The cellular response to DNA double-strand breaks: defining the sensors and mediators.
TL;DR: This work discusses the possible role of the Mre11 complex as a primary damage sensor and the complex relationship between DNA damage sensors, transducers and mediators and proposed criteria for defining sensor proteins.
About: This article is published in Trends in Cell Biology.The article was published on 2003-09-01. It has received 347 citations till now. The article focuses on the topics: G2-M DNA damage checkpoint & DNA repair.
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TL;DR: All life on earth must cope with constant exposure to DNA-damaging agents such as the Sun's radiation, and how cells respond to DNA damage are critical determinants of whether that individual will develop cancer.
Abstract: All life on earth must cope with constant exposure to DNA-damaging agents such as the Sun's radiation. Highly conserved DNA-repair and cell-cycle checkpoint pathways allow cells to deal with both endogenous and exogenous sources of DNA damage. How much an individual is exposed to these agents and how their cells respond to DNA damage are critical determinants of whether that individual will develop cancer. These cellular responses are also important for determining toxicities and responses to current cancer therapies, most of which target the DNA.
2,725 citations
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...Although the mediator proteins are unlikely to initially target the activated ATM to sites of DNA damage (this might be the role of the candidate damage sensors such as the MRN complex...
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TL;DR: Recent experiments have revealed how shelterin represses the ATM and ATR kinase signaling pathways and hides chromosome ends from nonhomologous end joining and homology-directed repair.
Abstract: The genomes of prokaryotes and eukaryotic organelles are usually circular as are most plasmids and viral genomes. In contrast, the nuclear genomes of eukaryotes are organized on linear chromosomes, which require mechanisms to protect and replicate DNA ends. Eukaryotes navigate these problems with the advent of telomeres, protective nucleoprotein complexes at the ends of linear chromosomes, and telomerase, the enzyme that maintains the DNA in these structures. Mammalian telomeres contain a specific protein complex, shelterin, that functions to protect chromosome ends from all aspects of the DNA damage response and regulates telomere maintenance by telomerase. Recent experiments, discussed here, have revealed how shelterin represses the ATM and ATR kinase signaling pathways and hides chromosome ends from nonhomologous end joining and homology-directed repair.
1,715 citations
Cites background from "The cellular response to DNA double..."
...The sensing step in the ATM pathway is thought to involve the interaction of the Mre11 complex with DNA ends (154), and it is therefore conceivable that ATM repression involves blocking the Mre11 complex from gaining access to telomere termini....
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TL;DR: Functional analysis of the minimal stress proteome yields information about key aspects of the cellular stress response, including physiological mechanisms of sensing membrane lipid, protein, and DNA damage; redox sensing and regulation; cell cycle control; macromolecular stabilization/repair; and control of energy metabolism.
Abstract: The cellular stress response is a universal mechanism of extraordinary physiological/pathophysiological significance. It represents a defense reaction of cells to damage that environmental forces inflict on macromolecules. Many aspects of the cellular stress response are not stressor specific because cells monitor stress based on macromolecular damage without regard to the type of stress that causes such damage. Cellular mechanisms activated by DNA damage and protein damage are interconnected and share common elements. Other cellular responses directed at re-establishing homeostasis are stressor specific and often activated in parallel to the cellular stress response. All organisms have stress proteins, and universally conserved stress proteins can be regarded as the minimal stress proteome. Functional analysis of the minimal stress proteome yields information about key aspects of the cellular stress response, including physiological mechanisms of sensing membrane lipid, protein, and DNA damage; redox sensing and regulation; cell cycle control; macromolecular stabilization/repair; and control of energy metabolism. In addition, cells can quantify stress and activate a death program (apoptosis) when tolerance limits are exceeded.
1,265 citations
TL;DR: It is shown that functional MRN is required for ATM activation, and consequently for timely activation of ATM‐mediated pathways, and explain the clinical resemblance between A‐T and A-TLD.
Abstract: The ATM protein kinase is a primary activator of the cellular response to DNA double-strand breaks (DSBs). In response to DSBs, ATM is activated and phosphorylates key players in various branches of the DNA damage response network. ATM deficiency causes the genetic disorder ataxia-telangiectasia (A-T), characterized by cerebellar degeneration, immunodeficiency, radiation sensitivity, chromosomal instability and cancer predisposition. The MRN complex, whose core contains the Mre11, Rad50 and Nbs1 proteins, is involved in the initial processing of DSBs. Hypomorphic mutations in the NBS1 and MRE11 genes lead to two other genomic instability disorders: the Nijmegen breakage syndrome (NBS) and A-T like disease (A-TLD), respectively. The order in which ATM and MRN act in the early phase of the DSB response is unclear. Here we show that functional MRN is required for ATM activation, and consequently for timely activation of ATM-mediated pathways. Collectively, these and previous results assign to components of the MRN complex roles upstream and downstream of ATM in the DNA damage response pathway and explain the clinical resemblance between A-T and A-TLD.
