Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of okadaic acid (OA), a protein phosphatase inhibitor, on transcriptional enhancement activity of rat glucocorticoid receptor (GR) were examined in transiently transfected cells. In the absence of hormone, GRs expressed in CV-1 and COS-1 fibroblasts were capable of enhancing transcription from cotransfected chloramphenicol acetyltransferase reporter plasmids in response to OA treatment. Synergistic enhancement resulted from combined hormone and OA treatment. The effects of OA on GR-mediated enhancement required the presence of linked glucocorticoid response elements and were observed with reporter plasmids that contained different promoters and glucocorticoid response elements. Since OA did not affect nuclear translocation of the receptor, enhancement mediated by unliganded GR was most likely accounted for by the accumulation of some unliganded GRs within nuclei of transfected CV-1 and COS-1 cells. Deletion of individual GR transactivation domains and point mutations within DNA- and hormone-binding domains severely reduced the response of receptors to OA, although some mutant receptors retained the capacity to elicit a synergistic response when exposed to OA and hormone. The effects of OA on transcriptional enhancement did not appear to correlate with major changes in GR phosphorylation, as visualized by two-dimensional tryptic mapping of in vivo 32P-labeled GRs. Thus, phosphorylation of various components of the GR signal transduction pathway, and not necessarily the receptor itself, may influence its transcriptional enhancement activity.
Mol Endocrinol 1992 Jan
PMID:Effects of okadaic acid, a protein phosphatase inhibitor, on glucocorticoid receptor-mediated enhancement. 131 Jul 97

The effects of protein kinase C (PKC) activators on gamma-aminobutyric acidA (GABAA) receptor function were studied by two-electrode voltage-clamp in Xenopus oocytes expressing brain mRNA or subunit cDNAs and in isolated mouse brain cerebellar membrane vesicles (microsacs), using 36Cl- uptake. Both oocytes and microsacs showed transient (desensitizing) and sustained (nondesensitizing) GABAA receptor responses. In oocytes expressing brain mRNA, the PKC activator phorbol myristoyl acetate (PMA), but not the inactive analog phorbol 12-monomyristate, inhibited both transient and sustained GABA-gated chloride currents. The inhibition by PMA was concentration dependent, with an EC50 of approximately 5 nM, and resulted in a decrease in the efficacy, but not the potency, of GABA. Additionally, PMA inhibited GABA-gated chloride currents in oocytes expressing alpha 1 beta 1 gamma 2L subunit cDNAs. The effect of PMA on recombinant receptors was significantly antagonized by PKC inhibitory peptide (PKCI). In the microsac preparation, the PKC activators (-)-7-octylindolactam V and PMA inhibited the sustained phase of 36Cl- flux without altering the transient phase. The action of PMA was blocked by kinase inhibitors and by depletion of Mg-ATP and was mimicked by protein phosphatase inhibitors. These results demonstrate that activation of PKC inhibits GABAA receptor function, and the results from the microsac experiments suggest that PKC-dependent phosphorylation preferentially inactivates a nondesensitized form or state of the receptor.
Mol Pharmacol 1992 Jun
PMID:Activation of protein kinase C selectively inhibits the gamma-aminobutyric acidA receptor: role of desensitization. 131 47

Type 2C protein phosphatase (PP2C) is one of four major serine-threonine specific phosphoprotein phosphatases which modulate various intracellular activities. By in situ hybridization analysis of the adult rat, expression signals of mRNA for PP2C were observed most highly in the granule cells and Purkinje cells of the cerebellum, the pyramidal cells of the hippocampus and granule cells of the dentate gyrus, and plexus choroideus of the lateral ventricle, whereas moderate levels of its expression were observed in the medial habenula, piriform cortex and the pineal body. Several discrete nuclei of the brainstem including pars compacta of the substantia nigra, the pontine nuclei, and the locus ceruleus expressed the mRNA moderately. Weak expression of PP2C mRNA was observed in mitral and internal granule cells of the olfactory bulb, spinal cord gray matter, the cerebral neocortex, thalamic and hypothalamic nuclei. Only faint expression was detected in the caudate putamen. These patterns of expression are different from that of calcineurin/PP2B reported by other immunohistochemical studies and it is suggested that various neuronal proteins are differentially dephosphorylated by the different types of PP.
Brain Res Mol Brain Res 1992 May
PMID:Localization of mRNA for protein phosphatase 2C in the brain of adult rats. 132 Jul 18

