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)

Inherited susceptibility to a wide variety of neoplasias (Li-Fraumeni syndrome), has been shown in studies of one cancer-prone family, to have an intriguing association with an aberrant c-raf-1 gene and inheritance of a radioresistant phenotype in their non-cancerous skin fibroblasts. This association together with observations that DNA topoisomerases, when defective, can introduce errors into DNA and that these enzymes are perturbed in vitro by serine/threonine kinases similar to raf encoded proteins, prompted investigation of DNA topoisomerase activity of the family's fibroblasts. Since radioresistance was transferred to murine cells (NIH-3T3) when the aberrant c-raf-1 gene from this family was transfected, we also examined transformants containing this and other oncogenes. V-raf/c-myc and EJ-ras transformants were examined, the former because the family's skin fibroblasts also have 3-8-fold elevated myc expression (not apparently relevant to radioresistance) and the latter because ras, like raf, conveys radioresistance. The family members' fibroblasts and the three transfected murine lines, showed a similar perturbation of a spermidine and ATP-dependent DNA catenation activity (typical of DNA topoisomerase II). There was a significant positive correlation (r = 0.93; P = 0.0026) between the degree of activation of topoisomerase II and one measure of radioresistance (the Dq value). Relaxation of DNA supercoiling (topoisomerase I activity and other DNA nicking enzymes) was not abnormal. Cytotoxicity assays and evaluation of the influence of topoisomerase II inhibitors on DNA/protein complex formation, corroborated the existence of a qualitative topoisomerase II defect in the family's cells and transfectants. Although the contention that the qualitative topoisomerase II abnormalities observed here may be associated with malfunction is highly speculative, these findings may be relevant to the mechanism of oncogenesis, not only in this family, but with raf and ras type oncogenes.
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PMID:Aberrant DNA topoisomerase II activity, radioresistance and inherited susceptibility to cancer. 184 52

beta-Lapachone and certain of its derivatives directly bind and inhibit topoisomerase I (Topo I) DNA unwinding activity and form DNA-Topo I complexes, which are not resolvable by SDS-K+ assays. We show that beta-lapachone can induce apoptosis in certain cells, such as in human promyelocytic leukemia (HL-60) and human prostate cancer (DU-145, PC-3, and LNCaP) cells, as also described by Li et al. (Cancer Res., 55: 0000-0000, 1995). Characteristic 180-200-bp oligonucleosome DNA laddering and fragmented DNA-containing apoptotic cells via flow cytometry and morphological examinations were observed in 4 h in HL-60 cells after a 4-h, > or = 0.5 microM beta-lapachone exposure. HL-60 cells treated with camptothecin or topotecan resulted in greater apoptotic DNA laddering and apoptotic cell populations than comparable equitoxic concentrations of beta-lapachone, although beta-lapachone was a more effective Topo I inhibitor. beta-Lapachone treatment (4 h, 1-5 microM) resulted in a block at G0/G1, with decreases in S and G2/M phases and increases in apoptotic cell populations over time in HL-60 and three separate human prostate cancer (DU-145, PC-3, and LNCaP) cells. Similar treatments with topotecan or camptothecin (4 h, 1-5 microM) resulted in blockage of cells in S and apoptosis. Thus, beta-lapachone causes a block in G0/G1 of the cell cycle and induces apoptosis in cells before, or at early times during, DNA synthesis. These events are p53 independent, since PC-3 and HL-60 cells are null cells, LNCaP are wild-type, and DU-145 contain mutant p53, yet all undergo apoptosis after beta-lapachone treatment. Interestingly, beta-lapachone treatment of p53 wild type-containing prostate cancer cells (i.e., LNCaP) did not result in the induction of nuclear levels of p53 protein, as did camptothecin-treated cells. Like other Topo I inhibitors, beta-lapachone may induce apoptosis by locking Topo I onto DNA, blocking replication fork movement, and inducing apoptosis in a p53-independent fashion. beta-Lapachone and its derivatives, as well as other Topo I inhibitors, have potential clinical utility alone against human leukemia and prostate cancers.
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PMID:Beta-lapachone-mediated apoptosis in human promyelocytic leukemia (HL-60) and human prostate cancer cells: a p53-independent response. 764 Nov 80

