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)

This study was designed to test the hypothesis that induction of the preconditioned state results in a sustained translocation of protein kinase C (PKC) which accounts for the memory associated with preconditioning. Isolated rabbit cardiomyocytes were subjected to established preconditioning protocols using either adenosine or transient ischemia. At timed intervals during induction of preconditioning (PC), post-incubation or final sustained ischemia, cells were harvested, subjected to digitonin lysis and separated into cytosolic and particulate fractions. Samples were evaluated by Western blot analysis with monoclonal antibodies to alpha, epsilon, zeta and gamma PKC isozymes, and bands were qualified by densitometry. Internal controls for each experiment included oxygenated cardiomyocytes and cell with PKC translocation evoked by treatment with phorbol 12-myristate 13-acetate (PMA). For control oxygenated cells, the particulate fraction contained about 30% of PKC epsilon, 5-10% of PKC alpha and 60-70% of PKC zeta. Preconditioning with adenosine (100 microM) or 10 min ischemia had no significant effect on these percentages. Furthermore, the relative amounts of PKC isozymes associated with the particulate fraction of control and preconditioned cells did not differ after a postincubation in oxygenated buffer or during a final ischemic incubation. PMA and ingenol completely translocated the epsilon and alpha isoforms, while thymeleatoxin totally translocated PKC alpha but only partially (50%) translocated PKC epsilon. The distribution of PKC zeta between fractions was not affected by any drug. The protein phosphatase inhibitor calyculin A protected cells mimicking preconditioning. This protection was blocked by preincubation with the selective PKC inhibitor calphostin C but was largely retained if calphostin C was added only during the final ischemic period. It is concluded that PKC activity is required for preconditioning, but a sustained translocation of PKC above basal levels is not necessary for protection of rabbit cardiomyocytes in vitro.
...
PMID:Translocation of PKC, protein phosphatase inhibition and preconditioning of rabbit cardiomyocytes. 884 35

We have reported that inhibition of protein phosphatase 2A (PP2A) by expression of SV40 small t stimulates the mitogenic MAP kinase cascade. Here, we show that SV40 small t can substitute for tumor necrosis factor-alpha (TNF-alpha) or serum and stimulate atypical protein kinase C zeta (PKC zeta) activity, resulting in MEK activation, cell proliferation and NF-kappaB-dependent gene transcriptional activation in CV-1 and NIH 3T3 cells. These effects were abrogated by co-expression of kinase-deficient PKC zeta and inhibition of phosphatidylinositol 3-kinase p85alpha-p110 by wortmannin, LY294002 and a dominant-negative mutant of p85alpha. In contrast, expression of kinase-inactive ERK2 inhibited small t-dependent cell growth but was unable to abolish small t-induced NF-kappaB transactivation. Our results provide the first in vivo evidence for a critical regulatory role of PP2A in bifunctional PKC zeta signaling pathways controlled by phosphatidylinositol 3-kinase. Constitutive activation of PKC zeta and NF-kappaB following inhibition of PP2A supports new mechanisms by which SV40 small t promotes cell growth and transformation. By establishing PP2A as a key player in the response of cells to growth factors and stress signals like TNF-alpha, our findings could explain why PP2A is a primary target utilized during SV40 infection to alter cellular behavior.
...
PMID:Protein phosphatase 2A is a critical regulator of protein kinase C zeta signaling targeted by SV40 small t to promote cell growth and NF-kappaB activation. 931 25

