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:3.1.3.16 (calcineurin)
17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Okadaic acid (OA), an inhibitor of protein phosphatases 1 and 2A, induces differentiation in human MCF-7, AU-565, and MB-231 breast tumor cells. In MCF-7 cells, OA elicited within 5 min an increase in the levels of a set of phosphorylated cellular proteins, within hours expression of the early response genes junB, c-jun, and c-fos, and within days manifestation of differentiation. Differentiation was also induced by two related protein phosphatase inhibitors, but not by an inactive OA derivative or by an inhibitor that penetrates epithelial cells poorly. These results indicate that OA and related agents can induce tumor breast cell differentiation, and this induction is correlated with their ability to inhibit PPH 1 and 2A.
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PMID:Differentiation induction in human breast tumor cells by okadaic acid and related inhibitors of protein phosphatases 1 and 2A. 133 63

To investigate a possible relationship between apoptosis induction and protein phosphorylation in human breast carcinoma cells, we treated three such cell types, MB-231, MCF-7, and AU-565, with okadaic acid (OA), an inhibitor of protein phosphatases 1 and 2A, or phorbol 12 myristate 13-acetate, an activator of protein kinase C. We then examined these cells for the appearance of apoptosis markers. While OA caused multiplication arrest and cytotoxicity in all three cell lines, apoptosis was induced in MB-231 and MCF-7 cells but not in AU-565 cells. A similar cell-specific apoptosis induction was also observed after treatment with dinophysistoxin-1 (an active OA analogue) and with calyculin A (a structurally unrelated protein phosphatase inhibitor) but not with analogues that either are inactive or penetrate epithelial cells poorly. Phorbol 12-myristate 13-acetate also inhibited cell multiplication but was without effect in inducing apoptosis in these cells. Levels of the apoptosis-inhibitory protein BCL2 were examined in these cells, but they did not correlate with this differential susceptibility. We additionally treated the three cell types with 1-beta-D-arabinofuranosylcytosine and genistein to determine whether the AU-565 cell line would also be resistant to apoptosis induction by other chemical stimuli. Both of these agents led to the induction of apoptosis in all three cell lines. These results indicate that the AU-565 cells are specifically resistant to apoptosis induction by inhibitors of protein phosphatases 1 and 2A. This cell-specific resistance may thus allow one to identify cellular mediators of apoptosis by comparing protein phosphorylation patterns in these cells before and after treatment with OA or related inhibitors.
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PMID:Differential induction of apoptosis in human breast tumor cells by okadaic acid and related inhibitors of protein phosphatases 1 and 2A. 781 37

The trimeric form of protein phosphatase 2A consisting of 36-, 65-, and 72-kDa subunits (previously termed polycation-stimulated protein phosphatase M) was purified from rabbit skeletal muscle. Amino acid sequence data of the 72-kDa regulatory subunit (termed PR72) were used to isolate cDNAs from human heart and fetal brain libraries and libraries derived from WI-38 and MCF-7 cells. The clones isolated from the heart cDNA library revealed an open reading frame encoding a protein with a predicted molecular mass of 62 kDa. All the peptides sequenced from the protein matched with the sequence predicted from the cDNA. However, in vitro transcription and translation from this cDNA yielded a protein with an apparent molecular mass of 72 kDa on sodium dodecyl sulfate-polyacrylamide gels. From brain we isolated cDNA clones spanning an open reading frame encoding a 130-kDa protein (termed PR130). The apparent molecular mass of the protein produced by in vitro transcription and translation was 130 kDa. This protein has exactly the same deduced C-terminal protein sequence as the PR72 subunit from amino acids 45 to 527 but has an N-terminal extension of 665 amino acids. It is likely, therefore, that these two proteins arise from the same gene by alternative splicing. In human tissues several transcripts were detected by Northern analysis generated probably by the use of different polyadenylation signals and alternative splicing. High levels of the PR72 mRNAs were detected in heart and muscle, while lower levels of PR130 transcripts were found in heart, brain, placenta, lung, muscle, and kidney.
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PMID:Structure and expression of a 72-kDa regulatory subunit of protein phosphatase 2A. Evidence for different size forms produced by alternative splicing. 839 71

