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

Homologous chromosome synapsis and meiotic recombination are facilitated by several meiosis-specific structures: the synaptonemal complex (SC), and two types of meiotic nodules: (1) early meiotic nodules (MNs), also called zygotene nodules or early recombination nodules, and (2) late recombination nodules (RNs). The former are thought to be nucleoprotein complexes involved in the check for homology preceding, or accompanying synapsis, while the latter have been shown to be involved in reciprocal recombination. We have examined by immunocytochemistry the meiotic localization of a series of proteins at sites along the asynapsed axial elements prior to homologous synapsis and at sites along the SCs following synapsis. Several of the proteins examined have been implicated in repair/recombination and include RAD51, a mammalian homolog of the Escherichia coli RecA protein; Replication Protein-A (RPA), a single-strand DNA binding protein; and MLH1, a mismatch repair protein which is a homolog of the E. coli MutL protein. In addition two proteins were examined that have been implicated in meiotic checkpoints: ATM, the protein mutated in the human disease Ataxia Telangiectasia, and ATR, another member of the same family of PIK kinases. We present evidence that these proteins are all components of meiotic nodules and document changes in protein composition of these structures during zygonema and pachynema of meiotic prophase in mouse spermatocytes. These studies support the supposition that a subset of MNs are converted into RNs. However, our data also demonstrate changes in protein composition within the context of early MNs, suggesting a differentiation of these nodules during the process of synapsis. The same changes in protein composition occurred on both the normal X axis, which has no homologous pairing partner in spermatocytes, and on the axes of aberrant chromosomes that nonhomologously synapse during synaptic adjustment. These findings suggest that DNA sequences associated with MNs still must undergo an obligatory processing, even in the absence of interactions between homologous chromosomes.
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PMID:Changes in protein composition of meiotic nodules during mammalian meiosis. 944 91

It is well known that defects in some aspects of DNA metabolism including telomere maintenance, nucleotide excision repair and mismatch repair contribute to tumor development. However, to account for the multiple mutations observed in cancer cells, the new fields of DNA metabolism that maintain genome integrity must be determined. I will show four new aspects of genetic instability that have recently emerged which helps toward the understanding of the links between defects in genome integrity and tumor development. First, mutations in DNA helicase genes cause rare genetic instability syndromes, suggesting that defects in DNA helicase activities are responsible for predispositions to cancers. Second, mutations of the gene for ataxia-telangiectasia in sporadic leukemias suggest that genes involved in rare syndromes are paradigms for understanding the mechanism underlying the genesis of sporadic tumors. Third, since the emergence of a link between breast cancer susceptibility gene products and RAD51, great interest has been shown in recombinational repair. Finally, a mutator phenotype is conditional in some mismatch-repair deficient cells, proposing that cancer arises under restrictive conditions even though stability genes are mutated.
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PMID:Genetic instability and cancer. 959 39

Infertility is a common feature of the human disorder ataxia-telangiectasia and Atm-deficient mice are completely infertile. To gain further insight into the role of ATM in meiosis, we examined meiotic cells in Atm-deficient mice during development. Spermatocyte degeneration begins between postnatal days 8 and 16.5, soon after entry into prophase I of meiosis, while oocytes degenerate late in embryogenesis prior to dictyate arrest. Using electron microscopy and immunolocalization of meiotic proteins in mutant adult spermatocytes, we found that male and female gametogenesis is severely disrupted in Atm-deficient mice as early as leptonema of prophase I, resulting in apoptotic degeneration. A small number of mutant cells progress into later stages of meiosis, but no cells proceed beyond prophase I. ATR, a protein related to ATM, DMC1, a RAD51 family member, and RAD51 are mislocalized to chromatin and have reduced localization to developing synaptonemal complexes in spermatocytes from Atm-deficient mice, suggesting dysregulation of the orderly progression of meiotic events. ATM protein is normally present at high levels primarily in ova cytoplasm of developing ovarian follicles, and in the nucleus of spermatogonia and to a lesser extent in spermatoctyes, but without localization to the synaptonemal complex. We propose a model in which ATM acts to monitor meiosis by participation in the regulation or surveillance of meiotic progression, similar to its role as a monitor of mitotic cell cycle progression.
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PMID:Atm deficiency results in severe meiotic disruption as early as leptonema of prophase I. 973 62

