Differential activation of protein kinase C isozymes by short chain phosphatidylserines and phosphatidylcholines

Equation of State for Phospholipid Self-Assembly

Phospholipid self-assembly is the basis of biomembrane stability. The entropy of transfer from water to self-assembled micelles of lysophosphatidylcholines and diacyl phosphatidylcholines with different chain lengths converges to a common value at a temperature of 44°C. The corresponding enthalpies of transfer converge at ∼-18°C. An equation of state for the free energy of self-assembly formulated from this thermodynamic data depends on the heat capacity of transfer as the sole parameter needed to specify a particular lipid. For lipids lacking calorimetric data, measurement of the critical micelle concentration at a single temperature suffices to define an effective heat capacity according to the model. Agreement with the experimental temperature dependence of the critical micelle concentration is then good. The predictive powers should extend also to amphiphile partitioning and the kinetics of lipid-monomer transfer.

Thermodynamics of phospholipid self-assembly

Negatively charged phospholipids are an important component of biological membranes. The thermodynamic parameters governing self-assembly of anionic phospholipids are deduced here from isothermal titration calorimetry. Heats of demicellization were determined for dioctanoyl phosphatidylglycerol (PG) and phosphatidylserine (PS) at different ionic strengths, and for dioctanoyl phosphatidic acid at different pH values. The large heat capacity (ΔC°(P) ∼ -400 J.mol(-1) K(-1) for PG and PS), and zero enthalpy at a characteristic temperature near the physiological range (T(∗) ~ 300 K for PG and PS), demonstrate that the driving force for self-assembly is the hydrophobic effect. The pH and ionic-strength dependences indicate that the principal electrostatic contribution to self-assembly comes from the entropy associated with the electrostatic double layer, in agreement with theoretical predictions. These measurements help define the thermodynamic effects of anionic lipids on biomembrane stability.

Analysis of mucins: role in laboratory diagnosis

Mucins are high molecular weight glycoproteins with complex oligosaccharide side chains attached to the apomucin protein backbone byO-glycosidic linkage; they are found in crude mucus gels that protect epithelial surfaces in the major tracts of the body and as transmembrane proteins expressed on the apical cell surface of glandular and ductal epithelia of various organs. Changes in the sequence of glycosylation of mucins in different settings generate a variety of epitopes in the oligosaccharide side chains of mucins, including newly expressed blood-group antigens, distinguishing between normal and diseased states. Tumour-associated epitopes on mucins and their antigenicity make them suitable as immunotargets on malignant epithelial cells and their secretions, creating a surge of interest in mucins as diagnostic and prognostic markers for various diseases, and even influencing the design of mucin-based vaccines. This review discusses the emerging roles of mucins such as MUC1 and MUC4 in cancer and some other diseases, and stresses how underglycosylated and truncated mucins are exploited as markers of disease and to monitor widespread metastasis, making them useful in patient management. Furthermore the type, pattern and amount of mucin secreted in some tissues have been considered in the classification and terminology of neoplasia and in specific organs such as the pancreas. These factors have been instrumental in pathological classification, diagnosis and prognostication of neoplasia.

Bile acid induces hydrophobicity-dependent membrane alterations

Elevated concentrations of fecal bile acids are a known risk factor for colon cancer, owing to alterations in cellular signaling. In colonic cells, where bile acid uptake is minimal, the hydrophobicity-induced membrane perturbation and alterations have been proposed, but these membrane alterations are largely uncharacterized. In this study, we examined the determinants and characteristics of bile acid-induced membrane alterations, utilizing PKCalpha activation and cholesterol up-regulation as model indicators. We found that bile acid-induced PKCalpha activation is a function of hydrophobicity and correlated with alteration in membrane lipid composition, as evident by the significant up-regulation in membrane cholesterol and phospholipid. We found that bile acid do not cause cell membrane disruption at a concentration sufficient to activate PKCalpha, but do induce drastic alterations in membrane composition. Bile acid also induced the modification and up-regulation of caveolin-1 in a hydrophobicity-dependent manner, implying widespread receptor dysregulation. Similarly, ERK1/2 activation was observed only in response to hydrophobic bile acids, suggesting hydrophobicity-induced caveolar or membrane stress. Experiments with sodium lauryl sarcosine and cholesteryl hemisuccinate showed that bile acid-induced membrane alterations can be mimicked by hydrophobic molecules unrelated to bile acids, strongly implicating hydrophobicity as an important determinant of bile acid signaling.

