Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.16 (calcineurin)
 17,112 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A phosphotyrosyl protein phosphatase (PTPase) activity has been characterized in the plasma membranes of confluent AR42J pancreatic tumor cells using 32P-labeled poly(Glu, Tyr) as substrate. Membrane PTPase activity exhibited an apparent Michaelis constant of 3 microM and an apparent maximal velocity of 0.9 nmol.min-1.mg-1. It was inhibited by orthovanadate, zinc, poly(Glu,Tyr) and was stimulated by EDTA and dithiothreitol. Gel filtration of solubilized plasma membranes gave a peak of enzyme activity at a relative molecular weight of 70,000. Plasma membrane PTPase activity was changed during AR42J cell growth. At the beginning of culture, the control PTPase activity was minimal. Over the 5 days of culture, PTPase activity increased to reach a maximum (3.5-fold over control activity) preceding confluency by 2 days. Then the high level of PTPase activity was sustained until confluency. Incubation of the cells with the stable somatostatin analogue SMS 201-995 (SMS) resulted in a rapid and transient activation of crude membrane PTPase activity. Activation reached a maximum level within 5 min of addition and return to control levels within 20 min. The effect of SMS was dose dependent with half-maximal and maximal activation occurring at 6 pM and 0.1 nM SMS respectively.
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PMID:Characterization of a membrane tyrosine phosphatase in AR42J cells: regulation by somatostatin. 135 86

In the present study the effect of somatostatin on amylase secretion was determined using in vivo cannulation and isolated acini from rat pancreas. In vivo somatostatin-14 inhibited amylase secretion in basal state and that stimulated with CCK8 and acetylcholine. Somatostatin-14 and somatostatin-28 failed to inhibit amylase secretion from isolated acini in basal state and that stimulated with CCK8 and bethanechol. Somatostatin-14 did not increase 45Ca uptake or efflux of label from acini preloaded with 45Ca. Cellular cyclic AMP levels were not significantly increased. Somatostatin-14 did not alter the synthesis of proteins in vitro, as judged by incorporation of a mixture of fifteen 14C-labeled amino acids. Somatostatin-14 stimulated phosphoprotein phosphatase in higher doses, whereas no effect was observed at lower doses. Inhibition of secretion in vivo and lack of stimulation of amylase secretion in isolated acini suggest that the somatostatin effect in vivo is mediated by an indirect effect similar to other peptides, for example, opiates and neurotensin. Stimulation of phosphoprotein phosphatase suggests that somatostatin may bind to the acinar cells and affect functions other than secretion and synthesis of enzymes.
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PMID:Effect of somatostatin on amylase secretion from in vivo and in vitro rat pancreas. 242 87

Inhibition of the phosphorylation of the synaptic plasma membrane (SPM) protein B50 by [D-Trp8]-somatostatin in vitro is time-dependent. Increasing the time of incubation of hippocampal synaptic plasma membranes with the peptide from 15 sec to 30 min prior to addition of 7.5 microM [gamma-32P]ATP results in a complete reduction of B50 phosphorylation. Incubation of synaptic plasma membranes for 30 min in the absence of peptide does not alter basal B50 phosphorylation. Neither ACTH nor beta-endorphin produces similar effects--inhibition of B50 phosphorylation by ACTH is maximal at 15 sec and beta-endorphin produces only a small inhibition, even after 30 min. [D-Trp8]-somatostatin is not activating a membrane-bound protease, since maximal inhibition of B50 phosphorylation by the peptide is seen in the presence of leupeptin or bacitracin. Hippocampal synaptic plasma membranes contain protein phosphatase activity. Assays of B50 phosphorylation in synaptic plasma membranes done under conditions that favor either net phosphorylation or dephosphorylation are consistent with inhibition of protein phosphatase activity by [D-Trp8]-somatostatin. This evidence suggests that [D-Trp8]-somatostatin interacts with SPM binding sites in the hippocampus, which may alter the activity of an endogenous protein phosphatase to determine the degree of B50 phosphorylation.
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PMID:Characteristics of [D-Trp8]-somatostatin-sensitive B50 phosphorylation. 287 46

