scholarly journals Common fragile sites are characterised by faulty condensin loading after replication stress

2018 ◽  
Author(s):  
Lora Boteva ◽  
Ryu-Suke Nozawa ◽  
Catherine Naughton ◽  
Kumiko Samejima ◽  
William C Earnshaw ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Chromosome Instability ◽  
Replication Stress ◽  
Fragile Sites ◽  
Molecular Configuration ◽  
Common Fragile Sites ◽  
Molecular Defects ◽  
Specific Manner ◽  
Chromatin Folding

Cells coordinate interphase to mitosis transition but recurrent cytogenetic lesions appear at common fragile sites (CFSs) in a tissue-specific manner following replication stress, marking regions of instability in cancer. Despite such a distinct defect no model fully explains their molecular configuration. We show that CFSs are characterised by impaired chromatin folding manifested as disrupted mitotic structures visible using molecular FISH probes in the presence and absence of replication stress. Chromosome condensation assays reveal that compaction-resistant chromatin lesions persist at CFSs throughout the cell cycle and mitosis. Subsequently cytogenetic and molecular lesions arise due to faulty condensin loading at CFSs, through a defect in condensin I mediated compaction and are coincident with mitotic DNA synthesis (MIDAS). This model suggests that in conditions of exogenous replication stress, aberrant condensin loading leads to molecular defects and CFS formation, concomitantly providing an environment for MIDAS, which, if not resolved, result in chromosome instability.

scholarly journals High-resolution mapping of mitotic DNA synthesis regions and common fragile sites in the human genome through direct sequencing

Cell Research ◽  
2020 ◽  
Vol 30 (11) ◽  
pp. 997-1008 ◽  
Author(s):  
Morgane Macheret ◽  
Rahul Bhowmick ◽  
Katarzyna Sobkowiak ◽  
Laura Padayachy ◽  
Jonathan Mailler ◽  
...  
Keyword(s):  
Dna Replication ◽  
High Resolution ◽  
Dna Synthesis ◽  
Direct Sequencing ◽  
Replication Stress ◽  
Fragile Sites ◽  
Common Fragile Sites ◽  
Dna Replication Stress ◽  
Genomic Regions ◽  
In Cells

Abstract DNA replication stress, a feature of human cancers, often leads to instability at specific genomic loci, such as the common fragile sites (CFSs). Cells experiencing DNA replication stress may also exhibit mitotic DNA synthesis (MiDAS). To understand the physiological function of MiDAS and its relationship to CFSs, we mapped, at high resolution, the genomic sites of MiDAS in cells treated with the DNA polymerase inhibitor aphidicolin. Sites of MiDAS were evident as well-defined peaks that were largely conserved between cell lines and encompassed all known CFSs. The MiDAS peaks mapped within large, transcribed, origin-poor genomic regions. In cells that had been treated with aphidicolin, these regions remained unreplicated even in late S phase; MiDAS then served to complete their replication after the cells entered mitosis. Interestingly, leading and lagging strand synthesis were uncoupled in MiDAS, consistent with MiDAS being a form of break-induced replication, a repair mechanism for collapsed DNA replication forks. Our results provide a better understanding of the mechanisms leading to genomic instability at CFSs and in cancer cells.

scholarly journals Transcription-Replication Collisions and Chromosome Fragility

2021 ◽  
Vol 12 ◽  
Author(s):  
Wei Wu ◽  
Jing Na He ◽  
Mengjiao Lan ◽  
Pumin Zhang ◽  
Wai Kit Chu
Keyword(s):  
Cell Division ◽  
Dna Synthesis ◽  
Tumor Development ◽  
Replication Stress ◽  
Fragile Sites ◽  
Repair Pathway ◽  
Entire Genome ◽  
Common Fragile Sites ◽  
Oncogene Activation ◽  
Chromosome Fragility

