Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: UNIPROT:P04637 (p53)
77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This paper studies the cytotoxic effect induced by the topoisomerase I inhibitor camptothecin in human osteosarcoma Saos-2 cells, which lack p53 and contain a non-functional form of the product of the retinoblastoma gene, pRb. Cytotoxicity induced by camptothecin was dose- and time-dependent; the treatment with 100 nM camptothecin reduced cell viability by 50% at 32 h and by 75% at 72 h of exposure. The cytotoxic effect was caused by apoptosis, as ascertained by morphological evidence, acridine orange-ethidium bromide staining and flow cytometric analysis. Apoptosis was accompanied by both the activation of caspase-3 and the fragmentation of poly(ADP-ribose) polymerase. Treatment with camptothecin caused a threefold increase in the activity of c-Jun N-terminal kinase (JNK) and an eightfold increase in the level of phosphorylated c-Jun. The introduction of the RB gene into Saos-2 cells reduced the rate of cell growth. Moreover, stable clones of transfected cells were resistant to camptothecin. Exposure to 100 nM camptothecin for 72 h reduced the viability of transfected cells by only 10%; moreover, very modest effects were observed on the activity of JNK as well as on the level of phosphorylated c-Jun. The results reported in this paper support the conclusion that the expression of wild-type pRb in Saos-2 cells exerts an anti-apoptotic influence through the control of JNK activity.
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PMID:pRb suppresses camptothecin-induced apoptosis in human osteosarcoma Saos-2 cells by inhibiting c-Jun N-terminal kinase. 1141 38

Neuronal death through activation of the p53 stress response pathway has been implicated in the pathogenesis of neurodegenerative disorders. The mechanisms regulating p53 accumulation and function in neurons are poorly understood. Recent evidence has demonstrated that Mdm2 is a major inhibitor of p53 that binds to and targets p53 for ubiquitin-mediated degradation. Here we demonstrate increased expression and co-localization of p53 and Mdm2 in the nuclei of degenerating neurons following treatment with either the excitotoxin, kainic acid, or the topoisomerase I inhibitor, camptothecin. Co-immunoprecipitation studies showed that p53-Mdm2 complexes were present in neuronal lysates. Dual immunofluorescence microscopy demonstrated that these complexes accumulated in neurons with a striking decrease in free ubiquitin levels. Exogenous ubiquitin restored p53 degradation to extracts from injured neurons confirming that Mdm2 function was intact. Finally, antisense-mediated downregulation of ubiquitin in cultured hippocampal neurons resulted in p53 and Mdm2 accumulation as well as apoptotic death. These results point to a novel mechanism to stabilize p53 and promote neuronal cell death in the central nervous system.
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PMID:Downregulation of free ubiquitin: a novel mechanism of p53 stabilization and neuronal cell death. 1145 8

The DNA mismatch repair (MMR) system is involved in the correction of base/base mismatches and insertion/deletion loops arising during replication. In addition, some of the MMR components participate in recombination and double-strand break repair as well as cell cycle regulation and apoptosis. The inactivation of MMR genes, usually hMSH2 or hMLH1, is associated with human colorectal cancers and is responsible for the characteristic microsatellite instability (MSI)+ phenotype of these tumors. Because MMR is assumed to modulate cytotoxicity to various chemotherapeutic agents that act upon DNA, our objectives have been to define its possible involvement in the cytotoxicity of topoisomerase inhibitors. We have shown that colorectal cancer cell lines defective in DNA MMR exhibit an increased sensitivity to both camptothecin, a topoisomerase I inhibitor, and etoposide, a topoisomerase II inhibitor. Sensitivity to these drugs cannot be predicted by measuring endogenous levels of topoisomerase I and II. Our results also indicate that neither p53 status, nor cell cycle alterations correlate with the sensitivity of colorectal cancer cells to topoisomerase inhibitors. On the other hand, our data showing that resistance to these drugs can be achieved by the functional complementation of hMLH1 in an hMLH1-defective cell line have allowed us to establish that MMR is a critical determinant for chemosensitivity. Interestingly, our observations provide the rationale for the better responsiveness of MSI+ tumors to CPT-11, a camptothecin derivative, which we have observed in patients with metastatic colorectal cancers.
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PMID:The role of the DNA mismatch repair system in the cytotoxicity of the topoisomerase inhibitors camptothecin and etoposide to human colorectal cancer cells. 1152 54

