Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cdc25C and p53 have been reported to be physiological targets of checkpoint kinase 2 (Chk2). Surprisingly, although Chk2 purified from DNA damage sustaining cells has dramatically increased ability to phosphorylate Cdc25C when compared with untreated cells, its ability to phosphorylate p53 is weak before treatment, and there is no increase in its activity toward p53 after DNA damage by gamma irradiation or the radiomimetic agent neocarzinostatin. Furthermore, introduction of Chk2 short interfering RNA into three different human tumor cell lines leads to marked reduction of Chk2 protein, but p53 is still stabilized and active after DNA damage. The results with Chk1 short interfering RNA indicate as well that Chk1 does not play a role in human p53 stabilization after DNA damage. Thus, Chk1 and Chk2 are unlikely to be regulators of p53 in at least some human tumor cells. We discuss our results in the context of previous findings demonstrating a requirement for Chk2 in p53 stabilization and activity.
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PMID:Questioning the role of checkpoint kinase 2 in the p53 DNA damage response. 1265 16

Cell cycle checkpoints are activated in response to DNA-damage to ensure that accurate copies of the cellular genome are passed on to the next generation and to avoid replication and segregation of damaged DNA. These cellular control systems can be overcome by combining conventional DNA-damaging agents with compounds that target the cell cycle regulatory pathways, to enhance cytotoxicity. Tumor cells often comprise a corrupted G(1) cell cycle checkpoint while the G(2) cell cycle checkpoint is still intact. This review describes the concept of G(2) checkpoint abrogation with recognized (methylxanthines, UCN-01) and novel G(2) checkpoint abrogators to potentiate the cytotoxicity of DNA-damaging drugs and ionizing radiation. It illustrates the potential of G(2) checkpoint abrogators to preferentially sensitize p53-mutated, treatment resistant tumor cells for genotoxic treatment. Identification of the targets of caffeine and UCN-01 to be key-players of the G(2) checkpoint (ATM/ATR and Chk1, respectively) promoted the search for novel inhibitors of this checkpoint. Even though a direct causal link between G(2) checkpoint abrogation and chemo-/radiosensitization is difficult to prove the multitude of these novel compounds validate that inhibition of critical elements of the G(2) checkpoint (ATM/ATR-Chk1/Chk2-CDC25C-cascade) potentiates the cytotoxicity of DNA-damaging agents.
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PMID:Potentiation of DNA-damage-induced cytotoxicity by G2 checkpoint abrogators. 1267 13

Checkpoints are biochemical pathways that provide cells a mechanism to detect DNA damage and respond by arresting the cell cycle to allow DNA repair. The conserved checkpoint kinase, Chk1, regulates mitotic progression in response to DNA damage by blocking the activation of Cdk1/cyclin B. In this study, we investigate the regulatory interaction between Chk1 and members of the Atm family of kinases and the functional role of the C-terminal non-catalytic domains of Chk1. Chk1 stimulates the kinase activity of DNA-PK (protein kinase) complexes, which leads to increased phosphorylation of p53 on Ser-15 and Ser-37. In addition, Chk1 stimulates DNA-PK-dependent end-joining reactions in vitro. We also show that Chk1 protein complexes bind to single-stranded DNA and DNA ends. These results indicate a connection between components that regulate the checkpoint pathways and DNA-PK complex proteins, which have a role in the repair of double strand breaks.
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PMID:Regulatory interactions between the checkpoint kinase Chk1 and the proteins of the DNA-dependent protein kinase complex. 1275 47

The p21(WAF1/Cip1) gene plays a central role in cell cycle regulation. Here we show that topoisomerase II inhibitors, genistein and etoposide, induce p21(WAF1/Cip1) expression mainly in a p53-dependent manner in human lung cancer cell line A549. However, although p53 accumulated, p21(WAF1/Cip1) expression did not depend on the level of Ser15 phosphorylation of p53. Caffeine, an ataxia telangiectasia-mutated (ATM), and ATM- and Rad3-related kinase (ATR) inhibitor, abrogated genistein-induced p21(WAF1/Cip1) and largely blocked etoposide-induced p21(WAF1/Cip1) expression. Wortmannin, an ATM- and DNA-dependent protein kinase inhibitor, partially inhibited p21(WAF1/Cip1) expression induced by genistein and etoposide, whereas UCN-01, a Chk1 inhibitor, partially blocked etoposide, but not genistein-induced p21(WAF1/Cip1) expression. These data suggest that both genistein and etoposide induce p21(WAF1/Cip1) expression in a p53-dependent manner. Genistein appears to stimulate p21(WAF1/Cip1) expression through p53 via ATM, whereas etoposide may activate both ATM and ATR pathways. Our results suggest different mechanisms participate in genistein and etoposide induced p21(WAF1/Cip1) expression.
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PMID:P21 response to DNA damage induced by genistein and etoposide in human lung cancer cells. 1276 22