The tumor suppressor protein p53 serves as a critical regulator of a G1 cell cycle checkpoint and of apoptosis following exposure of cells to DNA-damaging agents. The mechanism by which DNA-damaging agents elevate p53 protein levels to trigger G1/S arrest or cell death remains to be elucidated. In fact, whether damage to the DNA template itself participates in transducing the signal leading to p53 induction has not yet been demonstrated. We exposed human cell lines containing wild-type p53 alleles to several different DNA-damaging agents and found that agents which rapidly induce DNA strand breaks, such as ionizing radiation, bleomycin, and DNA topoisomerase-targeted drugs, rapidly triggered p53 protein elevations. In addition, we determined that camptothecin-stimulated trapping of topoisomerase I-DNA complexes was not sufficient to elevate p53 protein levels; rather, replication-associated DNA strand breaks were required. Furthermore, treatment of cells with the antimetabolite N(phosphonoacetyl)-L-aspartate (PALA) did not cause rapid p53 protein increases but resulted in delayed increases in p53 protein levels temporally correlated with the appearance of DNA strand breaks. Finally, we concluded that DNA strand breaks were sufficient for initiating p53-dependent signal transduction after finding that introduction of nucleases into cells by electroporation stimulated rapid p53 protein elevations. While DNA strand breaks appeared to be capable of triggering p53 induction, DNA lesions other than strand breaks did not. Exposure of normal cells and excision repair-deficient xeroderma pigmentosum cells to low doses of UV light, under conditions in which thymine dimers appear but DNA replication-associated strand breaks were prevented, resulted in p53 induction attributable to DNA strand breaks associated with excision repair. Our data indicate that DNA strand breaks are sufficient and probably necessary for p53 induction in cells with wild-type p53 alleles exposed to DNA-damaging agents.
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PMID:DNA strand breaks: the DNA template alterations that trigger p53-dependent DNA damage response pathways. 811 14

Cell cycle checkpoints regulate progression through the cell cycle. In yeast, loss of the G2 checkpoint by mutation of the rad9 gene results in increased genetic instability as well as increased sensitivity to ionizing radiation. In contrast, comparing clonogenic survival of cells which are isogeneic except for p53 functional status, we find that loss of a G1 checkpoint in mammalian cells is not associated with increased sensitivity to the lethal effects of ionizing radiation or a topoisomerase I inhibitor, camptothecin. These results indicate that increased sensitivity to DNA-damaging agents is not necessarily a defining feature of a mammalian cell cycle checkpoint. Furthermore, in light of a recent link of p53 function to radiation-induced apoptosis in hematopoietic cells, these observations suggest that p53-dependent apoptosis is a cell type-specific phenomenon and thus predict that the biological consequences of loss of p53 function will be cell type specific.
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PMID:Loss of a p53-associated G1 checkpoint does not decrease cell survival following DNA damage. 836 9

The tumor suppressor protein p53 plays a central role in the cellular response to genotoxic lesions and has been shown to be activated by most anticancer agents such as mitomycin C. We here show that mitomycin C treatment of human MCF7 breast adenocarcinoma cells results in increased topoisomerase I activity as measured by relaxation of supercoiled DNA and by phosphorylation of SR protein splicing factor. The increase in catalytic activity occurs in parallel with the nuclear accumulation of p53, resulting in detectable activation of topoisomerase I within less than 1 h of drug treatment. Furthermore, topoisomerase I co-immunoprecipitates with nuclear p53, suggesting that the activation of topoisomerase I may be a result of a direct interaction between the two proteins. In vitro experiments with purified recombinant proteins show that p53 increases the catalytic activities of topoisomerase I as measured by relaxation of supercoiled DNA, stabilization of the covalent topoisomerase I-DNA complex (in the presence of camptothecin), and phosphorylation of SR protein splicing factor ASF/SF2. Furthermore, topoisomerase I sediments at a higher molecular weight in the presence of p53 as revealed by sucrose density gradient analysis in the absence of DNA. Finally, p53 modifies the thermal stability of topoisomerase I, protecting it from heat denaturation. Taken together, our results show that topoisomerase I and p53 form molecular complexes in vitro as in vivo, and we suggest that the p53-mediated response to DNA damage may, at least in part, involve activation of topoisomerase I.
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PMID:Modulation of DNA topoisomerase I activity by p53. 863 38

