Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Synapsin I, a prominent phosphoprotein in nerve terminals, is proposed to modulate exocytosis by interaction with the cytoplasmic surface of small synaptic vesicles and cytoskeletal elements in a phosphorylation-dependent manner. Tetanus toxin (TeTx), a potent inhibitor of neurotransmitter release, attenuated the depolarization-stimulated increase in synapsin I phosphorylation in rat cortical particles and in synaptosomes. TeTx also markedly decreased the translocation of synapsin I from the small synaptic vesicles and the cytoskeleton into the cytosol, on depolarization of synaptosomes. The effect of TeTx on synapsin I phosphorylation was both time and TeTx concentration dependent and required active toxin. One- and two-dimensional peptide maps of synapsin I with V8 proteinase and trypsin, respectively, showed no differences in the relative phosphorylation of peptides for the control and TeTx-treated synaptosomes, suggesting that both the calmodulin- and the cyclic AMP-dependent kinases that label this protein are equally affected. Phosphorylation of synapsin IIb and the B-50 protein (GAP43), a known substrate of protein kinase C, was also inhibited by TeTx. TeTx affected only a limited number of phosphoproteins and the calcium-dependent decrease in dephosphin phosphorylation remained unaffected. In vitro phosphorylation of proteins in lysed synaptosomes was not influenced by prior TeTx treatment of the intact synaptosomes or by the addition of TeTx to lysates, suggesting that the effect of TeTx on protein phosphorylation was indirect. Our data demonstrate that TeTx inhibits neurotransmitter release, the phosphorylation of a select group of phosphoproteins in nerve terminals, and the translocation of synapsin I. These findings contribute to our understanding of the basic mechanism of TeTx action.
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PMID:Tetanus toxin inhibits depolarization-stimulated protein phosphorylation in rat cortical synaptosomes: effect on synapsin I phosphorylation and translocation. 132 20

Treatment of SH-SY5Y human neuroblastoma cells with the protein kinase inhibitor staurosporine, induced both morphological and functional differentiation in these cells. The effects of staurosporine were comparable to those induced by the protein kinase C (PKC) activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA), with respect to induction of neuronal differentiation, i.e. neurite outgrowth, inhibition of DNA synthesis, induction and down-regulation of c-myc protein expression, induction of mRNA for both neuropeptide Y (NPY) and growth associated protein 43 (GAP-43) and stimulation of tyrosine hydroxylase expression. Staurosporine failed to translocate PKC to the membrane fraction or to stimulate phosphorylation of the endogenous PKC substrate M(r) 80,000 (p80). Instead, staurosporine inhibited TPA-induced phosphorylation of p80.
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PMID:Staurosporine induces a neuronal phenotype in SH-SY5Y human neuroblastoma cells that resembles that induced by the phorbol ester 12-O-tetradecanoyl phorbol-13 acetate (TPA). 134 95

The growth-associated protein B-50 also termed GAP-43, F1, pp46, P-57 and neuromodulin is a nervous tissue-specific protein kinase C (PKC) substrate that is considered to play a major role in neurite formation, regeneration, and neuroplasticity. We describe the isolation of seven mouse monoclonal antibodies (Mabs) directed against B-50. The Mabs are produced against the bovine B-50, selected by ELISA for cross-reactivity with its human counterpart, and evaluated on Western blots in comparison with the well-characterized affinity-purified rabbit polyclonal antibodies to rat-B-50. The Western blots show that the Mabs NM1, NM4, and NM6 recognize specifically the B-50 of bovine, human, and rat brain extract and the purified PKC phosphorylated and unphosphorylated rat B-50 isoforms. The Mabs NM2 and NM3 cross-react with bovine B-50 immunoreactive c-kinase substrate (BICKS), a protein sharing a 17 amino acid sequence homology with B-50. Two Mabs are useful for the detection of B-50 immunoreactivity in formalin-fixed human and rat brain tissues. In human specimen of the hippocampus, a characteristic neuropil distribution of B-50 is detected by the Mabs. In human muscle, Mabs reveal B-50 in nerve bundles and in axons at motor end plates. Thus, these Mabs are useful in investigating the function and localization of the B-50 protein.
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PMID:Immunocytochemical detection of the growth-associated protein B-50 by newly characterized monoclonal antibodies in human brain and muscle. 138 23