Okadaic acid (OA) is a serine/threonine protein phosphatase inhibitor and has been shown to induce apoptosis in a number of different tumor cell lines, including human breast carcinoma (HBC) cells. The molecular basis of OA-induced apoptosis remains to be investigated. Here, we demonstrate that the OA concentration that inhibits only protein phosphatase 1 and 2A was sufficient to induce apoptosis in HBC cells. In MCF-7 cells, the OA-induced apoptosis was coupled with the overexpression of endogenous p53, p21Waf1/Cip1, and Bax proteins, whereas the Rb protein levels were decreased. OA also induced apoptosis and concomitantly enhanced the p21Waf1/Cip1 and Bex levels in human papilloma virus protein E6-transfected variants of MCF-7 cells, in which p53 function had been disrupted. OA, by contrast, had no effect on the levels or the subcellular localization of Gadd45 and Bcl2 proteins in either wild-type of E6-transfected MCF-7 cells. Bcl-xL, Bcl-xS, and Bak levels were also unchanged after OA treatment in both cell types. OA-induced apoptosis and its effect on the expression of the above molecular markers occurred in the absence of any detectable changes in the cell cycle phase distribution. On the basis of our findings, we conclude the following: (a) OA-induced apoptosis in HBC cells occurs independently of cell cycle arrest; (b) the wild-type p53 function is not an absolute prerequisite for OA-induced cell death; and (c) OA-induced apoptosis is associated with up-regulation of endogenous p21Waf1/Cip1 and Bax protein levels.
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PMID:Cell cycle-independent regulation of p21Waf1/Cip1 and retinoblastoma protein during okadaic acid-induced apoptosis is coupled with induction of Bax protein in human breast carcinoma cells. 895 27

Treatment of MCF-7 breast cancer cells with 50 nM okadaic acid triggers an apoptotic response which is accompanied by a 7-fold increase in the activity of a protein kinase with a relative molecular mass of 53 kDa. The activity of the kinase was stimulated by cell treatment with inhibitors of phosphoprotein phosphatase 1 and 2A, but not by stressing conditions. Okadaic acid-induced stimulation of the 53 kDa protein kinase was not abolished by coincubation of cells with cycloheximide. We conclude that stimulation of the 53 kDa protein kinase by inhibitors of phosphoprotein phosphatases involves pre-existing molecular components whose activity depends on the phosphorylation state of serine/threonine residues.
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PMID:Inhibitors of phosphoprotein phosphatases 1 and 2A cause activation of a 53 kDa protein kinase accompanying the apoptotic response of breast cancer cells. 923 60

Protein phosphatase 2A (PP2A) acts as a growth suppressor and is negatively influenced by oncogenic signals. We determined its activity in various human breast carcinoma (HBC) cell types to understand its relationship to estrogen receptor (ER) expression as well as to the distribution of protein kinase C (PKC), an opposing enzyme. PP2A activity was measured using a preferred substrate, histone H1 phosphorylated by PKC. PP2A activity was higher in both the soluble and nuclear fractions of ER-positive cell lines (MCF-7, T47D and ZR-75-1) than in the ER-negative cell lines (MDA-MB-231, Hs578T and BT-20). PP2A multiple forms (2A0, 2A1, 2A2), separated by DEAE-cellulose chromatography and immunoblot analysis of PP2A catalytic subunit, also showed similar differences in these two HBC cell types. In all cases, PP2A distribution was inversely correlated with the PKC activity profile. Moreover, PP2A activity in MCF-7 cells maintained in estrogen-depleted medium was low. Nonetheless, it was induced by a prolonged treatment with 17beta-estradiol, this induction being blocked by the antiestrogens, tamoxifen and ICI-182,780. Studies in both MCF-7 transfectants stably overexpressing ras and MDA-MB-231 transfectants stably expressing ER, suggested that a low PP2A distribution in ER-negative HBC cell types may be related to tumor progression rather than the loss of ER. Conceivably, the presence of high PP2A along with low PKC in ER-positive HBC cell types may be related to the restricted cell growth associated with the retention of a certain degree of differentiation or hormonal control. Conversely, the presence of low PP2A along with high PKC in ER-negative cell types may be related to hormone-independent enhanced cell growth.
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PMID:Differential distribution of protein phosphatase 2A in human breast carcinoma cell lines and its relation to estrogen receptor status. 1035 43

The protein phosphatase (PP) inhibitors nodularin and microcystin-LR induced apoptosis with unprecedented rapidity, more than 50% of primary hepatocytes showing extensive surface budding and shrinkage of cytoplasm and nucleoplasm within 2 min. The apoptosis was retarded by the general caspase inhibitor Z-VAD.fmk. To circumvent the inefficient uptake of microcystin and nodularin into nonhepatocytes, toxins were microinjected into 293 cells, Swiss 3T3 fibroblasts, promyelocytic IPC-81 cells, and NRK cells. All cells started to undergo budding typical of apoptosis within 0.5 - 3 min after injection. This was accompanied by cytoplasmic and nuclear shrinkage and externalization of phosphatidylserine. Overexpression of Bcl-2 did not delay apoptosis. Apoptosis induction was slower and Z-VAD.fmk independent in caspase-3 deficient MCF-7 cells. MCF-7 cells stably transfected with caspase-3 showed a more rapid and Z-VAD.fmk dependent apoptotic response to nodularin. Rapid apoptosis induction required inhibition of both PP1 and PP2A, and the apoptosis was preceded by increased phosphorylation of several proteins, including myosin light chain. The protein phosphorylation occurred even in the presence of apoptosis-blocking concentrations of Z-VAD.fmk, indicating that it occurred upstream of caspase activation. It is suggested that phosphatase-inhibiting toxins can induce caspase-3 dependent apoptosis in an ultrarapid manner by altering protein phosphorylation.
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PMID:Ultrarapid caspase-3 dependent apoptosis induction by serine/threonine phosphatase inhibitors. 1057 79