Differential inhibition by alpha and epsilonPKC pseudosubstrate sequences: a putative mechanism for preferential PKC activation in neonatal cardiac myocytes

The aims of the current study were: 1) to determine if the epsilonPKC pseudosubstrate peptide (epsilonphi) (NH(2)-RKRQGAVRRRVHQVNG-COOH) could be used as an epsilonPKC-selective inhibitor in neonatal cardiac myocytes (NCMs) and 2) to determine if differences in the alpha and epsilonPKC autoinhibitory pseudosubstrate mechanisms could play roles in alpha and epsilonPKC-selective functions. Introduction of the epsilonphi into NCMs by transient permeabilization modestly attenuated 3 nM 4-beta PMA-induced slowing of contraction rate, an epsilonPKC mediated response (Circ Res. 76:654-663; J. Biol. Chem. 271:24962-24966). In contrast, the alphaPKC pseudosubstrate peptide (alphaphi) (NH(2)-RFARKGALRQKNVHEVK-COOH) was 6- to 10-fold more potent at antagonizing the 3 nM 4-beta PMA-induced slowing of contraction rate. Addition of purified PKC to the particulate cell fraction of NCMs promoted (32)P incorporation into 3 proteins of approximately 18, approximately 46 and approximately 97 kDa. The alphaphi antagonized these phosphorylations with IC(50) values of 1 - 5 microM. These IC(50) values were 1.8 - 4.7-fold lower than those observed for the epsilonphi. In in vitro phosphorylation assays with recombinant alpha or epsilon PKC isozymes the phi failed to inhibit the PKC isozyme as potently as the alphaphi peptide but both the alphaphi and the epsilonphi were equally effective inhibitors of the recombinant alphaPKC isozyme. In addition, in vitro cleavage of the epsilonphi by the protease Arg-C in lysates from NCMs treated with 3 nM 4-beta PMA was greatly enhanced when compared to that of the alphaPKC isozyme. Our studies suggest that the epsilonphi cannot be used as a selective inhibitor of the epsilonPKC isozyme in NCMs and that there are differences in the epsilonPKC and alphaPKC autoinhibitory pseudosubstrate mechanisms.

Protein kinase C-like immunoreactive cells in embryo and adult chicken retinas

Morphological evidence of a temporal parallelism between the appearance of the alpha isoform of protein kinase C (PKC) and some processes such as synaptogenesis in the plexiform layers of the chicken retina is offered. Immunostaining experiments were performed throughout embryonic, young and adult chicken life. The results help to understand the development of rod bipolar cells.

Contributions to maxima in protein kinase C activation

In many lipid systems, the activity of protein kinase C (PKC) exhibits a peak followed by a decline as the mol % of one component is increased. In these systems, an increase in one lipid component is always at the expense of another or accompanied by a change in total lipid concentration. Here we report that in saturated phosphatidylserine (PS)/phosphatidylcholine (PC)/diacylglycerol (DAG) mixtures, increasing PS or DAG at the expense of PC revealed an optimal mol % PS, dependent on mol % DAG, with higher mol % PS diminishing activity. The decrease at high mol % PS is probably not attributable simply to more gel-phase lipid due to the higher melting temperature of saturated PS versus PC because a similar peak in activity occurred in unsaturated lipid systems. Increasing the total lipid concentration at suboptimal mol % PS provided the same activity as higher mol % PS at lower total lipid concentration. However, at optimal mol % PS, activity increased and then decreased as a function of total lipid concentration. PKC autophosphorylation also exhibited an optimum as a function of mol % PS, and increasing the PKC concentration increased the mol % PS at which activity decreased, both for autophosphorylation and for heterologous phosphorylation. Formation of two-dimensional crystals of PKC on lipid monolayers also exhibited a peak as a function of mol % PS, and the unit cell size of the crystals formed shifts from 50 x 50 A at low mol % PS to 75 x 75 A at higher PS. Collectively, these data suggest the existence of optimal lipid compositions for PKC activation, with increased quantity of these domains serving to dilute out enzyme-substrate aggregates and/or enzyme-enzyme aggregates on the lipid surface.

Myristoylation does not modulate the properties of MARCKS-related protein (MRP) in solution