Neuromodulin (also designated GAP-43, B-50, and F-1) is a prominent protein kinase C substrate attached to the membranes of neuronal growth cones during development and to presynaptic membranes in discrete subsets of adult synapses. In this study, we have examined the relationship between the attachment of neuromodulin to membranes and its phosphorylation by protein kinase C. To address this issue, we have compared wild-type and mutant neuromodulins expressed in cells that normally lack the protein. Wild-type neuromodulin expressed in Chinese hamster ovary cells was associated with membranes, incorporated [3H]palmitic acid, and was phosphorylated in response to phorbol ester treatment. Substitution of serine 41, the in vitro protein kinase C site, abolished the phorbol ester response, indicating that serine 41 serves as the sole protein kinase C phosphorylation site in vivo. Substitution of the putative fatty acylation sites, cysteines 3 and 4, abolished membrane association as well as [3H]palmitic acid labeling of neuromodulin. Fatty acylation therefore appears to serve as the mechanism for anchoring neuromodulin to membranes. Surprisingly, the soluble cysteine substitution mutant was phosphorylated by protein kinase C at a rate indistinguishable from that of the wild-type protein. Therefore, membrane association may not be required for the phosphorylation of neuromodulin by protein kinase C.
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PMID:Palmitylation of neuromodulin (GAP-43) is not required for phosphorylation by protein kinase C. 146 23

The rodent protein RC3 is expressed mainly by forebrain neurons during postnatal development and maturity. RC3 and its bovine homolog neurogranin/B-50 immunoreactive C-kinase substrate (BICKS) contain overlapping sites for protein kinase C phosphorylation and calmodulin binding that resemble those of the presynaptic 43-kDa growth-associated protein (GAP-43). However, morphological evidence suggests that RC3 has a postsynaptic localization. To test this hypothesis, we used two polyclonal antisera against synthetic peptides corresponding to nonoverlapping sequences within RC3 and compared cellular distributions of their binding in neostriatum of adult rats by immunohistochemistry, Golgi impregnation/gold toning, and correlative light/electron microscopy. Somatic and punctate patterns of RC3 immunoreactivity were observed. Somatic RC3 was found in cyto- and nucleoplasmic compartments of all neuronal phenotypes (medium spiny, medium aspiny, and large aspiny cells). Punctate RC3 was found mostly in dendritic spines. In contrast to the 43-kDa growth-associated protein, RC3 was seen infrequently in axons. We conclude that RC3 accumulates postsynaptically in dendritic spines of neostriatal neurons. We propose that RC3 acts as a "third messenger" substrate of protein kinase C-mediated molecular cascades during synaptic development and remodeling.
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PMID:Localization of the protein kinase C phosphorylation/calmodulin-binding substrate RC3 in dendritic spines of neostriatal neurons. 152 65

The protein B-50 (F1, GAP-43) is a presynaptic-specific substrate of protein kinase C, functionally related to neurotransmitter release. An increase in phosphorylation of this protein has been proposed as a molecular mechanism underlying long-term potentiation (LTP). B-50 phosphorylation measured by quantitative immunoprecipitation in rat hippocampal slices incubated in the presence of radiolabeled inorganic phosphate was increased for at least 1 hr after the induction of LTP in the CA1 region. No significant changes in B-50 phosphorylation were observed in untetanized slices stimulated at low frequency. The direct demonstration of an increased phosphorylation of the protein B-50 during LTP is consistent with the hypothesis that presynaptic mechanisms contribute to maintenance of LTP.
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PMID:Phosphorylation of the presynaptic protein B-50 (GAP-43) is increased during electrically induced long-term potentiation. 153 12

Vestibular compensation in the frog following unilateral labyrinthectomy is accompanied by distinct changes in the endogenous phosphoprotein patterns in total frog brain homogenate and isolated synaptosomes. The purpose of this study was to characterize one of these proteins, an acidic 45-kDa synaptosomal protein, resembling in some of its features the growth-associated protein GAP-43/B-50. Our results demonstrate by comparative analysis with purified rat B-50/GAP-43 that the 45-kDa protein (IP 4.8) in synaptosomal membranes of frog brain is phosphorylated by added purified PKC, cross-reacts with affinity-purified rabbit antibodies to rat B-50 and exhibits a Staphylococcus aureus V8 protease peptide digestion pattern corresponding to rat B-50. Therefore, we conclude that the acidic 45-kDa synaptosomal protein is a growth-associated B-50-like protein, probably involved in processes responsible for compensatory reorganization of the vestibular structures after hemilabyrinthectomy in the frog.
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PMID:Identification of a B-50-like protein in frog brain synaptosomes. 153 31

