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: EC:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DNA chip technology was used in an attempt to identify target genes responsible for apoptosis induced by etoposide, a p53 activating topoisomerase II inhibitor used clinically as an antitumor agent. 62 Individual mRNAs whose mass changed significantly were identified after screening oligonucleotide arrays capable of detecting 6591 unique human mRNA species. 12 (Nine induced and three repressed) of the etoposide-responsive genes were further studied by Northern analysis and an agreement rate of 92%, was reached. Among the 12 genes studied, two (WAF1/p21 and PCNA) are known p53 regulatory genes, two (glutathione peroxidase and S100A2 calcium-binding protein) appear to be the novel p53 target genes and the others appear to be p53-independent. Based upon these findings, the signalling pathways that possibly mediate etoposide-induced apoptosis are proposed.
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PMID:Identification of the genes responsive to etoposide-induced apoptosis: application of DNA chip technology. 1009 70

The eucaryotic cell cycle is regulated by the periodic synthesis and destruction of cyclins that associate with and activate cyclin-dependent kinases. Cyclin-dependent kinase inhibitors, such as p21 and p16, also play important roles in cell cycle control by coordinating internal and external signals and impeding proliferation at several key checkpoints. Understanding how these proteins interact to regulate the cell cycle has become increasingly important to researchers and clinicians with the discovery that many of the genes that encode cell cycle regulatory activities are targets for alterations that underlie the development of cancer. Several therapeutic agents, such as DNA-damaging drugs, microtubule inhibitors, antimetabolites, and topoisomerase inhibitors, take advantage of this disruption in normal cell cycle regulation to target checkpoint controls and ultimately induce growth arrest or apoptosis of neoplastic cells. Other therapeutic drugs being developed, such as UCN-01, specifically inhibit cell cycle regulatory proteins.
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PMID:Cyclins and cell cycle checkpoints. 1033 Oct 86

We examined the effect of overexpression of p21(waf1) on cytotoxicity of paclitaxel, a microtubule stabilizer, using a tetracycline-inducible expression system in human sarcoma cells (SaOs-2) that lack both functional retinoblastoma protein and p53. Under normal growth conditions, p21(waf1) is not detectable in SaOs-2 cells. Upon p21(waf1) induction by tetracycline withdrawal, we observed a reduced apoptotic response to paclitaxel with a 3- to 6-fold increase in IC50 values compared with that of cells not induced by p21(waf1). We also observed a 5-fold increase in the IC50 value when cytotoxicity to vincristine, another microtubule-disrupting agent, was assessed, whereas we observed a marked decrease in the IC50 value after p21(waf1) induction in response to etoposide, a topoisomerase II inhibitor. After treatment with paclitaxel, less accumulation of G2-M was observed in p21(waf1)-induced cells compared with non-p21(waf1)-induced cells (57% versus 74%). p21(waf1) induction also inhibited the increased cyclin B1-associated kinase activity induced by paclitaxel. Overexpression of p21(waf1) in SaOs-2 cells lacking both p53 and functional retinoblastoma protein may decrease the G2-M arrest induced by paclitaxel due to suppression of the S-G2 checkpoint, resulting in a decreased apoptotic response of cells to paclitaxel.
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PMID:Overexpression of p21(waf1) decreases G2-M arrest and apoptosis induced by paclitaxel in human sarcoma cells lacking both p53 and functional Rb protein. 1034 52