The members of the myristoylated alanine-rich C kinase substrate (MARCKS) family are proteins essential for brain development and phagocytosis. MARCKS proteins bind to actin filaments and calmodulin (CaM) and are phosphorylated by protein kinase C. In order to investigate how these interactions are regulated, we have characterized the properties of both the myristoylated (myr) and unmyristoylated (unmyr) forms of recombinant MARCKS-related protein (MRP), a 20-kDa member of the MARCKS family. Ultracentrifugation and circular dichroic spectroscopy reveal that MRP is an elongated protein, with an axis ratio estimated between 7 and 12 and with an apparent random coil conformation. MRP binds to CaM with high affinity (Kd,myr = 4 nM; Kd,unmyr = 7 nM) and with a second order rate constant, k+1,unmyr, of 1.6 x 10(8) M-1 s-1. In contrast to classical ligands such as the myosin light chain kinase, binding of MRP to CaM does not induce the formation of an alpha-helix in MRP. The catalytic subunit of protein kinase C (PKM) phosphorylates myr MRP with high affinity ([S]0.5 = 3.5 microM), positive cooperativity (nH = 2.5) and a turnover number of 130 min-1. CaM inhibits the phosphorylation of myr MRP with a half-maximum rate of phosphorylation at a [CaM]/[MRP] ratio of 0.7, indicating that CaM might efficiently regulate the phosphorylation of MRP in vivo. Interestingly, Ca2+ inhibits the binding of MRP to CaM as well as its phosphorylation by PKM in the millimolar concentration range, suggesting that MRP has a weak affinity for Ca2+. Finally, unmyr MRP can be stoichiometrically myristoylated by N-myristoyl transferase in vitro. Since neither binding of CaM nor phosphorylation by PKM inhibits myristoylation, the N terminus of unmyr MRP is exposed on the surface of the protein and is well separated from the effector domain. In view of the observations that unmyr and myr MRP do not exhibit significant differences in their properties in solution, the function of myristoylation is most probably to modulate the interactions of MRP with membranes.

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.

Developmental expression of protein kinase C immunoreactivity in rod bipolar cells of the rabbit retina

Rod bipolar cells constitute the second-order neuron in the rod pathway. Previous investigations of the rabbit retina have evaluated the development of other components of the rod pathway, namely the dopaminergic and AII amacrine cell populations. To gain further insights into the maturation of this retinal circuitry, we studied the development of rod bipolar cells, identified with antibodies directed to the alpha isoform of protein kinase C (PKC), in the rabbit retina. Lightly immunostained PKC-immunoreactive (IR) somata are first observed at postnatal day (PND) 6 in the distal inner nuclear layer (INI.). Immunostaining is also observed in the outer plexiform layer (OPL), indicating the presence of PKC-IR dendrites. PKC-IR axons are present in the INL oriented toward the inner plexiform layer (IPL). Several of them terminate with enlarged structures resembling growth cones. At PND 8, some immunostained terminal bulbs, characteristic of rod bipolar cells, are detected in the proximal IPL. PKC-IR cells at PND 11 (cye opening) display stronger immunostaining and more mature characteristics than at earlier ages. The dendritic arborizations of these cells in the OPL and their axon terminals in the IPL attain mature morphology at later ages (PND 30 or older). The density of PKC-IR cells shows a peak at PND 11 followed by a drastic decrease up to adulthood. The total number of PKC-IR cells increases from PND 6 to PND 11 and then it remains almost unchanged until adulthood. The mosaic of PKC-IR cells is nonrandom in some retinal locations at PND 6, but the overall regularity index at PND 6 is lower than at older ages. The present data provide a comprehensive evaluation of the development of rod bipolar cells in the postnatal rabbit retina and are consistent with those previously reported for dopaminergic and AII amacrine cell populations, indicating that different components of the rod pathway follow a similar pattern of maturation, presumably allowing the rod pathway to be functional at eye opening.

Soluble phospholipids enhance factor Xa-catalyzed prothrombin activation in solution

Acidic phospholipids play an important but incompletely understood role in prothrombin activation. Here we report the effect of short-chain phosphatidylserine (dicaproylphosphatidylserine, C6PS) and the corresponding phosphatidylglycerol (C6PG) and phosphatidylcholine (C6PC) derivatives on the rate of prothrombin activation by factor Xa. The critical micellar concentrations of these short-chained phospholipids have been determined under a variety of conditions that we used for kinetic and structural studies. Under conditions for which these lipids exist in a soluble form, the results demonstrate that: (i) the rate of human prothrombin activation by human factor Xa was enhanced in a calcium-dependent fashion up to 60-fold by addition of C6PS, roughly 20% of the optimal enhancement seen with bovine phosphatidylserine/palmitoyloleoylphosphatidylcholine (25/75 PS/POPC) membranes; (ii) C6PS inhibited the rate of hydrolysis of synthetic factor Xa substrate (S-2765), an effect that was mimicked, but at much lower lipid concentrations, by PS/POPC membranes; (iii) there was no enhancement of prothrombin activation and much less inhibition of hydrolysis of S-2765 by factor Xa in the presence of C6PG or C6PC; and (iv) the thermal denaturation of prothrombin was altered in a calcium-independent but dose-dependent fashion by either C6PS or C6PG. These results have been interpreted in terms of the existence of (a) specific PS binding site(s) on factor Xa (Kd approximately 73 microM) that regulate(s) the activity of this serine protease. Our results do not rule out the possibility that the rate of prothrombin activation is also influenced by a weaker, calcium-independent, and less specific acidic lipid binding site on prothrombin, the occupancy of which results in conformational changes in this protein. The results clearly suggest that PS binding regulates the rate of prothrombin activation.