Induced cell cycle delays were among the first described cellular responses to ionizing radiation (IR). To understand the sensitivity and the molecular events involved in the response to low doses of IR and to examine the role of p53 and its downstream effector p21Waf1, we measured changes in expression of genes postulated to be involved in the cellular response to IR. Expression levels were examined in normal human diploid fibroblasts irradiated and maintained in quiescent density-inhibited growth up to 24-48 h after exposure to X-ray doses as low as 0.1-0.3 Gy, which have negligible effects on cell survival. Among 31 genes analyzed, we observed down-regulation in response to IR of the mRNA levels of CDC2, cyclin A, cyclin B, thymidine kinase, topoisomerase IIalpha, and RAD51. A similar reduction in the expression levels of these genes occurred when irradiated cells were released from confluence and allowed to proliferate. This was not observed in cells in which p53 function was defective and up-regulation of p21Waf1 levels either did not occur (E6 transfected normal human fibroblasts and Li-Fraumeni fibroblasts) or was delayed (ataxia telangiectasia fibroblasts) after irradiation. Down-regulation was also absent in p21Waf1-null mouse embryo fibroblasts (MEFs) but occurred at a lower level in p53-null MEFs, due to slight increases in p21Waf1 levels by a p53-independent pathway. These findings indicate that the down-regulation of these cell cycle regulated genes in irradiated cells is p53-dependent and involves its effector p21Waf1. Although no down-regulation in the expression of genes involved in G2-M was observed in p53 or in p21Waf1-null MEFs, these cells showed a G2-M delay after irradiation, indicating that the expression levels of these genes does not regulate the G2-M delay.
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PMID:Regulation by ionizing radiation of CDC2, cyclin A, cyclin B, thymidine kinase, topoisomerase IIalpha, and RAD51 expression in normal human diploid fibroblasts is dependent on p53/p21Waf1. 983 Dec 41

The ATR (ataxia telangiectasia- and RAD3-related) protein is present on meiotic prophase chromosome cores and paired cores (synaptonemal complexes, SCs). Its striking characteristic is that the protein forms dense aggregates on the cores and SCs of the last chromosomes to pair at the zygotene-pachytene transition. It would appear that the ATR protein either signals delays in pairing or it is directly involved in the completion of the pairing phase. Atm-deficient spermatocytes, which are defective in the chromosome pairing phase, accumulate large amounts of ATR. The behaviour of ATR at meiotic prophase sets it apart from the distribution of the RAD51/DMC1 recombinase complex and our electron microscope observations confirm that they do not co-localize. We failed to detect ATM in association with cores/SCs and we have reported elsewhere that RAD1 protein does not co-localize with DMC1 foci. The expectation that putative DNA-damage checkpoint proteins. ATR, ATM and RAD1, are associated with RAD51/DMC1 recombination sites where DNA breaks are expected to be present, is therefore not supported by our observations.
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PMID:The association of ATR protein with mouse meiotic chromosome cores. 1038 71

Germline mutations of BRCA1 predispose women to breast and ovarian cancers. BRCA1 contains several functional domains that interact directly or indirectly with a variety of molecules, including tumor suppressors (p53, RB, BRCA2 and ATM), oncogenes (c-Myc, casein kinase II and E2F), DNA damage repair proteins (RAD50 and RAD51), cell-cycle regulators (cyclins and cyclin-dependent kinases), transcriptional activators and repressors (RNA polymerase II, RHA, histone deacetylase complex and CtIP) and others. Mounting evidence indicates that these physical associations are not artifacts; rather, BRCA1 is likely to serve as an important central component in multiple biological pathways that regulate cell-cycle progression, centrosome duplication, DNA damage repair, cell growth and apoptosis, and transcriptional activation and repression. This review examines our understanding of the significance of the interactions between BRCA1 and other proteins, through which BRCA1 maintains genome integrity and represses tumor formation. Published 2000 John Wiley & Sons, Inc.
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PMID:Roles of BRCA1 and its interacting proteins. 1091 3

