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

Polo-like kinases play multiple roles in different phases of mitosis. We have recently shown that the mammalian polo-like kinase, Plk1, is inhibited in response to DNA damage and that this inhibition may lead to cell cycle arrests at multiple points in mitosis. Here we have investigated the role of the checkpoint kinases ATM (ataxia telangiectasia mutated) and ATR (ATM- and Rad3-related) in DNA damage-induced inhibition of Plk1. We show that inhibition of Plk1 kinase activity is efficiently blocked by the radio-sensitizing agent caffeine. Using ATM(-/-) cells we show that under certain circumstances, inhibition of Plk1 by DNA-damaging agents critically depends on ATM. In addition, we show that UV radiation also causes inhibition of Plk1, and we present evidence that this inhibition is mediated by ATR. Taken together, our data demonstrate that ATM and ATR can regulate Plk1 kinase activity in response to a variety of DNA-damaging agents.
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PMID:Inhibition of Polo-like kinase-1 by DNA damage occurs in an ATM- or ATR-dependent fashion. 1151 40

Polo-like kinase 3 (Plk3, previously termed Prk) contributes to regulation of M phase of the cell cycle (Ouyang, B., Pan, H., Lu, L., Li, J., Stambrook, P., Li, B., and Dai, W. (1997) J. Biol. Chem. 272, 28646-28651). Plk3 physically interacts with Cdc25C and phosphorylates this protein phosphatase predominantly on serine 216 (Ouyang, B., Li, W., Pan, H., Meadows, J., Hoffmann, I., and Dai, W. (1999) Oncogene 18, 6029-6036), suggesting that the role of Plk3 in mitosis is mediated, at least in part, through direct regulation of Cdc25C. Here we show that ectopic expression of a kinase-active Plk3 (Plk3-A) induced apoptosis. In response to DNA damage, the kinase activity of Plk3 was rapidly increased in an ATM-dependent manner, whereas that of Plk1 was markedly inhibited. Recombinant Plk3 phosphorylated in vitro a glutathione S-transferase fusion protein containing p53, but not glutathione S-transferase alone. Recombinant Plk1 also phosphorylated p53 but on residues that differed from those targeted by Plk3. Co-immunoprecipitation and pull-down assays demonstrated that Plk3 physically interacted with p53 and that this interaction was enhanced upon DNA damage. In vitro kinase assays followed by immunoblotting showed that serine 20 of p53 was a target of Plk3. Furthermore, expression of a kinase-defective Plk3 mutant (Plk3(K52R)) resulted in significant reduction of p53 phosphorylation on serine 20, which was correlated with a decrease in the expression of p21 and with a concomitant increase in cell proliferation. These results strongly suggest that Plk3 functionally links DNA damage to cell cycle arrest and apoptosis via the p53 pathway.
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PMID:Plk3 functionally links DNA damage to cell cycle arrest and apoptosis at least in part via the p53 pathway. 1155 30

The Polo-like kinases (Plks) are a conserved family of kinases that contribute to cell cycle regulation, particularly in G2 and mitosis. In mammals, there are at least three members of the Plk family. Here we show that Plk3 is a stress response protein that becomes phosphorylated following DNA damage or mitotic spindle disruption. Phosphorylation enhances its kinase activity and is dependent upon ataxia telangiectasia-mutated (ATM) in the former case but not the latter. Plk3 associates with complexes of multiple sizes ranging from 150 to greater then 600 kDa. In its unphosphorylated form it elutes from a sizing column at about 400 kDa whereas it associates with complexes of 150 and 600 kDa when phosphorylated. Among the proteins with which it physically associates and utilizes, as substrates are Chk2 and P53. It phosphorylates Chk2 on a residue different from threonine 68 (Thr68), the principal target for ATM. While ATM is necessary for phosphorylation and activation of Chk2 in vivo, Plk3 seems to contribute to its full activation. In its phosphorylated form it also coelutes and forms a complex with unpolymerized tubulin. In aggregate, the data argue that Plk3 is a multifunctional protein that associates with multiple complexes and that contributes to response to stress incurred by DNA damage and mitotic spindle disruption, albeit via different pathways.
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PMID:Mammalian Polo-like kinase 3 (Plk3) is a multifunctional protein involved in stress response pathways. 1224 61

