Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The regulation of a pre-replicative complex (pre-RC) at origins ensures that the genome is replicated only once per cell cycle. Cdt1 is an essential component of the pre-RC that is rapidly degraded at G1-S and also inhibited by Geminin (Gem) protein to prevent re-replication. We have previously shown that destruction of the Drosophila homolog of Cdt1, Double-parked (Dup), at G1-S is dependent upon cyclin-E/CDK2 and important to prevent re-replication and cell death. Dup is phosphorylated by cyclin-E/Cdk2, but this direct phosphorylation was not sufficient to explain the rapid destruction of Dup at G1-S. Here, we present evidence that it is DNA replication itself that triggers rapid Dup destruction. We find that a range of defects in DNA replication stabilize Dup protein and that this stabilization is not dependent on ATM/ATR checkpoint kinases. This response to replication stress was cell-type specific, with neuroblast stem cells of the larval brain having the largest increase in Dup protein. Defects at different steps in replication also increased Dup protein during an S-phase-like amplification cell cycle in the ovary, suggesting that Dup stabilization is sensitive to DNA replication and not an indirect consequence of a cell-cycle arrest. Finally, we find that cells with high levels of Dup also have elevated levels of Gem protein. We propose that, in cycling cells, Dup destruction is coupled to DNA replication and that increased levels of Gem balance elevated Dup levels to prevent pre-RC reformation when Dup degradation fails.
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PMID:Levels of the origin-binding protein Double parked and its inhibitor Geminin increase in response to replication stress. 1614 Dec 38

The cycle inhibiting factor (Cif) belongs to a family of bacterial toxins and effector proteins, the cyclomodulins, that deregulate the host cell cycle. Upon injection into HeLa cells by the enteropathogenic Escherichia coli (EPEC) type III secretion system, Cif induces a cytopathic effect characterized by the recruitment of focal adhesion plates and the formation of stress fibres, an irreversible cell cycle arrest at the G(2)/M transition, and sustained inhibitory phosphorylation of mitosis inducer, CDK1. Here, we report that the reference typical EPEC strain B171 produces a functional Cif and that lipid-mediated delivery of purified Cif into HeLa cells induces cell cycle arrest and actin stress fibres, implying that Cif is necessary and sufficient for these effects. EPEC infection of intestinal epithelial cells (Caco-2, IEC-6) also induces cell cycle arrest and CDK1 inhibition. The effect of Cif is strikingly similar to that of cytolethal distending toxin (CDT), which inhibits the G(2)/M transition by activating the DNA-damage checkpoint pathway. However, in contrast to CDT, Cif does not cause phosphorylation of histone H2AX, which is associated with DNA double-stranded breaks. Following EPEC infection, the checkpoint effectors ATM/ATR, Chk1 and Chk2 are not activated, the levels of the CDK-activating phosphatases Cdc25B and Cdc25C are not affected, and Cdc25C is not sequestered in host cell cytoplasm. Hence, Cif activates a DNA damage-independent signalling pathway that leads to inhibition of the G(2)/M transition.
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PMID:Escherichia coli cyclomodulin Cif induces G2 arrest of the host cell cycle without activation of the DNA-damage checkpoint-signalling pathway. 1684 90