During the proliferation of T cells for successful immune responses against pathogens, the fine regulation of cell cycle is important to the maintenance of T cell homeostasis and the prevention of lymphoproliferative disorders. However, it remains to be elucidated how the cell cycle is controlled at the mitotic phase in proliferating T cells. Here, we show that during the proliferation of primary T cells, the disruption of the mitotic spindle leads to cell-cycle arrest at mitosis and that prolonged mitotic arrest results in not only apoptosis but also the form of chromosomal instability observed in human cancers. It is interesting that in response to spindle damage, the phosphorylation of BubR1, a mitotic checkpoint kinase, was significantly induced in proliferating T cells, and the expression of the dominant-negative mutant of BubR1 compromised mitotic arrest and subsequent apoptosis and thus led to the augmentation of polyploidy formation. We also show that in response to prolonged spindle damage, the expression of p53 but not of p73 was significantly induced. In addition, following sustained mitotic arrest, p53-deficient T cells were found to be more susceptible to polyploidy formation than the wild type. These results suggest that during flourishing immune response, mitotic checkpoint and p53 play important roles in the prevention of chromosomal instability and in the maintenance of the genomic integrity of proliferating T cells.
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PMID:p53 deficiency and defective mitotic checkpoint in proliferating T lymphocytes increase chromosomal instability through aberrant exit from mitotic arrest. 1277 18

The p53 protein is kept labile under normal conditions. This regulation is governed largely by its major negative regulator, Mdm2. In response to stress however, p53 accumulates and becomes activated. For this to occur, the inhibitory effects of Mdm2 have to be neutralized. Here we investigated the role of the promyelocytic leukemia protein (PML) in the activation of p53 in response to stress. We found that PML is critical for the accumulation of p53 in response to DNA damage under physiological conditions. PML protects p53 from Mdm2-mediated ubiquitination and degradation, and from inhibition of apoptosis. PML neutralizes the inhibitory effects of Mdm2 by prolonging the stress-induced phosphorylation of p53 on serine 20, a site of the checkpoint kinase 2 (Chk2). PML recruits Chk2 and p53 into the PML nuclear bodies and enhances p53/Chk2 interaction. Our results provide a novel mechanistic explanation for the cooperation between PML and p53 in response to DNA damage.
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PMID:The promyelocytic leukemia protein protects p53 from Mdm2-mediated inhibition and degradation. 1281 Jul 24

Mammalian Chk1 is an essential kinase for embryonic development and plays an important role in the cellular response to DNA damage. However, it remains unclear whether inhibition of Chk1 induces apoptosis in somatic cells. The uncertainty has become a critical issue for rationale design of Chk1 mechanism-based anticancer drugs. Here we show that Chk1 small interfering RNA (siRNA) effectively eliminates Chk1 protein expression without altering the cell cycle profile or inducing apoptosis in various human cancer cell lines under normal conditions. In the presence of DNA-damaging agents, however, Chk1 siRNA alone is sufficient to abrogate the DNA damage-induced G(2) checkpoint and significantly enhance apoptosis. Cell cycle kinetic profiles show that abrogation of G(2) arrest is mediated through shortening of the checkpoint. We also demonstrate that Chk1 siRNA enhances DNA damage-induced apoptosis in p53-deficient cancer cell lines and augments the growth inhibition conferred by DNA-damaging agents. These findings imply that Chk1 inhibitors will have low cytotoxicity on their own and can enhance the efficacy of DNA-damaging drugs.
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PMID:Human Chk1 expression is dispensable for somatic cell death and critical for sustaining G2 DNA damage checkpoint. 2207

