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)

We have previously demonstrated that cells from patients with ataxia-telangiectasia (A-T) fail to show initial delay at several cell cycle checkpoints post-irradiation. In addition a defect in the induction of p53 by ionizing radiation was evident. We demonstrate here that the radiation signal transduction pathway operating through p53, its target gene WAF1, cyclin-dependent kinases and the retinoblastoma (Rb) protein is defective in A-T cells. The defective p53 induction after ionizing radiation, observed previously in A-T cells, was also reflected at the functional level using p53-DNA binding activity, transactivation and transfection with wild type p53. Correction of the defect at the G1/S checkpoint was observed when wild type p53 was constitutively expressed in A-T cells. Exposure of control cells to radiation gave rise to p53 induction and as a consequence increased expression of WAF1 mRNA and protein, but A-T cells were defective in this response. As expected the WAF1 response in irradiated control cells resulted in an inhibition of cyclin-dependent kinase activity including cyclin E-cdk2, which plays an important role in the transition from G1 to S phase. No inhibition of cyclin-dependent kinase activity was observed in A-T cells correlating with the delayed WAF1 response. On the contrary an enhancement of cyclin-dependent kinase activity was seen in A-T cells post-irradiation. An accumulation of the hypophosphorylated form of Rb protein occurred in irradiated control cells compatible with the G1/S phase delay observed in these cells after exposure to radiation. In unirradiated A-T cells the amount of Rb protein was much higher compared to controls and it was mainly in the hyperphosphorylated (functionally inactive) form. In addition, accumulation of the hypophosphorylated form of Rb in A-T cells post-irradiation was defective, consistent with the lack of cell cycle arrest. Thus the failure of the G1/S checkpoint in A-T cells after exposure to ionizing radiation is consistent with a defective radiation signal transduction pathway operating through p53.
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PMID:Nature of G1/S cell cycle checkpoint defect in ataxia-telangiectasia. 765 23

The recent description of a novel gene (ATM) mutated in ataxia-telangiectasia (A-T), with homologies to genes encoding proteins involved in both G1/S and G2/M checkpoint control, points to a common defect in cell cycle control in A-T operating through the cyclin-dependent kinases. In this report we demonstrate that cyclin-dependent kinases are resistant to inhibition by ionizing radiation exposure in A-T cells, and this appears to be due to insufficient induction of WAF1. Exposure of control lymphoblastoid cells to radiation during S phase and in G2 phase causes a rapid inhibition of cyclin A-Cdk2 and cyclin B-Cdc2 activities, respectively. Irradiation led to a 5-20-fold increase in Cdk-associated WAF1 in these cells, which accounts at least in part for the decrease in cyclin-dependent kinase activity. In contrast, radiation did not inhibit any of the cyclin-dependent kinase activities in S phase or G2 phase in A-T cells at short times after irradiation nor was there any significant change in the level of Cdk-associated WAF1 compared to unirradiated cells. These results are similar to those reported previously for the G1 checkpoint and provide additional evidence for the involvement of ATM at multiple points in cell cycle regulation.
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PMID:Defect in multiple cell cycle checkpoints in ataxia-telangiectasia postirradiation. 870 89

The gene mutated in the human genetic disorder ataxia-telangiectasia (A-T) has been described recently (Savitsky et al., 1995a) and the complete coding sequence of this gene, ATM, has been reported (Savitsky et al., 1995b). The derived amino acid sequence demonstrates significant homologies to several proteins containing a phosphatidylinositol 3-kinase (PI3-kinase) domain, including the yeast TOR proteins and the human protein FRAP. Since the TOR and FRAP proteins are targets for the immunosuppressive drug rapamycin, we have investigated the effects of this compound on A-T cells. We report here that 3 A-T cell lines are more resistant than control cells to rapamycin's growth inhibiting effects but were more sensitive to the PI3-kinase inhibitor wortmannin. As expected rapamycin (1 nM) inhibited the rate of exit of control cells from G1 phase but failed to perturb the progression of A-T cells. This difference in cell cycle progress after rapamycin treatment is reflected in ribosomal S6 protein kinase (p70S6k) by both a downward mobility shift on SDS-PAGE and inhibition of activity. Furthermore, the G1 phase cyclin-dependent kinase, cyclin E-cdk2, was rapidly inhibited in control cells post-treatment, whereas in A-T cells it took considerably longer to observe inhibition. There was no evidence that a GST-FKBP12 fusion protein specifically precipitated the ATM protein in the presence of rapamycin in either cell type. These results demonstrate that the ATM protein is not a direct target for rapamycin but its functional loss renders cells more resistant to this compound.
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PMID:Rapamycin resistance in ataxia-telangiectasia. 880 86