PTEN, a tumor suppressor commonly targeted in human cancer, possesses phosphatase activities toward both protein and lipid substrates. While PTEN suppresses gliomas through cell cycle inhibition which requires its lipid phosphatase activity, PTEN's effects on other tumor types and the role of its protein phosphatase activity are controversial or unknown. Here we show that exogenous wild-type PTEN arrests some, but not all human breast cancer cell lines in G1, in a manner independent of endogenous PTEN. Unexpectedly, the G129E mutant of PTEN selectively deficient in the lipid phosphatase activity still blocked the cell cycle of MCF-7 cells, while the G129R and H123Y mutants lacking both phosphatase activities were ineffective. These results suggest that PTEN's protein phosphatase activity likely contributes to its tumor suppressor function in subsets of tumors and that elucidation of downstream targets which dictate cellular responses to PTEN may have important implications for future cancer treatment strategies.
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PMID:Cell cycle arrest by the PTEN tumor suppressor is target cell specific and may require protein phosphatase activity. 1077 29

The tumour suppressor gene PTEN/MMAC1/TEP1 encodes a dual-specificity phosphatase that recognizes phosphatidylinositol-3,4,5-triphosphate and protein substrates. We have shown previously that over-expression of PTEN in a tetracycline-controlled inducible system blocks cell cycle progression and induces apoptosis in MCF-7 breast cancer cells. Here, we demonstrate that over-expression of wild-type PTEN leads to the suppression of cell growth through the blockade of cell cycle progression, an increase in the abundance of p27, a decrease in the protein levels of cyclin D1 and the inhibition of Akt phosphorylation. In contrast, expression of the phosphatase-dead mutant, C124S, promotes cell growth and has the opposite effect on the abundance of p27, cyclin D1 levels and the phosphorylation of Akt. The G129E mutant, which does not have lipid phosphatase activity but retains protein phosphatase activity, behaves like C124S except that the former causes decreases in cyclin D1 levels similar to wild-type PTEN. Therefore, PTEN exerts its growth suppression through lipid phosphatase-dependent and independent activities and most likely, via the coordinate effect of both protein phosphatase and lipid phosphatase activities. Addition of either estrogen or insulin abrogates PTEN-mediated up-regulation of p27 and partially blocks PTEN-mediated growth suppression, whereas the combination of estrogen and insulin eliminates the alterations of p27 and cyclin D1 and completely blocks PTEN-mediated growth suppression. Our findings demonstrate that PTEN blocks cell cycle progression differentially through down-regulating the positive cell cycle regulator, cyclin D1, by its protein phosphatase activity, and up-regulating the negative cell cycle regulator, p27, by its lipid phosphatase activity.
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PMID:PTEN coordinates G(1) arrest by down-regulating cyclin D1 via its protein phosphatase activity and up-regulating p27 via its lipid phosphatase activity in a breast cancer model. 1123 Jan 79

The tumor suppressor PTEN possesses lipid and protein phosphatase activities. It has been well established that the lipid phosphatase activity is essential for its tumor-suppressive function via the phosphoinositide 3-kinase (PI3K) and Akt pathways. The precise role of the protein phosphatase activity is still unclear. In the current study, we demonstrate that overexpression of wild-type PTEN in the MCF-7 breast cancer line results in phosphatase activity-dependent decreases in the phosphorylation of ETS-2, which is a transcription factor whose DNA-binding ability is controlled by phosphorylation. Exposure of MCF-7 cells to insulin, insulin-like growth factor 1 (IGF-1) or epidermal growth factor (EGF) can lead to the phosphorylation of ETS-2, Akt and ERK1/2. The MEK inhibitor PD590089 abrogates insulin-stimulated phosphorylation of ETS-2. In contrast, the PI3K inhibitor LY492002 has no effect on insulin-stimulated phosphorylation of ETS-2, despite the fact that it diminishes insulin-stimulated phosphorylation of Akt. Interestingly, overexpression of PTEN in MCF-7 leads to blockade of insulin-stimulated, but not EGF-stimulated, phosphorylation of ERK, accompanied by dramatic decreases in ETS-2 phosphorylation. We further show that the relationship of PTEN and ETS-2 has functional significance by demonstrating that PTEN abrogates activation of the uPA Ras-responsive enhancer, a target of ETS-2 action, in a phosphatase-dependent manner, irrespective of the presence or absence of insulin. Our observations, therefore, suggest that PTEN blocks insulin-stimulated ETS-2 phosphorylation through inhibition of the ERK members of the MAP kinase family independently of PI3K, and that the PTEN effect on the phosphorylation status of ETS-2 may be mediated through PTEN's protein phosphatase activity.
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PMID:PTEN blocks insulin-mediated ETS-2 phosphorylation through MAP kinase, independently of the phosphoinositide 3-kinase pathway. 1209 11


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