Constitutive activity of membrane-inserted protein kinase C

Protein kinase Cɛ activity regulates mGluR5 surface expression in the rat nucleus accumbens

Type 5 metabotropic glutamate receptors (mGluR5) activate protein kinase C (PKC) via coupling to G_αq/11 protein signaling. We have previously demonstrated that the epsilon isoform of PKC (PKCɛ) is a critical downstream target of mGluR5 in regulating behavioral and biochemical responses to alcohol. Recent evidence suggests that PKC-mediated phosphorylation of mGluR5 can lead to receptor desensitization and internalization. We therefore sought to examine the specific involvement of PKCɛ in the regulation of mGluR5 surface expression in the nucleus accumbens (NAc), a key regulator of alcohol-associated behaviors. Coronal brain sections from male Wistar rats were analyzed for either colocalization of mGluR5 and PKCɛ via immunohistochemistry or changes in mGluR5 surface expression and PKCɛ phosphorylation following local application of PKCɛ translocation activator or inhibitor peptides and/or an orthosteric mGluR5 agonist. We observed colocalization of mGluR5 and PKCɛ in the NAc. We also showed that intra-NAc infusion of the PKCɛ translocation inhibitor ɛV1-2 increased mGluR5 surface expression under baseline conditions. Stimulation of mGluR5 with an orthosteric agonist DHPG, dose dependently increased ERK1/2 and PKCɛ phosphorylation as well as mGluR5 internalization in acute NAc slices. Finally, we observed that activation of PKCɛ translocation with Tat-ΨɛRACK peptide mediates agonist-independent mGluR5 internalization, whereas PKCɛ translocation inhibitor ɛV1-2 prevents agonist-dependent internalization of mGluR5 in NAc slice preparations. These findings suggest that the subcellular localization of mGluR5 in the NAc is regulated by PKCɛ under basal and stimulation conditions, which may influence the role of mGluR5-PKCɛ signaling in alcohol-related behaviors. © 2016 Wiley Periodicals, Inc.

Activation and impairment of platelet function in vitro by fatty acid ethyl ester, a nonoxidative ethanol metabolite: effect of fatty acid ethyl esters on human platelets

BACKGROUND

The goal of this study was to investigate the effect of fatty acid ethyl esters (FAEE), nonoxidative metabolites of ethanol, on platelet function. We hypothesized that FAEE increase the risk of bleeding by producing an alteration in platelet membrane structure or function.

METHODS

Isolated human platelets incubated with FAEE were prepared and multiple assays for platelet activation were performed; beta-thromboglobulin release from platelet granules, platelet aggregation, arachidonate release from phospholipids, and intracellular cyclic AMP (cAMP) levels. We examined also the combined effect of epinephrine and FAEE on platelet aggregation.

RESULTS

FAEE induced platelet shape change, release of alpha granules and release of arachidonate from phospholipids without an increase in eicosanoid production and decreased cAMP levels. The platelets did not aggregate in response to FAEE alone, but did shorten the time to maximum aggregation with epinephrine.

CONCLUSION

These studies show that FAEE potentiate platelet activation but do not induce aggregation, presumably because they do not stimulate thromboxane A(2) production.

Protein kinase C isoforms in normal and leukemic neutrophils: altered levels in leukemic neutrophils and changes during myeloid maturation in chronic myeloid leukemia

Protein kinase C (PKC) is reported to play a role in maturation of the myeloid cell and functions of the mature neutrophil. The neutrophils in chronic myeloid leukemia (CML) exhibit defects in several functions. As a step towards understanding the role of PKC in the defects in function of the leukemic cells, this study investigates the expression of PKC isoforms, their subcellular distribution, levels and kinase activity in the normal and leukemic neutrophils. It also investigates changes in representative PKC isoforms during myeloid maturation. This study confirms the presence of PKC alpha, beta and delta and shows, for the first time, the presence of non conventional PKC isoform theta, atypical PKC isoform lambda/iota and PKC isoform mu in normal human neutrophils. In unstimulated cells all the detected PKC isoforms showed a predominantly cytosolic localisation in normal and CML neutrophils. Cytosol-membrane distribution of PKC alpha and delta were significantly altered in leukemic neutrophils as compared to normal cells. Cytosolic levels of all PKC isoforms were reduced in CML neutrophils with PKC alpha, beta, iota, theta, and mu showing a significant decrease. Cytosolic levels of PKC delta contrary to the trend observed for other PKC isoforms showed a slight increase in CML cells, while its membrane levels were significantly reduced in CML neutrophils. Total PKC kinase activity in CML neutrophil cytosol was significantly reduced, while specific kinase activity of two representative isoforms, PKC alpha and delta, from normal and CML neutrophils were similar, thereby increasing the significance of the altered levels of PKC isoforms in CML, and highlighting their role in the defects in function exhibited by the leukemic neutrophils. The levels of PKC delta and iota increased and decreased respectively as the leukemic myeloid cell matured from the blast to the neutrophil, while the levels of PKC alpha and beta were not altered. This suggests a role for PKC delta and iota in the maturation of the leukemic myeloid cell.

Protein kinase C delta and eta isoenzymes control the shedding of the interleukin 6 receptor alpha in myeloma cells

The soluble interleukin 6 receptor alpha is an agonistic molecule of interleukin 6 (IL-6) and is important in the biology of multiple myeloma. More precisely, it potentiates the deleterious effects of IL-6 during tumour progression, facilitating angiogenesis and bone resorption. Because the mechanisms involved in the shedding of the interleukin 6 receptor alpha (IL-6Ralpha) in multiple myeloma are not known, we have investigated them in the XG-6 human myeloma cell line. Here we provide evidence that PMA-induced IL-6Ralpha shedding is controlled by a metalloproteinase and by protein kinase C (PKC) isoenzymes that do not require Ca(2+) for their activation. We show that XG-6 cells express PKC-delta, -eta and -zeta isoenzymes. However, after stimulation with PMA, only PKC-delta and PKC-eta are activated, as shown by their translocation to the membrane. Treatment with PMA induces an increase in PKC-delta phosphorylation in its active loop. In addition, by using rottlerin, a specific inhibitor of PKC-delta, we demonstrate that PKC-delta is involved in the PMA-induced shedding of IL-6Ralpha. With the use of UO126, a specific inhibitor of the mitogen-activated protein kinase (MAPK) pathway, we show that the PMA-induced IL-6Ralpha shedding is mediated in part by the MAPK pathway. Finally, whereas GF109203X, a general PKC inhibitor, inhibits the activation of ERK1/2 (extracellular signal-regulated protein kinase 1/2), rottlerin has no inhibitory effect, indicating that the Ras/MAPK activation is PKC-dependent but PKC-delta-independent. Taken together, these results suggest that the PMA-induced shedding of IL-6Ralpha is mediated by a PKC isoenzyme network.