Immunocytochemical identification of cone bipolar cells in the rat retina

We studied the morphology of bipolar cells in fixed vertical tissue sections of the rat retina by injecting the cells with Lucifer Yellow and neurobiotin. In addition to the rod bipolar cell, nine different putative cone bipolar cell types were distinguished according to the position of their somata in the inner nuclear layer and the branching pattern and stratification level of their axon terminals in the inner plexiform layer. Some of these bipolar cell populations were labeled immunocytochemically in vertical and horizontal sections using antibodies against the calcium-binding protein recoverin, the glutamate transporter GLT-1, the alpha isoform of the protein kinase C, and the Purkinje cell marker L7. These immunocytochemically labeled cell types were characterized in terms of cell density and distribution. We found that rod bipolar cells and GLT-1-positive cone bipolar cells occur at higher densities in a small region located in the upper central retina. This area probably corresponds to the central area, which is the region of highest ganglion cell density. A second peak of rod bipolar cell density in the lower temporal periphery matches the retinal area of binocular overlap. The population densities of the immunocytochemically characterized bipolar cells indicate that at least 50% of all bipolar cells are cone bipolar cells. The variety and total number of cone bipolar cells is surprising because the retina of the rat contains 99% rods. Our findings suggest that cone bipolar cells may play a more important role in the visual system of the rat than previously thought.

Two types of mitochondria are evidenced by protein kinase C immunoreactivity in the Müller cells of the carp retina

The localization of protein kinase C (PKC) was studied immunocytochemically in the Müller cells of the carp retina. Electron microscope immunocytochemistry (using a monoclonal antibody to the alpha and beta isoenzymes of PKC) showed PKC-immunoreactivity mainly inside some mitochondria, especially along the mitochondrial cristae whereas other mitochondria in the same Müller cells showed no staining. Despite a detailed analysis we did not find any significant morphological difference between labeled and unlabeled mitochondria. These results demonstrate, for the first time, the presence of PKC immunoreactivity inside mitochondria and suggest that individual mitochondria may differ in signal transduction pathway.

Immunocytochemical analysis of bipolar cells in the macaque monkey retina

Transfer of visual information from photoreceptors to ganglion cells within the retina is mediated by specialized groups of bipolar cells. At least 10 different morphological types of bipolar cells have been distinguished in Golgi studies of primate retina. In the present study, bipolar cell populations in the macaque monkey retina were identified by their differential immunoreactivity to a spectrum of antibody markers. This enabled their spatial density and photoreceptor connections to be analysed. An antibody against the beta isozyme of protein kinase C (PKCA beta) labelled many cone bipolar cells. Invaginating (presumed ON) cone bipolar cells and rod bipolar cells were preferentially labelled with a monoclonal antibody raised against rabbit olfactory bulb. Flat (presumed OFF) bipolar cells were labelled with an antiserum against the glutamate transporter protein (GLT-1). Different populations of diffuse cone bipolar cells, which contact 5-10 cones, could be distinguished. The GLT-1 antiserum preferentially labelled the flat diffuse bipolar cell type DB2 (Boycott and Wässle, 1991, Eur. J. Neurosci. 3:1069-1088) as well as flat midget bipolar cells. Antibodies to calbindin (CaBP D-28K) labelled the flat diffuse bipolar cell type DB3 and (possibly) the invaginating diffuse bipolar cell type DB5. An antibody against the alpha isozyme of PKC labelled an invaginating diffuse bipolar cell type (DB4) as well as rod bipolar cells. Comparison of the spatial density of cone bipolar cell populations with that of photoreceptors suggests that each bipolar cell class provides a complete coverage of the cone array (each cone is contacted by at least one member of every bipolar cell class). These results support the classification scheme of Boycott and Wässle (1991) by showing that different diffuse bipolar cell classes express different patterns of immunoreactivity, and they reinforce the view that different spatial and temporal components of the signal from the photoreceptor array are processed in parallel within the primate retina.

Lipid dynamics and peripheral interactions of proteins with membrane surfaces

A large body of evidence strongly indicates biomembranes to be organized into compositionally and functionally specialized domains, supramolecular assemblies, existing on different time and length scales. For these domains and intimate coupling between their chemical composition, physical state, organization, and functions has been postulated. One important constituent of biomembranes are peripheral proteins whose activity can be controlled by non-covalent binding to lipids. Importantly, the physical chemistry of the lipid interface allows for a rapid and reversible control of peripheral interactions. In this review examples are provided on how membrane lipid (i) composition (i.e., specific lipid structures), (ii) organization, and (iii) physical state can each regulate peripheral binding of proteins to the lipid surface. In addition, a novel and efficient mechanism for the control of the lipid surface association of peripheral proteins by [Ca2+], lipid composition, and phase state is proposed. The phase state is, in turn, also dependent on factors such as temperature, lateral packing, presence of ions, metabolites and drugs. Confining reactions to interfaces allows for facile and cooperative large scale integration and control of metabolic pathways due to mechanisms which are not possible in bulk systems.