Genetic evidence indicates that Ras plays a critical role in the initiation and progression of human thyroid tumors. Paradoxically, acute expression of activated Ras in normal rat thyroid cells induced deregulated cell cycle progression and apoptosis. We investigated whether cell cycle progression was required for Ras-stimulated apoptosis. Ras increased CDK-2 activity following its introduction into quiescent cells. Apoptotic cells exhibited a sustained increase in CDK-2 activity, accompanied by the loss of CDK-2-associated p27. Blockade of Ras-induced CDK-2 activity and S phase entry via overexpression of p27 inhibited apoptosis. Inactivation of the retinoblastoma protein in quiescent cells through expression of HPV-E7 stimulated cell cycle progression and apoptosis, indicating that deregulated cell cycle progression is sufficient to induce apoptosis. Ras failed to induce G1 phase growth arrest in normal rat thyroid cells. Rather, Ras-expressing thyroid cells progressed into S and G2 phases and evoked a checkpoint response characterized by the activation of ATR. Ras-stimulated ATR activity, as evidenced by Chk1 and p53 phosphorylation, was blocked by p27, suggesting that cell cycle progression triggers checkpoint activation, likely as a consequence of replication stress. These data reveal that Ras is capable of inducing a DNA damage response with characteristics similar to those reported in precancerous lesions. Our findings also suggest that the frequent mutational activation of Ras in thyroid tumors reflects the ability of Ras-expressing cells to bypass checkpoints and evade apoptosis rather than to simply increase proliferative potential.
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PMID:Ras triggers ataxia-telangiectasia-mutated and Rad-3-related activation and apoptosis through sustained mitogenic signaling. 1696 94

The molecular mechanisms responsible for the cellular effects of the nitrogen-containing bisphosphonate zoledronic acid (Zol) were assessed on several osteosarcoma cell lines differing in their p53 and retinoblastoma (Rb) status. Zol inhibited cell proliferation and increased atypical apoptosis. The Zol effects on proliferation were due to cell cycle arrest in S and G2/M phases subsequent to the activation of the intra-S DNA damage checkpoint with an increase in P-ATR, P-chk1, Wee1, and P-cdc2 levels and a decrease in cdc25c, regardless of the p53 and Rb status. In addition, the atypic apoptosis induced by Zol was independent of caspase activation, and it was characterized by nuclear alterations, increased Bax expression, and reduced Bcl-2 level. Furthermore, mitochondrial permeability was up-regulated by Zol independently of p53 in association with the translocation of apoptosis-inducing factor (AIF) and endonuclease-G (EndoG). Zol also disturbed cytoskeletal organization and cell junctions and inhibited cell migration and phosphorylation of focal adhesion kinases. The main difficulty encountered in treating cancer relates to mutations in key genes such as p53, Rb, or proteins affecting caspase signaling carried by many tumor cells. We have demonstrated for the first time that zoledronic acid activated the DNA damage S-phase checkpoint and the mitochondrial pathway via AIF and EndoG translocation, and it inhibited cell proliferation and induced cell death, bypassing these potentials mutations. Therefore, zoledronic acid may be considered as an effective therapeutic agent in clinical trials of osteosarcoma in which mutation for p53 and Rb very often occur, and where current treatment with traditional chemotherapeutic agents is ineffective.
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PMID:Zoledronic acid activates the DNA S-phase checkpoint and induces osteosarcoma cell death characterized by apoptosis-inducing factor and endonuclease-G translocation independently of p53 and retinoblastoma status. 1705 Aug 6

The S checkpoint response to ultraviolet radiation (UVC) that inhibits replicon initiation is dependent on the ATR and Chk1 kinases. Downstream effectors of this response, however, are not well characterized. Data reported here eliminated Cdc25A degradation and inhibition of Cdk2-cyclin E as intrinsic components of the UVC-induced pathway of inhibition of replicon initiation in human cells. A sublethal dose of UVC (1 J/m(2)), which selectively inhibits replicon initiation by 50%, failed to reduce the amount of Cdc25A protein or decrease Cdk2-cyclin E kinase activity. Cdc25A degradation was observed after irradiation with cytotoxic fluences of UVC, suggesting that severe inhibition of DNA chain elongation and activation of the replication checkpoint might be responsible for the UVC-induced degradation of Cdc25A. Another proposed effector of the S checkpoint is the Cdc7-Dbf4 complex. Dbf4 interacted weakly with Chk1 in vivo but was recognized as a substrate for Chk1-dependent phosphorylation in vitro. FLAG-Dbf4 formed complexes with endogenous Cdc7, and this interaction was stable in UVC-irradiated HeLa cells. Overexpression of FLAG- or Myc-tagged Dbf4 abrogated the S checkpoint response to UVC but not ionizing radiation. These findings implicate a Dbf4-dependent kinase as a possible target of the ATR- and Chk1-dependent S checkpoint response to UVC.
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PMID:Cdc7-Dbf4 and the human S checkpoint response to UVC. 1727 90