Changes in nuclear protein kinase C-delta holoenzyme, its catalytic fragments, and its activity in polyomavirus-transformed pyF111 rat fibroblasts while proliferating and following exposure to apoptogenic topoisomerase-II inhibitors

Protein kinase C-delta (PKC-delta) appears to be variously involved in proliferation and apoptosis. To compare the changes of this enzyme in these two processes, we have determined the levels and activities of the 79-kDa PKC-delta holoenzyme and its catalytically active 47- and 40-kDa C-terminal fragments in the nuclei of proliferating untreated polyomavirus-transformed pyF111 rat fibroblasts and pyF111 cells treated with the apoptogenic topoisomerase-II inhibitors VP-16 (etoposide), VM-26 (teniposide), and doxorubicin. PyF111 cells were chosen because they hyperexpress PKC-delta and they are hypersusceptible to apoptosis because they do not express the antiapoptotic proteins Bcl-2 and Bcl-XL. The highest PKC-delta activity in cells before they started proliferating or were exposed to one of the inhibitors was in the NM (nuclear envelope-containing) fraction, which contained the holoenzyme and both C-terminal fragments, while only the two fragments were in the nucleoplasmic (NP) fraction where they were tightly associated with chromatin. When the cells began proliferating the amounts of the PKC-delta holoenzyme and the two fragments increased in the NM and the NP fractions and the already high PKC-delta activity either increased or stayed the same in these fractions until the end of the 72-h incubation. And there was no leakage of cytochrome c from the mitochondria into the cytoplasm. VP-16 exposure caused a prompt release of cytochrome c from the mitochondria into the cytosol and at the same time triggered a sharp drop (35% by 3 h and 60% by 6 h) in the PKC-delta activity in the NM fraction without changing the actual amounts of the holoenzyme or its fragments. This prompt inactivation of PKC-delta and its fragments during the first 6 h of exposure to the drug was not due to their dephosphorylation and could not be reversed by phosphatidylserine and/or 12-O-tetradecanoylphorbol 13-acetate (TPA). Between 6 and 24 h the PKC-delta activity in the NM fraction dropped a further 20%, the kinase's activity transiently surged in the NP fraction, and cytoplasmic CPP-32-like (DEVD-specific caspase) activity increased without an increase in the proteolysis of nuclear PKC-delta or PARP. Between 24 and 72 h nuclear CPP-32-like activity increased along with a massive proteolysis of PKC-delta, an accumulation of various PKC-delta fragments, and the cleavage of PARP. But despite this proteolysis, the cells were still able to maintain or even increase the amounts of holoenzyme and 40- and 47-kDa fragments in the NM and NP fractions before dying. VM-26 and doxorubicin caused the same prompt release of cytochrome c from the mitochondria and dramatic drop of NM PKC-delta activity as did VP-16. Thus, high levels of activity of nuclear PKC-delta, particularly PKC-delta in the nuclear membrane, might have a role driving the cell cycle of pyF111 cells. On the other hand, the prompt and sustained large drop in the activity of PKC-delta at this site that precedes the onset of the caspase-mediated proteolysis of the isoform may be involved in starting and driving apoptogenesis in pyF111 fibroblasts exposed to topoisomerase-II inhibitors.

Expression of protein kinase C gene family members is temporally and spatially regulated during neural development in vitro

We used primary cultures of rat hippocampal neurons and PCC7-Mz1 cells to correlate the expression of the protein kinase C (PKC) gene family with specific events during neural differentiation. Multipotent PCC7-Mz1 embryonic carcinoma stem cells develop into a tissue-like pattern of neuronal, fibroblast-like and astroglial cells by all-trans retinoic acid (RA) treatment. Western blot analyses demonstrate that PKCalpha, betaI, gamma, theta, mu, lambda, and zeta were constitutively expressed but the expression of PKCbetaII, delta, epsilon, and eta was up-regulated three days after addition of RA when cells mature morphologically. While the protein levels of the PKC isoforms betaII, delta and eta decreased after d6, when the major phenotypical alterations of the developing neurons were completed, PKCepsilon expression remained at a high level. Immunofluorescence studies demonstrated that PKCalpha, lambda and zeta were constantly expressed in stem cells and the arising cell types. PKCdelta was detected in all differentiated cell types, whereby PKCbetaII, gamma, epsilon, and zeta were solely found in the neuronal derivatives with PKCgamma predominantly located in the nuclei. PKCeta was weakly expressed at the Golgi complex of stem cells but expanded throughout the entire somata of all developing neurons. In contrast, PKCbetaII was abundant only in the somata of a minor fraction of all neurons (approximately 2.5%). Also, PKCepsilon was exclusively synthesized by a subpopulation of neurons (40+/-5%), where it was localized in the somata and in the axons. PKCzeta was persistently expressed in two forms, the full-length PKCzeta and the constitutively active, proteolytic product PKMzeta, reasoning that permanent PKCzeta activity is important for PCC7-Mz1 physiology. Fractionation of extracts from undifferentiated and differentiating PCC7-Mz1 cells revealed that the conventional cPKCalpha was partly and the cPKCbetaI and the novel nPKCs delta and epsilon were mainly membrane bound, implying that they were also in an active state. However, when using the PKC substrate MARCKS (myristoylated alanine-rich C kinase substrate) to monitor cellular PKC activity, we observed that activation of PKC by phorbol ester was required for complete MARCKS phosphorylation and its translocation from the membrane to the cytoplasm. Our data show that the cell type-specific expression, subcellular localization and activation of PKCs are regulated in an isoform-specific manner during neurogenesis suggesting that they are involved in the control of neural development and in particular in neuronal differentiation.

The sevenfold way of PKC regulation

Protein kinase C (PKC) is a family of enzymes that are physiologically activated by 1,2-diacylglycerol (DAG) and other lipids. To date, 11 different isozymes, alpha, betaI, betaII, gamma, delta, epsilon, nu, lambda(iota), mu, theta and zeta, have been identified. On the basis of their structure and activators, they can be divided into three groups, two of which are activated by DAG or its surrogate, phorbol 12-myristate 13-acetate (PMA). PKC isozymes are remarkably different in number and prevalence in different cell lines and tissues. When activated, the isozymes bind to membrane phospholipids or to receptors that are located in and anchor the enzymes in a subcellular compartment. Some PKCs may also be activated in their soluble form. These enzymes phosphorylate serine and threonine residues on protein substrates, perhaps the best known of which are the myristoylated, alanine-rich C kinase substrate and nuclear lamins A, B and C. The enzymes clearly play a role in signal transduction, and, because of the importance of PMA as a tumor promoter, they are thought to affect some aspect of cell cycling. How PKC takes part in the regulation of cell transformation, growth, differentiation, ruffling, vesicle trafficking and gene expression, however, is largely unknown.

