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)

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.
 ...
PMID:The role of protein kinase C and its neuronal substrates dephosphin, B-50, and MARCKS in neurotransmitter release. 168 57

Ionomycin stimulated membrane-associated protein kinase Cs (PKCs) activity in C6 rat glioma cells as much as the potent PKCs stimulator 12-O-tetradecanoyl phorbol 13-acetate (TPA). However, while TPA, as expected, powerfully stimulated the phosphorylation of the PKCs' 85-kDa myristoylated alanine-rich protein kinase C substrate (MARCKS) protein, ionomycin unexpectedly did not. Instead, ionomycin reduced the basal MARCKS phosphorylation. Pretreating the glioma cells with ionomycin prevented TPA-stimulated PKCs from phosphorylating the MARCKS protein. The stimulation of membrane PKCs activity and the prevention of MARCKS phosphorylation by ionomycin required external Ca2+ because they were both abolished by adding 5 mM EGTA to the culture medium. Recently (Chakravarthy, B. R., Isaacs, R. J., Morley, P., Durkin, J. P., and Whitfield, J. F. (1995) J. Biol. Chem. 270, 1362-1368), we proposed that Ca2+ x calmodulin complexes block MARCKS phosphorylation by the activated PKCs in keratinocytes stimulated by raising the external Ca2+ concentration. In the present experiments calmodulin prevented MARCKS phosphorylation by TPA-stimulated PKCs in glioma cell lysates, and this blockade was lifted by a calmodulin antagonist, the calmodulin-binding domain peptide. But, physiologically more significant, pretreating intact glioma cells with a cell-permeable calmodulin antagonist, calmidazolium, prevented ionomycin from blocking MARCKS phosphorylation by PKCs in unstimulated and TPA-stimulated cells. The effect of ionomycin on MARCKS phosphorylation was not due to the stimulation of Ca2+ x calmodulin-dependent phosphoprotein phosphatase, calcineurin, because cyclosporin A, a potent inhibitor of this phosphatase, did not stop ionomycin from preventing MARCKS phosphorylation. The ability of ionomycin to prevent TPA-stimulated PKCs from phosphorylating MARCKS depended on whether ionomycin was added before, with, or after TPA. Maximum blockade occurred when ionomycin was added before TPA but was less effective when added with or after TPA. These results indicate that Ca2+ x calmodulin can profoundly affect PKCs' signaling at the substrate level.
 ...
PMID:Ca2+ x calmodulin prevents myristoylated alanine-rich kinase C substrate protein phosphorylation by protein kinase Cs in C6 rat glioma cells. 755 16

Neurogranin, neuromodulin, and MARCKS are among the most prominent substrates of protein kinase C (PKC) in the mammalian brain. These phosphoproteins were dephosphorylated by three isoforms of rat brain calcineurin, also known as calmodulin (CaM)-dependent protein phosphatase (CaMPP). The three CaMPP isozymes dephosphorylate neurogranin, the most favorable substrate among the three tested, with subtle differences in their responses to divalent metal ions, Mn2+ and Ni2+. Dephosphorylation of neurogranin by all three CaMPP isozymes, CaMPP-1, -2, and -3, were stimulated to a higher extent by Mn2+ than by Ni2+ in the presence of CaM and Ca2+. The Km values of neurogranin in the presence of Mn2+ were lower than those in the presence of Ni2+ for CaMPP-1 and -2, but that for CaMPP-3 was comparable with either divalent metal ion. The Vmax values were higher in the presence of Mn2+ than those of Ni2+ for all three isozymes. Neurogranin and neuromodulin, both phosphorylated by PKC at a single site, were dephosphorylated completely by CaMPP; however, MARCKS, phosphorylated by PKC at three sites, was partially dephosphorylated by this phosphatase. A higher extent of dephosphorylation of MARCKS could be achieved by the combination of CaMPP and protein phosphatase 2A and a complete dephosphorylation of this protein was observed with protein phosphatase 1. Protein phosphatase 1 and 2A were also effective in a complete dephosphorylation of neurogranin and neuromodulin. Amino acid sequence analysis of the tryptic phosphopeptides derived from MARCKS dephosphorylated by CaMPP and protein phosphatase 2A revealed that the former preferentially dephosphorylated Ser155 and the latter Ser162 of rat brain MARCKS. Both phosphatases dephosphorylated poorly of Ser151. Because of the high concentration of CaMPP in the brain and the colocalization of this phosphatase with major PKC substrates in the various brain regions, it is likely that CaMPP is a phosphatase with potential to reverse the action of PKC.
 ...
PMID:Dephosphorylation of protein kinase C substrates, neurogranin, neuromodulin, and MARCKS, by calcineurin and protein phosphatases 1 and 2A. 786 22

