Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The p53 protein is a critical participant in a signal transduction pathway which mediates a G1 cell cycle arrest and apoptotic cell death in mammalian cells after ionizing irradiation. Cells from patients with the cancer-prone, radiation-sensitive disorder, ataxia-telangiectasia (AT), exhibit suboptimal (delayed and/or defective) induction of p53 protein after ionizing radiation with some dependence on dose. Other protein products which participate in this signal transduction pathway, including p21WAF1/CIP1, Gadd45, and Mdm2, are also suboptimally induced in AT cells after ionizing radiation. Induction of p53 is also abnormal in AT cells following treatment with methylmethanesulfonate and bleomycin but appears relatively normal following treatment with UV-C irradiation or the topoisomerase inhibitors, etoposide and camptothecin. These results demonstrate a specific defect in this p53-dependent signal transduction pathway in AT cells. Potential models for this observed specificity of the AT defect as measured by p53 induction include problems with responses to: (a) single-strand, but not double-strand, DNA breaks; or (b) chemically, but not enzymatically, generated DNA ends.
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PMID:The p53-dependent G1 cell cycle checkpoint pathway and ataxia-telangiectasia. 792 16

Molecular analysis of hereditary nonpolyposis colorectal carcinomas (HNPCC) has identified DNA mismatch repair deficiencies with resulting microsatellite instability (MSI) as a pathway of carcinogenesis that appears to be relevant for prognosis, treatment, and possibly prevention. In this study, expression of cell cycle proteins and other known prognostic markers is correlated with the microsatellite status of colorectal cancers (CRC). One hundred consecutive cases from the CRC Registry at Thomas Jefferson University were analyzed for MSI. Immunohistochemistry was performed for the mismatch repair proteins hMLH1 and hMSH2, tumor suppressor p53, apoptosis inhibitor bcl-2, cell cycle proteins p21(WAF1/CIP1), and p27 and the proliferation markers Ki-67 and topoisomerase II. High MSI (MSI-H) is significantly correlated with loss of either hMLH1 or hMSH2, presence of bcl-2, and absence of p53. p21(WAF1/CIP1) is positive in all tumors with MSI-H. Previous findings of a lower proliferation rate were confirmed with a topoisomerase II stain. Microsatellite stable (MSS) tumors generally express both MSH2 and MLH1. Other highly significant differences are positive p53 in 56% of MSS cases and negative bcl-2 in 98% of MSS cases. p27 expression is found in approximately 50% of all CRCs irrespective of the microsatellite status. MSI-H tumors follow the mutator pathway, with loss of expression of one mismatch repair protein, wild-type p53, lower proliferation, and positivity for p21(WAF1/CIP1). MSS tumors follow the suppressor pathway, characterized by p53 overexpression, higher proliferation, and absence of bcl-2 expression; p21(WAF1/CIP1) expression can be variable. These data provide a molecular basis for the clinical observation that patients with HNPCC appear to have a more favorable prognosis. HUM PATHOL 31:1506-1514.
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PMID:Colorectal carcinomas with high microsatellite instability: defining a distinct immunologic and molecular entity with respect to prognostic markers. 1115 Mar 76

Induction of p21 (WAF1/CIP1/SDI1), a physiological mediator of cell cycle arrest, inhibits multiple genes involved in cell division. We have investigated the determinants of p21- mediated inhibition of two of these genes, polo-like kinase 1 (PLK1) and topoisomerase IIalpha (TOPO IIalpha) p21 expression from an inducible promoter in human HT1080 cells rapidly decreases cellular levels of PLK1 and TOPO IIalpha promoters in transient and stable transfection assays. Promoter mutagenesis studies show that inhibition of the PLK1 promoter by p21 is mediated in part by tandem sequences CDE (cell cycle-dependent element) and CHR (cell cycle genes homology region). p21 response of the TOPO IIalpha promoter inhibition and the effects of promoter mutations differ under the conditions of growth arrest produced by p21 induction or by mimosine, a cell cycle inhibitor that increases p21 RNA but not protein expression in HT1080 cells. These results indicate that inhibition of cell division-associated genes by p21 is mediated by different but overlapping mechanisms, which are not a general con-sequence of cell cycle arrest.
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PMID:Identification of promoter elements responsible for transcriptional inhibition of polo-like kinase 1 and topoisomerase IIalpha genes by p21(WAF1/CIP1/SDI1). 1242 7