Using cytostatic factor metaphase II-arrested extracts as a model system, we show that protein phosphatase 1 is regulated during early embryonic cell cycles in Xenopus. Phosphatase 1 activity peaks during interphase and decreases shortly before the onset of mitosis. A second peak of activity appears in mitosis at about the same time that cdc2 becomes active. If extracts are inhibited in S-phase with aphidicolin, then phosphatase 1 activity remains high. The activity of phosphatase 1 appears to determine the timing of exit from S-phase and entry into M-phase; inhibition of phosphatase 1 by the specific inhibitor, inhibitor 2 (Inh-2), causes premature entry into mitosis, whereas exogenously added phosphatase 1 lengthens the interphase period. Analysis of DNA synthesis in extracts treated with Inh-2, but lacking the A- and B-type cyclins, shows that phosphatase 1 is also required for the process of DNA replication. These data indicate that phosphatase 1 is a component of the signaling pathway that ensures that M-phase is not initiated until DNA synthesis is complete.
Mol Biol Cell 1992 Jun
PMID:Multiple roles for protein phosphatase 1 in regulating the Xenopus early embryonic cell cycle. 132 52

Growth factors regulate cellular proliferation and differentiation by activating plasma membrane tyrosine kinase receptors and triggering a cascade of events mediated by intracellular signaling proteins. The mechanism underlying growth factor modification of cellular functions, such as gap-junctional communication (gjc), has not been established clearly. Addition of epidermal growth factor (EGF) to T51B rat liver epithelial cells resulted in the rapid activation of EGF receptor tyrosine kinase activity followed by a transient dose-dependent disruption of gjc. This change did not result from the gross disturbance of membrane gap junction plaques as measured by immunofluorescence microscopy, but instead correlated with markedly elevated phosphorylation of the connexin43 (cx43) gap junction protein, a profound shift to predominantly phosphorylated forms of cx43, and the appearance of a novel phosphorylated cx43 protein. These changes in cx43 phosphorylation involved only serine residues. On restoration of gjc, these alterations in cx43 phosphorylation reverted to the pre-EGF treatment state. Both events were inhibited by the serine/threonine protein phosphatase inhibitor, okadaic acid. Therefore, unlike the case for pp60v-src, EGF-induced disruption of gjc is not associated with tyrosine phosphorylation of cx43, but instead may result from phosphorylation of cx43 by activated intracellular signaling serine protein kinase(s).
Mol Biol Cell 1992 Aug
PMID:Epidermal growth factor disrupts gap-junctional communication and induces phosphorylation of connexin43 on serine. 132 98

We describe the isolation of cDNA clones encoding type 1 serine/threonine protein phosphatase (PP1) from Brassica oleracea stigmas. We demonstrate that PP1 form a multigene family in Brassica. Within their most conserved domain, these phosphatases are 80-90% identical at the amino acid level. One cDNA (BoPP1) was found to encode a protein that shows 78-80% sequence identity to maize, rabbit, and yeast PP1. The accumulation of BoPP1 mRNA is developmentally regulated. Varying levels of BoPP1-homologous transcripts were detected in leaves, cotyledons, pistils, anthers and roots. In addition, distinct species of BoPP1 transcripts accumulated at different stages of Brassica microspore development, and mature trinucleate microspores contained a unique BoPP1 mRNA species not found at other stages of the plant's life cycle. Lastly, we show by genomic Southern blots that the Brassica genome might contain homologues of the mammalian PP1 inhibitor-1.
Plant Mol Biol 1992 Nov
PMID:Molecular characterization of type 1 serine/threonine phosphatases from Brassica oleracea. 133 67

Isolated adult rat myocytes were subjected to 180 min of metabolic inhibition or incubated in ischaemic pellets, in the presence and absence of 10 microM okadaic acid (OA) or calyculin A (CL-A). Contracture and viability was determined by light microscopic analysis of trypan blue-stained preparations and ATP levels by HPLC. Osmotic fragility was assessed by brief hypotonic swelling of cells in 170 or 85 mOsm media prior to determination of viability. Neither drug significantly affected the relatively rapid rates of contracture of myocytes during metabolic inhibition, and both afforded significant protection from development of trypan blue permeability and osmotic fragility. Both OA and CL-A significantly accelerated the rates of contracture and ATP depletion of myocytes during ischaemic incubations. Despite an enhanced rate of ATP depletion, which would be expected to accelerate development of injury, neither drug accelerated development of loss of viability or development of osmotic fragility as measured by 170 mOsm swelling. Mathematical compensation for different rates of ATP depletion confirmed that a protective effect of the drugs, during ischaemic incubation, was masked by their enhancement of the rate of injury, following swelling at 170 mOsm. When the effects of CL-A on ischaemic cells were examined at 85 mOsm, a more stringent test for osmotic fragility, protection was found without compensation for differing rates of ATP depletion. A dose/response curve for CL-A showed some effect at 100 nM and a nearly full effect during metabolic inhibition at 1 microM concentrations. It is concluded that protein phosphatase inhibitors reduce the rates of development of osmotic fragility of metabolically inhibited cells and reduces the rate of injury relative to the rate of ATP depletion of ischaemic cardiomyocytes. Phosphorylation mechanisms may be important to development of irreversible myocardial cell injury.
J Mol Cell Cardiol 1992 Aug
PMID:Effects of the protein phosphatase inhibitors okadaic acid and calyculin A on metabolically inhibited and ischaemic isolated myocytes. 133 72