Somatic changes in CpG dinucleotide methylation occur quite commonly in human cancer cell DNA. Relative to DNA from normal human colonic cells, DNA from human colorectal cancer cells typically displays regional CpG dinucleotide hypermethylation amid global CpG dinucleotide hypomethylation. The role of the maintenance DNA methyltransferase (DNMT1) in the acquisition of such abnormal CpG dinucleotide methylation changes in colorectal cancer cells remains controversial; in one study, 60-200-fold increases in DNMT1 mRNA expression were detected in colorectal polyps and cancers relative to normal colonic tissue [W. S. El-Deiry et al., Proc. Natl. Acad. Sci. USA, 88: 3470-3474, 1991], whereas in another study, only small increases in DNMT1 mRNA expression, commensurate with differences in cell proliferation accompanying colonic tumorigenesis, were observed [P. J. Lee et al., Proc. Natl. Acad. Sci. USA, 93: 10366-10370, 1996]. To definitively ascertain whether abnormal DNMT1 expression might accompany human colorectal carcinogenesis, we subjected a series of normal and neoplastic colonic tissues to immunohistochemical staining using a polyclonal antiserum raised against a DNMT1 polypeptide. A concordance of DNMT1 expression with the expression of PCNA and other cell proliferation markers, such as Ki-67 and DNA topoisomerase IIalpha, was observed in normal colonic epithelial cells and in cells comprising other normal epithelia and lymphoid tissues. The polypeptide p21, which has been reported to undermine DNMT1 binding to proliferating cell nuclear antigen at DNA replication sites, was not expressed by normal colonic cells containing DNMT1 and other cell proliferation markers. In adenomatous polyps, although DNMT1 expression coincided with the expression of other cell proliferation markers, many DNMT1-expressing cells also expressed p21. The fidelity of DNMT1 expression was further undermined in colorectal carcinomas, in which a striking heterogeneity in DNMT1 expression, with some carcinoma cells containing very high DNMT1 levels and others containing very low DNMT1 levels, was observed. These results indicate that human colorectal carcinogenesis is accompanied by a progressive dysregulation of DNMT1 expression and suggest that abnormalities in DNMT1 expression may contribute to the abnormal CpG dinucleotide methylation changes characteristic of human colorectal carcinoma cell DNA.
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PMID:Abnormal regulation of DNA methyltransferase expression during colorectal carcinogenesis. 1046 69

Drug resistance is a major problem in patients with small cell lung cancer; in fact, most die of resistant disease, despite an initial response. Several markers of drug resistance have been described in preclinical models, but the mechanism of drug resistance in lung cancer patients remains unknown. The objective of this study was to evaluate the role of the expression of a number of markers of drug resistance, proliferation, and apoptosis in relation to response to chemotherapy and survival in patients with small cell lung cancer. Tumor samples were derived from 93 previously untreated patients who were randomized in a Phase III study to receive cyclophosphamide, epirubicine, and etoposide or cyclophosphamide, epirubicine and vincristine alternating with carboplatin and etoposide. Paraffin-embedded samples, derived from the primary tumor site prior to chemotherapy, were analyzed by immunohistochemistry for expression of markers implicated in drug resistance [topoisomerase (topo) IIalpha, topo IIbeta, and multidrug resistance-associated protein], apoptosis (p53, p21, and bcl-2), or proliferation (Ki67). Response prediction was analyzed by chi2 test and logistic regression analysis; overall and disease-free survival curves were compared by log-rank test and Cox regression analysis. Shorter survival was observed in patients with extensive disease (P = 0.037) and poorer performance status (P = 0.028) and in patients whose tumors expressed high topo IIalpha levels (P = 0.01) and high Ki67 (P = 0.024). By multivariate analysis, the following factors were found to be predictive for worse survival: high expression levels of topo IIalpha, Ki67, and bcl-2; male sex; and extensive disease. High topo IIbeta expression was found to be predictive for lower overall and complete response rate. No relationship between apoptotic pathway markers or MRP and response to chemotherapy was observed. In conclusion, high expression of topo IIalpha was predictive of worse survival, and high expression of topo IIbeta was predictive of lower response rates. Furthermore, lower survival probability was observed in patients with bcl-2-positive tumors. Immunohistochemical assessment of these markers in diagnostic biopsies may give important prognostic information and may help selecting patients in the worse prognostic categories for new therapeutic strategies.
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PMID:Expression of DNA topoisomerase IIalpha and topoisomerase IIbeta genes predicts survival and response to chemotherapy in patients with small cell lung cancer. 1047 85

Overexpressed MDM2 inactivates wild-type (wt) p53 in various human tumors. However, whether and how the wild-type p53 can be activated by anticancer drug treatment in the presence of excess MDM2 is still unclear. In the present study, we showed that the topoisomerase II inhibitor of widely used anticancer drugs etoposide and doxorubicin activated wt p53 in BL2, a Burkitt's lymphoma cell line which overexpressed MDM2. Activation of p53 was followed by apoptosis in BL2 cells, while the same drug treatment did not induce apoptosis in Raji cells, another Burkitt's lymphoma cell line which carried mutant p53. Activation of p53 was accompanied by phosphorylation of p53 at Ser-15 and elevated p21 and MDM2, both of which were at least partly blocked by wortmannin, a kinase inhibitor against proteins with a PI3 kinase domain. Although MDM2 protein was rapidly cleaved and degraded after anticancer drug treatment, cotreatment with caspase inhibitor Z-VAD blocked degradation, while wt p53 remained activated, suggesting MDM2 degradation not to be essential for the activation of p53. Treatment with proteasome inhibitor stabilized p53 without being further phosphorylated. This p53 was co-immunoprecipitated with MDM2, but p53 activated by etoposide or doxorubicin barely complexed with MDM2. These results suggest that the wild-type p53 in MDM2-overexpressing cells can be activated by anticancer drugs through phosphorylation of p53, alleviating inhibitory action by MDM2, and activating caspases which in turn downregulates MDM2. The activation of p53 in MDM2-overexpressing tumor cells, which does not require the downregulation of MDM2, may have important implications in cancer therapy.
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PMID:Activation of p53 in MDM2-overexpressing cells through phosphorylation. 1054 21