The TP63 gene, a member of the TP53 gene family, encodes several isoforms with (TAp63) or without (DeltaNp63) transactivating properties. Whereas the role of p63 in the normal development of squamous epithelia is well established, its function in other cell types remains to be elucidated. Here, we have analysed the expression of TA and DeltaNp63 isoforms in liver cells, by using both primary hepatocytes from wild type and p53-null mice and three human hepatocellular carcinoma (HCC) cell lines, according to the transformation state and the TP53 status of the cells. We observed the expression of DeltaNp63 isoforms only in a p53-null context. On the other hand, the expression of TAp63 isoforms was restricted to the HCC cell lines, whatever the TP53 status. We then studied the expression of TP63 upon genotoxic treatment. When treated with UVB or H(2)O(2), hepatocytes did not exhibit any change in p63 mRNA level. At the opposite, upon treatment with topoisomerase II inhibitors (doxorubicin or etoposide), the expression of TAp63 isoforms was clearly induced, independently of the TP53 status of cells. The same treatment did not induce any variation in the expression of DeltaNp63 isoforms, both at mRNA and protein levels. In HCC cell lines, doxorubicin or etoposide treatment also resulted in an increase of TAp63 transcripts only. This increase was accompanied by an increase in the intracellular level of TAp63 alpha protein. In parallel, we observed an upregulation of some p53-target genes related to cell cycle regulation, such as WAF1/CIP1, PIG3, 14-3-3sigma or GADD45, independently of the TP53 status of cells. In conclusion, we report for the first time that TA and DeltaNp63 alpha proteins are present in liver cells. Furthermore, our results suggest that p63 may partially substitute for wild-type p53, in counteracting uncontrolled liver cell proliferation in response to certain forms of DNA-damage.
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PMID:The expression of TA and DeltaNp63 are regulated by different mechanisms in liver cells. 1554 31

Genotoxic stress causes a variety of cellular and molecular responses in mammalian cells, including cell cycle arrest, DNA repair, and apoptosis. These responses result from the interplay between the genotoxic events themselves, and the biological context in which they occur. To better understand this interplay, we investigated cytotoxicty, mutagenesis, cell cycle profile, and global gene expression in the human TK6 lymphoblastoid cell line exposed to six genotoxicants. The six compounds have broad structural diversity and cause genotoxic stress by many different mechanisms, including covalent modification (methyl methanesulfonate, mitomycin C), reactive oxygen species (hydrogen peroxide, bleomycin), and topoisomerase II inhibition (etoposide and doxorubicin). Cell cycle analysis was performed 4 and 20 h following a 4 h chemical exposure. Cells exposed to all compounds experienced S-phase arrest at the 8h time point, but by 24 h had markedly different cell cycle responses. Cells exposed to compounds that cause covalent modification had a strong G2/M arrest at 24 h. These cells also had a robust (>25-fold) increase in mutant frequency, and had a moderate but sustained p53 response at 4, 8, and 24h, detectable as approximately 2-5-fold increases in transcript levels for p21WAF1/CIP1, GADD45alpha, BTG2, and cyclin G1. In contrast, cells exposed to the reactive oxygen compounds had little or no G2/M arrest at 24 h and no increase in mutant frequency. In addition, these compounds caused a strong but transient induction of the p53 pathway, detectable as 15-25-fold increases in p21WAF1/CIP1 transcription at 4 h that decreased dramatically by 8h and was near control levels at 24 h. Thus, the mutagenic effect of compounds was consistent with G2/M arrest and sustained kinetics of p53 pathway activation. Global gene expression data were also consistent with the mutagenesis data. Activation of genes associated with cell cycle arrest, the p53 and TNF-related pathways, and chemokines and chemokine receptors, were particularly evident for the reactive oxygen compounds. In contrast, the most mutagenic compounds caused fewer and less robust changes in global gene expression. There was therefore an inverse relationship between global gene expression and mutagenic potency.
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PMID:Relationships between genomic, cell cycle, and mutagenic responses of TK6 cells exposed to DNA damaging chemicals. 1610 33

