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Query: UMLS:C0004135 (ATM)
 13,001 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We provide an overview of the functional interrelationship between genes and proteins related to DNA repair by homologous recombination and cell cycle regulation in relation to the progression and therapy resistance of human tumours. To ensure the high-fidelity transmission of genetic information from one generation to the next, cells have evolved mechanisms to monitor genome integrity. Upon DNA damage, cells initiate complex response pathways including cell cycle arrest, activation of genes and gene products involved in DNA repair, and under some circumstances, the triggering of programmed cell death. Deregulation of this co-ordinated response leads to genetic instability and is fundamental to the aetiology of human cancer. Homologous recombination involved in DNA repair is induced by environmental damage as well as misreplication during the normal cell cycle. However, when not regulated properly, it can result in the loss of heterozygocity or genetic rearrangements, central to the process of carcinogenesis. The central step of homologous recombination is the DNA strand exchange reaction catalysed by the eukaryotic Rad51 protein. Here, we describe the recent progress in our understanding of how Rad51 is involved in the signalling and repair of DNA damage and how tumour suppressors, such as p53, ATM, BRCA1, BRCA2, BLM and FANCD2 are linked to Rad51-dependent pathways. An increased knowledge of the role of Rad51 in DNA repair by homologous recombination and its effects on cell cycle progression, tumour development and tumour resistance may provide opportunities for identifying improved diagnostic markers and developing more effective treatments for cancer.
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PMID:Homologous recombination and cell cycle checkpoints: Rad51 in tumour progression and therapy resistance. 1459 70

Fanconi anemia (FA) is a genetic cancer-predisposition syndrome characterized by bone marrow failure and cellular and chromosomal hypersensitivity to DNA cross-linking agents. Seven FA genes have been isolated and their products associate to form a pathway that interacts functionally or physically with several DNA-damage response proteins involved in cell cycle checkpoints and/or DNA repair. These proteins include BLM, ATM, BRCA1, XPF and the MRE11/RAD50/NBS1 complex. In spite of several recent striking progresses in the biochemistry and the molecular biology of the disorder, the precise function(s) of the FA proteins remain(s) poorly determined. However, several recent data indicate that the FA pathway could be involved in the coordination of both cell cycle checkpoints and DNA repair.
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PMID:The Fanconi anemia pathway and the DNA interstrand cross-links repair. 1472 22

Bloom's syndrome (BS) is a human genetic disorder associated with cancer predisposition. The BS gene product, BLM, is a member of the RecQ helicase family, which is required for the maintenance of genome stability in all organisms. In budding and fission yeasts, loss of RecQ helicase function confers sensitivity to inhibitors of DNA replication, such as hydroxyurea (HU), by failure to execute normal cell cycle progression following recovery from such an S-phase arrest. We have examined the role of the human BLM protein in recovery from S-phase arrest mediated by HU and have probed whether the stress-activated ATR kinase, which functions in checkpoint signaling during S-phase arrest, plays a role in the regulation of BLM function. We show that, consistent with a role for BLM in protection of human cells against the toxicity associated with arrest of DNA replication, BS cells are hypersensitive to HU. BLM physically associates with ATR (ataxia telangiectasia and rad3(+) related) protein and is phosphorylated on two residues in the N-terminal domain, Thr-99 and Thr-122, by this kinase. Moreover, BS cells ectopically expressing a BLM protein containing phosphorylation-resistant T99A/T122A substitutions fail to adequately recover from an HU-induced replication blockade, and the cells subsequently arrest at a caffeine-sensitive G(2)/M checkpoint. These abnormalities are not associated with a failure of the BLM-T99A/T122A protein to localize to replication foci or to colocalize either with ATR itself or with other proteins that are required for response to DNA damage, such as phosphorylated histone H2AX and RAD51. Our data indicate that RecQ helicases play a conserved role in recovery from perturbations in DNA replication and are consistent with a model in which RecQ helicases act to restore productive DNA replication following S-phase arrest and hence prevent subsequent genomic instability.
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PMID:Phosphorylation of the Bloom's syndrome helicase and its role in recovery from S-phase arrest. 1472 72

Bloom syndrome and ataxia-telangiectasia are autosomal recessive human disorders characterized by immunodeficiency, genome instability and predisposition to develop cancer. Recent data reveal that the products of these two genes, BLM and ATM, interact and function together in recognizing abnormal DNA structures. To investigate the function of these two molecules in DNA damage recognition, we generated double knockouts of ATM(-/-) BLM(-/-) in the DT40 chicken B-lymphocyte cell line. The double mutant cells were viable and exhibited a variety of characteristics of both ATM(-/-) and BLM(-/-) cells. There was no evidence for exacerbation of either phenotype; however, the more extreme radiosensitivity seen in ATM(-/-) and the elevated sister chromatid exchange seen in BLM(-/-) cells were retained in the double mutants. These results suggest that ATM and BLM have largely distinct roles in recognizing different forms of damage in DNA, but are also compatible with partially overlapping functions in recognizing breaks in radiation-damaged DNA.
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PMID:Disruption of the BLM gene in ATM-null DT40 cells does not exacerbate either phenotype. 1498