Elevated expression of mammalian polo-like kinase (Plk)1 occurs in many different types of cancers, and Plk1 has been proposed as a novel diagnostic marker for several tumors. We used the recently developed vector-based small interfering RNA technique to specifically deplete Plk1 in cancer cells. We found that Plk1 depletion dramatically inhibited cell proliferation, decreased viability, and resulted in cell-cycle arrest with 4 N DNA content. The formation of dumbbell-like chromatin structure suggests the inability of these cells to completely separate the sister chromatids at the onset of anaphase. Plk1 depletion induced apoptosis, as indicated by the appearance of subgenomic DNA in fluorescence-activated cell-sorter (FACS) profiles, the activation of caspase 3, and the formation of fragmented nuclei. Plk1-depletion-induced apoptosis was partially reversed by cotransfection of nondegradable mouse Plk1 constructs. In addition, the p53 pathway was shown to be involved in Plk1-depletion-induced apoptosis. DNA damage occurred in Plk1-depleted cells and inhibition of ATM strongly potentiated the lethality of Plk1 depletion. Although p53 is stabilized in Plk1-depleted cells, DNA damage also occurs in p53(-/-) cells. These data support the notion that disruption of Plk1 function could be an important application in cancer therapy.
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PMID:Polo-like kinase (Plk)1 depletion induces apoptosis in cancer cells. 1273 29

Most anticancer drugs presently used clinically target genomic DNA. The selectivity of these anticancer drugs for tumor tissues is probably due to tumor-specific defects suppressing cell cycle checkpoints and DNA repair, and enhancing apoptotic response in the tumor. We will review the molecular interactions within the ATM-Chk2 pathway implicating the DNA damage sensor kinases (ATM, ATR and DNA-PK), the adaptor BRCT proteins (Nbs1, Brca1, 53BP1, MDC1) and the effector kinases (Chk2, Chk1, Plk3, JNK, p38). The molecular interaction map convention (MIM) will be used for presenting this molecular network (http://discover.nci.nih.gov/mim/). A characteristic of the ATM-Chk2 pathway is its redundancy. First, ATM and Chk2 phosphorylate common substrates including p53, E2F1, BRCA1, and Chk2 itself, which suggests that Chk2 (also known as CHECK2, Cds1 in fission yeast, and Dmchk2 or Dmnk or Loki in the fruit fly) acts as a relay for ATM and/or as a salvage pathway when ATM is inactivated. Secondly, redundancy is apparent for the substrates, which can be phosphorylated/activated at similar residues by Chk2, Chk1, and the polo kinases (Plk's). Functionally, Chk2 can activate both apoptosis (via p53, E2F1 and PML) and cell cycle checkpoint (via Cdc25A and Cdc25C, p53, and BRCA1). We will review the short list of published Chk2 inhibitors. We will also propose a novel paradigm for screening interfacial inhibitors of Chk2. Chk2 inhibitors might be used to enhance the tumor selectivity of DNA targeted agents in p53-deficient tumors, and for the treatment of tumors whose growth depends on enhanced Chk2 activity.
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PMID:Targeting chk2 kinase: molecular interaction maps and therapeutic rationale. 1610 42

Activation of the G2/M cell cycle checkpoint by DNA damage prevents cells from entering mitosis. Centrosome separation is initiated in G2 phase and completed in M phase. This critical process for cell division is targeted by G2/M checkpoint. Here we show that Plk1 signaling plays an important role in regulation of centrosome separation after DNA damage. Constitutively active Plk1 overrides the inhibition of centrosome separation induced by DNA damage. This inhibition is dependent on ATM, but not on Chk2 or Chk1. Nek2 is a key regulator of centrosome separation and is a target of Plk1 in blocking centrosome separation. We found that Plk1 can phosphorylate Nek2 in vitro and interacts with Nek2 in vivo. Down-regulation of Plk1 with RNA interference prevents Nek2-induced centrosome splitting. DNA damage is known to inhibit Plk1 activity. We propose that the DNA damage-induced inhibition of Plk1 leads to inhibition of Nek2 activity and thus prevents centrosome separation.
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PMID:The role of Polo-like kinase 1 in the inhibition of centrosome separation after ionizing radiation. 1615 94

