Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Toxins produced by marine phytoplankton represent a severe global health hazard to humans that eat seafood and are also responsible for massive natural fish kills in specialized bloom situations. Tumour-promoting hepatotoxins from the freshwater microcystin/nodularin class were identified in Northeastern Pacific Ocean, Eastern Canadian and European mussels for the first time. These hepatotoxins were detected at biologically active levels up to three-fold higher than accepted quarantine levels for the diarrhetic shellfish toxin okadaic acid (OA), based on their activity (in microcystin-LR equivalent units) in a liquid chromatography (LC)-linked protein phosphatase bioassay. The presence of microcystins/nodularins in oceanic shellfish identifies a potentially novel class of intoxication which is also prevalent in other forms of marine aquatic life, namely sponges and fish. The widespread presence of prokaryotic microcystins and nodularins in the marine environment may be indicative of the importance of signal transduction pathways involving potent inhibition of protein phosphatases in early marine eukaryotes.
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PMID:Identification of protein phosphatase inhibitors of the microcystin class in the marine environment. 831 Apr 42

We recently reported that tumor necrosis factor (TNF) induced the production of nitric oxide (NO) by TNF-sensitive, but not-resistant, tumor cells. Paradoxically, NO thus produced does not appear to be involved in the mechanism of TNF-mediated cytotoxicity as inhibitors of NO production and NO scavengers did not block cytotoxicity. Because the immunosuppressive drug cyclosporin A (CsA) inhibits several types of immune-mediated killing, we were interested in what effect CsA would have on TNF-mediated cytotoxicity as well as NO production. Treatment with CsA had no effect on the sensitivity L929 cells to TNF-mediated cytotoxicity, either in the presence or absence of interferon-gamma (IFN-gamma). In the presence of IFN-gamma alone, L929 cells were slightly less sensitive to the cytotoxic effects of TNF. In contrast to the effect on TNF-mediated cytotoxicity, CsA treatment had a profound effect on the ability of these cells to produce NO in response to TNF and IFN-gamma. Cells treated with CsA produced 75% less NO than did their untreated controls. Inhibition of calmodulin-dependent calcineurin-like phosphatases is one mechanism by which CsA may exert its effects. Therefore, we tested the effect of EGTA, which inhibits calcineurin by chelating calcium, on NO production and found that EGTA treatment resulted in a 15% decrease in the amount of NO produced. In addition, cells treated with the calmodulin antagonist W-13 produced 79% less NO than their untreated controls. Therefore, these results provide further evidence that NO produced by TNF-sensitive cells is not involved in the mechanism of TNF-mediated cytotoxicity because reduction of NO production by CsA has no effect on TNF-mediated killing of these same cells.
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PMID:Cyclosporin A inhibits nitric oxide production by L929 cells in response to tumor necrosis factor and interferon-gamma. 836 91

In these studies, Syrian hamster embryo cells (SHE), which were isolated at different stages of neoplastic progression, were used to test the ability of the protein phosphatase inhibitors, okadaic acid and sodium orthovanadate (Na3VO4) to induce neoplastic progression. We observed that these chemicals can induce transition of the cells from one stage to the other at different points in the multistep process of neoplastic transformation. Three steps in this multistep process were studied: escape from cellular senescence, loss of a tumor suppressor gene function in immortal cells, and aquisition of anchorage-independent growth. Treatment of normal, primary SHE cells with okadaic acid or Na3VO4 allowed the cells to escape senescence and become immortal at a low frequency. The induction of immortality was associated with nonrandom chromosome changes, including trisomy 8 and 11 and monosomy 13 and Xq. The transition of preneoplastic cells to more advanced stages was also studied in immortal, nontumorigenic cells that either have retained (supB+) or have lost (supB-) the ability to suppress tumorigenicity of a transformed cell line in cell hybrids. SupB+ and supB- cells do not normally grow in agar, but supB- cells will grow in agar if additional growth factors are added. However, upon addition of protein phosphatase inhibitors, supB+ cells exhibited the supB- phenotype; for example, colony formation of supB+ cells was observed in agar supplemented with growth factors and protein phosphatase inhibitors. Following treatment, selection of these colonies showed that 89% of these cells heritably acquired the phenotype of cells that have lost the suppressor gene function (supB-). SupB- cells were also treated with protein phosphatase inhibitors in soft agar in the presence of additional growth factors. While the frequency of colonies in agar supplemented with growth factors in agar was not greatly enhanced, approximately 50% of the colonies acquired the ability to grow in agar autonomously without the supplemented growth factors, similar to tumorigenic cells. These studies suggest that Na3VO4 and okadaic acid induce progression of cells through various stages in this multistep system.
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PMID:Induction of neoplastic progression in Syrian hamster embryo cells treated with protein phosphatase inhibitors. 838 70

