1,721,108 research outputs found
The DNA damage response during DNA replication
No full textEukaryotic chromosome replication is mediated by multiple replicons and is coordinated with sister chromatid cohesion, DNA recombination, transcription and cell cycle progression. Replication forks stall or collapse at DNA lesions or problematic genomic regions, and these events have often been associated with recombination and chromosomal rearrangements. Stalled forks generate single-stranded DNA that activates the replication checkpoint, which in turn functions to protect the stability of the fork until the replication can resume. Recombination-mediated and damage-bypass processes are the main mechanisms responsible for replication restart. New findings have helped to unmask the molecular mechanisms that sense replication stress, control the stability of replication forks, and regulate the mechanisms that promote replication restart, thereby giving us a better understanding of how genome integrity is preserved during replication
The checkpoint response to replication stress
No full textGenome instability is a hallmark of cancer cells, and defective DNA replication, repair and recombination have been linked to its etiology. Increasing evidence suggests that proteins influencing S-phase processes such as replication fork movement and stability, repair events and replication completion, have significant roles in maintaining genome stability. DNA damage and replication stress activate a signal transduction cascade, often referred to as the checkpoint response. A central goal of the replication checkpoint is to maintain the integrity of the replication forks while facilitating replication completion and DNA repair and coordinating these events with cell cycle transitions. Progression through the cell cycle in spite of defective or incomplete DNA synthesis or unrepaired DNA lesions may result in broken chromosomes, genome aberrations, and an accumulation of mutations. In this review we discuss the multiple roles of the replication checkpoint during replication and in response to replication stress, as well as the enzymatic activities that cooperate with the checkpoint pathway to promote fork resumption and repair of DNA lesions thereby contributing to genome integrity
Interplay of replication checkpoints and repair proteins at stalled replication forks
No full textDNA replication is an essential process that occurs in all growing cells and needs to be tightly regulated in order to preserve genetic integrity. Eukaryotic cells have developed multiple mechanisms to ensure the fidelity of replication and to coordinate the progression of replication forks. Replication is often impeded by DNA damage or replication blocks, and the resulting stalled replication forks are sensed and protected by specialized surveillance mechanisms called checkpoints. The replication checkpoint plays an essential role in preventing the breakdown of stalled replication forks and the accumulation of DNA structures that enhance recombination and chromosomal rearrangements that ultimately lead to genomic instability and cancer development. In addition, the replication checkpoint is thought to assist and coordinate replication fork restart processes by controlling DNA repair pathways, regulating chromatin structure, promoting the recruitment of proteins to sites of damage, and controlling cell cycle progression. In this review we focus mainly on the results obtained in budding yeast to discuss on the multiple roles of checkpoints in maintaining fork integrity and on the enzymatic activities that cooperate with the checkpoint pathway to promote fork resumption and repair of DNA lesions thereby contributing to genome integrity
Recombination at collapsed replication forks: the payoff for survival
No full textRecombination is believed to assist replication when forks collapse. By using an elegant system, Lambert et al. (2005) address the consequences of recombination at blocked forks. They show that chromosomal rearrangements are the price to pay for cell viability when forks collapse
Leaping forks at inverted repeats
No full textGenome rearrangements are often associated with genome instability observed in cancer and other pathological disorders. Different types of repeat elements are common in genomes and are prone to instability. S-phase checkpoints, recombination, and telomere maintenance pathways have been implicated in suppressing chromosome rearrangements, but little is known about the molecular mechanisms and the chromosome intermediates generating such genome-wide instability. In the December 15, 2009, issue of Genes & Development, two studies by Paek and colleagues (2861-2875) and Mizuno and colleagues (pp. 2876-2886), demonstrate that nearby inverted repeats in budding and fission yeasts recombine spontaneously and frequently to form dicentric and acentric chromosomes. The recombination mechanism underlying this phenomenon does not appear to require double-strand break formation, and is likely caused by a replication mechanism involving template switching
Dangerous liaisons : MYCN meets condensins