The existence of protein kinase C in cone photoreceptors in the rat retina

We examined the localization of protein kinase C (PKC) in the rat retina, using a monoclonal antibody against PKC. The PKC immunoreactivities were localized in bipolar cells as reported previously, and also in outer and inner segments (OS and IS) of photoreceptor cells. As the PKC immunoreactive OS and IS of photoreceptors were very few in number, we hypothesized that these were of cone photoreceptors. We then examined whether the PKC immunoreactive OS and IS were bound by peanut agglutinin which was shown to bind specifically to cone OS and IS. Almost all of the PKC immunoreactive OS and IS showed PNA binding.

In vitro activation of brain protein kinase C by the cannabinoids

The cannabinoids have been shown to affect both membrane lipid ordering and the activities of several membrane-associated proteins. We have investigated the effects of the cannabinoids on protein kinase C, a lipid-dependent enzyme that functions as an important regulator of signal-transduction processes in the brain. The naturally occurring cannabinoid delta 9-tetrahydrocannabinol (delta 9-THC) increased the activity of protein kinase C isolated from rat forebrain at concentrations of 10 microM and above. 11-OH-delta 9-THC, cannabinol and cannabidiol also increased protein kinase C activity in the same concentration range. delta 9-THC (10 microM) decreased the Kact of protein kinase C for calcium from 28 microM to 18 microM and had no effect on the phosphatidylserine concentration-stimulation relationship. At a concentration of 30 microM, delta 9-THC increased the binding of [3H]phorbol-12,13-dibutyrate ([3H]PDBu) to protein kinase C and decreased the Kd for [3H]PDBu from 8.2 nM to 5.4 nM. delta 9-THC also had effects on lipid ordering of PS micelles, producing a significant increase in the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene at a concentration of 10 microM. These data suggest that delta 9-THC activates protein kinase C via a novel mechanism, possibly as a result of effects on vesicle lipid physical characteristics.

The cholinergic stimulating effects of ciliary neurotrophic factor and leukemia inhibitory factor are mediated by protein kinase C

The intracellular mechanisms through which two trophic factors, ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF), regulate cholinergic development were examined in sympathetic neuron cultures. Treatment with CNTF or LIF increased levels of choline acetyltransferase (ChAT) activity by 375 and 350%, respectively. However, in neuronal cultures depleted of protein kinase C (PKC) activity by chronic phorbol ester treatment, neither CNTF nor LIF elevated ChAT activity. Further, the stimulation of ChAT due to increased cell density was not observed in PKC-depleted sympathetic neurons. The inhibition of CNTF-stimulated ChAT by phorbol ester occurred in a dose-dependent manner and chronic phorbol ester treatments did not alter the levels of the catecholamine biosynthetic enzyme tyrosine hydroxylase. Moreover, increased levels of diacylglycerol, an endogenous activator of PKC, were observed in sympathetic neurons treated with CNTF. However, neither CNTF nor LIF stimulated the hydrolysis of phosphatidylinositol 4,5-bisphosphate. These observations suggest that a common PKC-dependent pathway, which is independent of phosphatidylinositol 4,5-bisphosphate hydrolysis, mediates the cholinergic stimulating effects of CNTF, LIF, and cell-cell contact in cultured sympathetic neurons.

Activation and inhibition of protein kinase C isozymes alpha and beta by Gd3+

Gd3+ was evaluated as a probe for Ca2+ sites on protein kinase C (PKC) by studying its ability to replace Ca2+ in activation of PKC isozymes II (beta) and III (alpha) in the lipid systems phosphatidylserine/1,2-dioleoyl-sn-glycerol (PS/DO) and diheptanoylphosphatidylcholine (PC7)/DO. PKC beta was stimulated by Ca2+ or Gd3+ in PS/DO whereas activity in PC7/DO was independent of these metals. Thus, it is suggested that Gd3+ replaces Ca2+ at a site involving metal-lipid interactions. High concentrations of Ca2+ or Gd3+ inhibited activity in both lipid systems. Analysis of the Gd3+ inhibition in the PC7/DO system suggests that it is due to formation of GdATP, which competes at the MgATP site. Activity of PKC alpha was dependent on low concentrations of Ca2+ in both lipid systems. The ability of Gd3+ to substitute for Ca2+ could not be evaluated in the PS system due to the inability to completely remove contaminating Ca2+ without chelating buffers. Successful reduction of contaminating Ca2+ was achieved in the PC7 system but Gd3+ failed to substitute for Ca2+ in activating PKC alpha and only caused inhibition. This is consistent with binding of Gd3+ to a Ca2+ site at or near the active site of the enzyme rather than to a site on the lipid. These results indicate that interactions between PKC and Gd3+ are complex, involving occupation of more than one class of sites. Conditions for separately evaluating the individual sites can be manipulated by selection of isozyme and lipid system.