Cysteamine and propionitrile cause severe duodenal ulcers with perforation within 24-48 h after a single injection in rats. These animal models were used to gain insight into the early, preulcerogenic biochemical changes in the duodenal mucosa. The results indicate that a single sc injection of cysteamine and propionitrile induced dose- and time-dependent decreases in the activity of phosphoprotein phosphatase (PPPase) in homogenate and particulate fractions of rat duodenal mucosa. The decrease in enzyme activity was detectable 4 h after the injection of the ulcerogens, it was maximal at 12 h, and hardly detectable at 24 h. No effect on the enzyme activity was found under in vitro conditions. PPPase activity in the liver was not influenced by either cysteamine or propionitrile. Furthermore, the toxic but nonulcerogenic derivative of cysteamine ethanolamine had no effect on PPPase in the duodenum. Thus, the effect of the duodenal ulcerogens on PPPase activity was indirect and organ specific, related only to the target organ (i.e., duodenal mucosa). The effect of the drugs was also selective at the level of mucosal cells: both duodenal ulcerogens depleted protein and alkaline phosphatase but not lysosomal acid phosphatase. The decrease of PPPase activity could be a general property of the duodenal ulcerogens since it is independent of their effect on endogenous somatostatin.
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PMID:The influence of cysteamine and propionitrile on duodenal phosphoprotein phosphatase in rats. 289 91

Using 32P-labeled histone as exogenous substrate, we showed a potent stimulatory effect of somatostatin on cytosolic phosphoprotein phosphatases (PPPases; phosphoprotein phosphohydrolase, EC 3.1.3.16) in rat gastric mucosal cells. Partial purification of cytosolic fraction in DEAE-Sephadex ion-exchange chromatography and further gel filtration on Sephadex C-75 and Sephadex G-100 separated somatostatin-dependent PPPases into three distinct molecular species. One corresponding to Mr 130,000 was devoid of any PPPase activity but specifically bound [Tyr1]somatostatin 125I-labeled on the Tyr ([125I-Tyr1]somatostatin) with an apparent equilibrium dissociation constant of 3 x 10(-10) M. The two other molecular species corresponded to Mrs 64,000 and 13,000. They produced catalytic dephosphorylation of 32P-labeled histone, but they were not sensitive to somatostatin and did not show any specific binding to radiolabeled hormone. Mixing of the larger with either of the two smaller molecular species resulted in concentration -dependent inhibition of PPPase activity. However this inhibition was reversed by increased concentrations of somatostatin, with the concentration for half-maximal reactivation on being close to 0.1 nM. Furthermore somatostatin stimulation in reconstituted materials developed according to a rapid time course (t1/2, less than 5 sec), consistent with that observed for binding of [125I-Tyr1]somatostatin. These results strongly argue for the presence of an intracellular somatostatin receptor in gastric mucosal cells and characterize this receptor as a PPPase regulatory subunit. Thus, substrate dephosphorylation could be the primary event triggering physiological effects of somatostatin in stomach and perhaps other organs of the digestive tract [Reyl, F. & Lewin, M. J.l M. (1981) Biochim. Biophys. Acta 675, 297-300].
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PMID:Intracellular receptor for somatostatin in gastric mucosal cells: decomposition and reconstitution of somatostatin-stimulated phosphoprotein phosphatases. 612 13

Over a concentration range from 2 to 8 micrograms/ml, cyclic somatostatin inhibited cyclic AMP-dependent protein kinase and cyclic AMP binding activity in slices of mouse brain. An inverse pattern of variation was observed in the activity of phosphoprotein phosphatase. The action on kinase activity was observed in the presence of physiological concentrations of extracellular calcium, but when the concentration of calcium was increased the inhibition of kinase was not observed. These results support the idea that the protein kinase system may be involved in the action of somatostatin in the central nervous system and they are consistent with the hypothesis that somatostatin affects calcium flux.
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PMID:Inhibition of cyclic AMP-dependent protein kinase by somatostatin in slices of mouse brain: dependence on extracellular calcium. 613 8

Cyclic somatostatin inhibited phosphoprotein phosphatase activity in rat liver slices, as well as a partially purified phosphoprotein phosphatase from rat liver. This change was accompanied by a concomitant decrease in cyclic AMP-dependent protein kinase. Studies in vivo showed similar trends in the variation of both enzymes.
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PMID:Regulation of phosphoprotein phosphatase by somatostatin. 614 16