We studied the role of proteases in apoptosis using a cell-free system prepared from a human leukemia cell line. HL60 cells are p53 null and extremely sensitive to a variety of apoptotic stimuli including DNA damage induced by the topoisomerase I inhibitor, camptothecin. We measured DNA fragmentation induced in isolated nuclei by cytosolic extracts using a filter elution assay. Cytosol from camptothecin-treated HL60 cells induced internucleosomal DNA fragmentation in nuclei from untreated cells. This fragmentation was suppressed by serine protease inhibitors. Serine proteases (trypsin, endoproteinase Glu-C, chymotrypsin A, and proteinase K) and papain by themselves induced DNA fragmentation in naive nuclei. This effect was enhanced in the presence of cytosol from untreated cells. Cysteine protease inhibitors (E-64, leupeptin, Ac-YVAD-CHO [ICE inhibitor]) did not affect camptothecin-induced DNA fragmentation. The apopain/Yama inhibitor, Ac-DEVD-CHO, and the proteasome inhibitor, MG-132, were also inactive both in the cell-free system and in whole cells. Interleukin-1 beta converting enzyme (ICE) or human immunodeficiency virus protease failed to induce DNA fragmentation in naive nuclei. Together, these results suggest that DNA damage activates serine protease(s) which in turn activate(s) nuclear endonuclease(s) during apoptosis in HL60 cells.
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PMID:DNA fragmentation induced by protease activation in p53-null human leukemia HL60 cells undergoing apoptosis following treatment with the topoisomerase I inhibitor camptothecin: cell-free system studies. 880 33

Binding of simian virus 40 (SV40) large T antigen to human and calf thymus topoisomerase I (topo I) was readily detected by using modified enzyme-linked immunosorbent assays and immunoblots. In addition to WT T antigen, binding could also be readily demonstrated with T antigen fragments from the amino-terminal region as well as with fragments missing this region, but much less so with small t antigen or with human p53. Antibody-blocking experiments showed that a monoclonal antibody that binds to the N-terminal region and several antibodies that recognize the central region of T antigen interfere with the binding to topo I. Our data are consistent with the existence of two separate topo I-binding regions in T antigen, one mapping within residues 82 to 246 and an apparently weaker one present after residue 246. By comparing the binding of T antigen to topo I with that of T antigen to DNA polymerase alpha or RPA, a single-stranded DNA-binding protein, it was determined that the T antigen-topo I interaction is much stronger and that the binding sites for topo I and DNA polymerase overlap, whereas the one for RPA differs. Several unwinding-defective mutants of T antigen were partially defective in their binding to topo I, suggesting that the binding to topo I is required for unwinding circular DNA. Finally, immunoprecipitation experiments demonstrated that T antigen can interact with DNA-bound topo I, indicating that such an interaction may take place during SV40 DNA replication.
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PMID:Simian virus 40 large T antigen binds to topoisomerase I. 880 20

Camptothecin (CPT) traps covalent DNA topoisomerase I-linked DNA single-strand breaks (cleavable complexes). To determine the differences in DNA damage signalling leading to differential sensitivity to CPT, two human colon cancer cell lines, SW620 and KM12, with nonfunctional p53 and the same level of topoisomerase I cleavable complex formation but differential sensitivity to CPT (Cancer Res. 56:4430-7; 1996) were studied. The levels of mRNA expression of DNA damage-inducible or death-related genes were measured at different times after CPT treatment. KM12 cells exhibited 3-fold higher basal levels of BCL-2 mRNA. Consistently, secondary DNA fragmentation, quantitated using a filter elution assay, was detected 24 h later and was 2-4-fold lower in KM12 cells than in SW620 cells. No induction of BAX was detected in either cell line. Consistent with the absence of functional p53, p21CIP1/WAF1 and GADD45 genes were not induced within the first 24 h. However, in SW620 cells, both mRNA levels were increased more than 10-fold at 48 h. The BCL-2-related gene MCL-1 and topoisomerase II mRNA were induced at 24 h, and topoisomerase I mRNA levels increased 3-fold at 48 h, only in SW620 cells. We conclude that cellular response to CPT-induced DNA damage can involve p53-independent pathways leading to the induction of p53-effector genes. Induction of these genes at the onset of apoptosis is associated with CPT sensitivity.
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PMID:Differential GADD45, p21CIP1/WAF1, MCL-1 and topoisomerase II gene induction and secondary DNA fragmentation after camptothecin-induced DNA damage in two mutant p53 human colon cancer cell lines. 893 95