Angiotensin II (Ang II) induces hypertrophy of cultured proximal tubular epithelial cells including the LLC-PK1 cell line. We have previously shown that this hypertrophy appears in the G1-phase of the cell cycle. Since progression through the cell cycle is controlled by a series of cyclin and cyclin-dependent kinase (CdK) complexes that may be inactivated by CdK inhibitors, we studied the expression of the CdK-inhibitor p27Kip1 in LLC-PK1 cells challenged with Ang II. Compared to cells grown in serum-free medium, Ang II treatment enhanced p27Kip1 protein, but not mRNA expression. This p27Kip1 induction was mediated through AT1-receptors. Exogenous TGF-beta also stimulated p27Kip1 protein expression. Immunoprecipitation experiments revealed that p27Kip1 preferentially associated with CdK4 in Ang II-treated LLC-PK1 cells and that the activity of this kinase was inhibited after Ang II-treatment, an effect that may be generated by increased p27Kip1 binding to cyclin D1-CdK4 complexes. In contrast, p27Kip1 was not associated with cyclin E-CdK2 complexes in Ang II-stimulated cells. Treatment of LLC-PK1 cells with p27Kip1 antisense, but not missense, oligonucleotides abolished the Ang II-mediated cell hypertrophy as measured by de novo protein synthesis and total protein content, and facilitated entry into the S-phase of the cell cycle. Our findings suggest that Ang II stimulates p27Kip1 expression in renal cells. Furthermore, this induction of the CdK-inhibitor appears pivotal in the hypertrophy induced by Ang II and elucidates the molecular mechanisms associated with this growth response in proximal tubular cells.
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PMID:Angiotensin II-stimulated hypertrophy of LLC-PK1 cells depends on the induction of the cyclin-dependent kinase inhibitor p27Kip1. 894 98

Three DNA damage-responsive cell cycle checkpoints can be shown to operate in diploid human fibroblasts. One checkpoint arrests growth in G1, another inhibits replicon initiation in S phase cells, and the third delays progression from G2 into mitosis. Progression from G2 into M is controlled in part by a cyclin-dependent kinase (cyclin B/Cdk1) that is regulated by tyrosine phosphorylation. Phosphorylation of Tyr15 on Cdk1 is inhibitory for kinase activity. Activation of cyclin B/Cdk1 at the onset of mitosis is accomplished by a phosphatase, Cdc25C, that interacts with cyclin B/Cdk1 in an autocatalytic feedback loop to remove the inhibitory phosphate at Tyr15 and activate kinase activity. DNA damage triggers G2 delay by inhibiting formation of the autocatalytic feedback loop so that dephosphorylation of Tyr15 does not occur. This suppression of activation of cyclin B/Cdk1 appears to account for the failure of damaged G2 cells to progress into mitosis. Once the damage to DNA is repaired, cells resume progression into mitosis as the cycle is re-engaged. The isoflavone genistein inhibits tyrosine kinases, including one that phosphorylates Cdk1 on Tyr15. This kinase, p56/p53lyn is rapidly induced by treatments that trigger cell cycle checkpoints (ionizing radiation, cytosine arabinoside), suggesting that this kinase may actively delay the onset of mitosis by phosphorylating Tyr15 on Cdk1. Genistein also inhibits type II DNA topoisomerase to produce a form of DNA damage that triggers all of the DNA damage-responsive cell cycle checkpoints. A brief 10 min incubation with the topoisomerase poison amsacrine was sufficient to trigger the S phase checkpoint response and inhibit replicon initiation. Inhibition of replicon initiation by 1 microM amsacrine was maximal 20-30 min after drug treatment and by 120 min, the checkpoint response had decayed to allow near control rates of replicon initiation. Topoisomerase II poisons also are powerful clastogens inducing lethal and carcinogenic chromosomal aberrations. Type II topoisomerase can break DNA in a region of chromosome 11q23 that contains the ataxia telangiectasia gene (ATM). The ATM gene controls all of the DNA damage-responsive cell cycle checkpoints. Chromosomal aberrations in 11q23 are frequently seen in acute myeloid leukemia that develops as a consequence of etoposide chemotherapy. Thus, topoisomerase poisons such as genistein may trigger chromatid breakage to inactivate AT gene function, disable cell cycle control, and induce genetic instability.
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PMID:Human topoisomerase II function, tyrosine phosphorylation and cell cycle checkpoints. 949 43