The loss of p53 function is a key event in tumorigenesis. Inactivation of p53 in primary tumors and cell lines is mediated by several molecular mechanisms, including deletions and rearrangements. However, generation of a p53 fusion gene has not yet been reported. Here we report a novel p53/an autosomal homolog of the fragile X mental retardation (FXR2) chimeric gene generated by an interstitial deletion. Western blot analyses have shown that the p53/FXR2 protein is indeed expressed in a Down syndrome-related acute megakaryoblastic leukemia cell line, CMK11-5 cells. To investigate the properties of the p53/FXR2 protein, we observed its subcellular localization. Flag-tagged expression vectors were transfected into COS-7 cells and the proteins were stained with an anti-Flag antibody. The p53/FXR2 protein was expressed at high levels in the cytoplasm, whereas wild-type p53 and FXR2 were localized primarily in the nucleus and in the periphery of the nucleus, respectively. Treatment with a topoisomerase II inhibitor, VP16, failed to induce expression of a p53 target gene, the cyclin-dependent kinase inhibitor p21(WAF-1/CIP1), in CMK11-5 cells, and transient transfection analysis showed that the p53/FXR2 protein failed to transactivate the p21(WAF-1/CIP1) promoter. These results suggest that the p53/FXR2 fusion protein lacks the ability of wild-type p53 to function as a transcription factor. The p53/FXR2 gene is the first reported p53 fusion gene.
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PMID:Cloning and characterization of the novel chimeric gene p53/FXR2 in the acute megakaryoblastic leukemia cell line CMK11-5. 1677 63

Ochratoxin A (OTA) is a potent renal carcinogen, but little is known regarding the mechanism of OTA carcinogenicity. Early histopathological alterations induced by OTA in rat kidney include single cell death, stimulation of cell proliferation and prominent karyomegaly indicative of blocked nuclear division during mitosis. Based on these observations, it has been suggested that disruption of mitosis by OTA may be the principal cause of cell death and subsequent trigger for cell proliferation to compensate for cell loss. To gain further insight into the molecular mechanism of OTA toxicity, we used targeted quantitative real-time polymerase chain reaction arrays to investigate the expression of genes involved in cell cycle control and mitosis in kidneys of male F344 rats treated with 0, 21, 70 and 210 microg/kg body wt OTA for up to 90 days. Treatment with OTA resulted in overexpression of key regulators of mitosis, including the mitotic protein kinases Polo-like kinase 1, Aurora B and cyclin-dependent kinase 1 (Cdk1Cdc2), several cyclins and cyclin-dependent kinase inhibitors, topoisomerase II and survivin. Immunohistochemical analysis confirmed upregulation of Cdk1, p21(WAF1/CIP1), topoisomerase II and survivin in S3 proximal tubule cells, from which OTA-induced tumors in rats arise, and demonstrated increased phosphorylation of histone H3, a target of Aurora B. Importantly, many of the genes found to be deregulated in response to OTA have been linked to chromosomal instability and malignant transformation, supporting the hypothesis that aberrant mitosis, resulting in blocked or asymmetric cell division, accompanied by an increased risk of aneuploidy acquisition, may play a critical role in OTA carcinogenicity.
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PMID:Modulation of key regulators of mitosis linked to chromosomal instability is an early event in ochratoxin A carcinogenicity. 1923 4

The tumor suppressor p53 plays an important role in cellular emergency mechanisms through regulating the genes involved in cell cycle arrest and apoptosis. To identify small molecules that can activate p53-responsive transcription, we performed chemical screening using genetically engineered HCT116 reporter cells. We found that TopIn (7-phenyl-6H-[1,2,5]oxadiazolo[3,4-e]indole 3-oxide) efficiently activated p53-mediated transcriptional activity and induced phosphorylation of p53 at Ser15, thereby stabilizing the p53 protein. Furthermore, TopIn upregulated the expression of p21(WAF1/CIP1), a downstream target of p53, and suppressed cellular proliferation in various colon cancer cells. Additionally, TopIn induced DNA fragmentation, caspase-3/7 activation and poly ADP ribose polymerase cleavage, typical biochemical markers of apoptosis, in p53 wild-type and mutated colon cancer cells. Finally, we found that TopIn inhibited topoisomerase I activity, but not topoisomerase II, in vitro and induced the formation of the topoisomerase I-DNA complex in HCT116 colon cancer cells. Unlike camptothecin (CPT) and its derivative SN38, TopIn did not affect the activity of the ATP-binding cassette transporter breast cancer resistance protein (BCRP) or multidrug-resistant protein-1 (MDR-1). These results suggest that TopIn may present a promising new topoisomerase I-targeting anti-tumor therapeutics.
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PMID:Induction of apoptosis in colon cancer cells by a novel topoisomerase I inhibitor TopIn. 2154 95