Protein kinase C (PKC) isozymes play distinct roles in cellular function. In human K562 leukemia cells, PKC alpha is important for cellular differentiation and PKC betaII is required for proliferation. In this report, we assess the role of the atypical PKC isoform PKC iota in K562 leukemia cell physiology. K562 cells were stably transfected with expression plasmids containing the cDNA for human PKC iota in sense or antisense orientation to increase or decrease cellular PKC iota levels, respectively. Overexpression or inhibition of expression of PKC iota had no significant effect on the proliferative capacity of K562 cells nor their sensitivity to phorbol myristate acetate-induced cytostasis and megakaryocytic differentiation, suggesting that PKC iota does not play a critical role in these processes. Rather, PKC iota serves to protect K562 cells against drug-induced apoptosis. K562 cells, which are resistant to most apoptotic agents, undergo apoptosis when treated with the protein phosphatase inhibitor okadaic acid (OA). Overexpression of PKC iota leads to increased resistance to OA-induced apoptosis whereas inhibition of PKC iota expression sensitizes cells to OA-induced apoptosis. Overexpression of the related atypical PKC zeta has no protective effect, demonstrating that the effect is isotype-specific. PKC iota also protects K562 cells against taxol-induced apoptosis, indicating that it plays a general protective role against apoptotic stimuli. These data support a role for PKC iota in leukemia cell survival.
...
PMID:Atypical protein kinase C iota protects human leukemia cells against drug-induced apoptosis. 934 82

Protein phosphatase 2A (PP2A) is one of the most important and abundant serine/threonine phosphatases in mammalian tissues and plays a role in gene expression, cell division, and signal transduction. PP2A is activated by ceramide, which is produced by the hydrolysis of membrane sphingomyelin in response to a variety of stress-related stimuli. To further study the role of ceramide-mediated signal transduction in cellular processes such as senescence and apoptosis, we designed and synthesized a series of low molecular weight aromatic compounds, mainly of the isoquinolone and tetralone classes, and evaluated their ability to inhibit enzymes known to be activated by ceramide. Those enzymes studied were ceramide-activated protein kinase, protein kinase C zeta and PP2A. Of these, only PP2A was found to be inhibited. A few of the compounds inhibited both ceramide-activated as well as basal PP2A activity. In addition, several of the compounds activated PP2A by up to 300% above basal enzyme activity, but only in the presence of ceramide. Thus, modulation (both inhibition and activation) of the catatylic activity of ceramide-activated PP2A is demonstrated by certain low molecular weight aromatic compounds.
...
PMID:Modulation of ceramide-activated protein phosphatase 2A activity by low molecular weight aromatic compounds. 960 34

Several phosphoproteins are involved in stimulus-secretion coupling. The beta and gamma subunits of immunoglobulin E binding protein (FC epsilonRI) and three other protein bands get phosphorylated during stimulation of mast cell secretion. These additional proteins of 42, 59 and 68 kDa are also phosphorylated when secretion is stimulated by compound 48/80 (C48/80). A 78 kDa band, however, is phosphorylated as secretion wanes after stimulation with C48/80 and by the anti-allergic drug disodium cromoglycate (cromolyn). Phosphorylation was blocked by protein kinase C inhibitors. We investigated the isozyme involved by first showing that a cation ionophore prevented the phosphorylation of the 78 kDa protein, while a Ca2+ chelator did not affect phosphorylation even though it enhanced the inhibitory effect of cromolyn. This protein was identified as moesin by immunoprecipitation. Protein kinase C activators had no effect on 78 kDa protein phosphorylation either in the presence or absence of Ca2+ ions, but prevented its phosphorylation by cromolyn. Protein phosphatase inhibitors prolonged the duration, but not the amount of phosphate incorporated in the 78 kDa protein band while cromolyn had no effect on protein phosphatase action in vitro. The insensitivity of the 78 kDa protein phosphorylation to calcium and protein kinase C activators suggests that an atypical protein kinase C isozyme may be involved. Western blot analysis identified the presence of isozymes alpha, beta, delta and zeta, of which only the latter fits the profile suggested by the present findings.
...
PMID:Ca2+ and phorbol ester effect on the mast cell phosphoprotein induced by cromolyn. 1035 62