Inhibition of protein phosphatases has been suggested as an alternative mechanism of tumor promotion (H. Fujiki, Mol. Carcinog. 5:91, 1992). We have now used early melanocyte passages dependent on phorbol esters and serum for growth and later passages with partial phorbol ester independence, to investigate the role of protein phosphatases on melanocyte DNA synthesis. Neither okadaic acid, an inhibitor of ser/thr protein phosphatases, nor vanadate, an inhibitor of tyrosine phosphatases, can stimulate basal or serum-stimulated mitogenesis in contrast to phorbol esters. Moreover, both phosphatase inhibitors are able to suppress serum and phorbol ester-stimulated mitogenesis, if added within 4 hours of growth activation. Inhibition of mitogenesis by either inhibitor correlated with an early increase in a common set of tyrosine phosphoproteins, which included a major 33 Kd species. Our data suggest that protein phosphatase inhibitors are growth suppressors and antagonize phorbol ester effects in cells of melanocytic origin, implying an early requirement for protein phosphatase activity during mitogenic signalling in these cells.
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PMID:Early inhibition of protein phosphatases preferentially blocks phorbol ester-stimulated mitogenic signalling in melanocytes: increase in specific tyrosine phosphoproteins. 838 79

Papovavirus tumor antigens have been shown to associate with the cellular phosphoserine/threonine-specific protein phosphatase 2A (PP2A). We were interested in the consequences that T-antigen association might have on PP2A activity and so studies of the phosphatase activity in immunoprecipitates, prepared from polyoma virus-transformed or polyoma virus-infected mouse 3T3 fibroblasts, were performed. The phosphoserine/threonine phosphatase activity, measured with phosphorylase a as the substrate, showed all the characteristics of PP2A. It was stimulated by polycations, inhibited by fluoride or p-nitrophenyl phosphate, sensitive to okadaic acid and microcystin and insensitive to inhibitor-1 and inhibitor-2. Phosphotyrosyl phosphatase (PTPase) activity was associated with the middle-T/small-T-associated complex when reduced, carboxamidomethylated and maleylated lysozyme, phosphorylated exclusively on tyrosyl residues, was used as the substrate. This PTPase activity was as sensitive to okadaic acid as was the phosphorylase phosphatase activity; it could be inhibited by phosphorylase a and did not dephosphorylate poly(Glu80Tyr20). The level of middle-T/small-T-associated PTPase activity relative to the phosphorylase phosphatase activity was tenfold higher than that of the purified dimeric PP2A. A similar activity ratio was observed with the purified phosphatase after stimulation with a cellular protein, designated phosphotyrosyl phosphatase activator. These results suggest that the same enzyme may possess dual specificity. In contrast to the cellular trimeric PP2A, containing the 55-kDa putative regulatory subunit, the middle-T/small-T-associated enzyme had low activity towards a retinoblastoma peptide phosphorylated by p34cdc2. These results indicate how middle-T/small-T might effect the activity of PP2A in polyoma virus-transformed cells.
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PMID:Phosphatase 2A associated with polyomavirus small-T or middle-T antigen is an okadaic acid-sensitive tyrosyl phosphatase. 838 2

An immunohistochemical study was carried out on four cases of central neurocytoma, which had characteristic clinicopathological features including ultrastructural findings. Specific antibodies to calcineurin (CaN), microtubule-associated protein 2 (MAP2) and synaptophysin (SYP) were used. All tumor tissues examined showed specific immunoreactivity for CaN and MAP2. Immunolabelling of both molecules revealed that they were mainly localized in the perikarya and proximal processes of the tumor cells. SYP immunoreactivity was found in three of the four cases. SYP immunoreaction products were predominantly seen in the tumor cell processes, while the perikarya were weakly or moderately positive for SYP. The data suggest that CaN and MAP2, together with SYP, can be useful tools for identifying and characterizing of the central neurocytoma.
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PMID:Immunocytochemical detection of calcineurin and microtubule-associated protein 2 in central neurocytoma. 841 Jan 38

The non-12-O-tetadecanoylphorbol-13-acetate (TPA)-type tumor promoters, okadaic acid (OA) and calyculin-A (CAL-A), which neither interact with the phorbol ester receptor nor directly activate protein kinase C, mimic the stimulatory effects of and thapsigargin on hydroperoxide (HPx) production in mouse epidermis in vivo. The time course and dose dependency for the stimulation of HPx production by O and TPA are similar. HPx production is maximally stimulated 16 h after two applications of 2 nmol of OA at a 48-h interval. However CAL-A is a stimulator of HPx production about 4 times more potent than OA or TPA. Combinations of TPA and OA or CAL-A have subadditive effects on HPx production. The discrepancies between the abilities of various serine/threonine protein phosphatase (PP) inhibitors to stimulate HPx production suggest that PP inhibition alone is not sufficient for this response. Cycloheximide, Ca2+ antagonists, oxypurinol, diphenyliodonium, nordihydroguaiaretic acid, bromophenacyl bromide, antiinflammatory agents, and antihistamines block or decrease OA-stimulated HPx production. Although most of these inhibitors may have more than one action, their effects suggest that protein synthesis, Ca2+, xanthine oxidase and NADPH oxidase activities, the lipoxygenase pathway of arachidonic acid metabolism, and vascular permeability may be involved in the inflammatory and HPx responses that occur after tumor promoter treatment. The increased HPx-producing activity of the epidermis, therefore, may be a common event resulting from the inflammatory and tumor-promoting actions of diverse TPA- and non-TPA-type agents.
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PMID:Ability of okadaic acid and other protein phosphatase inhibitors to mimic the stimulatory effects of 12-O-tetradecanoylphorbol-13-acetate on hydroperoxide production in mouse epidermis in vivo. 855 15

