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

---

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

The sensitivity of red blood cells containing hemoglobins S and C to activation of K-Cl cotransport by osmotic swelling and acidification was reduced by okadaic acid, a specific protein phosphatase inhibitor. The dose-response curve for okadaic acid suggests its action is on a type 1 protein phosphatase. Okadaic acid has been previously shown to inhibit swelling-induced activation of K-Cl cotransport in red blood cells from rabbits, normal humans, and dogs. The present work confirms the observation that okadaic acid blunts the stimulation of K-Cl cotransport by cell swelling. The new information is that okadaic acid reduces the effects of hemoglobins S and C on the volume and pH sensitivity of K-Cl cotransport. Thus the influences of cell volume, pH, and mutant hemoglobins may all be mediated via a common mechanisms that affects the phosphorylation state, either of the K-Cl. cotransporter itself or of a protein that regulates its function.
...
PMID:Okadaic acid inhibits activation of K-Cl cotransport in red blood cells containing hemoglobins S and C. 165 66

Okadaic acid, a potent tumor promoter and inhibitor of phosphoserine/threonine protein phosphatases 1 and 2A, produces a large increase in epidermal growth factor (EGF) receptor phosphorylation in several cell types. The increases are limited to phosphoserine and phosphothreonine residues. 12-O-Tetradecanoylphorbol-13-acetate (TPA), a distinct tumor promoter and protein kinase C activator, also induces serine/threonine phosphorylation of the EGF receptor and is known to modulate receptor functions. Comparison of okadaic acid and TPA influences on the EGF receptor show significant differences. Okadaic acid did not promote phosphorylation of Thr-654, a major site of TPA-induced phosphorylation. However, other sites of phosphorylation were similar for the two tumor promoters. In vitro experiments with purified protein phosphatase 2A demonstrate the insensitivity of Thr-654 phosphorylation, which regulates EGF receptor function, to dephosphorylation by this okadaic acid-sensitive protein phosphatase. In contrast to TPA, okadaic acid did not attenuate the tyrosine kinase activity or ligand binding capacity of the EGF receptor. However, okadaic acid did produce a decrease in EGF-stimulated inositol phosphate formation in a manner distinct from that of TPA.
...
PMID:Okadaic acid-induced hyperphosphorylation of the epidermal growth factor receptor. Comparison with receptor phosphorylation and functions affected by another tumor promoter, 12-O-tetradecanoylphorbol-13-acetate. 165 56

Addition of tumor promoting phorbol esters, such as phorbol 12-myristate 13-acetate (PMA), to many cell lines results in a decrease of 125I-epidermal growth factor (EGF) binding and increased serine/threonine phosphorylation of the EGF receptor in a process termed transmodulation. It is, however, unclear whether or not receptor phosphorylation is causally related to the inhibition of high affinity EGF binding. We have investigated the significance of phosphorylation/dephosphorylation events in the mechanism of PMA-induced transmodulation using the adenylate cyclase activator cholera toxin and the serine/threonine protein phosphatase inhibitor okadaic acid. In Rat-1 fibroblasts treated at 37 degrees C, PMA induced a rapid decrease in EGF binding which persisted for 3 hours. In contrast, cells exposed to PMA in the presence of cholera toxin exhibited a marked recovery of binding within 60 minutes. The PMA-stimulated decrease in binding correlated with a rapid increase in the phosphorylation state of the EGF receptor. While phosphorylation of the receptor was sustained at an elevated level for at least three hours in cells receiving PMA alone, EGF receptor phosphorylation decreased between 1 and 3 hours in cells treated with PMA and cholera toxin. Furthermore, the cholera toxin-stimulated return of EGF binding was inhibited by treatment with the phosphatase inhibitor okadaic acid. These results suggest that a cholera toxin-activated phosphatase can increase binding capacity of the transmodulated EGF receptor in Rat-1 cells. Cholera toxin treatment elicited a qualitatively similar response in cells transmodulated by platelet-derived growth factor (PDGF). Okadaic acid antagonized the natural return of binding observed in cells stimulated with PDGF alone, indicating that a dephosphorylation event may be required for the recovery of normal EGF binding after receptor transmodulation.
...
PMID:Regulation of the transmodulated epidermal growth factor receptor by cholera toxin and the protein phosphatase inhibitor okadaic acid. 165 15