Many antineoplastic drugs and cytotoxic irradiation induce apoptosis in cancer cells. ICE and ICE-like proteases play important roles in drug-induced apoptosis of cancer cells. We evaluated the cellular factors affecting susceptibility to apoptosis using gene-transfected cells. Introduction of bcl 2 gene into human small cell lung cancer cells conferred resistance to mitomycin C and irinotecan. DNA fragmentation was reduced in these cells. These results indicate apoptosis is one of the mechanisms of cell death caused by some antineoplastic drugs. Investigations are ongoing to elucidate the contribution of the Bcl 2 family proteins to antineoplastic drug induced apoptosis. Wild type p53-transfected cancer cells were sensitive to anticancer drugs. On the other hand, p53-depleted cells were reported to be more sensitive to taxanes than p53-proficient cells. Introduction of Rb gene and p16-gene enhanced cytotoxicity of taxanes and topoisomerase I inhibitors, respectively. In clinical studies, patients of non small cell lung cancer with high expression of Bcl-2 were reported to show longer survival than patients with lower expression. However, this result may be confusing because Bcl-2 reduced the efficacy of antineoplastic drugs. Further evaluation is required to determine the cellular proteins serving as markers for treatment efficacy or prognosis.
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PMID:[Apoptosis and chemosensitivity]. 903 Feb 34

Over the past 20 years ovarian cancer has provided a vivid illustration of the successes, failures and challenges for the medical oncologist. During that time the results of treatment have substantially improved; in the West of Scotland for example, for women aged under 55, 3-year survival rates have increased from 36% to 50%. One reason for this was probably the introduction of effective agents such as cisplatin in the mid-1970s and then carboplatin in the mid-1980s. The recent introduction of taxoids promises further improvement in the future. It is important to remember, however, that the best results will be obtained by an optimal organization for the delivery of treatment; national audit studies have shown that factors such as management in integrated clinics can have a major impact on outcome. Nevertheless, the majority of patients still die from the disease; when relapse occurs, clinical drug resistance eventually proves fatal despite further treatment. What are the fundamental mechanisms by which this resistance develops, and what means are available to attempt its circumvention? Factors involved could be described as pharmacological or cellular. Pharmacological resistance might best be addressed by increasing the doses of the drugs used, particularly, cis- or carboplatin. Three years ago we published the results of a randomized trial of 2 doses of cisplatin in 191 patients. At that stage a highly significant median survival advantage for the higher dose (100 mg/m2) of cisplatin was seen. However, a recent updated analysis with a median follow-up of 4 1/2 years shows a reduction in the survival benefit, with 4-year overall survival rates for high- and low-dose cisplatin of 32.4% and 26.6%, respectively. This suggests that a population of drug resistant ovarian cancer cells will eventually emerge despite the use of initial higher doses of cisplatin. A more dose-intensive approach is being pursued with carboplatin, and it seems clear that dose-increments over standard therapy of at least 4-fold will be necessary, to justify further randomized trials. Meanwhile, the alternative approach to delivering high drug concentrations, i.e. intraperitoneal (i.p.) chemotherapy, clearly merits further study, particularly in the light of a recently reported study in patients with minimal disease, which showed a significant survival benefit for i.p. cisplatin treatment. Cellular factors will probably prove to be crucial; studies using various cell lines suggest that multiple mechanisms are likely to be involved and these will need to be examined in relevant clinical material. After DNA damage induced by a range of cytotoxic agents has taken place in ovarian cancer cells, the key to sensitivity/resistance may well be the ability of these cells to engage the process of apoptosis. Several genes are involved in control of this process; these include the p53 gene, mutations of which have been linked to cisplatin resistance in our laboratory studies, as well as in clinical trials with carboplatin. We have also demonstrated an association in ovarian cancer cell lines between cisplatin resistance and microsatellite instability (indicative of defective mismatch repair) and the clinical relevance of this link is also being pursued. A thorough understanding of underlying mechanisms may lead to the rational development of therapeutic means for circumventing cisplatin-resistance in ovarian cancer; the emergence of new classes of drug such as taxoids as topoisomerase I inhibitors offers further promise of improvement in outcome in the next few years.
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PMID:Ovarian cancer, from the laboratory to the clinic: challenges for the future. 908 99


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