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)

Premature chromatin condensation (PCC) is a hallmark of mammalian cells that begin mitosis before completing DNA replication. This lethal event is prevented by a highly conserved checkpoint involving an unknown, caffeine-sensitive mediator. Here, we have examined the possible involvement of the caffeine-sensitive ATM and ATR protein kinases in this checkpoint. We show that caffeine's ability to inhibit ATR (but not ATM) causes PCC, that ATR (but not ATM) prevents PCC, and that ATR prevents PCC via Chk-1 regulation. Moreover, mimicking cancer cell phenotypes by disrupting normal G(1) checkpoints sensitizes cells to PCC by ATR inhibition plus low-dose DNA damage. Notably, loss of p53 function potently sensitizes cells to PCC caused by ATR inhibition by a small molecule. We present a molecular model for how ATR prevents PCC and suggest that ATR represents an attractive therapeutic target for selectively killing cancer cells by premature chromatin condensation.
 ...
PMID:ATR inhibition selectively sensitizes G1 checkpoint-deficient cells to lethal premature chromatin condensation. 1148 75

The mechanisms involved in p53-mediated cell death remain controversial. In the present study, we investigated this cell death pathway by stably transfecting the p53-null H358 cell line with a tetracycline-dependent wild type p53-expressing vector. Restoration of p53 triggered a G(2)/M cell cycle arrest and enhanced BAX protein expression, without inducing apoptosis or potentiating the cytotoxic effect of etoposide, vincristine, and cis-platinum. Accordingly, overexpression of BAX in H358 cells, through stable transfection of a tetracycline-regulated expression vector, did not induce cell death. Interestingly, the methylxanthine caffeine (4 mm) promoted the translocation of BAX from the cytosol to the mitochondria. In the setting of an overexpression of BAX, caffeine induced a conformational change of the protein and apoptosis. The consequences of caffeine were independent of its cell cycle-related activities. All together, caffeine synergizes with p53 for inducing cell death through a cell cycle-independent mechanism, involving mitochondrial translocation and conformational change of BAX protein.
 ...
PMID:Caffeine sensitizes human H358 cell line to p53-mediated apoptosis by inducing mitochondrial translocation and conformational change of BAX protein. 1148 80

We analysed the effects of caffeine and taxol on the radiobiological behaviour of two human sarcoma cell lines (RD, SK-LMS-1) each with a p53 missense mutation. Treatment with 2 mM caffeine resulted in an inhibition of the irradiation induced G2/M arrest in both cell lines. This effect was coupled with a radiosensitization in cell line SK-LMS-1 after an irradiation with 6 Gy (enhancement factor of 5.0). However, the effect of radiosensitization was not correlated with an induction of apoptosis. Incubation with 20 nM taxol increased the irradiation induced apoptosis almost 3-fold in cell line SK-LMS-1, but not in cell line RD. However, taxol had no effect on the irradiation induced G2/M arrest or radiosensitivity in either cell line. The results support the hypothesis that the prevention of irradiation induced G2/M arrest but not the induction of apoptosis plays a critical role in determining radiosensitivity in sarcoma cell lines with p53 mutations.
 ...
PMID:Radiosensitization in sarcoma cell lines with a p53 missense mutation correlates with prevention of irradiation G2/M arrest but not with induction of apoptosis. 1149 6

We previously found that p53 upregulation by hypertonicity protected renal inner medullary collecting duct (mIMCD3) cells from apoptosis. The purpose of the present study was to investigate the mechanism by which p53 protects the cells. We now find that hypertonicity (NaCl added to a total of 500 mosmol) inhibits DNA replication and delays G(1)-S transition as concluded from analysis of cell cycle distributions and bromodeoxyuridine (BrDU) incorporation rates. Lowering of p53 with p53 antisense oligonucleotide attenuated such effects of hypertonicity, resulting in an increased number of apoptotic cells in S phase and cells with >4 N DNA. Results with synchronized cells are similar, showing that cells in the early S phase are more sensitive to hypertonicity. Immunocytochemistry revealed that p53 becomes phosphorylated on Ser(15) and translocates to the nucleus in S both in isotonic and hypertonic conditions. Caffeine (2 mM) greatly reduces the p53 level and Ser(15) phosphorylation, followed by a remarkable increase of DNA replication rate, by failure of hypertonicity to inhibit it, and by reduction of cell number during hypertonicity. Finally, inhibition of DNA replication by the DNA polymerase inhibitor aphidicolin significantly improves cell survival, confirming that keeping cells in G(1) and decreasing the rate of DNA replication is protective and that these actions of p53 most likely are what normally help protect cells against hypertonicity.
 ...
PMID:p53 Protects renal inner medullary cells from hypertonic stress by restricting DNA replication. 1150 1