Cohesin is a multiprotein complex essential for sister-chromatid cohesion. It plays a pivotal role in proper chromosome segregation and DNA damage repair. The mitotic behavior of cohesin is controlled through its phosphorylation, which possibly induces the dissociation of cohesin from chromosomes and enhances its susceptibility to separase. Here, we report using mass spectrometry and anti-phospho antibodies that the central domain of Rad21, the separase-target subunit of Schizosaccharomyces pombe cohesin, is regulated by various kinase-induced phosphorylation at nine residues, indicating the multiple roles for S. pombe cohesin. In vegetative and non-dividing G(0) cells, Rad21 is phosphorylated by unknown S/TP-consensus kinases, in mitotic and non-mitotic cells by polo/Plo1 and CDK, and in DNA-damaged cells by Rad3/ATR. While mitotic phosphorylation is implicated in the dissociation of Rad21 and its cleavage by separase in anaphase, the Rad3/ATR-dependent damage-induced phosphorylation occurs intensively at the time of repair completion, and only in post-replicative cells. This damage-induced Rad21 phosphorylation is involved in the recovery process of cells from checkpoint arrest, and needed for the removal of cohesin by separase after the completion of damage repair. These complex phospho-regulations of Rad21 indicate the functional significance of cohesin in cell adaptation to a variety of cellular conditions.
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PMID:Cut1/separase-dependent roles of multiple phosphorylation of fission yeast cohesion subunit Rad21 in post-replicative damage repair and mitosis. 1823 48

Ataxia telangiectasia mutated (ATM) is a phosphatidyl-3-kinase-related protein kinase that functions as a central regulator of the DNA damage response in eukaryotic cells. In humans, mutations in ATM cause the devastating neurodegenerative disease ataxia telangiectasia. Previously, we characterized the homolog of ATM (AtmA) in the filamentous fungus Aspergillus nidulans. In addition to its expected role in the DNA damage response, we found that AtmA is also required for polarized hyphal growth. Here, we extended these studies by investigating which components of the DNA damage response pathway are interacting with AtmA. The AtmA(ATM) loss of function caused synthetic lethality when combined with mutation in UvsB(ATR). Our results suggest that AtmA and UvsB are interacting and they are probably partially redundant in terms of DNA damage sensing and/or repairing and polar growth. We identified and inactivated A. nidulans chkA(CHK1) and chkB(CHK2) genes. These genes are also redundantly involved in A. nidulans DNA damage response. We constructed several combinations of double mutants for DeltaatmA, DeltauvsB, DeltachkA, and DeltachkB. We observed a complex genetic relationship with these mutations during the DNA replication checkpoint and DNA damage response. Finally, we observed epistatic and synergistic interactions between AtmA, and bimE(APC1), ankA(WEE1) and the cdc2-related kinase npkA, at S-phase checkpoint and in response to DNA-damaging agents.
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PMID:Genetic interactions of the Aspergillus nidulans atmAATM homolog with different components of the DNA damage response pathway. 1824 60

Cell cycle checkpoints are pivotal mechanisms safeguarding genome stability. Cells that harbor defects in checkpoints are predisposed to genome instability and neoplastic transformation. Two structurally-unrelated protein kinases, CHK1 and CHK2, are implicated in several major checkpoints of the cell cycle, providing a crucial linkage between the upstream sensors of the checkpoints and the cell cycle engine. Variations of the ATM/ATR-CHK1/CHK2-CDC25-CDK axis underlie the molecular basis of the replication checkpoint, the intra-S phase checkpoint, and the G2 DNA damage checkpoint. Although some aspects of the pathway remain contentious, the ATM/ATR-CHK1/CHK2-p53-p21CIP1/WAF1-CDK axis is believed to play an important role in the G1 DNA damage checkpoint. Recent data also reveal that CHK1 may play a role in the spindle-assembly checkpoint. Finally, CHK1 and CHK2 are implicated in linking the cell cycle to diverse processes such as senescence and the circadian cycle. In this review article, we provide an overview of how the multi-tasking nature of CHK1 and CHK2 is achieved in vertebrate cells.
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PMID:The multiple checkpoint functions of CHK1 and CHK2 in maintenance of genome stability. 1850 66

