Author(s):  
Y P Li ◽  
R Tomanin ◽  
J R Smiley ◽  
S Bacchetti
Keyword(s):  
Human Genome ◽  
Gene Cluster ◽  
Fragile Site ◽  
Adenovirus Type ◽  
Fragile Sites ◽  
Human Cells ◽  
Major Site ◽  
Chromosome 13 ◽  
Direct Assessment

Infection with adenovirus type 12 (Ad12) induces four fragile sites in the human genome (H.F. Stich, G.L. van Hoosier, and J.J. Trentin, Exp. Cell Res. 34:400-403, 1964; H. zur Hausen, J. Virol. 1:1174-1185, 1967). The major site, at 17q21-22, contains the U2 gene cluster, which is specifically disrupted by infection in at least a percentage of the cells (D.M. Durnam, J.C. Menninger, S.H. Chandler, P.P. Smith, and J.K. McDougall, Mol. Cell. Biol. 8:1863-1867, 1988). For direct assessment of whether the U2 locus is the target of the Ad12 effect, an artificial locus, constructed in vitro and consisting of tandem arrays of the U2 6-kbp monomer, was transfected into human cells. We report that integration of this artificial locus on the p arm of chromosome 13 creates a new Ad12-inducible fragile site.

scholarly journals Increased Common Fragile Site Expression, Cell Proliferation Defects, and Apoptosis following Conditional Inactivation of Mouse Hus1 in Primary Cultured Cells

2007 ◽  
Vol 18 (3) ◽  
pp. 1044-1055 ◽  
Author(s):  
Min Zhu ◽  
Robert S. Weiss
Keyword(s):  
Cell Cycle ◽  
Cultured Cells ◽  
Chromosomal Abnormalities ◽  
Fragile Site ◽  
Loxp Site ◽  
Fragile Sites ◽  
Cell Cycle Checkpoint ◽  
Dna Breaks ◽  
Common Fragile Sites ◽  
Histone H2ax

Targeted disruption of the mouse Hus1 cell cycle checkpoint gene results in embryonic lethality and proliferative arrest in cultured cells. To investigate the essential functions of Hus1, we developed a system for the regulated inactivation of mouse Hus1 in primary fibroblasts. Inactivation of a loxP site-flanked conditional Hus1 allele by using a cre-expressing adenovirus resulted in reduced cell doubling, cell cycle alterations, and increased apoptosis. These phenotypes were associated with a significantly increased frequency of gross chromosomal abnormalities and an S-phase–specific accumulation of phosphorylated histone H2AX, an indicator of double-stranded DNA breaks. To determine whether these chromosomal abnormalities occurred randomly or at specific genomic regions, we assessed the stability of common fragile sites, chromosomal loci that are prone to breakage in cells undergoing replication stress. Hus1 was found to be essential for fragile site stability, because spontaneous chromosomal abnormalities occurred preferentially at common fragile sites upon conditional Hus1 inactivation. Although p53 levels increased after Hus1 loss, deletion of p53 failed to rescue the cell-doubling defect or increased apoptosis in conditional Hus1 knockout cells. In summary, we propose that Hus1 loss leads to chromosomal instability during DNA replication, triggering increased apoptosis and impaired proliferation through p53-independent mechanisms.

scholarly journals Replication fork stalling elicits chromatin compaction for the stability of stalling replication forks

2019 ◽  
Vol 116 (29) ◽  
pp. 14563-14572 ◽  
Author(s):  
Gang Feng ◽  
Yue Yuan ◽  
Zeyang Li ◽  
Lu Wang ◽  
Bo Zhang ◽  
...  
Keyword(s):  
Replication Fork ◽  
Cellular Mechanism ◽  
Eukaryotic Cells ◽  
Replication Forks ◽  
Physical Separation ◽  
Replicative Helicase ◽  
Chromatin Compaction ◽  
Acetylation Site ◽  
Fork Stalling ◽  
The Stability

DNA replication forks in eukaryotic cells stall at a variety of replication barriers. Stalling forks require strict cellular regulations to prevent fork collapse. However, the mechanism underlying these cellular regulations is poorly understood. In this study, a cellular mechanism was uncovered that regulates chromatin structures to stabilize stalling forks. When replication forks stall, H2BK33, a newly identified acetylation site, is deacetylated and H3K9 trimethylated in the nucleosomes surrounding stalling forks, which results in chromatin compaction around forks. Acetylation-mimic H2BK33Q and its deacetylase clr6-1 mutations compromise this fork stalling-induced chromatin compaction, cause physical separation of replicative helicase and DNA polymerases, and significantly increase the frequency of stalling fork collapse. Furthermore, this fork stalling-induced H2BK33 deacetylation is independent of checkpoint. In summary, these results suggest that eukaryotic cells have developed a cellular mechanism that stabilizes stalling forks by targeting nucleosomes and inducing chromatin compaction around stalling forks. This mechanism is named the “Chromsfork” control: Chromatin Compaction Stabilizes Stalling Replication Forks.

scholarly journals Human Fbh1 helicase contributes to genome maintenance via pro- and anti-recombinase activities

2009 ◽  
Vol 186 (5) ◽  
pp. 655-663 ◽  
Author(s):  
Kasper Fugger ◽  
Martin Mistrik ◽  
Jannie Rendtlew Danielsen ◽  
Christoffel Dinant ◽  
Jacob Falck ◽  
...  
Keyword(s):  
Small Interfering Rna ◽  
Ectopic Expression ◽  
Dna Lesions ◽  
Premature Aging ◽  
Genome Integrity ◽  
Helicase Activity ◽  
Genome Maintenance ◽  
Dna Helicases ◽  
Replication Block ◽  
Interfering Rna

Homologous recombination (HR) is essential for faithful repair of DNA lesions yet must be kept in check, as unrestrained HR may compromise genome integrity and lead to premature aging or cancer. To limit unscheduled HR, cells possess DNA helicases capable of preventing excessive recombination. In this study, we show that the human Fbh1 (hFbh1) helicase accumulates at sites of DNA damage or replication stress in a manner dependent fully on its helicase activity and partially on its conserved F box. hFbh1 interacted with single-stranded DNA (ssDNA), the formation of which was required for hFbh1 recruitment to DNA lesions. Conversely, depletion of endogenous Fbh1 or ectopic expression of helicase-deficient hFbh1 attenuated ssDNA production after replication block. Although elevated levels of hFbh1 impaired Rad51 recruitment to ssDNA and suppressed HR, its small interfering RNA–mediated depletion increased the levels of chromatin-associated Rad51 and caused unscheduled sister chromatid exchange. Thus, by possessing both pro- and anti-recombinogenic potential, hFbh1 may cooperate with other DNA helicases in tightly controlling cellular HR activity.

Fragile sites in chromosomes: possible model for the study of spontaneous chromosome breakage

Science ◽  
1983 ◽  
Vol 220 (4592) ◽  
pp. 69-70 ◽  
Author(s):  
P. Jacky ◽  
B Beek ◽  
G. Sutherland
Keyword(s):  
Chromosome Breakage ◽  
Fragile Sites ◽  
Spontaneous Chromosome
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