Checkpoints activated in response to DNA damage cause arrest in the G(1) and G(2) phases of the cell cycle. Inhibitors of the G(2) checkpoint may be used as tools to study this response and also to increase the effectiveness of DNA-damaging therapies against cancers lacking p53 function. Using a cell-based assay for G(2) checkpoint inhibitors, we have screened extracts from the NCI National Institutes of Health Natural Products Repository and have identified 13-hydroxy-15-oxozoapatlin (OZ) from the African tree Parinari curatellifolia. Flow cytometry with a mitosis-specific antibody showed that checkpoint inhibition by OZ was maximal at 10 microm, which released 20% of irradiated MCF-7 cells expressing defective p53 and 30% of irradiated HCT116p53(-/-) cells from G(2) arrest. OZ additively increased the response to the checkpoint inhibitors isogranulatimide and debromohymenialdisine, but it did not augment the effects of UCN-01 or caffeine. Unlike other checkpoint inhibitors, OZ did not inhibit ataxia-telangiectasia mutated (ATM), ATM and Rad3-related (ATR), Chk1, Chk2, Plk1, or Ser/Thr protein phosphatases in vitro. Treatment with OZ also caused G(2)-arrested and cycling cells to arrest in mitosis in a state resembling prometaphase. In these cells, the chromosomes were condensed and scattered over disordered mitotic spindles. The results demonstrate that OZ is both a G(2) checkpoint inhibitor and an antimitotic agent.
 ...
PMID:G2 DNA damage checkpoint inhibition and antimitotic activity of 13-hydroxy-15-oxozoapatlin. 1157 54

DNA damage checkpoints are complex signal transduction pathways that are critical for normal cellular recovery following potentially lethal genotoxic insults. The ataxia-telangiectasia mutated (ATM) protein kinase is a critical component in these pathways and integrates the cellular response to damage by phosphorylating key proteins involved in cell cycle regulation and DNA repair. Lack of normal ATM function in the inherited ataxia-telangiectasia (A-T) syndrome results in a pleiotropic clinical syndrome characterized by a marked increased risk of cancer and profound hypersensitivity to ionizing radiation. Cells derived from patients with A-T share some of these attributes with genomic instability, loss of normal cell cycle arrest pathways, defects in DNA repair and increased radiation sensitivity. The radiosensitivity of A-T cells suggests that pharmacological inhibitors of the ATM kinase should be effective radiosensitizing agents. In fact, caffeine inhibits ATM kinase activity at concentrations that result in an A-T-like phenotype with loss of cell cycle checkpoints and hypersensitivity to ionizing radiation. Although the clinical use of caffeine as a radiosensitizer is limited by potentially lethal systemic toxicities, more potent methyl xanthines may selectively inhibit the ATM pathway at clinically achievable levels. Interestingly, caffeine and other methyl xanthines preferentially radiosensitize cells that lack normal p53 function. Because p53 is commonly inactivated in epithelial malignancies, this suggests that small molecule inhibitors of ATM might selectively sensitize the majority of tumors to the lethal effects of ionizing radiation while sparing normal tissues.
 ...
PMID:ATM as a target for novel radiosensitizers. 1167 56

We have isolated and characterized an isoform of protein kinase Chk1 gene from rat liver and a rat liver cDNA library by 5'-rapid amplification of cDNA ends. The gene (Cil) contains the C-terminal region of the Chk1 gene, but the 5'-end is derived from a sequence in the intron of Chk1 preceding the C-terminal domain by differential RNA splicing. The kinase domain of Chk1 gene is absent in this isoform. Tissue RNA and protein blot analyses indicated that Cil was specifically expressed only in rat liver, and its expression increased with liver development. Expression of Cil was found to be reduced in three rat hepatoma cell lines examined. A promoter trap experiment suggested that a promoter was located in the intron preceding the C-terminal domain of Chk1, and transcription from this novel promoter generated the new 5' noncoding exon of Cil. Thus Cil was generated by both alternate promoter usage and differential RNA splicing. UV irradiation induced caffeine-sensitive phosphorylation of both Chk1 and Cil at Ser-345 in Chk1 and its equivalent site in Cil, implying a role for ATR kinase in the phosphorylation of both proteins. We demonstrated the interaction between the kinase domain of Chk1 and Cil using a yeast two-hybrid assay and pull-down technique. In contrast to the effect of Chk1, Cil was found to decrease the transactivating function of p53, and the S63A mutation of Cil abolished this effect. These results suggest that Cil may serve as a dominant negative competitor of Chk1 as suggested previously.
 ...
PMID:Cloning and characterization of liver-specific isoform of Chk1 gene from rat. 1168 78