Lipid-dependent modulation of Ca2+ availability in isolated mossy fiber nerve endings

An enhancement of glutamate release from hippocampal neurons has been implicated in long-term potentiation, which is thought to be a cellular correlate of learning and memory. This phenomenom appears to be involved the activation of protein kinase C and lipid second messengers have been implicated in this process. The purpose of this study was to examine how lipid-derived second messengers, which are known to potentiate glutamate release, influence the accumulation of intraterminal free Ca2+, since exocytosis requires Ca2+ and a potentiation of Ca2+ accumulation may provide a molecular mechanism for enhancing glutamate release. The activation of protein kinase C with phorbol esters potentiates the depolarization-evoked release of glutamate from mossy fiber and other hippocampal nerve terminals. Here we show that the activation of protein kinase C also enhances evoked presynaptic Ca2+ accumulation and this effect is attenuated by the protein kinase C inhibitor staurosporine. In addition, the protein kinase C-dependent increase in evoked Ca2+ accumulation was reduced by inhibitors of phospholipase A2 and voltage-sensitive Ca2+ channels, as well as by a lipoxygenase product of arachidonic acid metabolism. That some of the effects of protein kinase C activation were mediated through phospholipase A2 was also indicated by the ability of staurosporine to reduce the Ca2+ accumulation induced by arachidonic acid or the phospholipase A2 activator melittin. Similarly, the synergistic facilitation of evoked Ca2+ accumulation induced by a combination of arachidonic acid and diacylglycerol analogs was attenuated by staurosporine. We suggest, therefore, that the protein kinase C-dependent potentiation of evoked glutamate release is reflected by increases in presynaptic Ca2+ and that the lipid second messengers play a central role in this enhancement of chemical transmission processes.

Activation of protein kinase C by intracellular free calcium in the motoneuron cell line NSC-19

The relationship between intracellular free calcium ([Ca2+]i) and the activation of protein kinase C (PKC) and Ca2+/calmodulin-dependent protein kinase II (CaMKII) was investigated in the NSC-19 motoneuron cell line. Increased extracellular calcium ([Ca2+]o) up to 10 mM resulted in sustained elevations of [Ca2+]i. Control cell cultures (1.3 mM [Ca2+]o, [Ca2+]i = 83 +/- 17 nM) contained Ca2+- and PS/DO lipid-dependent PKC activity predominantly in the cytosol. However, elevation of [Ca2+]o up to 5 mM ([Ca2+]i = 232 +/- 24 nM) resulted in almost complete loss of cytosolic PKC activity. Cells incubated in 10 mM [Ca2+]o ([Ca2+]i = 365 +/- 13 nM) showed increased levels of both cytosolic and membrane PKC activity compared to control. These alterations in PKC activity appeared to be translocation-independent, since PKC protein levels were unchanged as demonstrated by Western blotting analysis. When cells were exposed to 25 or 50 mM [Ca2+]o, [Ca2+]i rose transiently to over 600 and 900 nM, respectively, and then returned to near basal values. Under these conditions, total PKC activity decreased, and increased amounts of the catalytic fragment of PKC, protein kinase M, were generated. Extracts from cells exposed to [Ca2+]o between 1.3 and 25 mM did not differ significantly in the levels of measurable CaMKII activity 10 min following the change in [Ca2+]o.

Historical review of research on protein kinase C in learning and memory

1. In 1977, the discovery of a new type of kinase was reported, which turned out to be a receptor for phorbol esters. Thereafter, several mechanisms regulating PKC activity and various PKC subtypes have been discovered. 2. A role for PKC in synaptic plasticity and information storage has been postulated in the mid-1980s. An important role for PKC has since been suggested in several learning and memory models, in which persistent changes in the activation of PKC outlasting the initial stimulating event are thought to be crucial. 3. A vast number of experiments have further substantiated a role of PKC in learning and memory using, molecular genetic, behavioral, pharmacological, electrophysiological or immunocytochemical approaches in the late 1980s and the 1990s. PKC research of the past decade or so of has shown some exciting aspects of the putative role of PKC in synaptic plasticity and information storage. 4. The authors have provided highlights (Table 1) on research on PKC.

Protein kinase C, learning and memory: a circular determinism between physiology and behaviour

1. In vertebrates as in invertebrates, protein kinase C appears to have a key role in learning and memory, probably given its involvement in synaptic plasticity. 2. Hippocampal PKC in mammalians is activated by learning in a large variety of memory tasks. However, the kind of information processed, the type of task, and the dynamics of learning processes all induce differential changes in the mode of PKC activation and in its anatomy. 3. The behaviourally induced changes in PKC activity are often varying in their magnitude. Inter-individual differences in PKC basal activity are generally correlated to the ability to learn. 4. Pharmacologic activation and inhibition of brain PKC shows that PKC activation plays an important role in cognitive function. 5. Basal PKC stores characterising each individual could be determined by genetic factors and modulated through life by individual experience. 6. The issue of PKC and memory relationships is reformulated through a comprehensive interactionist model which leads to formulating some new testable predictions.

Protein kinase C in IL-2 signal transduction

Interleukin-2 (IL-2), secreted principally by activated helper T-cells, plays a pivotal role in the generation and regulation of the immune response. The various biologic functions of IL-2 have been the focus of intensive study over the years and have been well worked out. By contrast, an understanding of the intracellular signals coupled to the IL-2 receptor and responsible for mediating IL-2 effects in T-cells is far less developed, and the role that protein kinase C (PKC) may play in the various cellular responses to IL-2 receptor activation is unclear. In this article we will discuss IL-2, its receptors, and IL-2 signal transduction in relation to the physiological roles PKC activation may play in IL-2-mediated activation of T-cells and other hematopoietic cells.

Synergistic activation of protein kinase C by arachidonic acid and diacylglycerols in vitro: generation of a stable membrane-bound, cofactor-independent state of protein kinase C activity

The present study examines the synergistic activation of PKC by arachidonic acid and diacylglycerols in phospholipid vesicles and demonstrates that this combination of activators leads to the formation of a constitutively active, phospholipid-bound form of the enzyme. Activation of PKC was almost entirely calcium-dependent with vesicles containing dioleoylglycerol alone. In contrast, considerable calcium-independent activity was observed when vesicles contained both a diacylglycerol and free arachidonic acid. High-affinity association of enzyme activity with diacylglycerol-containing vesicles was calcium dependent and reversible. However, addition of arachidonic acid to diacylglycerol-containing vesicles resulted in irreversible PKC binding in the absence of calcium. Immunoblot analysis indicated that the calcium-independent binding was not isozyme-specific. The activity of the vesicle-associated PKC, bound to vesicles in the absence of calcium, was predominantly calcium-dependent. On the other hand, when the binding and isolation of vesicle-bound enzyme was conducted in the presence of calcium, the subsequent activity was almost entirely resistant to calcium chelation. This vesicle-associated form of the enzyme, when detergent extracted and recombined with phospholipid vesicles, maintained significant 'constitutive' activity (activity in the absence of both diacylglycerol and calcium). The data from this in vitro system provide the basis for a model of the physiological regulation of PKC in which the combined actions of arachidonate and diacylglycerol facilitate the stable formation of a tightly membrane-associated, intrinsically active form of PKC.

A biochemist's view of long-term potentiation

This review surveys the molecular mechanisms of long-term potentiation (LTP) from the point of view of a biochemist. On the basis of available data, LTP in area CA1 of the hippocampus is divided into three phases--initial, early, and late--and the mechanisms contributing to the induction and expression of each phase are examined. We focus on evidence for the involvement of various second messengers and their effectors as well as the biochemical strategies employed in each phase to convert a transient signal into a lasting change in the neuron. We also consider, from a biochemical perspective, the implications of a multiphase model for LTP.