An intraocular injection of kainate induces expression of c-fos-like protein and activation of protein kinase C (alpha) in specific rabbit retinal neurones

Intraocular injection of kainate into the rabbit eye causes both a translocation and transport of the bipolar cell's alpha PKC 6 h later. Although this effect is similar to what occurs for the phorbol ester, phorbol 12,13-dibutyrate (PDbut), it shows specificity in that N-methyl-D-aspartate (NMDA), 5,7-dihydroxytryptamine and 2-amino-4-phosphonobutyrate (APB) are ineffective. However, preliminary experiments suggest that, when injected into the eye, quisqualate also influences the alpha PKC of the bipolar cells. Injection of kainate into the rabbit eye shows that c-fos-like protein is expressed in certain amacrine and ganglion but not in bipolar cells 6 h later. This expression of c-fos immunoreactivity is transient because 15 h after the injection of kainate no positive staining was seen. It was not possible to analyse the kainate-induced c-fos expression for periods of less than 6 h because the anaesthetic used, Hypnorm, induced c-fos-like protein expression which lasted for 2-4 h.

High-affinity Ca(2+)- and substrate-binding sites on protein kinase C alpha as determined by nuclear magnetic resonance spectroscopy

Water proton nuclear magnetic resonance (NMR) relaxation rates were used to identify metal sites on protein kinase C (PKC) isozymes alpha and beta using paramagnetic Gd3+ as a probe. The paramagnetic effect of Gd3+ on water proton relaxation was enhanced with PKC isozymes alpha and beta in the presence of diheptanoylphosphatidylcholine/1,2-dioleoyl-sn-glycerol (PC7/DO). The data are consistent with a single class of metal-binding sites on PKC beta and two classes of sites on PKC alpha: a single high-affinity site with a KD for Gd3+ of 0.2 microM and a larger class of sites with a lower affinity for Gd3+. Titration with Ca2+ abolished the observed enhancement of water proton relaxation by the PKC alpha.Gd3+ complex, consistent with displacement of Gd3+ by Ca2+. Titrations of the PKC alpha.Gd3+ complex with Co(NH3)4ATP, a substitution-inert analogue of ATP, caused a substantial decrease in the observed water proton relaxation enhancement, consistent with formation of a ternary enzyme.metal.substrate complex with a KPKC alpha.Gd.[CoATP] of 30-100 nM. Titration of the metal enzyme complex with a model peptide substrate derived from the pseudosubstrate sequence of PKC alpha caused a similar decrease in enhancement at stoichiometric concentrations consistent with the formation of a PKC alpha.Gd3+.peptide complex with a KPKC alpha.Gd.[peptide] of less than or equal to 13 nM. Titrations of the fully formed PKC alpha.Gd3+.peptide complex with Co(NH3)4ATP caused a further decrease in enhancement consistent with formation of a quaternary complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Two protein kinase C activators, bryostatin-1 and phorbol-12-myristate-13-acetate, have different effects on haemopoietic cell proliferation and differentiation

Primary B lymphocytes can be induced to proliferate and certain haemopoietic cell lines such as HL60 and U937 can be induced to differentiate by the addition of phorbol esters, which have been shown to activate protein kinase C. Several non-phorbol esters, such as the bryostatins, have also been shown to bind to and activate protein kinase C. Although bryostatin-1 and 12-O-tetradecanoylphorbol-13-acetate (TPA) compete for and activate protein kinase C to the same degree and with similar kinetics and also induce similar levels of expression of the CD23 cell-surface antigen, bryostatin-1 is a weak mitogen for B lymphocytes and fails to induce the differentiation of both HL60 and U937 cells. Such an outcome suggests that these two activators have different binding properties for the enzyme that have a physiological consequence which may be useful for analysing the role that protein kinase C plays in both differentiation and proliferation. Analysis of competition assays between bryostatin-1 and TPA leads us to put forward a model where protein kinase C is required to be constantly reactivated and recycled during proliferation and differentiation which can be accomplished by TPA but not by bryostatin, although we cannot exclude the differential activation of some of the sub-species of the kinase by the two agonists.