Several lines of evidence indicate that serine/threonine protein phosphatases may act as negative regulators of cellular growth. For example, treatment of cells with the tumor-promoter okadaic acid, an inhibitor of certain types of these phosphatases, resulted in the increased expression of several proto-oncogenes, indicating a negative role of the respective phosphatases in gene regulation. However, it was puzzling to find that okadaic acid-treated cells, even in the presence of highly expressed proto-oncogenes, did not proliferate, but were arrested at certain points of the cell cycle. To further analyze this discrepancy, we investigated the involvement of protein phosphatases in the control of other cell cycle regulatory genes, such as cdc2 which encodes an essential cell cycle regulatory kinase. We found that cdc2 gene expression was blocked by okadaic acid, but stimulated by protein phosphatase 2A. Protein phosphatase 2A is shown to be a positive regulator of cdc2 gene activity and to be required for cdc2 expression. Thus, our findings identify protein phosphatase 2A as a positive regulator of a major cell cycle regulatory gene and therefore suggest a stimulatory role of this enzyme in this aspect of cellular growth control.
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PMID:Positive regulation of cdc2 gene activity by protein phosphatase type 2A. 862 81

Epidermal growth factor (EGF), which plays an important role in the growth regulation of a large variety of normal and tumor cells, has been shown to display an ambivalent dose-dependent effect on the proliferation of epithelial cells overexpressing EGF receptor. In a previous study aimed at dissecting the biochemical events leading to this dual action in A431 cells which over express EGF receptor, we have reported a relationship between the dual stimulator/inhibitor effect of EGF and the activity of the serine/threonine p42 mitogen-activated protein (MAP) kinase. Indeed, a growth stimulatory concentration of EGF is shown to lead to a moderate but persistent activation of p42 MAP kinase. Conversely, an early peak of MAP kinase activation, that rapidly falls below the basal level, is observed in the presence of a growth-inhibitory concentration of EGF. To assess the mechanism of the p42 MAP kinase inactivation under circumstances of negative growth regulation by EGF, we have investigated the role of the serine/threonine phosphatase 2A in this process. A constitutive phosphatase 2A activity was observed in untreated cells, that decreases rapidly in response to both high and low EGF concentrations. However, after this early inactivation, the phosphatase 2A activity was completely reversed concurrently with MAP kinase inactivation, after 40 min of treatment with 10 nM EGF. Conversely, in cells treated with 1 pM EGF, phosphatase 2A activity remained below the control level during all the time of the treatment, in association with a sustained MAP kinase activation. These results suggest that MAP kinase inactivation is closely related to phosphatase 2A activation. We then investigated the effect of the serine/threonine phosphatase inhibitor okadaic acid on the MAP kinase inactivation and observed that okadaic acid, at a concentration reported to specifically inhibit phosphatase 2A activity, totally reverses the MAP kinase inactivation induced by long-term treatment with 10 nM EGF. Additionally, we have shown that the protein synthesis inhibitor cycloheximide fails to affect the EGF-induced MAP kinase regulation, indicating that mitogen-induced protein phosphatases are not, or are only slightly, required in this regulation. In conclusion, our data demonstrate that the ambivalent action of EGF on the proliferation of A431 cells is associated with differential mechanisms of p42 MAP kinase regulation catalysed by the serine/threonine phosphatase 2A.
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PMID:Regulation of p42 mitogen-activated-protein kinase activity by protein phosphatase 2A under conditions of growth inhibition by epidermal growth factor in A431 cells. 863 73

Fostriecin is an antitumor drug in phase I clinical trials. We have recently shown that it is a potent inhibitor of protein phosphatases 1 and 2A in vitro, a property not previously described for an antitumor drug. We have investigated its effects on protein phosphorylation in baby hamster kidney cells. Fostriecin strongly stimulated the phosphorylation of a single protein, which we identified as the intermediate filament vimentin. Fostriecin also caused rounding of the cells and a reorganization of the vimentin filaments. These effects are similar to those of the known protein phosphatase 1 and 2A inhibitors okadaic acid and calyculin A, which are also tumor promoters. Fostriecin induced vimentin hyperphosphorylation mostly at two sites, which were sensitive to staurosporine and could be phosphorylated by protein kinase C in vitro. Fostriecin-induced vimentin hyperphosphorylation also occurred in cells that lack p34cdc2 kinase activity. These results suggest that protein kinase C plays a direct or indirect role in vimentin hyperphosphorylation during exposure to fostriecin. The results also provide strong evidence that fostriecin inhibits protein phosphatases 1 and 2A in vivo and raise the possibility that it may have tumor-promoting activity.
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PMID:The antitumor drug fostriecin induces vimentin hyperphosphorylation and intermediate filament reorganization. 864 Sep 45


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