1,093 citations
TL;DR: Many of the engineered nanomaterials assessed were found to cause genotoxic responses, such as chromosomal fragmentation, DNA strand breakages, point mutations, oxidative DNA adducts and alterations in gene expression profiles.
1,056 citations
Cites background from "The cellular response to DNA double..."
...The presence of g-H2AX is therefore a sensitive reporter of DNA damage and these sites can be detected by immunofluorescence microscopy utilising fluorescently labelled antibodies specific to g-H2AX [208]....
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References
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TL;DR: It is shown that ATM is held inactive in unirradiated cells as a dimer or higher-order multimer, with the kinase domain bound to a region surrounding serine 1981 that is contained within the previously described ‘FAT’ domain.
Abstract: The ATM protein kinase, mutations of which are associated with the human disease ataxia-telangiectasia, mediates responses to ionizing radiation in mammalian cells. Here we show that ATM is held inactive in unirradiated cells as a dimer or higher-order multimer, with the kinase domain bound to a region surrounding serine 1981 that is contained within the previously described 'FAT' domain. Cellular irradiation induces rapid intermolecular autophosphorylation of serine 1981 that causes dimer dissociation and initiates cellular ATM kinase activity. Most ATM molecules in the cell are rapidly phosphorylated on this site after doses of radiation as low as 0.5 Gy, and binding of a phosphospecific antibody is detectable after the introduction of only a few DNA double-strand breaks in the cell. Activation of the ATM kinase seems to be an initiating event in cellular responses to irradiation, and our data indicate that ATM activation is not dependent on direct binding to DNA strand breaks, but may result from changes in the structure of chromatin.
3,411 citations
TL;DR: The inability to repair DNA damage properly in mammals leads to various disorders and enhanced rates of tumour development, and this work has shown that direct activation of DNA repair networks is needed to correct this problem.
Abstract: The inability to repair DNA damage properly in mammals leads to various disorders and enhanced rates of tumour development. Organisms respond to chromosomal insults by activating a complex damage response pathway. This pathway regulates known responses such as cell-cycle arrest and apoptosis (programmed cell death), and has recently been shown to control additional processes including direct activation of DNA repair networks.
3,230 citations
TL;DR: The results offer direct visual confirmation that γ-H2AX forms en masse at chromosomal sites of DNA double-strand breaks and suggest the possible existence of units of higher order chromatin structure involved in monitoring DNA integrity.
Abstract: The loss of chromosomal integrity from DNA double-strand breaks introduced into mammalian cells by ionizing radiation results in the specific phosphorylation of histone H2AX on serine residue 139, yielding a specific modified form named γ-H2AX. An antibody prepared to the unique region of human γ-H2AX shows that H2AX homologues are phosphorylated not only in irradiated mammalian cells but also in irradiated cells from other species, including Xenopus laevis, Drosophila melanogaster, and Saccharomyces cerevisiae. The antibody reveals that γ-H2AX appears as discrete nuclear foci within 1 min after exposure of cells to ionizing radiation. The numbers of these foci are comparable to the numbers of induced DNA double-strand breaks. When DNA double-strand breaks are introduced into specific partial nuclear volumes of cells by means of a pulsed microbeam laser, γ-H2AX foci form at these sites. In mitotic cells from cultures exposed to nonlethal amounts of ionizing radiation, γ-H2AX foci form band-like structures on chromosome arms and on the end of broken arms. These results offer direct visual confirmation that γ-H2AX forms en masse at chromosomal sites of DNA double-strand breaks. The results further suggest the possible existence of units of higher order chromatin structure involved in monitoring DNA integrity.
2,451 citations
TL;DR: The evidence presented strongly supports a role for the gamma-H2AX and the PI-3 protein kinase family in focus formation at sites of double-strand breaks and suggests the possibility of a change in chromatin structure accompanying double-Strand break repair.
2,107 citations
TL;DR: The results clearly establish ATM as the major kinase involved in the phosphorylation of H2AX and suggest that ATM is one of the earliest kinases to be activated in the cellular response to double-strand breaks.
1,909 citations