The cellular response to DNA damage involves checkpoint controls that delay cell cycle progression in order to provide time for repair of damaged DNA. Chk2/hCds1 is a recently identified homolog of the yeast Cds1 kinase that is involved in cell cycle checkpoint response to DNA damage. To investigate the functions of Chk2/hCds1 in response to DNA damage in mammalian cells, we established a stable human kidney embryonic cell line (HEK-293) that expresses antisense Chk2/hCds1 (Chk2AS) under the control of an inducible promoter. Cells that express Chk2AS display defective S-phase delay in response to DNA replication-mediated DNA damage induced by the topoisomerase I inhibitor camptothecin. The defective G2 checkpoint was also observed in Chk2AS cells exposed to the DNA damaging agent VP-16 or gamma-radiation. Enhanced apoptosis was observed in Chk2AS cells after exposure to gamma-radiation or camptothecin. No p53 activation was observed after DNA damage in HEK-293 or Chk2AS cells. Our results indicate that perturbation of Chk2/hCds1 expression adversely affects the S- and G2-phase checkpoints following DNA damage or DNA replication block, and suggest that reduced expression of Chk2/hCds1 might promote a p53-independent apoptotic response.
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PMID:Antisense inhibition of Chk2/hCds1 expression attenuates DNA damage-induced S and G2 checkpoints and enhances apoptotic activity in HEK-293 cells. 1155 32

The ability of DNA damage to stabilize p53 in all cell cycle stages has not been examined in actively growing cells. The chemotherapeutic drug camptothecin is a topoisomerase I poison. Zeocin is a member of the bleomycin/phleomycin family of antibiotics, known to bind DNA. Both increase the level of p53 albeit by different mechanisms. We have utilized centrifugal elutriation to separate exponentially growing ML-1 cells (containing wild-type p53) into cell cycle fractions and have subsequently treated these cells with the two drugs. We provide evidence that both drugs can mediate an increase in p53 protein levels independent of the cell cycle stage. The p53 induced by both drugs was able to bind to DNA; however, only the p53 induced by camptothecin was phosphorylated at serine-392. This is the first demonstration that camptothecin and Zeocin can differentially signal for increased levels of modified p53 during all stages of the cell cycle.
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PMID:Camptothecin and Zeocin can increase p53 levels during all cell cycle stages. 1174 Dec 90

The adeno-associated virus type 2 (AAV-2) Rep proteins are essential for AAV DNA replication and regulation of AAV gene expression. We have identified a cellular protein interacting with Rep78 and Rep68 in yeast two-hybrid analysis and in GST pull-down assays. This protein has recently been described as both a p53 (p53BP3) and a topoisomerase I interacting protein (Topors). It contains an arginine/serine-rich domain, a RING finger domain and five PEST sequences. A minimal sequence sufficient for interaction with Rep was mapped to Topors amino acids 871 to 917. We show that the same region is also involved in the interaction with p53. Rep sequences involved in interaction with Topors were mapped to Rep amino acids 172 to 481. Overexpression of Topors stimulated AAV gene expression in the absence of helper virus, suggesting a function of Topors as a transcriptional regulator.
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PMID:Topors, a p53 and topoisomerase I binding protein, interacts with the adeno-associated virus (AAV-2) Rep78/68 proteins and enhances AAV-2 gene expression. 1184 45

Treatment of cells with the anti-cancer drug camptothecin (CPT) induces topoisomerase I (Top1)-mediated DNA damage, which in turn affects cell proliferation and survival. In this report, we demonstrate that treatment of the wild-type HCT116 (wt HCT116) human colon cancer cell line and the isogenic p53(-/-) HCT116 and p21(-/-) HCT116 cell lines with a high concentration (250 nm) of CPT resulted in apoptosis, indicating that apoptosis occurred by a p53- and p21-independent mechanism. In contrast, treatment with a low concentration (20 nm) of CPT induced cell cycle arrest and senescence of the wt HCT116 cells, but apoptosis of the p53(-/-) HCT116 and p21(-/-) HCT116 cells. Further investigations indicated that p53-dependent expression of p21 blocked apoptosis of wt HCT116 cells treated with 20 nm, but not 250 nm CPT. Interestingly, blocking of the apoptotic pathway, by Z-VAD-FMK, in p21(-/-) HCT116 cells following treatment with 20 nm CPT did not permit the cells to develop properties of senescence. These observations demonstrated that p21 was required for senescence development of HCT116 cells following treatment with low concentrations of CPT.
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PMID:Role of p21 in apoptosis and senescence of human colon cancer cells treated with camptothecin. 1187 36