The tumour suppressor p53 is a tetrameric protein that is phosphorylated in its BOX-I transactivation domain by checkpoint kinase 2 (CHK2) in response to DNA damage. CHK2 cannot phosphorylate small peptide fragments of p53 containing the BOX-I motif, indicating that undefined determinants in the p53 tetramer mediate CHK2 recognition. Two peptides derived from the DNA-binding domain of p53 bind to CHK2 and stimulate phosphorylation of full-length p53 at Thr 18 and Ser 20, thus identifying CHK2-docking sites. CHK2 can be fully activated in trans by the two p53 DNA-binding-domain peptides, and can phosphorylate BOX-I transactivation-domain fragments of p53 at Thr 18 and Ser 20. Although CHK2 has a basal Ser 20 kinase activity that is predominantly activated towards Thr 18, CHK1 has constitutive Thr 18 kinase activity that is predominantly activated in trans towards Ser 20. Cell division cycle 25C (CDC25C) phosphorylation by CHK2 is unaffected by the p53 DNA-binding-domain peptides. The CHK2-docking site in the BOX-V motif is the smallest of the two CHK2 binding sites, and mutating certain amino acids in the BOX-V peptide prevents CHK2 activation. A database search identified a p53 BOX-I-homology motif in p21(WAF1) and although CHK2 is inactive towards this protein, the p53 DNA-binding-domain peptides induce phosphorylation of p21(WAF1) at Ser 146. This provides evidence that CHK2 can be activated allosterically towards some substrates by a novel docking interaction, and identify a potential regulatory switch that may channel CHK2 into distinct signalling pathways in vivo.
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PMID:Allosteric effects mediate CHK2 phosphorylation of the p53 transactivation domain. 1289 1

Hyperoxia has been shown to cause DNA damage resulting in growth arrest of cells in p53-dependent, as well as p53-independent, pathways. Although H2O2 and other peroxides have been shown to induce ataxia telangiectasia-mutated (ATM)-dependent p53 phosphorylation in response to DNA damage, the signal transduction mechanisms in response to hyperoxia are currently unknown. Here we demonstrate that hyperoxia phosphorylates the Ser15 residue of p53 independently of ATM. Hyperoxia phosphorylated p53 (Ser15) in DNA-dependent protein kinase null (DNA-PK-/-) cells, indicating that it may not depend on DNA-PK for phosphorylation of p53 (Ser15). We show that Ser37 and Ser392 residues of p53 are also phosphorylated in an ATM-independent manner in hyperoxia. In contrast, H2O2 did not phosphorylate Ser37 in either ATM+/+ or ATM-/- cells. Furthermore, H2O2 failed to phosphorylate Ser15 in ATM-/- cells. Additionally, overexpression of kinase-inactive ATM-and-Rad3-related (ATR) in HEK293T cells diminished Ser15, Ser37, and Ser392 phosphorylation compared with vector-only transfected cells. In contrast, wild-type ATR overexpression did not diminish Ser15, Ser37, or Ser392 phosphorylation. We also show that checkpoint kinase 1 (Chk1) is phosphorylated on Ser345 in response to hyperoxia, which could be inhibited by caffeine or wortmannin, potent inhibitors of phosphoinositide 3-kinase-related kinases. Hyperoxia also phosphorylated Chk1 in ATM+/+ as well as in ATM-/- cells, demonstrating an ATM-independent mechanism in Chk1 phosphorylation. Together, our data suggest that hyperoxia activates the ATR-Chk1 pathway and phosphorylates p53 at multiple sites in an ATM-independent manner, which is different from other forms of oxidative stress such as H2O2 or UV light.
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PMID:Hyperoxia activates the ATR-Chk1 pathway and phosphorylates p53 at multiple sites. 1295 29

Chk1 kinase is a key signal transducer in the checkpoint pathways responding to DNA damage. Chk1 has been shown to be transcriptionally down-regulated in response to cis-dichloro-diamino platinum treatment in a p53-dependent manner. Now we isolated and characterised the 5' flanking region of the Chk1 gene. We demonstrated that the isolated region has promoter activity when cloned upstream to a reporter luciferase gene and we could define the minimal promoter region. The modulation of the transcriptional activity of the cloned Chk1 promoter region by different transcription factors was investigated by co-transfection experiments and by using different isogenic systems. It was shown that p53 is indeed able to down-regulate the promoter activity of the cloned region, providing a mechanistic explanation to the observation that p53 decreases Chk1 protein levels after DNA damage. Several E2F binding sites were detected in the genomic sequence and E2F1 induced Chk1 promoter activity in co-transfection experiments. This induction was abolished when a mutated form of E2F1, not able to bind DNA, was used. Over-expression of E2F1 sustained an increased Chk1 promoter activity, whereas overexpression of Rb protein, which binds E2F factors, decreased Chk1 promoter activity. We discuss our results in the context of Chk1 involvement in DNA damage checkpoint pathways.
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PMID:Characterization of the 5'flanking region of the human Chk1 gene: identification of E2F1 functional sites. 1450 77


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