Protein kinase Calpha contains two activator binding sites that bind phorbol esters and diacylglycerols with opposite affinities

Based on marked differences in the enzymatic properties of diacylglycerols compared with phorbol ester-activated protein kinase C (PKC), we recently proposed that activation induced by these compounds may not be equivalent (Slater, S. J., Kelly, M. B., Taddeo, F. J., Rubin, E., and Stubbs, C. D. (1994) J. Biol. Chem. 269, 17160-17165). In the present study, direct evidence is provided showing that phorbol esters and diacylglycerols bind simultaneously to PKC alpha. Using a novel binding assay employing the fluorescent phorbol ester, sapintoxin-D (SAPD), evidence for two sites of high and low affinity was obtained. Thus, both binding and activation dose-response curves for SAPD were double sigmoidal, which was also observed for dose-dependent activation by the commonly used phorbol ester, 4beta-12-O-tetradecanoylphorbol-13-acetate (TPA). TPA removed high affinity SAPD binding and also competed for the low affinity site. By contrast with TPA, low affinity binding of SAPD was inhibited by sn-1,2-dioleoylglycerol (DAG), while binding to the high affinity site was markedly enhanced. Again contrasting with both TPA and DAG, the potent PKC activator, bryostatin-I (B-I), inhibited SAPD binding to its high affinity site, while low affinity binding was unaffected. Based on these findings, a model for PKC activation is proposed in which binding of one activator to the low affinity site allosterically promotes binding of a second activator to the high affinity site, resulting in an enhanced level of activity. Overall, the results provide direct evidence that PKCalpha contains two distinct binding sites, with affinities that differ for each activator in the order: DAG > phorbol ester > B-I and B-I > phorbol ester > DAG, respectively.

Cellular distribution of protein kinase C isozymes in CD3-mediated stimulation of human T lymphocytes with aging

Protein kinase C (PKC) is involved in a variety of cellular responses, such as the expression and secretion of IL-2, the regulation of cytotoxic killing and cell proliferation. It is known that these immune functions are altered with aging. Here, we show that anti-CD3-triggered T cell proliferation is significantly decreased with aging and that H7, an inhibitor of PKC, impairs the anti-CD3-induced T cell proliferation in a differential manner, lymphocytes of healthy young subjects being more sensitive to the PKC inhibitor than those of elderly subjects. We examined (Western blot) the presence and the cellular distribution of PKC isozymes in T lymphocytes of healthy young and elderly subjects in the resting state and after anti-CD3 mAb stimulation using antibodies directed against PKC alpha, beta, delta, epsilon and zeta isoforms in the cytosol and the plasma membrane fractions. These five PKC isotypes were present in human T cells of young and elderly subjects. However, their distribution between the cytosolic and membrane fractions varied according to the isozymes and the age of the subjects. In resting lymphocytes of young subjects, all the PKC isozymes were found in the cytosolic fraction, except PKC-zeta. In resting lymphocytes of elderly subjects PKC-zeta and -epsilon were almost equally distributed between the cytosolic and the membrane fractions, whereas PKC-alpha and -zeta were mainly found in the membrane fraction and PKC-beta was almost exclusively located in the cytosolic fraction. The translocation of PKC-alpha, -beta, -delta and -epsilon could be observed under anti-CD3 mAb stimulation in lymphocytes of young subjects, while in the case of elderly subjects only the PKC beta isoform was translocated. Our results suggest tha the decreased availability of cytosolic PKC may contribute to the diminished PKC-dependent responses to CD3-triggered stimulation of human T lymphocytes with aging.

The effect of spermine on calcium requirement for protein kinase C association with phospholipid vesicles

We have previously reported that polyamines interfere with protein kinase C-membrane interactions. With the aim of clarifying the influence of the relationship between calcium and polyamines on this process we have investigated the effect of spermine on the formation of active protein kinase C-membrane complexes as a function of Ca++ concentrations. Protein kinase C, purified from rat brain, was allowed to interact with phospholipid vesicles of defined composition. The active complex protein kinase C-liposomes was determined by its ability to bind radioactive phorbol ester with an exact 1:1 stoichiometry. The results show that, at Ca++ levels below 0.1 microM, spermine inhibits the formation of complexes between protein kinase C and membranes. At higher Ca++ concentrations, spermine does not prevent the association process but does influence the ratio between the enzyme molecules irreversibly inserted into the membrane and those reversibly associated with it. We have also demonstrated that spermine, by reducing the density of acidic component of liposomes, influences the calcium requirement for protein kinase C-membrane binding. This study indicates that spermine may regulate the activation of protein kinase C and affects the calcium requirement for the association of this enzyme with the phospholipid bilayer. The results suggest a possible role for polyamines in signal transduction when protein kinase C is involved.

Inactive membrane protein kinase Cs: a possible target for receptor signalling

The activation of the multifunctional cell signalling enzymes, the protein kinase Cs (PKCs), is generally thought to result from the translocation of inactive cytosolic enzymes to activation sites in cell membranes. However, recent studies suggest that PKCs may also be stimulated in cells by processes independent of translocation. One possible mechanism is the modulation of the activity of PKCs already resident in membranes. A PKC assay that measures enzyme activity directly in isolated native membranes has revealed the presence of an activatable pool of PKCs resident in native membranes of various cells and tissues. In 3T3-L1 cells, some or all of this pool of membrane PKCs was stimulated within 10 min of exposing the cells to 10 ng/ml epidermal growth factor or 100 ng/ml fibroblast growth factor. Similar increases in PKC activity were observed in native membranes isolated from CTLL-2, WEHI-231 and S49 lymphoma cells that had been exposed to interleukin-2. These growth factors all stimulated membrane PKC activity without detectably translocating cytosolic enzymes to the membranes. In intact WEHI cells, low concentrations (5-10 microM) of a diacylglycerol, 1-oleoyl-2-acetyl-sn-glycerol (OAG), or low concentrations (2-10 nM) of phorbol 12-myristate 13-acetate sufficed to activate PKCs already resident in membranes, but much higher concentrations (50-100 microM and 50-100 nM respectively) were needed to detectably stimulate the translocation of cytosolic PKCs. A phosphatidylcholine-specific phospholipase C also selectively stimulated membrane PKCs in WEHI cells at concentrations that were much less than those needed to induce the translocation of cytosolic enzymes. Furthermore, interleukin-2 and low concentrations of OAG both stimulated the phosphorylation of the 85 kDa PKC-selective substrate protein in intact WEHI cells in which translocation of PKCs was not evident. These results suggest that the membranes of some cells maintain a pool of activatable PKCs that respond to lower levels of extracellular stimuli than cytosolic PKCs, and that can be stimulated by signals which produce diacylglycerols through the hydrolysis of phospholipids other than polyphosphoinositides.