The expression of the death receptor Fas/CD95 is cell type-specific and can be modulated by different cytotoxic treatments. In spite of a frequent expression of Fas/CD95 in high-grade gliomas, these tumours are typically refractory to conventional therapy. Using a human glioblastoma cell line (GBM), we explored the possibility of modulating susceptibility to Fas/CD95-mediated apoptosis following cytotoxic treatment. GBM cells were sensitive to the antiproliferative effects of topoisomerase I inhibitors (topotecan and a novel lipophilic analog CPT83) and taxol, less sensitive to cisplatin and, in any case, rather resistant to drug-induced apoptosis. This pattern of cellular response was consistent with p53 mutation. GBM cells expressed low levels of Fas/CD95, which was associated with low susceptibility to antibody-stimulated Fas/CD95-mediated apoptosis. A significant up-regulation of Fas/CD95 expression was detected after exposure to topotecan and CPT83, whereas cisplatin induced a low increase and taxol did not modify Fas/CD95 expression. In addition, after treatment with topoisomerase I inhibitors, the up-regulation of Fas/CD95 resulted in an increased susceptibility of GBM cells to antibody-stimulated Fas/CD95-mediated apoptosis, while no synergistic effects were detected after treatment with cisplatin or taxol. Our data suggest that Fas/CD95 up-regulation can be a common response to DNA damage, whereas sensitisation to Fas/CD95-mediated apoptosis appears to be dependent on the type of DNA damage and on the pathway of cellular response. The observed effects might have important therapeutic implications for the design of novel therapeutic strategies in the treatment of malignant gliomas.
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PMID:Fas/CD95-mediated apoptosis in human glioblastoma cells: a target for sensitisation to topoisomerase I inhibitors. 1191 40

cDNA microarray technology can be used to establish associations between characteristic gene expression patterns and molecular responses to drug therapy. In this study, we used cDNA microarrays of 1694 cancer-related genes to monitor the gene expression consequences of the treatment of HCT116 colon cancer cells with the topoisomerase I inhibitor camptothecin (CPT). To obtain a more homogeneous cellular response, we synchronized the cells in S-phase using aphidicolin (APH) before CPT treatment. Brief incubation with 20 and 1000 nM CPT caused reversible and irreversible G(2) arrest, respectively, and the patterns of gene expression change (with reference to untreated controls) were strikingly different at the two concentrations. Thirty-three genes, mainly divided into three groups, showed characteristic changes in the first 20 h as a consequence of treatment. Northern blots performed for five of these genes (each under eight experimental conditions) were quite consistent with the microarray results (average correlation coefficient, 0.86). Several p53-activated stress response genes were up-regulated after treatment with 1000 nM CPT or prolonged exposure to APH, but it seemed that the up-regulation did not directly cause cell cycle arrest because the up-regulation induced by prolonged treatment with APH did not prevent cell cycle progression after removal of APH. In contrast, cell cycle-dependent up-regulation of a group of mitosis-related genes was delayed or blocked after CPT treatments. The interrupted up-regulation of this group of genes was directly associated with G(2) arrest. In addition, we observed down-regulation of gene expression in cells that were recovering from cell cycle delay. The observations reported here suggest a fundamental difference at the gene expression level between the molecular mechanism of reversible G(2) delay that follows mild DNA damage and the mechanism of permanent G(2) arrest that follows more extensive DNA damage.
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PMID:Transcriptional regulation of mitotic genes by camptothecin-induced DNA damage: microarray analysis of dose- and time-dependent effects. 1191 41

DNA damage causes cell cycle arrest in G(1), S, or G(2) to prevent replication on damaged DNA or to prevent aberrant mitosis. The G(1) arrest requires the p53 tumor suppressor, yet the topoisomerase I inhibitor SN38 induces p53 after the G(1) checkpoint such that the cells only arrest in S or G(2). Hence, SN38 facilitates comparison of p53 wild-type and mutant cells with regard to the efficacy of drugs such as 7-hydroxystaurosporine (UCN-01) that abrogate S and G(2) arrest. UCN-01 abrogated S and G(2) arrest in the p53 mutant breast tumor cell line MDA-MB-231 but not in the p53 wild-type breast line, MCF10a. This resistance to UCN-01 in the p53 wild-type cells correlated with suppression of cyclins A and B. In the p53 mutant cells, low concentrations of UCN-01 caused S phase cells to progress to G(2) before undergoing mitosis and death, whereas high concentrations caused rapid premature mitosis and death of S phase cells. UCN-01 inhibits Chk1/2, which should activate the mitosis-inducing phosphatase Cdc25C, yet this phosphatase remained inactive during S phase progression induced by low concentrations of UCN-01, probably because Cdc25C is also inhibited by the constitutive kinase, C-TAK1. High concentrations of UCN-01 caused rapid activation of Cdc25C, which is attributed to inhibition of C-TAK1, as well as Chk1/2. Hence, UCN-01 has multiple effects depending on concentration and cell phenotype that must be considered when investigating mechanisms of checkpoint regulation.
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PMID:Abrogation of the S phase DNA damage checkpoint results in S phase progression or premature mitosis depending on the concentration of 7-hydroxystaurosporine and the kinetics of Cdc25C activation. 1195 32


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