In the literature the sensitization of DNA to radiation-induced damage by caffeine has been attributed to an override of the G2/M block. This process was supposed to involve the tumor suppressor gene p53 as it was described that p53 negative cells were more sensitive to checkpoint inhibition by caffeine than the wildtype phenotype. We have recently shown that caffeine does not cause an override of the G2/M block induced by radiation in normal human fibroblasts. We demonstrate here that this also applies to a human transformed cell line, the thyroid carcinoma K1, when submitted to gamma- rays irradiation. Within 9 hr after irradiation over 70% of the cells accumulated in the G2/M phase. This block persisted at 16 hr. In caffeine containing cultures the percentage of cells attaining the G2/M phase was reduced by over 30% at 16 hr. This was reflected in an accumulation of the cells in G1 phase and an inhibition of the S phase traverse. Cell cycle analyses from further time points combined with cell proliferation measurements confirmed these data. These results were independent of p53 status as experiments performed with variant K1 cell lines having defective p53 functions, led to similar conclusions. In addition, caffeine restored a G1 delay after irradiation in the cell lines with abrogated p53 functions. The effects of caffeine undeniably cumulate with damages induced by irradiation but probably by inhibiting DNA repair mechanisms or by intervening with purine and pyrimidine metabolisms and not by causing a G2/M block override.
 ...
PMID:Caffeine and the G2/M block override: a concept resulting from a misleading cell kinetic delay, independent of functional p53. 1174 15

Caffeine is a model radiosensitizing agent that is thought to work by abrogating the radiation-induced G(2)-phase checkpoint. In this study, we examined the effect that various concentrations of caffeine had on cell cycle checkpoints and apoptosis in cells of a human lung carcinoma cell line and found that a concentration of 0.5 mM caffeine could abrogate the G(2)-phase arrest normally seen after exposure to ionizing radiation. Surprisingly, at a concentration of 5 mM, caffeine not only induced apoptosis by itself and acted synergistically to enhance radiation-induced apoptosis, but also induced a TP53-independent G(1)-phase arrest. Examination of the molecular mechanisms by which caffeine produced these effects revealed that caffeine had opposing effects on different cyclin-dependent kinases. CDK2 activity was suppressed by caffeine, whereas activity of CDC2 was enhanced by suppressing phosphorylation on Tyr15 and by interfering with 14-3-3 binding to CDC25C. These data indicate that the effect of caffeine on cell cycle checkpoints and apoptosis is dependent on dose and that caffeine acts through differential regulation of cyclin-dependent kinase activity.
 ...
PMID:Caffeine induces TP53-independent G(1)-phase arrest and apoptosis in human lung tumor cells in a dose-dependent manner. 1183 80

We have investigated the mechanism of S-phase arrest elicited by the carcinogen benzo(a)pyrene dihydrodiol epoxide (BPDE) in p53-deficient cells. Inhibition of DNA synthesis after BPDE treatment was rapid and dose dependent (approximately 50% inhibition after 2 h with 50 nM BPDE). Cells treated with low doses (50-100 nM) of BPDE resumed DNA synthesis after a delay of approximately 4-8 h, whereas cells that received high doses of BPDE (600 nM) failed to recover from S-phase arrest. The checkpoint kinase Chk1 (but not Chk2) was phosphorylated after treatment with low doses of BPDE. High concentrations of BPDE elicited phosphorylation of both Chk1 and Chk2. Adenovirus-mediated expression of "dominant-negative" Chk1 (but not dominant-negative Chk2) and the Chk1 inhibitor UCN-01 abrogated the S-phase delay elicited by low doses of BPDE. Consistent with a role for the caffeine-sensitive ATM or ATR protein kinase in low-dose BPDE-induced S-phase arrest, both Chk1 phosphorylation and S-phase arrest were abrogated by caffeine. However, low doses of BPDE elicited Chk1 phosphorylation and S-phase arrest in AT cells (from ataxia telangiectasia patients), demonstrating that ATM is dispensable for S-phase checkpoint responses to this genotoxin. BPDE-induced Chk1 phosphorylation and S-phase arrest were abrogated by caffeine treatment in AT cells, suggesting that a caffeine-sensitive kinase other than ATM is an important mediator of responses to BPDE-adducted DNA. Overall, our data demonstrate the existence of a caffeine-sensitive, Chk1-mediated, S-phase checkpoint that is operational in response to BPDE.
 ...
PMID:Carcinogen-induced S-phase arrest is Chk1 mediated and caffeine sensitive. 1186 11


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>