Neurotransmission requires rapid docking, fusion, and recycling of neurotransmitter vesicles. Several of the proteins involved in this complex Ca2+-regulated mechanism have been identified as substrates for protein kinases and phosphatases, e.g., the synapsins, synaptotagmin, rabphilin3A, synaptobrevin, munc18, MARCKS, dynamin I, and B-50/GAP-43. So far most attention has focused on the role of kinases in the release processes, but recent evidence indicates that phosphatases may be as important. Therefore, we investigated the role of the Ca2+/calmodulin-dependent protein phosphatase calcineurin in exocytosis and subsequent vesicle recycling. Calcineurin-neutralizing antibodies, which blocked dynamin I dephosphorylation by endogenous synaptosomal calcineurin activity, but had no effect on the activity of protein phosphatases 1 or 2A, were introduced into rat permeabilized nerve terminals and inhibited Ca2+-induced release of [3H]noradrenaline and neuropeptide cholecystokinin-8 in a specific and concentration-dependent manner. Our data show that the Ca2+/calmodulin-dependent phosphatase calcineurin plays an essential role in exocytosis and/or vesicle recycling of noradrenaline and cholecystokinin-8, transmitters stored in large dense-cored vesicles.
 ...
PMID:Role of calcineurin in Ca2+-induced release of catecholamines and neuropeptides. 979 22

While the determination of postmortem interval (PMI) is a crucial and fundamental step in any death investigation, the development of appropriate biochemical methods for PMI estimation is still in its infancy. This study focused on the temperature-dependent postmortem degradation of calcineurin A (CnA), calmodulin-dependent kinase II (CaMKII), myristoylated alanine-rich C-kinase substrate (MARCKs), and protein phosphatase 2A (PP2A) in mice. The results show that MARCKS, CaMKII, and the use of lung tissue do not appear to warrant further study for the determination of PMI in humans. In skeletal muscle, CnA underwent a rapid temperature-dependent cleavage (60 --> 57 kDa) over the first 48 h of postmortem interval. At 21 degrees C, this transformation was completed within 24 h. In contrast, PP2A increased within the first 24 h after which it degraded at 21 degrees C but remained stable for up to 96 h at 5 degrees C and 10 degrees C. The 60 --> 57 kDa postmortem conversion of CnA was inhibited by addition of protease inhibitors and MDL-28170 indicating a calpain pathway mediates this breakdown. Proteasome inhibition (MG-132) and calmodulin antagonism (calmidazolium) also inhibited this conversion suggesting that other protein degradation pathways also are in play. In contrast, all of the protease inhibitors and calmidazolium but not ethylene glycol tetraacetic acid led to increased levels of PP2A. The data are discussed in terms of developing a useable field-based biochemical assay for postmortem interval determination in humans and understanding the protein degradation pathways that are initiated upon death.
 ...
PMID:Determining time of death: temperature-dependent postmortem changes in calcineurin A, MARCKS, CaMKII, and protein phosphatase 2A in mouse. 1932 39

Cyclosporin A (CsA) is an inhibitor of calcineurin, a calcium/calmodulin dependent serine/threonine phosphatase. Protein kinase C (PKC) is a family of serine/threonine kinases. Both calcineurin and PKC are implicated in psychiatric diseases and the therapeutic mechanisms of treatment agents. It has been reported that calcineurin interacts with components of PKC signaling pathways. We administrated 50mg/kg CsA into rats by intraperitoneal injection and examined the acute effect of single systemic CsA on the locomotor activity of rats and the phosphorylation of PKC and its substrates GAP43 and MARCKS. Systemic CsA increased locomotor activity beginning 1h after injection. The immunoreactivity of p-MARCKS(S152/156) was higher in the CsA group 1h after injection, whereas p-GAP43(S41) immunoreactivity was increased by CsA after 5h. The immunoreactivity of p-PKC pan was increased by CsA at both 1 and 5h after administration. Our data suggest that activation of the PKC pathway might be related to CsA-induced hyperlocomotion.
 ...
PMID:The effect of systemic injection of cyclosporin A on the phosphorylation of the PKC substrates MARCKS and GAP43 in the rat hippocampus. 2151 60

MARCKS (Myristoylated Alanine-Rich C Kinase Substrate) is a peripheral membrane protein, especially abundant in the nervous system, and functionally related to actin organization and Ca-calmodulin regulation depending on its phosphorylation by PKC. However, MARCKS is susceptible to be phosphorylated by several different kinases and the possible interactions between these phosphorylations have not been fully studied in intact cells. In differentiating neuroblasts, as well as some neurons, there is at least one cell-type specific phosphorylation site: serine 25 (S25) in the chick. We demonstrate here that S25 is included in a highly conserved protein sequence which is a Cdk phosphorylatable region, located far away from the PKC phosphorylation domain. S25 phosphorylation was inhibited by olomoucine and roscovitine in neuroblasts undergoing various states of cell differentiation in vitro. These results, considered in the known context of Cdks activity in neuroblasts, suggest that Cdk5 is the enzyme responsible for this phosphorylation. We find that the phosphorylation by PKC at the effector domain does not occur in the same molecules that are phosphorylated at serine 25. The in situ analysis of the subcellular distribution of these two phosphorylated MARCKS variants revealed that they are also segregated in different protein clusters. In addition, we find that a sustained stimulation of PKC by phorbol-12-myristate-13-acetate (PMA) provokes the progressive disappearance of phosphorylation at serine 25. Cells treated with PMA, but in the presence of several Ser/Thr phosphatase (PP1, PP2A and PP2B) inhibitors indicated that this dephosphorylation is achieved via a phosphatase 2A (PP2A) form. These results provide new evidence regarding the existence of a novel consequence of PKC stimulation upon the phosphorylated state of MARCKS in neural cells, and propose a link between PKC and PP2A activity on MARCKS.
 ...
PMID:A novel effect of MARCKS phosphorylation by activated PKC: the dephosphorylation of its serine 25 in chick neuroblasts. 2363 31