Last Modified: November 1, 2001
Table of Contents
CancerMail from the National Cancer Institute
UI - 21380113
AU - Stewart GS; Last JI; Stankovic T; Haites N; Kidd AM; Byrd PJ; Taylor AM
TI - Residual ataxia telangiectasia mutated protein function in cells from ataxia telangiectasia patients, with 5762ins137 and 7271T-->G mutations, showing a less severe phenotype.
SO - J Biol Chem 2001 Aug 10;276(32):30133-41
AD - CRC Institute for Cancer Studies, the University of Birmingham, Vincent Drive, Edgbaston, Birmingham B15 2TT, United Kingdom.
We have assessed several ataxia Telangiectasia mutated (ATM)-dependent functions in cells derived from ataxia telangiectasia patients, carrying either an ATM 5762ins137 splice site or a 7271T-->G missense mutation, with a less severe phenotype compared with the classical disorder. ATM kinase in vitro, from 5762ins137 cells, showed the same specific activity as ATM in normal cells, but the protein was present at low levels. In contrast, mutant ATM kinase activity in the 7271T-->G cells was only about 6% that of the activity in normal cells, although the level of mutant protein expressed was similar to normal cells. Phosphorylation of the DNA double strand break repair proteins Nbs1 and hMre11, following DNA damage, was observed in normal and 7271T-->G cells but was almost absent in both 5762ins137 and classical ataxia telangiectasia cells. The kinetics of p53 response was intermediate between normal and classical ataxia telangiectasia cells in both the 7271T-->G and 5762ins137 cells, but interestingly, c-Jun kinase activation following DNA damage was equally deficient in cell lines derived from all the ataxia telangiectasia patients. Our results indicate that levels of ATM kinase activity, but not induction of p53 or c-Jun kinase activity, in these cells correlate with the degree of neurological disorder in the patients.
UI - 21385738
AU - Lohrer HD; Tangen U
TI - Investigations into the molecular effects of single nucleotide polymorphism.
SO - Pathobiology 2000;68(6):283-90
AD - Radiobiological Institute, Ludwig Maximilians University, Munich, Germany.
OBJECTIVES: DNA sequences are very rich in short repeats and their pattern can be altered by point mutations. We wanted to investigate the effect of single nucleotide polymorphism (SNP) on the pattern of short DNA repeats and its biological consequences. METHODS: Analysis of the pattern of short DNA repeats of the Thy-1 sequence with and without SNP. Searching for DNA-binding factors in any region of significance. RESULTS: Comparing the pattern of short repeats in the Thy-1 gene sequences of Turkish patients with ataxia telangiectasia (AT) with the "wild type" sequence from the DNA database, we identified a missing 8-bp repeat element due to an SNP in position 1271 (intron II) in AT-DNA sequences. Only the mutated sequence had the potential for the formation of a stem loop in DNA or pre-mRNA. In super-shift experiments we found that DNA oligomers covering the area of this SNP formed a complex with proteins amongst which we identified the proliferating cell nuclear antigen (PCNA) protein. CONCLUSION: SNPs have the potential to alter DNA or pre-mRNA conformation. Although no SNP-depeding formation of the DNA-protein complex was evident, future investigations could reveal differential molecular mechanisms of cellular regulation. Copyright 2001 S. Karger AG, Basel
UI - 21369915
AU - Kishi S; Zhou XZ; Ziv Y; Khoo C; Hill DE; Shiloh Y; Lu KP
TI - Telomeric protein Pin2/TRF1 as an important ATM target in response to double strand DNA breaks.