Okadaic acid, dinophysistoxin-1 (35-methylokadaic acid), and calyculin A are the okadaic acid class of non-12-O-tetradecanoylphorbol-13-acetate (TPA)-type tumor promoters, which do not bind to the phorbol ester receptors in cell membranes or activate protein kinase C in vitro. They have potent tumor-promoting activities on mouse skin, as strong as TPA-type tumor promoters, such as TPA, teleocidin, and aplysiatoxin. DNA samples isolated from tumors induced by dimethylbenz[alpha]anthracene and each of the okadaic acid class tumor promoters had the same mutation at the second nucleotide of codon 61 (CAA to CTA) in the c-H-ras gene. Okadaic acid receptors, protein phosphatases 1 and 2A, are present in the particulate as well as cytosolic fractions of various mouse tissues. The apparent "activation" of protein kinases by the okadaic acid class tumor promoters, after their incubation with 32P-ATP, protein kinases, and protein phosphatases, was observed. This activation was caused by inhibition of protein phosphatases 1 and 2A by the okadaic acid class tumor promoters. Treatment of primary human fibroblasts and human keratinocytes with the okadaic acid class tumor promoters induced the hyperphosphorylation of a 60-kDa protein in nuclear and cytosolic fractions, due to the inhibition of protein phosphatases. The 60-kDa protein is a proteolytic fragment of nucleolin, a major nonhistone protein and is designated as "N-60." The mechanisms of action of the okadaic acid class tumor promoters are discussed with emphasis on the inhibition of protein phosphatase activity.
...
PMID:Mechanisms of action of okadaic acid class tumor promoters on mouse skin. 166 50

1. The effects of the protein phosphatase inhibitors okadaic acid and microcystin LR on the regulation by insulin of pyruvate dehydrogenase and acetyl-CoA carboxylase have been studied in rat epididymal fat-pads and isolated cells. These inhibitors both completely blocked the phosphatase activity (against phosphorylase a) present in extracts of epididymal fat-pads, with half-maximal effects in the nanomolar range. 2. Okadaic acid treatment of pads and cells lowered the activity of acetyl-CoA carboxylase assayed in tissue extracts, both before and after treatment of the extracts with the activator, citrate. Further, okadaic acid treatment abolished the 2-3-fold difference in activity observed between extracts from control and insulin-treated tissues, assayed without prior treatment with citrate. 3. Incubation of pads with [32P]Pi, sufficient to label the intracellular pool of ATP, demonstrated that okadaic acid increased the overall phosphorylation of acetyl-CoA carboxylase on a number of distinct sites, as judged by two-dimensional mapping of tryptic peptides. These included the 'I-peptide' [Brownsey & Denton (1982) Biochem. J. 202, 77-86], the phosphorylation of which may be associated with the stimulation of the activity of the enzyme by insulin, as well as inhibitory phosphorylation sites. 4. Incubation with 1 microM-okadaic acid had no effect on the basal level of active pyruvate dehydrogenase apparent after tissue extraction, but abolished the 2-3-fold increase in this parameter which was elicited by insulin in the absence of okadaic acid. However, okadaic acid treatment did not affect the persistent increase in active pyruvate dehydrogenase levels which was apparent in mitochondria subsequently isolated from insulin-treated pads and re-incubated with an oxidizable substrate. It is concluded that the effects of okadaic acid are exerted through changes in metabolite concentrations rather than some direct action on the signalling pathway whereby insulin stimulates pyruvate dehydrogenase. 5. Microcystin LR did not mimic the effects of okadaic acid on intact cells and pads described above.
...
PMID:Effects of protein phosphatase inhibitors on the regulation of insulin-sensitive enzymes within rat epididymal fat-pads and cells. 167 87

This study examined tyrosine hydroxylase (TH) activity in the stalk-median eminence (SME) and TH messenger RNA (mRNA) signal levels in the arcuate nuclei of the hypothalamus during early, middle, and late pregnancy and related these to circulating levels of ovarian steroids. In addition, this study evaluated the intracellular mechanism(s) which contributes to the semicircadian rhythm in tuberoinfundibular dopaminergic neuronal activity during early pregnancy. The catalytic activity of TH in the SME was determined from the in vitro rate of 3,4,dihydroxyphenylalanine accumulation after inhibiting DOPA decarboxylase with brocresine. TH mRNA signal levels were evaluated by in situ hybridization. TH mRNA signal levels in the arcuate nuclei were 30% lower at 1000 h on day 20 of pregnancy as compared to days 7 and 11, whereas TH activity in the SME at 1000 h was not significantly different on days 7, 11, 16, and 20. Serum PRL levels were low (3-6 ng/ml) and unchanged at 1000 h on days 7, 11, 16, and 20. Circulating progesterone levels increased from 111 to 191 ng/ml on days 7 and 16, respectively, and then declined to 69 ng/ml by day 20. Serum estradiol levels increased from 38 to 106 pg/ml on day 7 and 16, respectively, and then remained elevated on day 20. Thus, the reduction in TH mRNA signal levels during late pregnancy is temporally related to the increased estradiol/progesterone ratio. Elevated serum PRL levels at 0330 h and 1800 h on day 7 were characteristic of the nocturnal and diurnal PRL surges of early pregnancy. Circulating PRL levels were low during the intersurge times (2330 and 1000 h) on day 7 and at all times examined on day 11. TH activity in the SME on day 7 was lower during the PRL surges as compared to the intersurge times, whereas TH activity on day 11 was similar at all times and comparable to the intersurge levels of early pregnancy. Okadaic acid, a protein phosphatase inhibitor, reversed the reduction in TH activity during the nocturnal and diurnal PRL surges, but did not significantly alter TH activity during the intersurge period on day 7. TH mRNA signal levels in the arcuate nuclei were similar throughout day 7. These data indicate that protein dephosphorylation, but not changes in the TH gene expression, may contribute to the semicircadian rhythm in TH activity during early pregnancy.
...
PMID:Mechanisms of tyrosine hydroxylase regulation during pregnancy: evidence for protein dephosphorylation during the prolactin surges. 168 38