Accurate replication of the entire genome is critical for cell division and propagation. Certain regions in the genome, such as fragile sites (common fragile sites, rare fragile sites, early replicating fragile sites), rDNA and telomeres, are intrinsically difficult to replicate, especially in the presence of replication stress caused by, for example, oncogene activation during tumor development. Therefore, these regions are particularly prone to deletions and chromosome rearrangements during tumorigenesis, rendering chromosome fragility. Although, the mechanism underlying their “difficult-to-replicate” nature and genomic instability is still not fully understood, accumulating evidence suggests transcription might be a major source of endogenous replication stress (RS) leading to chromosome fragility. Here, we provide an updated overview of how transcription affects chromosome fragility. Furthermore, we will use the well characterized common fragile sites (CFSs) as a model to discuss pathways involved in offsetting transcription-induced RS at these loci with a focus on the recently discovered atypical DNA synthesis repair pathway Mitotic DNA Synthesis (MiDAS).

scholarly journals Genome Instability at Common Fragile Sites: Searching for the Cause of Their Instability

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Annapaola Franchitto
Keyword(s):  
Human Cancer ◽  
Chromosome Instability ◽  
Replication Stress ◽  
Fragile Sites ◽  
Chromosomal Breakage ◽  
Common Fragile Sites ◽  
New Findings ◽  
Frequent Event ◽  
Fork Stalling

Common fragile sites (CFS) are heritable nonrandomly distributed loci on human chromosomes that exhibit an increased frequency of chromosomal breakage under conditions of replication stress. They are considered the preferential targets for high genomic instability from the earliest stages of human cancer development, and increased chromosome instability at these loci has been observed following replication stress in a subset of human genetic diseases. Despite their biological and medical relevance, the molecular basis of CFS fragility in vivo has not been fully elucidated. At present, different models have been proposed to explain how instability at CFS arises and multiple factors seem to contribute to their instability. However, all these models involve DNA replication and suggest that replication fork stalling along CFS during DNA synthesis is a very frequent event. Consistent with this, the maintenance of CFS stability relies on the ATR-dependent checkpoint, together with a number of proteins promoting the recovery of stalled replication forks. In this review, we discuss mainly the possible causes that threaten the integrity of CFS in the light of new findings, paying particular attention to the role of the S-phase checkpoint.

scholarly journals Replication Stress and Telomere Dysfunction Are Present in Cultured Human Embryonic Stem Cells

2015 ◽  
Vol 146 (4) ◽  
pp. 251-260 ◽  
Author(s):  
Christine Janson ◽  
Kristine Nyhan ◽  
John P. Murnane
Keyword(s):  
Stem Cells ◽  
Dna Damage ◽  
Embryonic Stem Cells ◽  
Human Embryonic Stem Cells ◽  
Chromosome Instability ◽  
Embryonic Stem ◽  
Replication Stress ◽  
Activin A ◽  
Fragile Sites ◽  
Telomere Dysfunction

Replication stress causes DNA damage at fragile sites in the genome. DNA damage at telomeres can initiate breakage-fusion-bridge cycles and chromosome instability, which can result in replicative senescence or tumor formation. Little is known about the extent of replication stress or telomere dysfunction in human embryonic stem cells (hESCs). hESCs are grown in culture with the expectation of being used therapeutically in humans, making it important to minimize the levels of replication stress and telomere dysfunction. Here, the hESC line UCSF4 was cultured in a defined medium with growth factor Activin A, exogenous nucleosides, or DNA polymerase inhibitor aphidicolin. We used quantitative fluorescence in situ hybridization to analyze individual telomeres for dysfunction and observed that it can be increased by aphidicolin or Activin A. In contrast, adding exogenous nucleosides relieved dysfunction, suggesting that telomere dysfunction results from replication stress. Whether these findings can be applied to other hESC lines remains to be determined. However, because the loss of telomeres can lead to chromosome instability and cancer, we conclude that hESCs grown in culture for future therapeutic purposes should be routinely checked for replication stress and telomere dysfunction.