No full textThe condensin complex is required for chromosome condensation during mitosis; however, the role of this complex during interphase is unclear. Neuroblastoma is the most common extracranial solid tumor of childhood, and it is often lethal. In human neuroblastoma, MYCN gene amplification is correlated with poor prognosis. This study demonstrates that the gene encoding the condensin complex subunit SMC2 is transcriptionally regulated by MYCN. SMC2 also transcriptionally regulates DNA damage response genes in cooperation with MYCN. Downregulation of SMC2 induced DNA damage and showed a synergistic lethal response in MYCN-amplified/overexpression cells, leading to apoptosis in human neuroblastoma cells. Finally, this study found that patients bearing MYCN-amplified tumors showed improved survival when SMC2 expression was low. These results identify novel functions of SMC2 in DNA damage response, and we propose that SMC2 (or the condensin complex) is a novel molecular target for the treatment of MYCN-amplified neuroblastoma
ATM and ATR signaling at a glance
Full text linkATM and ATR signaling pathways are well conserved throughout evolution and are central to the maintenance of genome integrity. Although the role of both ATM and ATR in DNA repair, cell cycle regulation and apoptosis have been well studied, both still remain in the focus of current research activities owing to their role in cancer. Recent advances in the field suggest that these proteins have an additional function in maintaining cellular homeostasis under both stressed and non-stressed conditions. In this Cell Science at a Glance article and the accompanying poster, we present an overview of recent advances in ATR and ATM research with emphasis on that into the modes of ATM and ATR activation, the different signaling pathways they participate in - including those that do not involve DNA damage - and highlight their relevance in cancer
Analysis of Top1 and Top2 contribution to chromosomal DNA replication
No full textProliferating cells must accurately duplicate their genomes and segregate them into daughter cells in order to
preserve their genetic information. Several events can compromise genome integrity during DNA replication,
such as dNTPs misincorporation or damaging of the template.
DNA replication can also be challenged by the accumulation of topological constraints generated by the
separation of the two strands of the DNA double helix. The stress created by the progressing replication
machinery can be converted into positive supercoiling (helical overwinding) or precatenates (intertwines the
daughter duplexes). Accumulation of supercoiling can cause a block to the progression of replication forks,
while accumulation of precatenates represents a physical linkage between chromosomes that impede their
correct segregation. DNA topoisomerases are enzymes able to modify the topological state of DNA molecules.
Type IB topoisomerases mediate the passage of one strand through another and can efficiently remove
supercoiling. Differently, type II topoisomerases mediate the passage of one duplex through another and can
act both on supercoiling and precatenates. Moreover, this class of enzymes can unlink sister chromatids prior
to chromosome segregation. It is currently unknown what is the cellular response to the accumulation of
unresolved topological constraints generated by the replication machinery during S-phase.
Cells have evolved different surveillance mechanisms to monitor the correct progression through the
different phases of the cell cycle, which are known as checkpoints.
In particular, during the S phase, two different checkpoint pathways act to preserve genome integrity: the
replication checkpoint and the intra-S phase DNA damage checkpoint.
When replication is inhibited or DNA lesions arise in S-phase, a signalling cascade is activated leading to the
block of the cell cycle progression and promoting the resolution of replication impediments or the repair of
the DNA damage. Rad53 is an essential kinase in this cascade, and is rapidly activated by phosphorylation in
response to DNA damage. For this reason the phosphorylation status of this protein can be used as an
indicator of checkpoint activation.
In this project we investigated the roles of Top1 (Type IB) and Top2 (Type IIA) DNA topoisomerases during
the synthesis (S) phase of the cell cycle, and their contribution to genomic DNA replication. By
contemporarily inactivating both topoisomerases in budding yeast Saccharomyces cerevisiae cells, we were
able to investigate how the accumulation of torsional stress affects replication fork stability and DNA damage
checkpoint response
Cohesion by topology: sister chromatids interlocked by DNA
No full textSister chromatid cohesion is coupled with chromosome replication and influences chromosome segregation and intra-S repair. Specialized proteins, the cohesins, together with other pathways contribute to tether sister chromatids. In this issue of Genes & Development, Wang and colleagues (pp. 2426-2433) demonstrate that TopoIV, a type II DNA topoisomerase, modulates cohesion in Escherichia coli, by removing interlocked DNA junctions between sister chromatids. They propose that DNA precatenanes, arising during replication fork progression, hold sister chromatids together
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