Activation of (His)6-Raf-1 in vitro by partially purified plasma membranes from v-Ras-transformed and serum-stimulated fibroblasts

The serine-threonine protein kinase Raf-1 is an important signal transducer in mitogenesis, phosphorylating and activating mitogen-activated protein (MAP) kinase kinase. Raf-1 activation in vivo is dependent on Ras, but the mechanism of Raf activation is unknown. The ability of preparations of plasma membranes to activate exogenous (His)6-Raf-1 was studied. Plasma membranes of v-Ras-transformed NIH 3T3 cells, but not parental cells, enhanced MAP kinase kinase kinase (MAPKKK) activity dependent on addition of (His)6-Raf-1 and ATP/Mg. Treatment of membranes with concentrations of Bacillus cereus phosphatidylcholine-specific phospholipase C that activated Raf-1 in vivo failed to enhance MAPKKK activity in vitro. Activation of (His)6-Raf-1 in vitro by membranes was dependent on binding to Ras. Membranes from v-Src-transformed cells also activated (His)6-Raf-1 and synergized with v-Ras membranes. Serum-treatment of NIH 3T3 cells stimulated the ability of membranes to activate (His)6-Raf-1. Activated (His)6-Raf-1 could be recovered on Ni(2+)-agarose, and this methodology was used to demonstrate that activation by membranes was ATP dependent. These findings demonstrate Ras- and ATP-dependent step(s) for Raf-1 activation by plasma membranes in vitro.

Modulation of P-glycoprotein by protein kinase C alpha in a baculovirus expression system

The modulation of P-glycoprotein by protein kinase C alpha (PKC alpha) was examined in a baculovirus expression system. PGP was phosphorylated in membrane vesicle preparations in vitro only when coexpressed with PKC alpha, and phosphorylation was Ca(2+)-dependent and inhibited by the PKC inhibitor Ro 31-8220. PGP and PKC alpha were tightly associated in membrane vesicles and were coimmunoprecipitated with antibodies against either PGP or PKC alpha. Photoaffinity labeling of membrane vesicles with [3H]azidopine indicated that drug binding to PGP was slightly increased in the presence of PKC alpha. In contrast, PGP ATPase activity was increased by PKC alpha as well as by verapamil, but only PKC-stimulated activity in the presence of verapamil was inhibited by Ro 31-8220. Mutation of serine-671 to asparagine in the linker region of PGP abolished PKC alpha-stimulated ATPase activity, and also inhibited to a lesser degree verapamil-stimulated ATPase activity. These results indicate that PKC alpha in a positive regulator of PGP ATPase activity and suggest that this mechanism may account for the increased multidrug resistance observed in MDR1-expressing cells when PKC alpha activity is elevated.

Enhancement by calcitonin gene-related peptide of nicotinic receptor-operated noncontractile Ca2+ mobilization at the mouse neuromuscular junction

1. The involvement of calcitonin gene-related peptide (CGRP) in the mechanism of nicotinic acetylcholine receptor-operated noncontractile Ca2+ mobilization (not accompanied by twitch tension) was investigated by measuring Ca(2+)-aequorin luminescence at the neuromuscular junction of mouse diaphragm muscle treated with neostigmine. 2. Noncontractile Ca2+ transients were enhanced by 4-aminopyridine (100 microM), a K+ channel blocker, and inhibited by botulinum toxin (1-100 micrograms, i.p.) and hexamethonium (10-100 microM), a neuronal nicotinic receptor antagonist. 3. Noncontractile Ca2+ transients were diminished by CGRP8-37 (10-20 microM), a CGRP antagonist. CGRP (0.3-10 nM) prolonged the duration of noncontractile Ca2+ transients. The effect of CGRP was suppressed by CGRP8-37 (0.1 microM). 4. Noncontractile Ca2+ transients were inhibited by H-89 (0.1-1 microM), a protein kinase-A inhibitor. The catalytic subunit of protein kinase-A and AA373 (300 microM), a protein kinase-A activator, prolonged the duration of noncontractile transients. The prolongations either by CGRP or by AA373 were not observed in the presence of H-89 (0.1 microM). 5. Contractile (accompanied by twitch tension) but not noncontractile Ca2+ transients were decreased by 12-O-tetradecanoyl phorbol 13-acetate (TPA, 0.3-1 microM), a protein kinase-C activator. Phospholipase A2 increased only contractile Ca2+ transients. Calmodulin-related agents affected neither type of Ca2+ transients. 6. These results provide the first evidence that nicotinic acetylcholine receptor-operated noncontractile Ca2+ mobilization is promoted by nerve-released CGRP activating protein kinase-A, and is dependent on the accumulated amounts of acetylcholine at the neuromuscular junction where desensitization might readily develop.

Mechanism of protein kinase C activation during the induction and maintenance of long-term potentiation probed using a selective peptide substrate

Previous reports using various protein kinase inhibitors have suggested that protein kinase activity is necessary for both the induction and maintenance of hippocampal long-term potentiation (LTP), a cellular phenomenon likely to contribute to mammalian memory formation. We designed and characterized a selective peptide substrate for protein kinase C (PKC), corresponding to amino acids 28 to 43 of the neuronal protein neurogranin, and used the substrate to obtain direct biochemical evidence for activation of PKC in both the induction and maintenance phases of LTP. As the effect cannot be accounted for by either of two well-known mechanisms for persistent PKC activation, membrane insertion, or proteolysis, the persistent activation of PKC in the maintenance phase of LTP appears to occur via another mechanism. The maintenance phase of LTP is associated with decreased immunoreactivity of PKC, an effect that can be reversed with phosphatase treatment. Thus, PKC appears to be both phosphorylated and persistently activated in the maintenance phase of LTP.

Effect of spermine on membrane-associated and membrane-inserted forms of protein kinase C

Protein kinase C is reported to exist in two membrane-bound states: a reversible one which can be dissociated by calcium chelators (membrane-associated form) and an irreversible one which is chelator stable (membrane-inserted form). In the present work the effects of a naturally occurring polyamine (spermine) on the membrane-associated and membrane-inserted forms of protein kinase C were investigated using a reconstituted system consisting of partially purified protein kinase C from rat brain and phospholipid vesicles of defined composition. The active membrane-bound complex was conveniently determined by its ability to bind radioactive phorbol ester with an exact 1:1 stoichiometry. Our experimental data show that, in the absence of calcium ions, the amount of enzyme bound to phospholipids vesicles was dramatically reduced by the presence of spermine whereas the PDBu binding affinity was not significantly affected. The addition of the divalent cation increased the affinity of phorbol ester for the active complex but had no effect on Nmax; spermine added in this experimental conditions was no longer able to decrease the total number of enzyme molecules bound to liposomes. Moreover gel filtration experiments of the protein kinase C-phospholipids complex formed in the presence of calcium, indicated that polyamine added during the association process was able to reduce the extent of enzyme insertion into liposomes. Since the increase in phospholipid concentration resulted in a higher level of non-dissociable protein kinase C-liposomes complex we propose that spermine, complexing to membrane binding sites both in the absence and in the presence of Ca++, could promote binding conditions that oppose to the formation of the inserted form of the enzyme. As a consequence the distribution between the reversible and the irreversible membrane-bound forms of protein kinase C is affected.

Protein kinase C and annexins: unusual calcium response elements in the cell

Protein kinase C and the annexins appear to share some unusual and potentially important membrane- and calcium-binding properties. While these proteins are calcium response elements, they are not calcium-binding proteins in the formal sense; at intracellular calcium concentrations, they only bind significant amounts of calcium when membranes or other suitable surfaces are present. The number of calcium ions bound per protein is large (> 8) and this stoichiometry, at the protein-membrane interface, may provide the large number of contact points needed for the very high-affinity interaction that is observed. The further ability of annexins and PKC to form structures with properties of integral membrane proteins may be important to provide a type of long-term cell signalling that produces a constitutively active kinase or ion channel activity. Selectivity for phospholipids in bilayer form is modest with respect to the acidic phospholipids but there is a surprising preference for phosphatidylethanolamine as the neutral phospholipid matrix. Along with other unusual properties, these proteins offer the potential for unique types of cell regulation events.