Effect of phospholipid unsaturation on protein kinase C activation

To examine the hypothesis that physical features of the membrane contribute to protein kinase C activation, phosphatidylcholine/phosphatidylserine/diolein (70:25:5) vesicles of defined acyl chain composition were tested for their ability to activate the enzyme. Maximal activation was found to correlate with the mole percent unsaturation in the system. Unsaturation could be provided by either the phosphatidylserine or the phosphatidylcholine component. Vesicles containing 5 mol% diolein but lacking any unsaturation in the phospholipid did not support activity, indicating that acidic head groups alone are not sufficient for activity. The saturated lipid vesicles could be rendered effective but only at very high (25 mol%) concentrations of diolein. The degree of acyl chain unsaturation and the positioning of the double bond had little effect on the activity, suggesting that the effect of the unsaturation is due to some physical property of the lipid rather than to a specific lipid-protein interaction. Addition of cholesterol to both saturated and unsaturated systems indicated that fluidity, as assessed by fluorescence anisotropy, did not correlate with activity. These results suggest that a physical property of the membrane other than fluidity is important for the activation of protein kinase C. A model for protein kinase C activation involving phase separation and/or head group spacing is discussed.

Evidence for clonal heterogeneity of the expression of six protein kinase C isoforms in murine B and T lymphocytes

Protein kinase C (PKC), which plays a pivotal role in lymphocyte activation, represents a homologous family of at least nine proteins. Seven genes that encode PKC proteins have been identified. Since the regulatory properties and substrate specificities of the isoforms are not identical in vitro, it is possible that each isoform plays a unique role in cell activation. Toward an understanding of the role of PKC isoforms in lymphocyte activation we have studied the expression of mRNA encoding six of the isoforms (alpha, beta, gamma, delta, epsilon, and zeta) in T cell clones and B cell lines. PKC isoform phenotyping was done by MAPPing using isoform-specific primers and slot-blot analyses of mRNA were performed using specific probes. T cell clones and B cell lines were determined to express levels of the delta, epsilon, and zeta isoforms of PKC that were detectable by MAPPing. Plasmacytomas did not express PKC-beta message detectable by MAPPing. Slot blot analyses and Western blot analyses with peptide-specific antibody confirmed that B cell plasmacytomas did not express PKC-beta mRNA or protein. T cell clones and B cell lines were similar in that none expressed PKC-gamma. In cells that expressed PKC isoforms that were detectable by the MAPPing protocol, there was heterogeneity in the relative abundance of isoform mRNA (PKC-delta and -beta) and protein (PKC-beta and -epsilon). Such diversity of isoform expression could be responsible for the differential responsiveness of lymphocyte clones to activating stimuli.

Interaction of phospholipids with proteins and peptides. New advances 1990

1. The review deals with the recent achievements in the study of the various interactions of phospholipids with proteins and peptides. 2. The interactions are classified according to the hydrophobic, hydrophilic or mixed character of the interactive forces. 3. The effect of the interaction on the structure and biological activity of the interacting molecules is also discussed.

Protein kinase C isozymes have distinct roles in neural induction and competence in Xenopus

The restricted ability of embryonic tissue to respond to inductive signals is controlled by a poorly understood phenomenon, termed competence. In Xenopus, dorsal ectoderm is more competent than ventral ectoderm to become induced to neural tissue. We tested whether the Xenopus protein kinase C (PKC) isozymes alpha and beta have a role in neural induction and competence. We found that PKC alpha is predominantly localized in dorsal ectoderm, whereas PKC beta is uniformly distributed. Overexpression of PKC beta conveys a higher propensity for neural differentiation to both dorsal and ventral ectoderm, but their difference in competence remains. However, ectopic expression of PKC alpha elevates the level of neural competence of ventral ectoderm to that of dorsal ectoderm. These data indicate that different PKC isozymes have distinct roles in mediating both neural induction and competence.

The occurrence of three isoenzymes of protein kinase C (alpha, beta and gamma) in retinas of different species

The localisation and immunochemical identification of 3 different forms of protein kinase C (PKC-alpha, PKC-beta and PKC-gamma) in retinas of different species were analysed by immunohistochemistry and SDS-PAGE-Western blotting, respectively. Only in some cases was there a correlation between the findings from each procedure. One reason for the lack of correlation could be the small amounts of PKC present in some retinas, which made detection possible only by first concentrating the antigen by SDS-PAGE and then carrying out Western blotting. Another possible reason is that an antibody recognises unknown antigens immunohistochemically, but, because of their specific characteristics, they are denatured when subjected to SDS-PAGE and Western blotting and therefore remain undetected. PKC-beta immunoreactivity is present in rabbit, frog and goldfish retinas but absent from the rat retina. However, SDS-PAGE and Western blotting experiments showed that the PKC-beta isoenzyme is absent from the fish retina but present in the rat retina. PKC-beta immunoreactivity in rabbit retina is present in ganglion and/or amacrine cells; in the frog retina the enzyme is associated with some bipolar cells. In the goldfish retina, PKC-beta is associated with a large population of cells in the ganglion cell layer as well as with some amacrine cell bodies. PKC-alpha is present primarily in bipolar cells of rat, fish and rabbit retinas and was not detected by immunohistochemistry or blotting experiments in the frog retina. SDS-PAGE and Western blotting of retinal extracts from different species showed that PKC-gamma occurs in the rabbit where it was associated with ganglion and/or amacrine cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin inhibits the atrial natriuretic factor stimulated cGMP production by activating the protein kinase C in rat aortic smooth muscle cells