Ionizing radiation is known to activate multiple signal transduction pathways, but the targets of these pathways are poorly understood. Phosphorylation of histone H1 is thought to have a role in chromatin condensation/decondensation, and we asked whether ionizing radiation (IR) would alter H1 phosphorylation. Our data demonstrate that low doses of IR result in a dramatic, but transient, dephosphorylation of H1 isoforms. The in vivo IR-induced dephosphorylation of H1 is completely blocked by wortmannin and is abrogated in ataxia telangiectasia cells. Furthermore, we measured radiation-induced inhibition of cyclin dependent kinase activity and activation of histone H1 phosphatase activity. Both activities were affected by radiation-induced signals in an ATM-dependent manner. Thus, the rapid IR-induced dephosphorylation of H1 involves a pathway including ATM and a wortmannin-sensitive step leading to both inhibition of cyclin-dependent kinase activities as well as activation of H1 phosphatase(s).
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PMID:Histone H1 dephosphorylation is mediated through a radiation-induced signal transduction pathway dependent on ATM. 1037 85

Ataxia-telangiectasia mutated (ATM) is the product of the gene mutated in the human genetic disorder ataxia-telangeictasia (A-T). It is a 370 kDa protein that is a member of the phosphatidyl inositol 3-kinases superfamily. A-T cells and those derived from Atm-/- mice are characterized by hypersensitivity to ionizing radiation and defective cell cycle checkpoints. Defects are observed at all cell cycle checkpoints in A-T cells post-irradiation including the G1/S interface where ATM plays an important role in the activation of the tumour suppressor gene product p53. Activation leads to the induction of p21/WAF1, inhibition of cyclin-dependent kinase activity, failure to phosphorylate key substrates such as the retinoblastoma protein and consequently G1 arrest. ATM also plays an important role in the regulation and surveillance of meiotic progression. Absence of ATM gives rise to a spectrum of defects including immunodeficiency, neurodegeneration, radiosensitivity and cancer predisposition. It is clear that a better definition of the role of ATM in DNA damage recognition, cell cycle control and cell signalling may assist in the treatment of the progressive neurodegeneration in this syndrome.
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PMID:ATM: the product of the gene mutated in ataxia-telangiectasia. 1046 28

The heterotrimeric DNA-binding protein, replication protein A (RPA), consists of 70-, 34-, and 14-kDa subunits and is involved in maintaining genomic stability by playing key roles in DNA replication, repair, and recombination. RPA participates in these processes through its interaction with other proteins and its strong affinity for single-stranded DNA (ssDNA). RPA-p34 is phosphorylated in a cell-cycle-dependent fashion primarily at Ser-29 and Ser-23, which are consensus sites for Cdc2 cyclin-dependent kinase. By systematically examining RPA-p34 phosphorylation throughout the cell cycle, we have found there are distinct phosphorylated forms of RPA-p34 in different cell-cycle stages. We have isolated and purified a unique phosphorylated form of RPA that is specifically associated with the mitotic phase of the cell cycle. The mitotic form of RPA (m-hRPA) shows no difference in ssDNA binding activity as compared with recombinant RPA (r-hRPA), yet binds less efficiently to double-stranded DNA (dsDNA). These data suggest that mitotic phosphorylation of RPA-p34 inhibits the destabilization of dsDNA by RPA complex, thereby decreasing the binding affinity for dsDNA. The m-hRPA also exhibits altered interactions with certain DNA replication and repair proteins. Using highly purified proteins, m-hRPA exhibited decreased binding to ATM, DNA pol alpha, and DNA-PK as compared to unphosphorylated recombinant RPA (r-hRPA). Dephosphorylation of m-hRPA was able to restore the interaction with each of these proteins. Interestingly, the interaction of RPA with XPA was not altered by RPA phosphorylation. These data suggest that phosphorylation of RPA-p34 plays an important role in regulating RPA functions in DNA metabolism by altering specific protein-protein interactions.
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PMID:RPA phosphorylation in mitosis alters DNA binding and protein-protein interactions. 1264 57