Bloom syndrome (BS) and ataxia-telangiectasia (A-T) are rare autosomal recessive diseases associated with chromosomal instability. The genes responsible for BS and A-T have been identified as BLM and ATM, respectively, whose products were recently found to be components of BRCA1-associated genome surveillance complex (BASC), a supercomplex possibly involved in the recognition and repair of aberrant DNA structures. Based on experiments using BLM(-/-) DT40 cells and BLM(-/-)/RAD54(-/-) DT40 cells, we previously suggested that BLM functions to reduce the formation of double-strand breaks (DSBs) during DNA replication. To examine whether ATM is involved in the recognition and/or repair of DSBs generated in BLM(-/-) DT40 cells and to address the functional relationship between the two BASC components, we generated BLM(-/-)/ATM(-/-) DT40 cells and characterized their properties as well as those of ATM(-/-) and BLM(-/-) DT40 cells. BLM(-/-)/ATM(-/-) cells proliferated slightly more slowly than either BLM(-/-) or ATM(-/-) cells. The sensitivity of BLM(-/-)/ATM(-/-) cells to gamma-irradiation was similar to that of ATM(-/-) cells, while BLM(-/-) cells were slightly resistant to gamma-irradiation compared with wild-type cells. BLM(-/-) cells showed sensitivity to methyl methanesulfonate (MMS) and UV irradiation while ATM(-/-) cells did not show sensitivity to either agent. The sensitivity of BLM(-/-)/ATM(-/-) cells to MMS and UV was similar to that of BLM(-/-) cells. Disrupting the function of ATM reduced the targeted integration frequency in BLM(-/-) DT40 cells. However, a defect in ATM only slightly reduced the increased sister chromatid exchanges (SCEs) in BLM(-/-) DT40 cells.
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PMID:The absence of a functional relationship between ATM and BLM, the components of BASC, in DT40 cells. 1499 Mar 44

Ataxia-telangiectasia mutated (ATM) is a serine/threonine protein kinase that plays a central role in controlling the cellular response to ionizing radiation and other DNA-damaging agents. ATM is a 3056 amino acid polypeptide that is present in low abundance in the nucleus of human cells. Here, we describe the purification and characterization of ATM from the nuclear fraction of HeLa cells. Microgram quantities of highly stable, kinase-active ATM were prepared. Purified ATM was phosphorylated on serine 1981 and was active towards a variety of known ATM substrates, including p53 and the Bloom Syndrome helicase, BLM. The protein kinase activity of ATM was selectively inhibited by wortmannin, caffeine and LY294002 and was stimulated by charged biological polymers, including single-stranded M13 DNA (ssDNA), sheared double-stranded calf thymus DNA, heparin sulfate and poly ADP-ribose (PAR), raising the possibility that charged structures may contribute to regulation of ATM activity. However, chemical inhibition of the formation of poly ADP-ribose in cells had no effect on the activation of ATM-dependent pathways by ionizing radiation. Using gel filtration chromatography, we also show that purified ATM, as well as ATM in crude nuclear extracts from unirradiated and irradiated cells elutes with an estimated native molecular weight of approximately 600 kDa. Moreover, dephosphorylation of serine 1981 did not affect the apparent molecular weight of ATM in irradiated extracts. Our results suggest that phosphorylation of serine 1981 alone may not directly regulate the subunit composition of ATM.
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PMID:Biochemical characterization of the ataxia-telangiectasia mutated (ATM) protein from human cells. 1517 84

As many as 5% of human cancers appear to be of hereditable etiology. Of the more than 50 characterized familial cancer syndromes, most involve disease affecting multiple organs and many can be traced to one or more abnormalities in specific genes. Studying these syndromes in humans is a difficult task, especially when it comes to genes that may manifest themselves early in gestation. It has been made somewhat easier with the development of genetically engineered mice (GEM) that phenotypically mimic many of these inheritable human cancers. The past 15 years has seen the establishment of mouse lines heterozygous or homozygous null for genes known or suspected of being involved in human cancer syndromes, including APC, ATM, BLM, BRCA1, BRCA2, LKB1, MEN1, MLH, MSH, NF1, TP53, PTEN, RB1, TSC1, TSC2, VHL, and XPA. These lines not only provide models for clinical disease and pathology, but also provide avenues to investigate molecular pathology, gene-gene and protein-tissue interaction, and, ultimately, therapeutic intervention. Possibly of even greater importance, they provide a means of looking at placental and fetal tissues, where genetic abnormalities are often first detected and where they may be most easily corrected. We will review these mouse models, examine their usefulness in medical research, and furnish sources of animals and references.
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PMID:Mouse models of human familial cancer syndromes. 1520 8