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 Oncogene-induced replication stress preferentially targets common fragile sites in preneoplastic lesions. A genome-wide study

Oncogene ◽  
2007 ◽  
Vol 27 (23) ◽  
pp. 3256-3264 ◽  
Author(s):  
P K Tsantoulis ◽  
A Kotsinas ◽  
P P Sfikakis ◽  
K Evangelou ◽  
M Sideridou ◽  
...  
Keyword(s):  
Replication Stress ◽  
Fragile Sites ◽  
Preneoplastic Lesions ◽  
Common Fragile Sites ◽  
Genome Wide ◽  
A Genome ◽  
Genome Wide Study

scholarly journals Protein phosphatase 2A (PP2A) promotes anaphase entry after DNA replication stress in budding yeast

2021 ◽  
Author(s):  
Cory Haluska ◽  
Fengzhi Jin ◽  
Yanchang Wang
Keyword(s):  
Cell Cycle ◽  
Dna Replication ◽  
Dna Synthesis ◽  
Protein Phosphatase ◽  
Budding Yeast ◽  
Replication Stress ◽  
S Phase ◽  
Viability Loss ◽  
Phosphatase 2A ◽  
Dna Replication Stress

DNA replication stress activates the S-phase checkpoint that arrests the cell cycle, but it is poorly understood how cells recover from this arrest. Cyclin-dependent kinase (CDK) and Protein Phosphatase 2A (PP2A) are key cell cycle regulators, and Cdc55 is a regulatory subunit of PP2A in budding yeast. We found that yeast cells lacking functional PP2ACdc55 showed slow growth in the presence of hydroxyurea (HU), a DNA synthesis inhibitor, without obvious viability loss. Moreover, PP2A mutants exhibited delayed anaphase entry and sustained levels of anaphase inhibitor Pds1 after HU treatment. A DNA damage checkpoint Chk1 phosphorylates and stabilizes Pds1. We showed that chk1Δ and mutation of the Chk1 phosphorylation sites in Pds1 largely restored efficient anaphase entry in PP2A mutants after HU treatment. In addition, deletion of SWE1 that encodes the inhibitory kinase for CDK or mutation of the Swe1 phosphorylation site in CDK ( cdc28F19) also suppressed the anaphase entry delay in PP2A mutants after HU treatment. Our genetic data suggest that Swe1/CDK acts upstream of Pds1. Surprisingly, cdc55Δ showed significant suppression to the viability loss of S-phase checkpoint mutants during DNA synthesis block. Together, our results uncover a PP2A-Swe1-CDK-Chk1-Pds1 axis that promotes recovery from DNA replication stress.

scholarly journals Replication stress induces specific enrichment of RECQ1 at common fragile sites FRA3B and FRA16D

2013 ◽  
Vol 12 (1) ◽  
pp. 29 ◽  
Author(s):  
Xing Lu ◽  
Swetha Parvathaneni ◽  
Toshifumi Hara ◽  
Ashish Lal ◽  
Sudha Sharma
Keyword(s):  
Replication Stress ◽  
Fragile Sites ◽  
Common Fragile Sites

scholarly journals RPA shields inherited DNA lesions for post-mitotic DNA synthesis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Aleksandra Lezaja ◽  
Andreas Panagopoulos ◽  
Yanlin Wen ◽  
Edison Carvalho ◽  
Ralph Imhof ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Dna Synthesis ◽  
Cancer Cells ◽  
Cell Cycle Progression ◽  
Protein A ◽  
Low Frequency ◽  
Replication Stress ◽  
Dna Lesions ◽  
Checkpoint Control ◽  
Cycle Progression

AbstractThe paradigm that checkpoints halt cell cycle progression for genome repair has been challenged by the recent discovery of heritable DNA lesions escaping checkpoint control. How such inherited lesions affect genome function and integrity is not well understood. Here, we identify a new class of heritable DNA lesions, which is marked by replication protein A (RPA), a protein primarily known for shielding single-stranded DNA in S/G2. We demonstrate that post-mitotic RPA foci occur at low frequency during unperturbed cell cycle progression, originate from the previous cell cycle, and are exacerbated upon replication stress. RPA-marked inherited ssDNA lesions are found at telomeres, particularly of ALT-positive cancer cells. We reveal that RPA protects these replication remnants in G1 to allow for post-mitotic DNA synthesis (post-MiDAS). Given that ALT-positive cancer cells exhibit high levels of replication stress and telomere fragility, targeting post-MiDAS might be a new therapeutic opportunity.

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