Silencing ATM gene gave rise to enhanced apoptotic response to irradiation and irradiation-like chemotherapy agents, this paper explored the crucial identities of the molecular elements responsible for the enhanced apoptotic response in U937 cells mediated by silencing ATM gene. Two U937 cell mutants named U937-ASPI3K (ATM, negative) and U937-pZeosv2(+) (ATM, wild-type) were used as a cell model system to identify the critical molecule(s) responsible for the varied apoptotic response in the absence or presence of ATM gene. Apoptosis was examined by measuring concentrations of free nucleosome in U937 cells. Western blot was employed to measure nuclear protein abundance of CDC25A, CDC25B, CDC25C, total p34cdc2, p34cdc2, (Thr 161) or p34cdc2 (Thr 14, Tyr 15). RT-PCR was used to estimate CDC25 transcript levels. U937-ASPI3K exhibited an enhanced apoptotic response to lower dosage of irradiation, which could not be blocked by protein synthesis inhibitor. Protein serine-threonine phosphatase inhibitor or cyclin-dependent kinase (CDK) inhibitors, on the other hand, abolished the enhancement indicated that protein phosphorylation/dephosphorylation modification and CDK activity are required for the enhanced apoptotic response in the absence of ATM gene. Upon irradiation, p34cdc2 in U937-pZeosv2(+) was maintained in an inactive state by phosphorylation on threonine 14 (Thr 14) and tyrosine 15 (Tyr 15), which was associated with a dramatic decrease of nuclear CDC25A, CDC25B and CDC25C proteins. In contrast, p34cdc2 in U937-ASPI3K maintained in an active state by dephosphorylation on threonine 14 (Thr 14) and tyrosine 15 (Tyr 15), which was associated with constant nuclear CDC25A, CDC25B and CDC25C protein abundance before and after irradiation. The responsive decrease of nuclear CDC25 proteins occurred at the post-transcription level. Silencing ATM gene blocks the responsive decrease of nuclear CDC25 proteins, which is responsible for failure to inactivate p34cdc2 after irradiation. Active p34cdc2 and CDK2, in turn, acts as the death executors to trigger apoptosis. In summary, aberrantly activated CDK activity is the critical molecular mechanism central to enhanced apoptotic responses in the absence of ATM gene.
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PMID:Failure to inactivate CDK activity is responsible for the enhanced apoptotic response in U937 cells mediated by silencing ATM gene. 1265 1

The impact of disruption of the PI3K (phosphatidylinositol 3-kinase) pathway on the response of human leukemia cells to pharmacological cyclin-dependent kinase (CDK) inhibitors has been examined. Exposure of U937 monocytic leukemia cells to minimally toxic concentrations of flavopiridol (FP), roscovitine, or CGP74514A for 3 h in conjunction with the PI3K inhibitor LY294002 (abbreviated LY in the article) resulted in a marked decrease in Akt phosphorylation. Coexposure of cells to LY and CDK inhibitors also resulted in an early (i.e., within 3 h) and striking increase in mitochondrial damage [e.g., cytochrome c, second mitochondria-derived activator of caspases/direct inhibitor of apoptosis (IAP)-binding protein with low isoelectric point (Smac/DIABLO), and apoptosis-initiating factor (AIF) release], caspase activation, and apoptosis. Similar interactions were observed in a variety of other leukemia cell types (e.g., HL-60, Jurkat, Raji, and NB4). Apoptosis, induced by FP/LY, was substantially blocked by ectopic expression of Bcl-2, but to a considerably lesser extent by dominant-negative caspase-8. FP-induced apoptosis was not enhanced by agents that inhibited protein kinase (PK) A (H89), PKC (GFX), mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase (MEK1/2; U0126), p38 MAP kinase (MAPK; SB202190), m-target of rapamycin (TOR; rapamycin), or ataxia-telangiectasia mutation (ATM; caffeine), whereas the PI3K inhibitor wortmannin exerted effects similar to those of LY. The dramatic potentiation of CDK inhibitor-induced apoptosis by LY was accompanied by diminished Bad phosphorylation, induction of Bcl-2 cleavage, and down-regulation of X-linked IAP (XIAP) and Mcl-1. Cells exposed to CDK inhibitors + LY also exhibited reduced phosphorylation of glycogen synthase kinase (GSK)-3, forkhead transcription factor (FKHR), p70(S6K), and ERK, but increased activation of p34(cdc2) and p38 MAPK. LY/CDK inhibitor-treated cells also displayed diminished pRb dephosphorylation on CDK2- and CDK4-specific sites, retinoblastoma protein cleavage, and down-regulation of cyclin D(1). Inducible expression of constitutively active (myristolated) Akt significantly, albeit partially, attenuated apoptosis in Jurkat leukemia cells treated with either FP alone or the combination of FP and LY. Finally, cotreatment with LY and FP resulted in a dramatic increase in apoptosis in primary leukemic blasts obtained from a patient with acute myeloblastic leukemia. Together, these findings suggest that the PI3K/Akt pathway plays a major role in regulating the apoptotic response of human leukemia cells to pharmacological CDK inhibitors and raise the possibility that combined interruption of CDK- and PI3K-related pathways may represent a novel therapeutic strategy in hematological malignancies.
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PMID:The lethal effects of pharmacological cyclin-dependent kinase inhibitors in human leukemia cells proceed through a phosphatidylinositol 3-kinase/Akt-dependent process. 1270 69


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