Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0004135 (ATM)
 13,001 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The bacterial cytolethal distending toxin (CDT) triggers a G2/M cell cycle arrest in eukaryotic cells by inhibiting the CDC25C phosphatase-dependent CDK1 dephosphorylation and activation. We report that upon CDT treatment CDC25C is fully sequestered in the cytoplasmic compartment, an effect that is reminiscent of DNA damage-dependent checkpoint activation. We show that the checkpoint kinase CHK2, an upstream regulator of CDC25C, is phosphorylated and activated after CDT treatment. In contrast to what is observed with other DNA damaging agents, we demonstrate that the activation of CHK2 can only take place during S-phase. Use of wortmannin and caffeine suggests that this effect is not dependent on ATM but rather on another as yet unidentified PI3 kinase family member. These results confirm that the CDT is therefore responsible for specific genomic injuries that block cell proliferation by activating a cell cycle checkpoint.
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PMID:Study of the cytolethal distending toxin (CDT)-activated cell cycle checkpoint. Involvement of the CHK2 kinase. 1124 Jan 39

The antitumor drug adozelesin is a potent cytotoxic DNA-damaging agent. Here we determined how adozelesin affects chromosomal DNA replication at a molecular level in a yeast model system and examined the influence of checkpoint kinase genes, the human homologues of which are mutated in cancer. Analysis of replication intermediates using two-dimensional gel electrophoresis showed that adozelesin inhibited the activity of a replication origin and stalled replication fork progression through chromosomal DNA at the origin. RAD53 and MEC1 protein kinase genes, homologues of human CHK2 and ATM, respectively, regulate an intra-S-phase DNA damage checkpoint and, when mutated, permit unchecked replication of damaged DNA in S-phase. Mutations in these genes did not abrogate adozelesin-induced inhibition of origin activity and fork progression at the replication origin. However, novel replication intermediates indicative of DNA breaks were detected only in the rad53 mutant, suggesting a role for the wild-type gene in maintaining chromosome integrity in the presence of the drug. In contrast to the inhibition of the active replication origin by adozelesin, normally silent origins present in the same chromosome were activated by adozelesin in rad53 and mec1 mutant cells. Thus, an antitumor drug that damages DNA can induce an abnormal replication pattern in a chromosome by activating silent origins, depending upon defects in yeast checkpoint kinase genes, the homologues of which are mutated in cancer. Implications of an abnormal replication pattern for the epigenetic regulation of gene expression are discussed.
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PMID:Antitumor drug adozelesin differentially affects active and silent origins of DNA replication in yeast checkpoint kinase mutants. 1132 53

Here we report the first characterization of replication timing and its regulation in the fission yeast Schizosaccharomyces pombe. We used three different synchronization methods: centrifugal elutriation, cdc10 temperature-shift and release, and starvation for deoxyribonucleoside triphosphates (dNTPs) by treatment with hydroxyurea (HU) followed by removal of HU, to study the times when specific autonomously replicating sequence elements (ARS elements; potential replication origins) replicate during S phase. We found that individual ARS elements replicate at characteristic times, some early and some late, independently of synchronization method. In wild-type cells treated with HU, early ARS elements replicated but late ones did not. However, in HU-treated mutant cells lacking the Rad3 (similar to human ATR and ATM) or Cds1 (similar to human CHK2) checkpoint kinase, both early and late ARS elements were able to replicate. Thus under conditions of dNTP starvation the Rad3 and Cds1 kinases are needed to suppress the replication of normally late-replicating regions.
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PMID:Regulation of replication timing in fission yeast. 1168 51

Structural maintenance of chromosomes (SMC) proteins (SMC1, SMC3) are evolutionarily conserved chromosomal proteins that are components of the cohesin complex, necessary for sister chromatid cohesion. These proteins may also function in DNA repair. Here we report that SMC1 is a component of the DNA damage response network that functions as an effector in the ATM/NBS1-dependent S-phase checkpoint pathway. SMC1 associates with BRCA1 and is phosphorylated in response to IR in an ATM- and NBS1-dependent manner. Using mass spectrometry, we established that ATM phosphorylates S957 and S966 of SMC1 in vivo. Phosphorylation of S957 and/or S966 of SMC1 is required for activation of the S-phase checkpoint in response to IR. We also discovered that the phosphorylation of NBS1 by ATM is required for the phosphorylation of SMC1, establishing the role of NBS1 as an adaptor in the ATM/NBS1/SMC1 pathway. The ATM/CHK2/CDC25A pathway is also involved in the S-phase checkpoint activation, but this pathway is intact in NBS cells. Our results indicate that the ATM/NBS1/SMC1 pathway is a separate branch of the S-phase checkpoint pathway, distinct from the ATM/CHK2/CDC25A branch. Therefore, this work establishes the ATM/NBS1/SMC1 branch, and provides a molecular basis for the S-phase checkpoint defect in NBS cells.
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PMID:SMC1 is a downstream effector in the ATM/NBS1 branch of the human S-phase checkpoint. 1187 77