Repair of DSBs is important to prevent chromosomal fragmentation, translocations and deletions. To investigate the process in NHEJ, we have established an in vitro system to clarify the measurement and analysis of the efficiency and the fidelity of rejoining of DSBs, and applied the method to investigate NHEJ in human cells derived from patients suffering from cancer-prone hereditary diseases. A DSB was introduced in plasmid pZErO-2 at a specific site within the ccdB gene that is lethal to E. coli cells, and treated with nuclear extracts from human cells. The efficiency of rejoining in the nuclear extract from an A-T cell line was comparable to that from a control cell line. However, the accuracy of rejoining was much lower for the A-T cell extract than for the control cell extract. All mutations were deletions, most of which contained short direct repeats at the breakpoint junctions. The deletion spectrum caused by the A-T nuclear extract was distinct from that by the control extract. These results indicate that A-T cells have certain deficiencies in end-joining of double-strand breaks in DNA. The extract from BS cells also showed the similar activity and the lower fidelity of rejoing compared to that from normal cells. From the sequencing analysis of the junction of DSBs, it is speculated that the defect in the BLM helicase might cause irregular rejoining of DSBs. Radioadaptive response is the acquirement of cellular resistance to ionizing radiation by prior exposure to low dose. We investigated the in vitro end-joining activity of DNA ends in radioadaptive cells. Both the efficiency and the fidelity of rejoining in the cells pre-exposed to low dose are increased comparing to those without pre-exposure. We also investigated the joining activity of DNA ends in p53-deficient cells. Pre-irradiation caused no apparent alteration in both the efficiency and fidelity of end-joining. These results suggest that the exposure to low dose activates a cellular function to repair DSBs efficiently, which is dependent on p53. These results indicate that NHEJ pathway is regulated by many factors; genetic regulation by ATM and BLM, and physiological conditions such as irradiation with ionizing radiation. The observations also suggest that in some occasions p53 might play a key role in NHEJ.
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PMID:Genetic and physiological regulation of non-homologous end-joining in mammalian cells. 1547 91

Bloom syndrome is a rare autosomal recessive genetic disorder characterized by lupus-like erythematous telangiectasias of the face, sun sensitivity, stunted growth, and immunodeficiency. Chromosome instability syndromes have a common feature, being associated at high frequency with neoplasia. BS is considered as one of the chromosome instability syndromes since the fibroblasts or lymphocytes of BS patients show excessive spontaneous chromosome instability. The causative gene of BS (BLM) was identified as a RecQ helicase homologue. In this review, we showed the characteristic phenotypes of BS, especially two Japanese siblings. In the latter of the review, the functional domains of BLM, those are nuclear localization signal and the interacting proteins such as ATM, are shown. Several lines of reports indicates that BLM helicase is involved in the re-initiation of DNA replication at sites where replication forks have arrested or collapsed. To elucidate the precise function of RecQ helicase in DNA repair and replication aims not only to improve our understanding of the molecular basis for tumorigenesis, but also to extend the range of potential therapeutic targets.
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PMID:The function of RecQ helicase gene family (especially BLM) in DNA recombination and joining. 1547 92

Repair of DSBs is important to prevent chromosomal fragmentation, translocations and deletions. To investigate the process in NHEJ, we have established an in vitro system to clarify the measurement and analysis of the efficiency and the fidelity of rejoining of DSBs, and applied the method to investigate NHEJ in human cells derived from patients suffering from cancer-prone hereditary diseases. A DSB was introduced in plasmid pZErO-2 at a specific site within the ccdB gene that is lethal to E. coli cells, and treated with nuclear extracts from human cells. The efficiency of rejoining in the nuclear extract from an A-T cell line was comparable to that from a control cell line. However, the accuracy of rejoining was much lower for the A-T cell extract than for the control cell extract. All mutations were deletions, most of which contained short direct repeats at the breakpoint junctions. The deletion spectrum caused by the A-T nuclear extract was distinct from that by the control extract. These results indicate that A-T cells have certain deficiencies in end-joining of double-strand breaks in DNA. The extract from BS cells also showed the similar activity and the lower fidelity of rejoing compared to that from normal cells. From the sequencing analysis of the junction of DSBs, it is speculated that the defect in the BLM helicase might cause irregular rejoining of DSBs. Radioadaptive response is the acquirement of cellular resistance to ionizing radiation by prior exposure to low dose. We investigated the in vitro end-joining activity of DNA ends in radioadaptive cells. Both the efficiency and the fidelity of rejoining in the cells pre-exposed to low dose are increased comparing to those without pre-exposure. We also investigated the joining activity of DNA ends in p53-deficient cells. Pre-irradiation caused no apparent alteration in both the efficiency and fidelity of end-joining. These results suggest that the exposure to low dose activates a cellular function to repair DSBs efficiently, which is dependent on p53. These results indicate that NHEJ pathway is regulated by many factors; genetic regulation by ATM and BLM, and physiological conditions such as irradiation with ionizing radiation. The observations also suggest that in some occasions p53 might play a key role in NHEJ.
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PMID:Genetic and physiological regulation of non-homologous end-joining in mammalian cells. 1549 26


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