The transcription factor Sp1 regulates the activity of a large number of eukaryotic gene promoters, including early SV40 and human immunodeficiency virus type 1 (HIV-1). Here, we report that expression of SV40 small tumor antigen (small t) in quiescent CV-1 cells transactivates two Sp1-responsive promoters, including a deletion mutant of HIV-1 LTR, through specific inhibition of endogenous AC and ABalphaC forms of protein phosphatase 2A (PP2A). Expression of a small t mutant, lacking the PP2A-binding domain, failed to transactivate Sp1. Overexpression of the B56alpha, B56beta, and B56gamma1 regulatory PP2A subunits strongly inhibited the ability of small t, but not the phosphatase inhibitor, okadaic acid, to enhance Sp1-driven gene expression. Using inhibitors and co-expression of kinase-deficient mutants, we also show that functional phosphatidylinositol 3-kinase (PI 3-kinase) and atypical protein kinase C zeta are required for small t-induced Sp1-dependent promoter transcriptional activation. Moreover, two inhibitors of PI 3-kinase, wortmannin and LY294002, inhibit the initiation of SV40 DNA replication in quiescent CV-1 cells. Taken together, these results suggest that PP2A and PI 3-kinase contribute to the ability of small t to regulate Sp1 activity, stimulate early SV40 DNA replication, and enhance the transformation of resting cells during SV40 infection.
...
PMID:Protein phosphatase 2A and phosphatidylinositol 3-kinase regulate the activity of Sp1-responsive promoters. 1073 82

We have investigated glycogen synthase (GS) activation in L6hIR cells expressing a peptide corresponding to the kinase regulatory loop binding domain of insulin receptor substrate-2 (IRS-2) (KRLB). In several clones of these cells (B2, F4), insulin-dependent binding of the KRLB to insulin receptors was accompanied by a block of IRS-2, but not IRS-1, phosphorylation, and insulin receptor binding. GS activation by insulin was also inhibited by >70% in these cells (p < 0.001). The impairment of GS activation was paralleled by a similarly sized inhibition of glycogen synthase kinase 3 alpha (GSK3 alpha) and GSK3 beta inactivation by insulin with no change in protein phosphatase 1 activity. PDK1 (a phosphatidylinositol trisphosphate-dependent kinase) and Akt/protein kinase B (PKB) activation by insulin showed no difference in B2, F4, and in control L6hIR cells. At variance, insulin did not activate PKC zeta in B2 and F4 cells. In L6hIR, inhibition of PKC zeta activity by either a PKC zeta antisense or a dominant negative mutant also reduced by 75% insulin inactivation of GSK3 alpha and -beta (p < 0.001) and insulin stimulation of GS (p < 0.002), similar to Akt/PKB inhibition. In L6hIR, insulin induced protein kinase C zeta (PKC zeta) co-precipitation with GSK3 alpha and beta. PKC zeta also phosphorylated GSK3 alpha and -beta. Alone, these events did not significantly affect GSK3 alpha and -beta activities. Inhibition of PKC zeta activity, however, reduced Akt/PKB phosphorylation of the key serine sites on GSK3 alpha and -beta by >80% (p < 0.001) and prevented full GSK3 inactivation by insulin. Thus, IRS-2, not IRS-1, signals insulin activation of GS in the L6hIR skeletal muscle cells. In these cells, insulin inhibition of GSK3 alpha and -beta requires dual phosphorylation by both Akt/PKB and PKC zeta.
...
PMID:Insulin receptor substrate-2 phosphorylation is necessary for protein kinase C zeta activation by insulin in L6hIR cells. 1148 24

We have shown previously that palmitate treatment of C2C12 skeletal muscle myotubes causes inhibition of the protein kinase B (PKB) pathway and hence reduces insulin-stimulated glycogen synthesis through the elevation of intracellular ceramide levels. Ceramide is known to activate both atypical protein kinase C (aPKC) zeta and protein phosphatase (PP) 2A, and each of these effectors has been reported to inhibit PKB. In the present study, palmitate pretreatment was found to elevate PP2A-like activity in myotubes and to prevent its inhibition by insulin. Incubation with the phosphatase inhibitor okadaic acid before insulin stimulation protected against the effect of the fatty acid on PKB phosphorylation. Palmitate was unable to inhibit PKB activity and glycogen synthesis in cells overexpressing the activated PKB mutant (T308D,S473D)-PKBalpha, which is unaffected by phosphatase. In contrast, PKB activity and glycogen synthesis were still inhibited by palmitate in cells overexpressing a membrane-targeted and, hence, activated PKB mutant that retains sensitivity to phosphatase. Although aPKC activity was also increased in palmitate-treated cells, overexpression of wild-type or kinase-dead aPKCzeta did not alter the inhibitory effects of the lipid on either stimulation of PKB or glycogen synthesis by insulin. We conclude that palmitate disrupts insulin signaling in C2C12 myotubes by promoting PP2A-like activity and, therefore, the dephosphorylation of PKB, which in turn reduces the stimulation of glycogen synthesis.
...
PMID:A role for protein phosphatase 2A-like activity, but not atypical protein kinase Czeta, in the inhibition of protein kinase B/Akt and glycogen synthesis by palmitate. 1157