In this report we describe a novel in vitro phenomenon involving the interaction of insulin with purified protein phosphatases. Evidence is presented that porcine insulin is capable of activating and binding to rabbit skeletal muscle protein phosphatases in vitro. Its effects were examined on four rabbit skeletal muscle protein phosphatases. Two of these, phosphatases C-I and C-II, are of Mr approximately 35,000 and are the dissociated forms of protein phosphatase. The two other phosphatases, H-I and H-II, have Mr approximately 250,000 by gel filtration and represent nondissociated forms of phosphatase. Insulin reproducibly activated homogeneous preparations of protein phosphatase C-II and H-II approximately 3-5-fold in vitro. The activation was dependent on temperature, time, and insulin concentration. The activities of the phosphatases toward both phosphorylase alpha and histone were affected, indicating that this was not a substrate-directed effect. The activation phenomenon was not mimicked by insulin A or B chains, somatostatin, glucagon, or bovine serum albumin, and could be prevented by insulin antiserum. 125I-Insulin was shown to bind to the protein phosphatases by solid phase binding assays. Phosphatases C-I, C-II, and H-II, but not phosphatase H-I, were found to bind insulin reversibly. Half-maximal binding to the protein phosphatases was observed at approximately 5 X 10(-10) M insulin. Labeled insulin was found to coelute with protein phosphatase H-II on gel filtration when a mixture of the two was chromatographed, providing evidence for the formation of an enzyme-insulin complex. These findings suggest that certain protein phosphatases may have a specific binding site(s) for insulin and that these insulin-phosphatase complexes may also exhibit enhanced catalytic activity.
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PMID:A novel in vitro interaction of insulin with rabbit skeletal muscle protein phosphatases. 632 53

The cAMP-responsive element (CRE) and its cognate transcription factor CREB can mediate induction of gene transcription in response to membrane depolarization and calcium influx. In this study, the effect of cyclosporin A (CsA) and FK506 on depolarization-induced glucagon gene transcription was investigated in a pancreatic islet cell line by transfection of reporter fusion genes. CsA and FK506 inhibited depolarization-induced glucagon gene transcription, FK506 being more potent than CsA. CsA/FK506 responsiveness was mediated by the glucagon CRE and also by well characterized CREs of the choriogonadotropin and somatostatin genes. Rapamycin antagonized the inhibitory effect of FK506 but not CsA, suggesting that FK506 and CsA may act through complex formation with distinct intracellular immunophilins. Overexpression of calcineurin, which is known to be inhibited by drug-immunophilin complexes, rendered pancreatic islet cells more resistant to the inhibitory effects of CsA and FK506. These results demonstrate an inhibition by CsA and FK506 of CRE-mediated, calcium-induced transcription and suggest that membrane depolarization relies on calcineurin phosphatase activity for activation of CREB/CRE-mediated gene transcription. The interference with CRE-mediated gene transcription represents a novel mechanism of CsA/FK506 action, which may underlie pharmacological effects and toxic manifestations of these potent immunosuppressive drugs.
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PMID:Inhibition of cAMP-responsive element-mediated gene transcription by cyclosporin A and FK506 after membrane depolarization. 769 84

We previously reported the immunopurification of a somatostatin receptor from the human tumoral gastric cell HGT1 using the monoclonal antibody 30F3 (Reyl-Desmars, F., Le Roux, S., Linard, C., Benkouka, F., and Lewin, M. J. M. (1989) J. Biol. Chem. 264, 18789-18795). Screening of a lambda gt11 HGT1-cDNA library with 30F3 led us to isolate a cDNA encoding an 86-kDa polypeptide displaying 100% structural identity with the 86-kDa subunit (p86-Ku) of the Ku autoantigen. Recombinant p86 expressed in Escherichia coli cross-reacted with 30F3 and specifically bound [125I-Tyr11]somatstatin-14. Binding was totally displaced by somatostatin-14, somatostatin-28, and SMS 201-995, with IC50 values of 0.7, 1.0, and 1.2 nM, respectively. In a search for a biological effect associated with binding, we purified a 36-kDa, okadaic acid-sensitive phosphatase (protein phosphatase-2A (PP2A)) from rat gastric cytosol. PP2A catalyzed 32P release from p34cdc2-phosphorylated histone H1. However, PP2A-induced 32P release was concentration dependently inhibited by recombinant p86-Ku, with a decrease in maximal velocity without a change in Km. Steric exclusion high pressure chromatography indicated that the inhibition resulted from direct interaction of the enzyme with p86-Ku. Furthermore, it was antagonized by increased concentrations of somatostatin-14 and prevented by preincubating p86-Ku with 30F3. Given the key role played by PP2A in cell cycle regulation, the current findings suggest that p86-Ku could be a physiological target of somatostatin antiproliferative action.
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PMID:The 86-kDa subunit of autoantigen Ku is a somatostatin receptor regulating protein phosphatase-2A activity. 802 Dec 51


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