GCN2 is a protein kinase in Saccharomyces cerevisiae that is required for increased expression of the transcriptional activator GCN4 in amino acid-starved cells. GCN2 stimulates GCN4 synthesis at the translational level by phosphorylating the alpha subunit of eukaryotic translation initiation factor 2 (eIF-2). We identified a truncated form of the GLC7 gene, encoding the catalytic subunit of a type 1 protein phosphatase, by its ability to restore derepression of GCN4 expression in a strain containing the partially defective gcn2-507 allele. Genetic analysis suggests that the truncated GLC7 allele has a dominant negative phenotype, reducing the level of native type 1 protein phosphatase activity in the cell. The truncated form of GLC7 does not suppress the regulatory defect associated with a gcn2 deletion or a mutation in the phosphorylation site of eIF-2 alpha (Ser-51). In addition, the presence of multiple copies of wild-type GLC7 impairs the derepression of GCN4 that occurs in response to amino acid starvation or dominant-activating mutations in GCN2. These findings suggest that the phosphatase activity of GLC7 acts in opposition to the kinase activity of GCN2 in modulating the level of eIF-2 alpha phosphorylation and the translational efficiency of GCN4 mRNA. This conclusion is supported by biochemical studies showing that the truncated GLC7 allele increases the level of eIF-2 alpha phosphorylation in the gcn2-507 mutant to a level approaching that seen in wild-type cells under starvation conditions. The truncated GLC7 allele also leads to reduced glycogen accumulation, indicating that this protein phosphatase is involved in regulating diverse metabolic pathways in yeast cells.
Mol Cell Biol 1992 Dec
PMID:Truncated protein phosphatase GLC7 restores translational activation of GCN4 expression in yeast mutants defective for the eIF-2 alpha kinase GCN2. 133 44

We have used a monoclonal antibody (MAb E12), one of several such antibodies raised against theophylline-treated Necturus gallbladder epithelial cells, to isolate a chloride channel protein by the use of an immunoaffinity column and FPLC. This protein (M(r) 219,000) has been reconstituted into a planar lipid bilayer, where it behaves as a chloride-selective channel (PCl/PNa = 20.2; PNa/PK = 1) whose unit conductance is 62.4 +/- 4.6 pS. Antibody added to the trans side (there is no effect from the cis side) causes channel open probability to drop to virtually zero, but has no effect on the conductance or the selectivity of single channels. To test the role of phosphorylation in the activity of the native channel, we studied the effects of the protein phosphatase inhibitor okadaic acid (OA) on intact gallbladders, and showed that channels opened by theophylline treatment and closed by antibody are reopened reversibly by OA (0.01-1.0 microM). Addition of the catalytic subunit of protein phosphatase 2A (PP-2A) to the cis side of a bilayer containing reconstituted chloride channels caused closure of the channels after a delay, and subsequent addition of ATP and the catalytic subunit of cAMP-dependent protein kinase (PKA) caused immediate reopening. These data indicate that (a) this chloride channel protein inserts in a directed way into the bilayer such that the cis side is 'intracellular', (b) the purified channel protein is phosphorylated, and (c) gating from the cellular side is controlled by the direct phosphorylation and dephosphorylation of the channel protein.
Mol Cell Biochem 1992 Sep 08
PMID:Reconstitution and regulation of an epithelial chloride channel. 133 26

The actin-based cytomatrix generates stress fibers containing a host of proteins including actin and myosin II and whose dynamics are easily observable in living cells. We developed a dual-radioisotope-based assay of myosin II phosphorylation and applied it to serum-deprived fibroblasts treated with agents that modified the dynamic distribution of stress fibers and/or altered the phosphorylation state of myosin II. Serum-stimulation induced an immediate and sustained increase in the level of myosin II heavy chain (MHC) and 20-kDa light chain (LC20) phosphorylation over the same time course that it caused stress fiber contraction. Cytochalasin D, shown to cause stress fiber fragmentation and contraction, had little effect on myosin II phosphorylation. Okadaic acid, a protein phosphatase inhibitor, induced a delayed but massive cell shortening preceded by a large increase in MHC and LC20 phosphorylation. Staurosporine, a kinase inhibitor known to effect dissolution but not contraction of stress fibers, immediately caused an increase in MHC and LC20 phosphorylation followed within minutes by the dephosphorylation of LC20 to a level below that of untreated cells. We therefore propose that the contractility of the actin-based cytomatrix is regulated by both modulating the activity of molecular motors such as myosin II and by altering the gel structure in such a manner as to either resist or yield to the tension applied by the motors.
Mol Biol Cell 1992 Sep
PMID:Myosin II phosphorylation and the dynamics of stress fibers in serum-deprived and stimulated fibroblasts. 142 76


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