Cell cycle checkpoints are evolutionarily conserved surveillance systems that protect genomic stability and prevent oncogenesis in mammals. One important target of checkpoint control is ribonucleotide reductase (RNR), which catalyzes the rate-limiting step in dNTP and DNA synthesis. In both yeast and humans, RNR is transcriptionally induced after DNA damage via Mec1/Rad53 (yeast) and ATM/CHK2 (human) checkpoint pathways. In addition, yeast checkpoint proteins Mec1 and Rad53 also regulate the RNR inhibitor Sml1. After DNA damage or at S phase, Mec1 and Rad53 control the phosphorylation and concomitant degradation of Sml1 protein. This new layer of control contributes to the increased dNTP production likely necessary for DNA repair and replication; however, the molecular mechanism is unclear. Here we show that Dun1, a downstream kinase of Mec1/Rad53, genetically and physically interacts with Sml1 in vivo. The absence of Dun1 activity leads to the accumulation of Sml1 protein at S phase and after DNA damage. As a result, dun1Delta strains need more time to finish DNA replication, are defective in mitochondrial DNA propagation, and are sensitive to DNA-damaging agents. Moreover, phospho-Sml1 is absent or dramatically reduced in dun1Delta cells. Finally, Dun1 can phosphorylate Sml1 in vitro. These results suggest that Dun1 kinase function is the last step required in the Mec1/Rad53 cascade to remove Sml1 during S phase and after DNA damage.
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PMID:The Dun1 checkpoint kinase phosphorylates and regulates the ribonucleotide reductase inhibitor Sml1. 1190 30

The tumor suppressor gene CHK2 encodes a versatile effector serine/threonine kinase involved in responses to DNA damage. Chk2 has an amino-terminal SQ/TQ cluster domain (SCD), followed by a forkhead-associated (FHA) domain and a carboxyl-terminal kinase catalytic domain. Mutations in the SCD or FHA domain impair Chk2 checkpoint function. We show here that autophosphorylation of Chk2 produced in a cell-free system requires trans phosphorylation by a wortmannin-sensitive kinase, probably ATM or ATR. Both SQ/TQ sites and non-SQ/TQ sites within the Chk2 SCD can be phosphorylated by active Chk2. Amino acid substitutions in the SCD and the FHA domain impair auto- and trans-kinase activities of Chk2. Chk2 forms oligomers that minimally require the FHA domain of one Chk2 molecule and the SCD within another Chk2 molecule. Chk2 oligomerization in vivo increases after DNA damage, and when damage is induced by gamma irradiation, this increase requires ATM. Chk2 oligomerization is phosphorylation dependent and can occur in the absence of other eukaryotic proteins. Chk2 can cross-phosphorylate another Chk2 molecule in an oligomeric complex. Induced oligomerization of a Chk2 chimera in vivo concomitant with limited DNA damage augments Chk2 kinase activity. These results suggest that Chk2 oligomerization regulates Chk2 activation, signal amplification, and transduction in DNA damage checkpoint pathways.
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PMID:Chk2 activation and phosphorylation-dependent oligomerization. 1202 51

Somatic genetic alterations in tumors are known to correlate with survival, but little is known about the prognostic significance of germ-line variation. We assessed the effect of germ-line variation on survival among women with breast cancer participating in a British population-based study. Up to 2430 cases for whom current vital status data were available were screened for BRCA1/2 mutations and genotyped for polymorphisms in 22 DNA repair, hormone metabolism, carcinogen metabolism, and other genes. The effect of genotype on outcome was assessed by Cox regression analysis. The largest effect was observed for the silent polymorphism D501D (t>c) in LIG4, a gene involved in DNA double-strand break repair. The estimated hazard ratio (HR) in cc homozygotes relative to tt homozygotes was 4.0 (95% confidence interval, 2.1-7.7; P = 0.002), and this effect remained after stratification by stage, grade, and tumor type [HR, 4.2 (1.8-9.4); P = 0.01]. Total length of a CYP19 IVS4 (ttta)(n) repeat was also associated with survival [HR, 0.9 (0.8-1.0); P = 0.01], but this became nonsignificant after stratification by stage, grade, and tumor type. Poorer survival was observed for 10 BRCA1 mutation carriers [HR, 4.1 (1.3-13); P = 0.047]; however, after adjustment for known prognostic factors, the HR estimate decreased to 2.0 and became nonsignificant (P = 0.4). CYP17 (P = 0.05) and TP53 (P = 0.06) polymorphisms showed marginally significant associations in unstratified analyses. No effect on survival was seen for polymorphisms in ATM, BRCA1/2, CHK2, KU70, NBS1, RAD51, RAD52, XRCC3, AR, COMT, NQO1, VDR, ADH3, CYP1A1, GSTP1, TGF-beta, or CDH1. Even if confirmed, the prognostic markers identified in this study are unlikely to replace current markers of prognosis such as estrogen receptor status. However, our results demonstrate the potential of the analysis of germ-line variation to provide insight into the biological determinants of response to treatment and prognosis in breast cancer.
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PMID:Effect of germ-line genetic variation on breast cancer survival in a population-based study. 1203 13

