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

During mitosis, the phosphatidylinositol-3 (PI-3) family-related DNA damage checkpoint kinases ATM and ATR were found on the centrosomes of human cells. ATRIP, an interaction partner of ATR, as well as Chk1 and Chk2, the downstream targets of ATR or ATM, were also localized to the centrosomes. Surprisingly, the DNA-PK inhibitor vanillin enhanced the level of ATM on centrosomes. Accordingly, DNA-PKcs, the catalytic subunit of DNA-PK, was also found on the centrosomes. Vanillin altered the phosphorylation of Chk2 in the centrosomes and in whole cell extracts. Nucleoplasmic ATM co-immunoprecipitated with Ku70/86, the DNA binding subunits of DNA-PK, while vanillin diminished this association. Vanillin did not affect microtubule polymerization at the centrosomes but, surprisingly, caused a transient enhancement of alpha-tubulin foci in the nucleus. Interestingly, gamma-tubulin was also present in the nucleus and co-immunoprecipitated with ATR or BRCA1. DNA damage led to a reduction of the mentioned checkpoint proteins on the centrosomes but increased the level of gamma-tubulin at this organelle. Taken together, these results indicate that DNA damage checkpoint proteins may control the formation of gamma-tubulin and/or the kinetics of microtubule formation at the centrosomes, and thereby couple them to the DNA damage response.
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PMID:Centrosomal localization of DNA damage checkpoint proteins. 1717 39

The ATM and ATR kinases function at the apex of checkpoint signaling pathways. These kinases share significant sequence similarity, phosphorylate many of the same substrates, and have overlapping roles in initiating cell cycle checkpoints. However, they sense DNA damage through distinct mechanisms. ATR primarily senses single stranded DNA (ssDNA) through its interaction with ATRIP, and ATM senses double strand breaks through its interaction with Nbs1. We determined that the N-terminus of ATR contains a domain that binds ATRIP. Attaching this domain to ATM allowed the fusion protein (ATM*) to bind ATRIP and associate with RPA-coated ssDNA. ATM* also gained the ability to localize efficiently to stalled replication forks as well as double strand breaks. Despite having normal kinase activity when tested in vitro and being phosphorylated on S1981 in vivo, ATM* is defective in checkpoint signaling and does not complement cellular deficiencies in either ATM or ATR. These data indicate that the N-terminus of ATR is sufficient to bind ATRIP and to promote localization to sites of replication stress.
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PMID:Function of the ATR N-terminal domain revealed by an ATM/ATR chimera. 1737 33

DNA replication stress triggers the activation of Checkpoint Kinase 1 (Chk1) in a pathway that requires the independent chromatin loading of the ATRIP-ATR (ATR-interacting protein/ATM [ataxia-telangiectasia mutated]-Rad3-related kinase) complex and the Rad9-Hus1-Rad1 (9-1-1) clamp. We show that Rad9's role in Chk1 activation is to bind TopBP1, which stimulates ATR-mediated Chk1 phosphorylation via TopBP1's activation domain (AD), a domain that binds and activates ATR. Notably, fusion of the AD to proliferating cell nuclear antigen (PCNA) or histone H2B bypasses the requirement for the 9-1-1 clamp, indicating that the 9-1-1 clamp's primary role in activating Chk1 is to localize the AD to a stalled replication fork.
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PMID:The Rad9-Hus1-Rad1 (9-1-1) clamp activates checkpoint signaling via TopBP1. 1757 48

In both yeast and mammals, uncapped telomeres activate the DNA damage response (DDR) and undergo end-to-end fusion. Previous work has shown that the Drosophila HOAP protein, encoded by the caravaggio (cav) gene, is required to prevent telomeric fusions. Here we show that HOAP-depleted telomeres activate both the DDR and the spindle assembly checkpoint (SAC). The cell cycle arrest elicited by the DDR was alleviated by mutations in mei-41 (encoding ATR), mus304 (ATRIP), grp (Chk1) and rad50 but not by mutations in tefu (ATM). The SAC was partially overridden by mutations in zw10 (also known as mit(1)15) and bubR1, and also by mutations in mei-41, mus304, rad50, grp and tefu. As expected from SAC activation, the SAC proteins Zw10, Zwilch, BubR1 and Cenp-meta (Cenp-E) accumulated at the kinetochores of cav mutant cells. Notably, BubR1 also accumulated at cav mutant telomeres in a mei-41-, mus304-, rad50-, grp- and tefu-dependent manner. Our results collectively suggest that recruitment of BubR1 by dysfunctional telomeres inhibits Cdc20-APC function, preventing the metaphase-to-anaphase transition.
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PMID:Unprotected Drosophila melanogaster telomeres activate the spindle assembly checkpoint. 1824 67

The kinases ATM and ATR (Tel1 and Mec1 in the yeast Saccharomyces cerevisiae) control the response to DNA damage. We report that S. cerevisiae Tel2 acts at an early step of the TEL1/ATM pathway of DNA damage signaling. We show that Tel1 and Tel2 interact, and that even when Tel1 protein levels are high, this interaction is specifically required for Tel1 localization to a DNA break and its activation of downstream targets. Computational analysis revealed structural homology between Tel2 and Ddc2 (ATRIP in vertebrates), a partner of Mec1, suggesting a common structural principle used by partners of phoshoinositide 3-kinase-like kinases.
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PMID:Tel2 mediates activation and localization of ATM/Tel1 kinase to a double-strand break. 1833 20