The mixed lineage leukemia (MLL) gene located at chromosome band 11q23 is frequently rearranged in patients with therapy-related acute monocytic leukemia who received topoisomerase II inhibitors. We have identified a novel fusion partner of MLL (FAB M5b) in a patient who developed t-AML 9 years after treatment for acute lymphoblastic leukemia (ALL). The leukemic cells had a sole karyotypic abnormality of t(3;11) (p21;q23). Screening of a genomic DNA library, prepared from leukemic cell DNA, identified rearranged clones composed of MLL and a novel gene on chromosome 3p21 (AF3p21). The AF3p21 gene encodes a protein of 722 amino acids, which contains an Src homology 3 (SH3) domain, a proline-rich domain, and a bipartite nuclear localizing signal (NLS). RNA analysis demonstrated that exon 6 of the MLL gene fused to exon 2 of the AF3p21 gene. The resulting chimeric protein consists of AT-hooks, methyltransferase, and transcription repressor domains of MLL in addition to the AF3p21 proline-rich domain and NLS but not the AF3p21 SH3 domain.
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PMID:Novel SH3 protein encoded by the AF3p21 gene is fused to the mixed lineage leukemia protein in a therapy-related leukemia with t(3;11) (p21;q23). 1064 23

Deoxynybomycin was identified as an inducer of p21the/WAF1 gene following screening using a reporter, p21/luciferase. The present study examined its anti-proliferative effect on human tumor cell lines. Deoxynybomycin selectively inhibited growth of human osteoblastic sarcoma Saos-2, gastric cancer TMK-1, and monocytic leukemia THP-1 cells, but did not affect survival of normal human fibroblasts at doses up to 5 microg/ml. Results from an assay system using a panel of 39 human cancer cell lines indicated that deoxynybomycin has selective cytotoxic activity against lung carcinoma cell lines. Deoxynybomycin induced apoptosis in Saos-2, TMK-1, and THP-1 cells as revealed by DNA fragmentation and TUNEL assays. It inhibited topoisomerase I but not topoisomerase II. These results suggest that deoxynybomycin may be useful in cancer chemotherapy.
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PMID:Deoxynybomycin is a selective anti-tumor agent inducing apoptosis and inhibiting topoisomerase I. 1099

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

Recurrent respiratory papillomatosis (RRP) has a juvenile aggressive form and an adult more indolent form. Most cases of RRP are cytologically benign; however, some undergo malignant transformation. At present, there are no known markers that help identify patients at risk for aggressive disease. We investigated by immunohistochemistry expressions of topoisomerase alpha II, MIB-1, p53, p21, E-cadherin, retinoblastoma (RB) gene protein product, HER-2/neu, and steroid hormone receptors in a case of juvenile respiratory papillomatosis with malignant transformation to determine whether these markers are associated with malignant transformation. Histologic examination of the pulmonary lobectomy specimen revealed well-differentiated squamous carcinoma and invasive papillomatosis. Increased staining was found in areas of invasive papillomatosis for topoisomerase alpha II, p53, and MIB-1, with highest labeling indices in areas of squamous carcinoma. Staining intensity for RB gene protein product showed gradual decline from benign papilloma (3+) and invasive papillomatosis (2+) to squamous carcinoma (0-1+). Expression of p21 was similar in benign papilloma and invasive papillomatosis but showed reduction in squamous carcinoma. Expressions of E-cadherin, HER-2/neu, and steroid hormone receptors did not appear to correlate with biologic behavior. Increased topoisomerase alpha II and p53 expression along with reduced RB gene protein product and p21 expression may serve as markers of transformation to invasive papillomatosis and squamous carcinoma.
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PMID:Topoisomerase alpha II, retinoblastoma gene product, and p53: potential relationships with aggressive behavior and malignant transformation in recurrent respiratory papillomatosis. 1127 21


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