Protein kinase C activity and its relationship to myo-inositol uptake during hyperglycemic conditions in cultured bovine lens epithelial cells

Incubation of cultured bovine lens epithelial cells (BLECs) in minimal essential medium (MEM) containing 40 mM galactose for 20 hr results in an attenuation of 3H-myo-inositol (3H-MI) concentrating ability. Decreased MI uptake could negatively impact on normal phosphoinositide turnover and diacylglycerol production, and presumably, protein kinase C (PKC) activation. The present report examines the relationship between PKC activity, myo-inositol transport and hyperglycemic conditions. PKC activities in the cytosol and particulate fractions of bovine lens epithelial cells in culture were quantitated using a mixed micelle assay following DEAE-cellulose (DE52) and Sephadex G-25 chromatography. Protein kinase C activity was assessed as Ca2+ and phospholipid-dependent Ac-myelin basic protein substrate peptide phosphorylation and confirmed using a PKC pseudosubstrate inhibitor peptide (PKC 19-36). Total PKC activity was similar in galactose-incubated cells (871 +/- 64 pmol/mg total protein/min) and control cells (881 +/- 8 pmol/mg total protein/min) after 20 hr. In unstimulated cells, approximately 90% of the total cellular PKC activity was recovered in the cytosolic fraction. Enzyme translocation was induced with the tumor promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), resulting in a 6-fold increase in membrane-associated PKC activity. A similar PMA-induced translocation was observed in BLECs incubated with 40 mM galactose MEM-maintained cells briefly treated with PMA or the non-phorbol PKC activators, SC-10 and mezerein, displayed a rate of 3H-MI uptake similar to the untreated control cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinase C isoenzymes: divergence in signal transduction?

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Demonstration of presynaptic protein kinase C activation following long-term potentiation in rat hippocampal slices

Pharmacological and biochemical evidence implicate the Ca2+ and phospholipid-dependent protein kinase C in long-term potentiation. The in vitro hippocampal slice preparation was used to demonstrate redistribution of protein kinase C from cytosol to membrane and protein kinase C-dependent phosphorylation of the presynaptic growth-associated protein-43 substrate following long-term potentiation induction in area CA1. Protein kinase C translocation was assessed using both quantitative immunoblotting with a monoclonal antibody recognizing a common epitope in the alpha and beta isoforms of protein kinase C and Ca2+ and phospholipid-dependent phosphorylation of exogenous histone substrate. Slices examined 5 min after tetanus-induced spike potentiation showed no change in protein kinase C redistribution, whereas slices examined at 15-, 30- and 60-min intervals all showed a similar degree of protein kinase C translocation to membrane, although only at 15 min was the effect statistically significant. Additionally, an increase in protein kinase C-dependent growth-associated protein 43 phosphorylation was observed 10 min after high-frequency stimulation. The translocation of protein kinase C and phosphorylation of growth-associated protein 43 were dependent upon high-frequency (repetitive 400 Hz) afferent stimulation, as no effects were observed in slices receiving low-frequency (1 Hz) or no stimulation. The N-methyl-D-aspartate receptor antagonist, DL-2-amino-5-phosphonovaleric acid (50 microM), inhibited induction of long-term potentiation, redistribution of protein kinase C and phosphorylation of growth-associated protein 43. A significant redistribution of the predominantly presynaptic protein kinase C isoform, protein kinase C-alpha, was also detected 15 min after induction of long-term potentiation using an alpha-isoform-specific monoclonal antibody. These observations support a presynaptic role for protein kinase C and growth-associated protein 43 in the early maintenance phase of LTP, and further suggest that a retrograde messenger produced postsynaptically following N-methyl-D-aspartate receptor activation mediates these effects.

Receptors for tumor-promoting phorbol esters in rat ventral prostate

The presence of tumor-promoting phorbol ester receptors in rat prostate was investigated by studying the binding of phorbol diester 12,13-dibutyrate (PDBu) in both soluble and particulate subcellular fractions. Binding of [3H]PDBu to the soluble fraction was optimal after the addition of phosphatidylserine (0.1 mg/ml) and Ca2+ (1 mM). Both subcellular fractions exhibited a single class of PDBu receptor (Kd between 97 and 128 nM) as shown by saturation binding experiments. Phorbol esters with tumor-promoting activity showed a higher affinity for these receptors than did endogenous ligands such as diacylglycerols whereas phorbol esters without tumor-promoting activity were ineffective even at concentrations as high as 1 microM. These properties are highly representative of protein kinase C activity.

Amygdala kindling alters protein kinase C activity in dentate gyrus

Kindling is a use-dependent form of synaptic plasticity and a widely used model of epilepsy. Although kindling has been widely studied, the molecular mechanisms underlying induction of this phenomenon are not well understood. We determined the effect of amygdala kindling on protein kinase C (PKC) activity in various regions of rat brain. Kindling stimulation markedly elevated basal (Ca(2+)-independent) and Ca(2+)-stimulated phosphorylation of an endogenous PKC substrate (which we have termed P17) in homogenates of dentate gyrus, assayed 2 h after kindling stimulation. The increase in P17 phosphorylation appeared to be due at least in part to persistent PKC activation, as basal PKC activity assayed in vitro using an exogenous peptide substrate was increased in kindled dentate gyrus 2 h after the last kindling stimulation. A similar increase in basal PKC activity was observed in dentate gyrus 2 h after the first kindling stimulation. These results document a kindling-associated persistent PKC activation and suggest that the increased activity of PKC could play a role in the induction of the kindling effect.

The protein kinase C family

Protein kinase C represents a structurally homologous group of proteins similar in size, structure and mechanism of activation. They can modulate the biological function of proteins in a rapid and reversible manner. Protein kinase C participates in one of the major signal transduction systems triggered by the external stimulation of cells by various ligands including hormones, neurotransmitters and growth factors. Hydrolysis of membrane inositol phospholipids by phospholipase C or of phosphatidylcholine, generates sn-1,2-diacylglycerol, considered the physiological activator of this kinase. Other agents, such as arachidonic acid, participate in the activation of some of these proteins. Activation of protein kinase C by phorbol esters and related compounds is not physiological and may be responsible, at least in part, for their tumor-promoting activity. The cellular localization of the different calcium-activated protein kinases, their substrate and activator specificity are dissimilar and thus their role in signal transduction is unlike. A better understanding of the exact cellular function of the different protein kinase C isoenzymes requires the identification and characterization of their physiological substrates.