In this issue of Genes & Development, Mordes and colleagues (pp. 1478-1489) reveal intriguing mechanistic insights into activation of the ATR (ATM and Rad3-related) kinase critical for DNA damage resistance. They identify conserved regulatory domains within ATR and its binding partner ATRIP (ATR-interacting protein), which are contacted by the ATR activator TopBP1. These discoveries expand on our understanding of the regulation of other PIKK family members, which also contain these domains, and illustrate how functional diversity has been achieved among these kinases.
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PMID:How ATR turns on: TopBP1 goes on ATRIP with ATR. 1851 40

The ATR (ATM and Rad3-related) kinase and its regulatory partner ATRIP (ATR-interacting protein) coordinate checkpoint responses to DNA damage and replication stress. TopBP1 functions as a general activator of ATR. However, the mechanism by which TopBP1 activates ATR is unknown. Here, we show that ATRIP contains a TopBP1-interacting region that is necessary for the association of TopBP1 and ATR, for TopBP1-mediated activation of ATR, and for cells to survive and recover DNA synthesis following replication stress. We demonstrate that this region is functionally conserved in the Saccharomyces cerevisiae ATRIP ortholog Ddc2, suggesting a conserved mechanism of regulation. In addition, we identify a domain of ATR that is critical for its activation by TopBP1. Mutations of the ATR PRD (PIKK [phosphoinositide 3-kinase related kinase] Regulatory Domain) do not affect the basal kinase activity of ATR but prevent its activation. Cellular complementation experiments demonstrate that TopBP1-mediated ATR activation is required for checkpoint signaling and cellular viability. The PRDs of ATM and mTOR (mammalian target of rapamycin) were shown previously to regulate the activities of these kinases, and our data indicate that the DNA-PKcs (DNA-dependent protein kinase catalytic subunit) PRD is important for DNA-PKcs regulation. Therefore, divergent amino acid sequences within the PRD and a unique protein partner allow each of these PIK kinases to respond to distinct cellular events.
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PMID:TopBP1 activates ATR through ATRIP and a PIKK regulatory domain. 1851 33

The DNA damage response kinase ATR is an essential regulator of genome integrity. TopBP1 functions as a general activator of ATR. We have recently shown that TopBP1 activates ATR through its regulatory subunit ATRIP and a PIKK regulatory domain (PRD) located adjacent to its kinase domain. This mechanism of ATR activation is conserved in the S. cerevisiae ortholog Mec1. ATR is a member of the PIKK family of protein kinases that includes ATM, DNA-PKcs, mTOR and SMG1. The PRD regulates the kinase activity of other PIKKs and may serve as a site of interaction between these kinase and their respective activators. Activation of ATR by TopBP1 is maximal at low substrate concentrations and declines exponentially as substrate concentration increases. These data are consistent with a model in which TopBP1 acts to alter the conformation of ATR-ATRIP to increase the ability of ATR to bind substrates. A further understanding of the mechanism of ATR activation will likely provide insights into the regulation of related PIKKs.
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PMID:Activation of ATR and related PIKKs. 1876 53

The activation of ATR-ATRIP in response to double-stranded DNA breaks (DSBs) depends upon ATM in human cells and Xenopus egg extracts. One important aspect of this dependency involves regulation of TopBP1 by ATM. In Xenopus egg extracts, ATM associates with TopBP1 and thereupon phosphorylates it on S1131. This phosphorylation enhances the capacity of TopBP1 to activate the ATR-ATRIP complex. We show that TopBP1 also interacts with the Mre11-Rad50-Nbs1 (MRN) complex in egg extracts in a checkpoint-regulated manner. This interaction involves the Nbs1 subunit of the complex. ATM can no longer interact with TopBP1 in Nbs1-depleted egg extracts, which suggests that the MRN complex helps to bridge ATM and TopBP1 together. The association between TopBP1 and Nbs1 involves the first pair of BRCT repeats in TopBP1. In addition, the two tandem BRCT repeats of Nbs1 are required for this binding. Functional studies with mutated forms of TopBP1 and Nbs1 suggested that the BRCT-dependent association of these proteins is critical for a normal checkpoint response to DSBs. These findings suggest that the MRN complex is a crucial mediator in the process whereby ATM promotes the TopBP1-dependent activation of ATR-ATRIP in response to DSBs.
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PMID:The Mre11-Rad50-Nbs1 complex mediates activation of TopBP1 by ATM. 1927 41

Human checkpoint kinase 1 (CHK1) is an essential kinase required to preserve genome stability, and is activated by DNA replication blockage through the ataxia-telangiectasia-mutated-and-Rad3-related (ATR)/ATRIP-signaling pathway. In this report, we show that a novel CHK1-interacting protein, FEM1B (human homologue of the Caenorhabditis elegans sex determination fem1 protein), identified by a yeast two-hybrid screen, is involved in the activation of CHK1 by replication stress. Depletion of FEM1B by small interfering RNA in cancer cells impairs the activation of CHK1 kinase activity and attenuates the induction of CHK1 Ser345 phosphorylation upon replication interference. It is to be noted that, CHK2 Thr68 phosphorylation is not altered by FEM1B downregulation. By fractionation, we further demonstrated that FEM1B is able to associate with chromatin, and such association facilitates chromatin loading of the Rad9 protein. Consistently, ATR activity is poorly maintained in FEM1B knockdown cells; and FEM1B-ablated cells are as sensitive to replication block as CHK1-depleted cells. Our study has uncovered an adaptor protein FEM1B, which acts as a bridge linking CHK1 and Rad9, thus facilitating checkpoint signaling induced by replication stress.
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PMID:Human FEM1B is required for Rad9 recruitment and CHK1 activation in response to replication stress. 1933 22


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