Centrosomes are cytoplasmic organelles playing a fundamental role in organizing both the interphase cytoskeleton and the bipolar mitotic spindle. In addition, the centrosome has recently come into focus as part of the network that integrates cell cycle arrest and repair signals in response to genotoxic stress--the DNA damage response. One important mediator of this response, the checkpoint kinase Chk1, has been shown to negatively regulate the G(2)/M transition via its centrosomal localization. Moreover, there is growing evidence that a centrosome inactivation checkpoint exists, which utilizes DNA damage-induced centrosome fragmentation or amplification to provoke a "mitotic catastrophe" and eliminate damaged cells. Candidate regulators of this centrosomal checkpoint include the checkpoint kinase Chk2 and its upstream regulators ATM and ATR. In addition, a growing number of other proteins have been implicated in centrosomal regulation of the DNA damage response, e.g. the tumor suppressor p53, the breast cancer susceptibility gene product BRCA1 and mitotic regulators such as Aurora A, Nek2 and the Polo-like kinases Plk1 and Plk3. However, many missing links and discrepancies between different model systems remain.
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PMID:Structure meets function--centrosomes, genome maintenance and the DNA damage response. 1685 12

Plk1 (Polo-like kinase 1) has been documented as a critical regulator of many mitotic events. However, increasing evidence supports the notion that Plk1 might also have functions outside of mitosis. Using biochemical fractionation and RNA interference approaches, we found that Plk1 was required for both G(1)/S and G(2)/M phases and that DNA topoisomerase IIalpha (topoIIalpha) was a potential target for Plk1 in both interphase and mitosis. Plk1 phosphorylates Ser(1337) and Ser(1524) of topoIIalpha. Overexpression of an unphosphorylatable topoIIalpha mutant led to S phase arrest, suggesting that Plk1-associated phosphorylation first occurs in S phase. Moreover, overexpression of the unphosphorylatable topoIIalpha mutant activated the ATM/R-dependent DNA damage checkpoint, probably due to reduced catalytic activity of topoIIalpha, and resulted in accumulation of catenated DNA. Finally, we showed that wild type topoIIalpha, but not the unphosphorylatable mutant, was able to rescue topoIIalpha depletion-induced defects in sister chromatid segregation, indicating that Plk1-associated phosphorylation is essential for the functions of topoIIalpha in mitosis.
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PMID:Plk1-dependent phosphorylation regulates functions of DNA topoisomerase IIalpha in cell cycle progression. 1817 81

Polo-like kinase (Plk)1 is required for mitosis progression. However, although Plk1 is expressed throughout the cell cycle, its function during S-phase is unknown. Using Xenopus laevis egg extracts, we demonstrate that Plx1, the Xenopus orthologue of Plk1, is required for DNA replication in the presence of stalled replication forks induced by aphidicolin, etoposide or reduced levels of DNA-bound Mcm complexes. Plx1 binds to chromatin and suppresses the ATM/ATR-dependent intra-S-phase checkpoint that inhibits origin firing. This allows Cdc45 loading and derepression of DNA replication initiation. Checkpoint activation increases Plx1 binding to the Mcm complex through its Polo box domain. Plx1 recruitment to chromatin is independent of checkpoint mediators Tipin and Claspin. Instead, ATR-dependent phosphorylation of serine 92 of Mcm2 is required for the recruitment of Plx1 to chromatin and for the recovery of DNA replication under stress. Depletion of Plx1 leads to accumulation of chromosomal breakage that is prevented by the addition of recombinant Plx1. These data suggest that Plx1 promotes genome stability by regulating DNA replication under stressful conditions.
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PMID:Plx1 is required for chromosomal DNA replication under stressful conditions. 1830 93

Inhibition of Topo II function using poisons and catalytic inhibitors triggers checkpoints that act to delay progression of G2 cells into mitosis. Topo II poisons induce Topo II-associated DNA double-strand breaks that activate ATM and the DNA damage G2 checkpoint. Topo II catalytic inhibitors do not induce DNA double-strand breaks but block decatenation of intertwined daughter chromatids. Complete decatenation before anaphase of mitosis is required for chromatid segregation. G2 cells appear to sense the degree of chromatid arm catenations and actively delay the onset of mitosis by sustaining the inhibition of mitosis-promoting factor (MPF) and polo-like kinase 1 (Plk-1) kinase activities that normally propel G2 cells into mitosis. This chapter details the methods for assay of decatenation G2 checkpoint function and checkpoint kinase activities.
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PMID:Analysis of the topoisomerase II-dependent decatenation G2 checkpoint and checkpoint kinases in human cells. 1976 49


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