Breast cancer is considered to display a high degree of intratumor heterogeneity, without any obvious morphological and pathological steps to define sequential evolution, and its progression may vary among individual tumors. In an attempt to elucidate these etiological and phenotypic complexities, the present study, based on the fundamental concept that genomic instability is the engine of both tumor progression and tumor heterogeneity, was conducted to test the hypothesis that breast cancer pathogenesis is driven by double-strand break (DSB)-initiated chromosome instability (CIN). The rationale underlying this hypothesis is derived from the clues provided by family breast cancer syndromes, in which susceptibility genes, including p53, ATM, BRCA1 and BRCA2, are involved within the common functional pathway of DSB-related checkpoint/ repair. Because genomic deletion caused by DSB is reflected in the genetic mechanism of loss of heterozygosity (LOH), this genome-wide LOH study was conducted, using 100 tumors and 400 microsatellite markers. To minimize the effect of heterogeneity within tumors, the experimental technique of laser capture microdissection was used to ensure that genetic and phenotypic examinations were based on the same tumor cells. Support for our hypothesis comes from the observations that: (a) the extent of DSB-initiated CIN in tumors significantly increased as tumors progressed to poorer grades or later stages; (b) in the sequential steps toward CIN, the loci of p53 and ATM, the key checkpoint genes against DSB, were lost at the earliest stage; and (c) many loci identified to be important in breast tumorigenesis were the genomic sites possibly harboring the genes involved in DSB-related checkpoint/repair (including RAD51, RAD52, and BRCA1) or CIN (including FA-A, FA-D, and WRN), and a higher number of these loci showing LOH was significantly associated with increased level of DSB-initiated CIN (P < 0.0001). Breast cancers are thus considered to be sequentially progressive with CIN. However, CIN might also cause genetic heterogeneity, which was revealed by the findings that LOH at some markers was observed only in the component of ductal carcinoma in situ but not in the invasive component of the same tumors. In addition, some markers were found to preferentially lose at specific tumor grades, implying their contribution to genetic heterogeneity during tumor development. Therefore, this study suggests that breast cancer progression is clonal with regard to CIN, but different breast cancers would present distinct molecular profiles resulting from genetic heterogeneity caused by CIN.
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PMID:Genome-wide search for loss of heterozygosity using laser capture microdissected tissue of breast carcinoma: an implication for mutator phenotype and breast cancer pathogenesis. 1091 64

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

DNA double-strand breaks (DSBs) are the major lethal lesion induced by ionizing radiation or by replication block. However, cells can take advantage of DSB-induced recombination in order to generate genetic diversity in physiological processes such as meiosis and V(D)J recombination. Two main alternative pathways compete for DSB repair: homologous recombination (HR) and non-homologous end-joining (NHEJ). This review will briefly present the mechanisms and the enzymatic complex for HR and NHEJ. The signalling of the DSB through the ATM pathway will be presented. Then, we will focus on the case of the RAD51 protein, which plays a pivotal role in HR and is conserved from bacteria to humans. Post-translational regulation of RAD51 is presented. Two contrasting situations are discussed: one with up-regulation (expression of the oncogene BCR/ABL) and one with a down-regulation (expression of the oncogene BCL-2) of RAD51, associated with apoptosis inhibition and tumour predisposition.
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PMID:DNA double-strand break repair signalling: the case of RAD51 post-translational regulation. 1235 2

To facilitate association-based linkage studies we have studied the linkage disequilibrium (LD) and haplotype architecture around five genes of interest for cancer risk: ATM, BRCA1, BRCA2, RAD51, and TP53. Single nucleotide polymorphisms (SNPs) were identified and used to construct haplotypes that span 93-200 kb per locus with an average SNP density of 12 kb. These markers were genotyped in four ethnically defined populations that contained 48 each of African Americans, Asian Americans, Hispanic Americans, and European Americans. Haplotypes were inferred using an expectation maximization (EM) algorithm, and the data were analyzed using D', R(2), Fisher's exact P-values, and the four-gamete test for recombination. LD levels varied widely between loci from continuously high LD across 200 kb to a virtual absence of LD across a similar length of genome. LD structure also varied at each gene and between populations studied. This variation indicates that the success of linkage-based studies will require a precise description of LD at each locus and in each population to be studied. One striking consistency between genes was that at each locus a modest number of haplotypes present in each population accounted for a high fraction of the total number of chromosomes. We conclude that each locus has its own genomic profile with regard to LD, and despite this there is the widespread trend of relatively low haplotype diversity. As a result, a low marker density should be adequate to identify haplotypes that represent the common variation at a locus, thereby decreasing costs and increasing efficacy of association studies.
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PMID:Haplotype and linkage disequilibrium architecture for human cancer-associated genes. 1246 88


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