Hepatitis B virus (HBV) X protein (pX) is implicated in hepatocellular carcinoma (HCC) pathogenesis by an unknown mechanism. Deletions or mutations of genes involved in the p53 pathway are often associated with HBV-mediated HCC, indicating rescue from p53 apoptosis is a likely mechanism in HBV-HCC pathogenesis. Herein, we determined the mechanism by which pX sensitizes hepatocytes to p53-mediated apoptosis. Although it is well established that the Rb/E2F/ARF pathway stabilizes p53, and the DNA damage-activated ATM/ATR kinases activate p53, the mechanism that coordinates these two pathways has not been determined. We demonstrate that the p38MAPK pathway activated by pX serves this role in p53 apoptosis. Specifically, the activated p38MAPK pathway stabilizes p53 via E2F1-mediated ARF expression, and also activates the transcriptional function of p53 by activating ATR. Knockdown of p53, E2F1, ATR, or p38MAPKalpha abrogates pX-mediated apoptosis, demonstrating that E2F1, ATR, and p38MAPKalpha are all essential in p53 apoptosis in response to pX. Specifically, in response to pX expression, the p38MAPK pathway activates Cdk4 and Cdk2, leading to phosphorylation of Rb, release of E2F1, and transcription of ARF. The p38MAPK pathway also activates ATR, leading to phosphorylation of p53 on Ser-18 and Ser-23, transcription of pro-apoptotic genes Bax, Fas, and Noxa, and apoptosis. In conclusion, pX sensitizes hepatocytes to p53 apoptosis via activation of the p38MAPK pathway, which couples p53 stabilization and p53 activation, by E2F1 induction and ATR activation, respectively.
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PMID:Hepatitis B virus X protein via the p38MAPK pathway induces E2F1 release and ATR kinase activation mediating p53 apoptosis. 1860 16

We previously reported Chk1 to be phosphorylated at Ser286 and Ser301 by cyclin-dependent kinase (Cdk) 1 during mitosis [T. Shiromizu et al., Genes Cells 11 (2006) 477-485]. Here, we demonstrated that Chk1-Ser286 and -Ser301 phosphorylation also occurs in hydroxyurea (HU)-treated or ultraviolet (UV)-irradiated cells. Unlike the mitosis case, however, Chk1 was phosphorylated not only at Ser286 and Ser301 but also at Ser317 and Ser345 in the checkpoint response. Treatment with Cdk inhibitors diminished Chk1 phosphorylation at Ser286 and Ser301 but not at Ser317 and Ser345 with the latter. In vitro analyses revealed Ser286 and Ser301 on Chk1 to serve as two major phosphorylation sites for Cdk2. Immunoprecipitation analyses further demonstrated that Ser286/Ser301 and Ser317/Ser345 phosphorylation occur in the same Chk1 molecule during the checkpoint response. In addition, Ser286/Ser301 phosphorylation by Cdk2 was observed in Chk1 mutated to Ala at Ser317 and Ser345 (S317A/S345A), as well as Ser317/Ser345 phosphorylation by ATR was in S286A/S301A. Therefore, Chk1 phosphorylation in the checkpoint response is regulated not only by ATR but also by Cdk2.
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PMID:Chk1 phosphorylation at Ser286 and Ser301 occurs with both stalled DNA replication and damage checkpoint stimulation. 1898 24


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