Okadaic acid (OA), a specific inhibitor of protein phosphatases, induces a rapid activation (30 min) of MPF when microinjected into the Xenopus oocyte. Neither protein synthesis inhibitors nor cAMP counteract the action of OA. These results indicate that the inhibition of protein phosphatase(s) is sufficient for the in vivo activation of MPF even after the full activation of cAMP-dependent protein kinase. In all experimental conditions (plus or minus inhibitors of protein synthesis; normal or elevated cAMP levels) OA induces a burst of protein phosphorylation together with the activation of MPF. Cytological analysis shows that OA provokes the breakdown of the nuclear envelope, the depolymerization of lamin and the condensation of the chromosomes. However, no metaphase spindles are organized, indicating that inhibition of protein phosphatases strongly affects the function of the microtubule organizing center.
...
PMID:Characterization of MPF activation by okadaic acid in Xenopus oocyte. 168 4

To evaluate the role of protein phosphorylation in amylase exocytosis, we studied the effects of okadaic acid, a potent inhibitor of protein phosphatase types 1 and 2A, on amylase release and protein phosphorylation in rat parotid acini. Although okadaic acid by itself weakly stimulated amylase release, it did not potentiate amylase release stimulated by half-maximum doses of isoproterenol or cAMP, and markedly inhibited their maximum effects. Okadaic acid dose-dependently increased cAMP-independent phosphorylation of some proteins and enhanced cAMP-dependent phosphorylation of 21- and 26-kDa proteins. These results indicate that increase in protein phosphorylation does not necessarily enhance the exocytosis of amylase from parotid acini.
...
PMID:Okadaic acid inhibits amylase exocytosis from parotid acini stimulated by cyclic AMP. 171 18

Microcystin-LR (MCYST-LR), a cyclic peptide hepatotoxin, associates with high-molecular-weight, liver cytosolic components. Repetitive cycles of heat denaturation and pronase digestion released 80 +/- 6% of the bound radiolabel from these components, parent toxin (22%), and two biotransformation products, with high-performance liquid chromatography (HPLC) retention times of 6.7 (52%) and 5.6 (13%) min. Both parent and the biotransformed (6.7 min) toxin appeared to be covalently bound to a monomeric protein of molecular weight 40,000 (protein plus radiolabeled toxin). Binding and biotransformation reactions were time- and temperature-dependent and did not require endogenous molecules less than 6,000 daltons. The binding appeared to be saturable with a maximum of 20 pmol MCYST-LR bound per mg protein. The binding protein(s) and biotransformation activity were present in rat liver, brain, kidney, heart, lung, small intestine, large intestine, testes, skeletal muscle, and to a lesser extent, in fat. Okadaic acid, a specific protein phosphatase inhibitor, showed a concentration-dependent inhibition of [3H]MCYST-LR binding to hepatic cytosol. The molecular weight and organ distribution of the binding protein(s), and inhibition of binding by okadaic acid were consistent with one of the binding sites being the catalytic subunit of protein phosphatase type 2A.
...
PMID:Association of microcystin-LR and its biotransformation product with a hepatic-cytosolic protein. 177 May 1

We investigated the effects of okadaic acid, a novel highly specific inhibitor of protein phosphatases on swelling-activated transport in human erythrocytes. Nanomolar concentrations of this compound inhibited swelling-activated K transport. Complete inhibition of this transport was observed at 1 microM. Analysis of the time course of activation of K transport upon swelling revealed that okadaic acid not only decreased the final steady-state flux but also markedly increased the time lag for activation. These results suggest that okadaic acid decreases the rate constant for the conversion of KCl transporters from the resting to the active form. Okadaic acid also inhibited N-ethylmaleimide (NEM)-stimulated K transport, and this inhibition was also observed when cells were first treated with NEM before exposure to okadaic acid. The latter finding suggests that NEM activation of KCl transport is reversible and that a later step for this activation may involve the net dephosphorylation of the KCl transport protein. These results provide the first evidence that activation of KCl cotransport in human erythrocytes is regulated by phosphoprotein phosphatase.
...
PMID:Role of protein phosphatase in activation of KCl cotransport in human erythrocytes. 184 71


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---