Lipid vesicles which can bind to protein kinase C and activate the enzyme in the presence of EGTA

Maximal protein kinase C activity with vesicles of phosphatidic acid and 1,2-dioleoyl-sn-glycerol is observed in the absence of added Ca2+. Addition of phosphatidylcholine to these vesicles restores some calcium dependence of enzyme activity. 1,2-Dioleoyl-sn-glycerol eliminates the Ca(2+)-dependence of protein kinase C activity found with phosphatidic acid alone. Phorbol esters do not mimic the action of 1,2-dioleoyl-sn-glycerol in this respect. This suggests that the 1,2-dioleoyl-sn-glycerol effect is a result of changes it causes in the physical properties of the membrane rather than to specific binding to the enzyme. The effect of 1,2-dioleoyl-sn-glycerol on the phosphatidic-acid-stimulated protein kinase C activity is dependent on the molar fraction of 1,2-dioleoyl-sn-glycerol used and results in a gradual shift from Ca2+ stimulation at low 1,2-dioleoyl-sn-glycerol concentrations to calcium inhibition at higher concentrations of 1,2-dioleoyl-sn-glycerol. Phosphatidylserine-stimulated activity is also shown to be largely independent of the calcium concentration at higher molar fractions of 1,2-dioleoyl-sn-glycerol. Thus, with certain lipid compositions, protein kinase C activity becomes independent of the calcium concentration or requires only very low, stoichiometric binding of Ca2+ to high affinity sites on the enzyme. Protein kinase C can bind to phosphatidic acid vesicles more readily than it can bind to phosphatidylserine vesicles in the absence of calcium. Addition of 1,2-dioleoyl-sn-glycerol to phosphatidylserine vesicles promotes the partitioning of protein kinase C into the membrane in the absence of added Ca2+. There is no isozyme specificity in this binding. These results suggest that a less-tightly packed headgroup region of the bilayer causes increased insertion of protein kinase C into the membrane. This is a necessary but not sufficient condition for activation of the enzyme in the presence of EGTA.

Suppression by wortmannin of platelet responses to stimuli due to inhibition of pleckstrin phosphorylation

Studies were made of inhibition by wortmannin, a fungal metabolite, of human platelet responses to various stimuli. Wortmannin at concentrations as low as 1-100 nM inhibited several receptor-agonist-induced 5-hydroxytryptamine release from platelets, without affecting agonist-induced increases in the intracellular concentration of Ca2+. Phorbol 12-myristate 13-acetate (PMA), an active tumour promoter, caused 5-hydroxytryptamine release when combined with a low concentration of ionomycin, and platelet aggregation by itself; these effects of the phorbol ester were also inhibited by wortmannin as well as by staurosporine, a potent, although non-specific, protein kinase C (PKC) inhibitor, in a similar molar concentration range. The platelet responses to the receptor agonists or PMA were accompanied by increased incorporation of [32P]Pi into pleckstrin, a protein selectively expressed in platelets and other blood cells arising from haematopoietic stem cells, as a result of PKC activation in the intact cells. The pleckstrin phosphorylation was inhibited by wortmannin in ways mostly similar to those in which it inhibited the 5-hydroxytryptamine-release responses. Nevertheless, wortmannin failed to inhibit PKC activity measurable in a cell-free assay system which is highly susceptible to staurosporine. Nor did it inhibit the translocation of cytosolic PKC to membranes induced by addition of PMA to platelet cells. Thus wortmannin, which is not a direct inhibitor of PKC, could interfere with the kinase-dependent phosphorylation of pleckstrin, which may play an important role in the cellular responses to receptor stimulation.

The activation of inactive membrane-associated protein kinase C is associated with DMSO-induced erythroleukemia cell differentiation

The rapid redistribution of cytosolic protein kinase C (PKC) to membranes and its subsequent proteolytic activation to PKM have been implicated in the DMSO/HMBA-induced differentiation of murine erythroleukemia (MEL) cells. However, DMSO was found not to induce detectable changes in PKC distribution in a MEL cell subline (MEL1) which differentiated normally in response to the agent. Nevertheless, the differentiation of MEL1 cells appeared dependent on an early PKC-related event because hemoglobinization was partially blocked by the PKC inhibitor H-7 added to cells within the first 2 h after DMSO induction. Indeed, a rapid (15-60 min) increase in membrane PKC activity was detected in DMSO-treated MEL1 cells using a novel method which quantitates the amount of 'active' PKC in intact membranes. This transient PKC increase resulted from the activation of 'inactive' enzyme already associated with membranes, and not from the translocation of cytosolic PKC. Conventional PKC assays cannot distinguish between active and inactive membrane PKC pools. DMSO also activated inactive membrane PKC in HL-60 cells, but not in S49T-lymphoma and WEHI-231 B-lymphoma cells which do not differentiate in response to DMSO. The results suggest that a rapid and transient increase in membrane PKC activity may be an important early step in DMSO-induced differentiation of erythroleukemia cells.

Identification of two distinct populations of protein kinase C in rat brain membranes

The regulatory enzyme protein kinase C (PKC) is proposed to be activated on its translocation from the cytosol to the membrane. However, a portion of the native activity is always associated with the membrane fraction. Using a noninvasive procedure to extract this endogenous activity from rat brain membranes, it has been possible to characterize the activity in a partially purified reconstituted system bearing resemblance to the in vivo system. Two subpopulations of membrane-associated PKC were identified and characterized at the level of activation, inhibition, and isozyme immunologic characteristics and chromatographic properties. One peak had properties similar to those of cytosolic PKC, whereas the second population, extracted as protein-lipid complexes, had considerable constitutive activity that could be stimulated further on addition of PKC activators. This latter activity was relatively resistant to staurosporine inhibition and phorbol ester treatment, but it phosphorylated the exogenous PKC substrates, histone 1 and the epidermal growth factor receptor peptide KTRLRR. The constitutive activity was totally dependent on its endogenous associated lipids coextracted by the solubilization procedure. The ratio between these two populations was ontogenetically regulated and modulated by phorbol ester treatment, suggesting that different PKC populations may serve unique functions in the rat brain regulated by the lipid environment. Analyses of the phospholipids extracted in these protein-lipid complexes showed differences in the major classes correlating to age. However, apart from a markedly lower cholesterol content in these complexes, no direct relationship between a specific lipid composition and the amount of constitutive PKC activity was evident.

Membrane-bound annexin V isoforms (CaBP33 and CaBP37) and annexin VI in bovine tissues behave like integral membrane proteins

The distribution of annexin V isoforms (CaBP33 and CaBP37) and of annexin VI in bovine lung, heart, and brain subfractions was investigated with special reference to the fractions of these proteins which are membrane-bound. In addition to EGTA-extractable pools of the above proteins, membranes from lung, heart, and brain contain EGTA-resistant annexins V and VI which can be solubilized with detergents (Triton X-100 or Triton X-114). A strong base like Na2CO3, which is usually effective in extracting membrane proteins, only partially solubilizes the membrane-bound, EGTA-resistant annexins analyzed here. Also, only 50-60% of the Triton X-114-soluble annexins partition in the aqueous phase, the remaining fractions being recovered in the detergent-rich phase. Altogether, these findings suggest that, by an as yet unknown mechanism, following Ca(2+)-dependent association of annexin V isoforms and annexin VI with membranes, substantial fractions of these proteins remain bound to membranes in a Ca(2+)-independent way and behave like integral membrane proteins. These results further support the possibility that the above annexins might play a role in membrane trafficking and/or in the regulation of the structural organization of membranes.