Following the induction of apoptosis in mammalian cells, protein kinase C zeta (PKC zeta) is processed between the regulatory and catalytic domains by caspases, which increases its kinase activity. The catalytic domain fragments of PKC isoforms are considered to be constitutively active, because they lack the autoinhibitory amino-terminal regulatory domain, which includes a pseudosubstrate segment that plugs the active site. Phosphorylation of the activation loop at Thr(410) is known to be sufficient to activate the kinase function of full-length PKC zeta, apparently by inducing a conformational change, which displaces the amino-terminal pseudosubstrate segment from the active site. Amino acid substitutions for Thr(410) of the catalytic domain of PKC zeta (CAT zeta) essentially abolished the kinase function of ectopically expressed CAT zeta in mammalian cells. Similarly, substitution of Ala for a Phe of the docking motif for phosphoinositide-dependent kinase-1 prevented activation loop phosphorylation and abolished the kinase activity of CAT zeta. Treatment of purified CAT zeta with the catalytic subunit of protein phosphatase 1 decreased activation loop phosphorylation and kinase activity. Recombinant CAT zeta from bacteria lacked detectable kinase activity. Phosphoinositide-dependent kinase-1 phosphorylated the activation loop and activated recombinant CAT zeta from bacteria. Treatment of HeLa cells with fetal bovine serum markedly increased the phosphothreonine 410 content of CAT zeta and stimulated its kinase activity. These findings indicate that the catalytic domain of PKC zeta is intrinsically inactive and dependent on the transphosphorylation of the activation loop.
...
PMID:Lack of constitutive activity of the free kinase domain of protein kinase C zeta. Dependence on transphosphorylation of the activation loop. 1224 1

The sphingolipid ceramide has proven to be a powerful second-signal effector molecule that regulates diverse cellular processes including apoptosis, cell senescence, the cell cycle, and cellular differentiation. Ceramide has been shown to activate a number of enzymes involved in stress signaling cascades including both protein kinases and protein phosphatases. Ceramide kinase targets include stress-activated protein kinases (SAPKs) such as the jun kinases (JNKs), kinase suppressor of Ras (KSR), and the atypical protein kinase C (PKC) isoform, PKC zeta. Ceramide also is capable of activating protein phosphatases such as protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A). It is through these protein phosphatases that ceramide can indirectly inhibit kinases that are key components of pro-growth signaling processes such as the classical and novel PKC isoforms and protein kinase B (PKB; also known as Akt). However, the mechanisms how ceramide directly activates enzymes such as JNK and PP2A are still not clear. Elucidation of these mechanisms will reveal how ceramide functions in stress signaling cascades and will provide important information on cellular processes such as apoptosis. It is becoming clear that the ceramide generation is a near universal feature of programmed cell death. It is possible that during at least some apoptotic events, ceramide may be required to activate stress-signal cascades that lead to cell death, while concurrently, suppressing growth and survival pathways in the dying cell. Such a versatile role for ceramide is not unreasonable since ceramide has been implicated as having a role in both intrinsic (i.e. mitochondrial) and extrinsic (i.e. death receptor-mediated) apoptotic pathways. The recent data suggesting that aberrant glycosylation of ceramide (i.e. inactivation of the molecule) may be an important cause of drug resistance in certain cancers suggests that ceramide-mediated signaling cascades are critical components of chemotherapy-induced cell killing. Taken together, these properties of ceramide suggest that this important second-signal molecule may be an important target in anti-neoplastic strategies.
...
PMID:Intracellular signal transduction pathways activated by ceramide and its metabolites. 1267 12


1 2 3 Next >>

---