The CHK2 gene codifies for a serine/threonine kinase that plays a central role in DNA damage response pathways. To determine the potential role of CHK2 alterations in the pathogenesis of lymphoid neoplasms we have examined the gene status, protein, and mRNA expression in a series of tumors and nonneoplastic lymphoid samples. A heterozygous Ile157Thr substitution, also present in the germ line of the patient, was detected in a blastoid mantle cell lymphoma (MCL). CHK2 protein and mRNA expression levels were similar in all types of lymphomas and reactive samples, and these levels were independent of the proliferative activity of the tumors. However, 5 tumors, one typical MCL, 2 blastoid MCLs, and 2 large cell lymphomas, showed marked loss of protein expression, including 2 samples with complete absence of CHK2 protein. These 2 lymphomas showed the highest number of chromosomal imbalances detected by comparative genomic hybridization in the whole series of cases. However, no mutations, deletions, or hypermethylation of the promoter region were identified in any of these tumors. mRNA levels were similar in cases with low and normal protein expression, suggesting a posttranscriptional regulation of the protein in these tumors. CHK2 gene and protein alterations were not related to p53 and ATM gene status. In conclusion, CHK2 alterations are uncommon in malignant lymphomas but occur in a subset of aggressive tumors independently of p53 or ATM alterations. The high number of chromosomal imbalances in tumors with complete absence of CHK2 protein suggests a role of this gene in chromosomal instability in human lymphomas.
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PMID:CHK2-decreased protein expression and infrequent genetic alterations mainly occur in aggressive types of non-Hodgkin lymphomas. 1239 93

Defective S-phase checkpoint activation results in an inability to downregulate DNA replication following genotoxic insult such as exposure to ionizing radiation. This 'radioresistant DNA synthesis' (RDS) is a phenotypic hallmark of ataxia-telangiectasia, a cancer-prone disorder caused by mutations in ATM. The mismatch repair system principally corrects nucleotide mismatches that arise during replication. Here we show that the mismatch repair system is required for activation of the S-phase checkpoint in response to ionizing radiation. Cells deficient in mismatch repair proteins showed RDS, and restoration of mismatch repair function restored normal S-phase checkpoint function. Catalytic activation of ATM and ATM-mediated phosphorylation of the protein NBS1 (also called nibrin) occurred independently of mismatch repair. However, ATM-dependent phosphorylation and activation of the checkpoint kinase CHK2 and subsequent degradation of its downstream target, CDC25A, was abrogated in cells lacking mismatch repair. In vitro and in vivo approaches both show that MSH2 binds to CHK2 and that MLH1 associates with ATM. These findings indicate that the mismatch repair complex formed at the sites of DNA damage facilitates the phosphorylation of CHK2 by ATM, and that defects in this mechanism form the molecular basis for the RDS observed in cells deficient in mismatch repair.
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PMID:The mismatch repair system is required for S-phase checkpoint activation. 1511 72

The intra-S-phase checkpoint in yeast responds to stalled replication forks by activating the ATM-like kinase Mec1 and the CHK2-related kinase Rad53, which in turn inhibit spindle elongation and late origin firing and lead to a stabilization of DNA polymerases at arrested forks. A mutation that destabilizes the second subunit of the Origin Recognition Complex, orc2-1, reduces the number of functional replication forks by 30% and severely compromises the activation of Rad53 by replication stress or DNA damage in S phase. We show that the restoration of the checkpoint response correlates in a dose-dependent manner with the restoration of pre-replication complex formation in G1. Other forms of DNA damage can compensate for the reduced level of fork-dependent signal in the orc2-1 mutant, yet even in wild-type cells, the amount of damage required for Rad53 activation is higher in S phase than in G2. Our data suggest the existence of an S-phase-specific threshold that may be necessary to allow cells to tolerate damage-like DNA structures present at normal replication forks.
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PMID:ORC and the intra-S-phase checkpoint: a threshold regulates Rad53p activation in S phase. 1250 44


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