The neuronal tissue-specific protein kinase C (PKC) substrate B-50 can be dephosphorylated by endogenous protein phosphatases (PPs) in synaptic plasma membranes (SPMs). The present study characterizes membrane-associated B-50 phosphatase activity by using okadaic acid (OA) and purified 32P-labeled substrates. At a low concentration of [gamma-32P]ATP, PKC-mediated [32P]phosphate incorporation into B-50 in SPMs reached a maximal value at 30 s, followed by dephosphorylation. OA, added 30 s after the initiation of phosphorylation, partially prevented the dephosphorylation of B-50 at 2 nM, a dose that inhibits PP-2A. At the higher concentration of 1 microM, a dose of OA that inhibits PP-1 as well as PP-2A, a nearly complete blockade of B-50 dephosphorylation was seen. Heat-stable PP inhibitor-2 (I-2) also inhibited dephosphorylation of B-50. The effects of OA and I-2 on B-50 phosphatase activity were additive. Endogenous PP-1- and PP-2A-like activities in SPMs were also demonstrated by their capabilities of dephosphorylating [32P]phosphorylase a and [32P]casein. With these exogenous substrates, sensitivities of the membrane-bound phosphatases to OA and I-2 were found to be similar to those of purified forms of these enzymes. These results indicate that PP-1- and PP-2A-like enzymes are the major B-50 phosphatases in SPMs.
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PMID:Okadaic acid-induced inhibition of B-50 dephosphorylation by presynaptic membrane-associated protein phosphatases. 165 92

This article focuses on the role of protein phosphorylation, especially that mediated by protein kinase C (PKC), in neurotransmitter release. In the first part of the article, the evidence linking PKC activation to neurotransmitter release is evaluated. Neurotransmitter release can be elicited in at least two manners that may involve distinct mechanisms: Evoked release is stimulated by calcium influx following chemical or electrical depolarization, whereas enhanced release is stimulated by direct application of phorbol ester or fatty acid activators of PKC. A markedly distinct sensitivity of the two pathways to PKC inhibitors or to PKC downregulation suggests that only enhanced release is directly PKC-mediated. In the second part of the article, a framework is provided for understanding the complex and apparently contrasting effects of PKC inhibitors. A model is proposed whereby the site of interaction of a PKC inhibitor with the enzyme dictates the apparent potency of the inhibitor, since the multiple activators also interact with these distinct sites on the enzyme. Appropriate PKC inhibitors can now be selected on the basis of both the PKC activator used and the site of inhibitor interaction with PKC. In the third part of the article, the known nerve terminal substrates of PKC are examined. Only four have been identified, tyrosine hydroxylase, MARCKS, B-50, and dephosphin, and the latter two may be associated with neurotransmitter release. Phosphorylation of the first three of these proteins by PKC accompanies release. B-50 may be associated with evoked release since antibodies delivered into permeabilized synaptosomes block evoked, but not enhanced release. Dephosphin and its PKC phosphorylation may also be associated with evoked release, but in a unique manner. Dephosphin is a phosphoprotein concentrated in nerve terminals, which, upon stimulation of release, is rapidly dephosphorylated by a calcium-stimulated phosphatase (possibly calcineurin [CN]). Upon termination of the rise in intracellular calcium, dephosphin is phosphorylated by PKC. A priming model of neurotransmitter release is proposed where PKC-mediated phosphorylation of such a protein is an obligatory step that primes the release apparatus, in preparation for a calcium influx signal. Protein dephosphorylation may therefore be as important as protein phosphorylation in neurotransmitter release.
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PMID:The role of protein kinase C and its neuronal substrates dephosphin, B-50, and MARCKS in neurotransmitter release. 168 57

B-50 (= GAP-43, F1, and P-57 or neuromodulin) is a nervous tissue-specific, growth-associated protein, localized in the presynaptic membrane. Phosphorylation by protein kinase C at Ser41 appears to play a role in B-50/calmodulin interaction and neurotransmitter release. Previous studies have shown that digestion of the phosphorylated protein with S. aureus V8 protease (SAP) resulted consecutively in 28- and 15-kDa phospho fragments, the latter containing all incorporated phosphate. These proteolytic products of digestion with SAP have frequently been used to identify B-50 in various systems. Therefore we were interested to find out the location of these fragments in the rat B-50 molecule. For this purpose, the rat cDNA for B-50 was used to generate full-length and truncated cRNAs for cell-free translation. B-50 and B-50 peptides were either N-terminally labeled with [35S]methionine (residues 1 and 5) as a tracer, or they were phosphorylated in vitro by protein kinase C. SAP digestion of the immunoprecipitated, 35S-labeled translation products produced similar 28- and 15-kDa fragments as were obtained from 32P-labeled B-50, indicating that these fragments are N-terminal. Relative mobilities of the N-terminal B-50 fragments of known length were used as internal standards for the calculation of the length of SAP and phospho fragments. Comparing the 35S- and 32P-labeled products, four SAP sites at Glu12, Glu28, Glu65, and Glu132 could be deduced. The latter two sites are in accordance with sequence data of C-terminal fragments from the literature. All available data could be fitted into one scheme.
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PMID:Phosphoprotein B-50: localization of proteolytic sites for S. aureus V8 protease using truncated cRNAs for cell-free translation. 172 45


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