SO - J Biol Chem 2001 Aug 3;276(31):29282-91
AD - Cancer Biology Program, Division of Hematology/Oncology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
ATM mutations are responsible for the genetic disease ataxia-telangiectasia (A-T). ATM encodes a protein kinase that is activated by ionizing radiation-induced double strand DNA breaks. Cells derived from A-T patients show many abnormalities, including accelerated telomere loss and hypersensitivity to ionizing radiation; they enter into mitosis and apoptosis after DNA damage. Pin2 was originally identified as a protein involved in G(2)/M regulation and is almost identical to TRF1, a telomeric protein that negatively regulates telomere elongation. Pin2 and TRF1, probably encoded by the same gene, PIN2/TRF1, are regulated during the cell cycle. Furthermore, up-regulation of Pin2 or TRF1 induces mitotic entry and apoptosis, a phenotype similar to that of A-T cells after DNA damage. These results suggest that ATM may regulate the function of Pin2/TRF1, but their exact relationship remains unknown. Here we show that Pin2/TRF1 coimmunoprecipitated with ATM, and its phosphorylation was increased in an ATM-dependent manner by ionizing DNA damage. Furthermore, activated ATM directly phosphorylated Pin2/TRF1 preferentially on the conserved Ser(219)-Gln site in vitro and in vivo. The biological significance of this phosphorylation is substantiated by functional analyses of the phosphorylation site mutants. Although expression of Pin2 and its mutants has no detectable effect on telomere length in transient transfection, a Pin2 mutant refractory to ATM phosphorylation on Ser(219) potently induces mitotic entry and apoptosis and increases radiation hypersensitivity of A-T cells. In contrast, Pin2 mutants mimicking ATM phosphorylation on Ser(219) completely fail to induce apoptosis and also reduce radiation hypersensitivity of A-T cells. Interestingly, the phenotype of the phosphorylation-mimicking mutants is the same as that which resulted from inhibition of endogenous Pin2/TRF1 in A-T cells by its dominant-negative mutants. These results demonstrate for the first time that ATM interacts with and phosphorylates Pin2/TRF1 and suggest that Pin2/TRF1 may be involved in the cellular response to double strand DNA breaks.
UI - 21391619
AU - Djuzenova CS; Flentje M
TI - Light scatter and DNA accessibility to propidium iodide of ataxia telangiectasia and fanconi anemia cells.
SO - Biochem Biophys Res Commun 2001 Aug 17;286(2):365-71
AD - Klinik fur Strahlentherapie, Universitat Wurzburg, Josef-Schneider-Strasse 11, Wurzburg, D-97080, Germany. firstname.lastname@example.org
Cells from individuals with genetic diseases ataxia telangiectasia (AT) and Fanconi anemia (FA) exhibit hypersensitivity to ionizing radiation (AT) or DNA cross-linking agents (FA) which may be caused by multiple factors including defects in chromatin structure and DNA repair. In this study, a combination of cytometric techniques was employed to study the chromatin conformation of AT and FA cells. Nuclei of peripheral blood mononuclear cells (PBMCs) and of skin fibroblasts established from AT and FA patients were analyzed by light scattering and fluorimetric titration with the DNA-intercalating dye propidium iodide. The light scatter measurements revealed the presence of small-sized nuclei with reduced granularity in PBMCs and fibroblasts from both AT and FA patients. The fluorometric titration data could be interpreted by assuming two classes of propidium iodide binding sites with different affinities. The number of high-affinity sites in AT and FA fibroblasts was significantly larger (by 20%) than in control cells. Our findings show the applicability of cytometric techniques for the rapid assessment of chromatin conformation and also suggest the possibility to identify AT and FA carriers. Copyright 2001 Academic Press.
UI - 21408165
AU - Lee Y; Chong MJ; McKinnon PJ
TI - Ataxia telangiectasia mutated-dependent apoptosis after genotoxic stress in the developing nervous system is determined by cellular differentiation status.
SO - J Neurosci 2001 Sep 1;21(17):6687-93
AD - Department of Genetics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Ataxia-telangiectasia (A-T) is a neurodegenerative syndrome resulting from dysfunction of ATM (ataxia telangiectasia mutated). The molecular details of ATM function in the nervous system are unclear, although the neurological lesions in A-T are probably developmental because they appear during childhood. The nervous systems of Atm-null mice show a pronounced defect in apoptosis that is induced by DNA damage, suggesting that ATM may function to eliminate DNA-damaged neurons. Here we show that Atm-dependent apoptosis occurs at discrete stages of neurogenesis. Analysis of gamma-irradiated mouse embryos showed that Atm-dependent apoptosis occurred only in the postmitotic populations that were present in the neuroepithelial subventricular zone of the developing nervous system. Notably, Atm deficiency did not prevent radiation-induced apoptosis in multipotent precursor cells residing in the proliferating ventricular zone. Atm-dependent apoptosis required p53 and coincided with the specific phosphorylation of p53 and caspase-3 activation. Thus, these data show that Atm functions early in neurogenesis and underscore the selective requirement for Atm in eliminating damaged postmitotic neural cells. Furthermore, these data demonstrate that the differentiation status of neural cells is a critical determinant in the activation of certain apoptotic pathways.