Cellular distribution of gastric chief cell protein kinase C activity: differential effects of diacylglycerol, phorbol esters, carbachol, and cholecystokinin

Stimulation of chief cells with carbachol or cholecystokinin (CCK) results in the production of inositol trisphosphate (IP3) and diacylglycerol (DAG). Although IP3 increases cell calcium concentration, thereby stimulating pepsinogen secretion, the role of DAG and its target, protein kinase C (PKC), is less clear. To examine the relation between the cellular distribution of PKC activity and pepsinogen secretion, we determined PKC activity in cytosolic and membrane fractions from dispersed chief cells from guinea pig stomach. To validate our assay, we studied the actions of the phorbol ester PMA. PMA caused a rapid, dose-dependent, 6-fold increase in pepsinogen secretion and membrane-associated PKC activity. Similarly, dose-response curves for pepsinogen secretion and the increase in membrane-associated PKC activity induced by a membrane-permeant DAG (1-oleoyl-2-acetylglycerol) were superimposable. In contrast, CCK (0.1 nM to 1.0 microM) and carbachol (0.1 microM to 1.0 mM) caused a 4-fold increase in pepsinogen secretion, but did not alter the distribution of PKC activity. These results indicate that in gastric chief cells, PMA- and DAG-induced pepsinogen secretion is accompanied by increased membrane-associated PKC activity. However, the cellular distribution of PKC activity is not altered by CCK or carbachol.

Response of brain protein kinase C isozymes to ethyl oleate, an alcohol metabolite

Rat brain protein kinase C (PKC) isozymes I, II and III were stimulated by fatty acids in the absence and presence of calcium. Ethyl oleate, which by itself has no effect on PKC activity, had a potentiating effect on fatty acid-induced activation of all 3 isozymes. Potentiation was observed predominantly in the presence of calcium. Interaction of ethyl oleate with a signalling mechanism involving PKC may underlie the cognitive disturbances noted after alcohol consumption.

The direct measurement of protein kinase C (PKC) activity in isolated membranes using a selective peptide substrate

A protein kinase C (PKC)-selective peptide substrate was used to develop a method for measuring PKC activity directly and quantitatively in isolated cell membranes without prior detergent extraction and reconstitution of the enzyme with phosphatidylserine and TPA in the presence of excess Ca2+. This simple and rapid method can reliably measure changes in membrane-associated PKC activity induced by various bioactive compounds such as hormones and growth factors. Also, this method, which measures PKC activity in its native membrane-associated state, has the advantage of being able to distinguish between active and inactive PKC associated with cell membranes.

Different regulation of vascular tone by angiotensin II and endothelin-1 in rat aorta

The effects of moderate cooling and of phenylarsine oxide on the contraction induced by two vasoactive peptides, angiotensin II (AII) and endothelin (ET-1), were investigated on endothelium-free rings of rat aortas. At 37 degrees C, the contraction induced by AII (0.1 microM) was transient. This decline in tension is unlikely to be due to rapid degradation of AII. In contrast, ET-1 (10 nM) induced a slowly developing and sustained contraction similar to the one observed with phorbol 12-13 dibutyrate (PDB, 22 nM). Moderate cooling (25 degrees C) significantly potentiated and prolonged the effect of AII but reduced the velocity of the ET-1 and PDB contraction, although the rate of the phenylephrine (1 microM) response remained unchanged. Phenylarsine oxide (100 microM) reduced the decline in tension in response to AII but inhibited the contraction elicited by ET-1 and PDB. In rings incubated in calcium-free medium (37 degrees C), AII induced a phasic contraction. This was followed by a second phasic contraction after calcium (2.5 mM) had been restored to the bath. The intensity of this second contraction decreased as the time between AII and calcium injection increased. This method, using regression analysis, permitted us to determine the time taken to reduce the contraction by half (4.8 min; r: 0.96), which may reflect the half-time of receptor sequestration. In calcium-free medium, the contractions induced by ET-1 and PDB were slow and sustained. Thus, rapid AII-receptor internalization leads to a short-term regulation of vascular tone whereas activation of protein kinase C by ET-1 may induce a long-term regulation.

Changes in the activity of protein kinase C and the differential subcellular redistribution of its isozymes in the rat striatum during and following transient forebrain ischemia

The changes in the levels of protein kinase C [PKC(alpha, beta II, gamma)] were studied in cytosolic and particulate fractions of striatal homogenates from rats subjected to 15 min of cerebral ischemia induced by bilateral occlusion of the common carotid arteries and following 1 h, 6 h, and 48 h of reperfusion. During ischemia the levels of PKC(beta II) and -(gamma) increased in the particulate fraction to 390% and 590% of control levels, respectively, concomitant with a decrease in the cytosolic fraction to 36% and 20% of control, respectively, suggesting that PKC is redistributed from the cytosol to cell membranes. During reperfusion the PKC(beta II) levels in the particulate fraction remained elevated at 1 h postischemia and decreased to below control levels after 48 h reperfusion, whereas PKC(gamma) rapidly decreased to subnormal levels. In the cytosol PKC(beta II) and -(gamma) decreased to 25% and 15% of control levels at 48 h, respectively. The distribution of PKC(alpha) did not change significantly during ischemia and early reperfusion. The PKC activity in the particulate fraction measured in vitro by histone IIIS phosphorylation in the presence of calcium, 4 beta-phorbol 13-myristate 12-acetate, and phosphatidylserine (PS) significantly decreased by 52% during ischemia, and remained depressed over the 48-h reperfusion period. In the cytosolic fraction PKC activity was unchanged at the end of ischemia, and decreased by 47% after 6 h of reperfusion. The appearance of a stable cytosolic 50-kDa PKC-immunoreactive peptide or an increase in the calcium- and PS-independent histone IIIS phosphorylation was not observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Difference between the calcium- and the phorbol ester-induced association of protein kinase C with phospholipid membrane

1. Membrane association of protein kinase C is thought to be a prerequisite for the activation of the enzyme. 2. We studied the association of the enzyme with liposome. 3. We show here that the mechanisms for the calcium- and the phorbol ester-induced association of protein kinase C with liposome are different from each other. 4. Diacylglycerol is not crucial for the association of the enzyme with liposome.

Memory formation in the chick depends on membrane-bound protein kinase C

The role of protein kinase C (PKC) in the formation of memory for a one-trial passive avoidance task in 1-day-old chicks has been studied, following earlier observations that training on this task results in transient and lateralised changes in the phosphorylation state of presynaptic B-50 protein, a PKC substrate. In accord with hypotheses that the activity of PKC is regulated by translocation from cytosol to membrane, a significant increase was found in the fraction of the alpha/beta forms of the enzyme, assayed immunologically, present in a synaptic-membrane-bound, Triton-extractable form in the left intermediate medial hyperstriatum ventrale (IMHV) of chicks 30 min after training on the passive avoidance task. Two inhibitors of PKC, melittin (10 microliters, 120 microM) and H7 (10 microliters, 10 mM), if injected intracerebrally 10 min prior to or 10 min after training, were without effect on the general behaviour of the chicks or their training. However, these injections of the inhibitors produced amnesia in birds tested 3 h later. This effect was lateralised; only left hemisphere injections of the inhibitors produced amnesia. A possible state-dependency interpretation of these results was ruled out. The results are discussed in the context of hypotheses as to the regulatory role of PKC in neural plasticity and memory formation.