Preincubation of rat thoracic aortic smooth muscle cells with endothelin inhibits the atrial natriuretic factor (ANF)-induced cGMP accumulation in these cells in a concentration dependent manner. The maximal inhibition of 64% was afforded by 1 x 10(-6) M endothelin and the half maximal inhibition (IC50) was achieved with 1 x 10(-9) M endothelin. Endothelin (1 x 10(-6) M) also increased the plasma membrane bound protein kinase C (PKC) activity by 4 fold. Hormone-dependent increase in PKC activity was limited to plasma membranes only and some decrease in cytosolic PKC activity was observed. However, phorbol 12-myristate 13-acetate (PMA) (1 x 10(-6)M) provoked a total loss of cytosolic PKC activity and a net gain in membranous PKC activity indicative of the translocation of the enzyme. Pretreatment of these cells with H-7, a PKC inhibitor, released the endothelin and PMA-mediated attenuation of ANF-stimulated cGMP formation. These results suggest that PKC is involved in the regulation of ANF-induced cGMP accumulation and that the vasoconstrictor activity of endothelin might involve inhibition of the vasorelaxant activity of ANF through the inhibition of cGMP accumulation in smooth muscle cells (SMCs) of the rat aorta.

Contrasting effects of sn-1,2-dioctanoyl glycerol as compared to other protein kinase C activators in adrenal glomerulosa cells

Angiotensin II acts on adrenal glomerulosa cells to induce the phospholipase C-mediated generation of inositol trisphosphate and sn-1,2-diacylglycerol as the major products of inositol phospholipid breakdown. This last product is known to activate protein kinase C, but its role in the action of angiotensin II on steroidogenesis has not been defined. We report herein that, in bovine adrenal glomerulosa cells, protein kinase C activators, such as phorbol 12,13-dibutyrate, 12-O-tetradecanoylphorbol-13-acetate, mezerein and sn 1,2 oleoyl acetoylglycerol, each failed to increase steroidogenesis. These results contrast with our recent report on the enhancement of aldosterone output by sn-1,2-dioctanoylglycerol (DiC8) [J. Steroid Biochem. 35 (1990) 19-33]. In addition, the difference between DiC8 and the other protein kinase activators was also observed in the pattern of 86Rb efflux from preloaded glomerulosa cells; only DiC8 mimicked the effect of angiotensin II on ion fluxes. Furthermore, staurosporine, a potent inhibitor of protein kinase C, was capable of amplifying the aldosterone output induced by a maximally effective concentration of DiC8 or angiotensin II. These data suggest that the effect of the cell permeant DiC8 on aldosterone biosynthesis either is not mediated by protein kinase C activation, or is mediated by a phorbol ester-insensitive isoenzyme of protein kinase C.

Effects of the ether phospholipid AMG-PC on mast cells are similar to that of the ether lipid AMG but different from that of the analogue hexadecylphosphocholine

The ether lipid AMG (1-O-hexadecyl-2-O-methylglycerol) has previously been shown to have both enhancing and inhibitory effects on histamine release from isolated rat mast cells. In addition, a synergistic interaction with the phorbol ester TPA indicated protein kinase C activation. In the present investigation the effects of the related ether phospholipid AMG-PC (1-O-hexadecyl-2-O-methylglycero-3-phosphocholine) and the analogue hexadecylphosphocholine (miltefosine (HPC) are compared with those of AMG. HPC had only inhibitory effects, in contrast to AMG-PC which acted similarly on histamine release induced by compound 48/80, but had dual influence on responses to antigen and the ionophore A23187 and mainly exhibited a synergistic interaction with combinations of the ionophore and TPA. The influence of AMG-PC differed from that of AMG in some aspects whereas the character of its synergistic interaction with A23187 resembled that of AMG, in particular after pre-incubation with TPA. The results show that HPC does not share all biological activities of the antineoplastic ether lipids. They indicate that the effects of AMG-PC under appropriate conditions may be due to activation of protein kinase C but do not permit a distinction between direct effects and indirect through metabolic conversion to AMG.

Differential effects of omega-3 fish oils on protein kinase activities in vitro

We studied the in vitro effects of omega-3 fish oils and other fatty acids on the activity of crude protein kinase C from S49 lymphoma cells, on partially purified enzyme from rat cerebrum, on homogeneous protein kinase C from bovine brain, and, for comparison, on type I adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. In the absence of exogenous phospholipid, the fish oils cis-5,8,11,14,17-eicosapentaenoic acid (EPA) and acid (DCHA) enhance the catalytic cis-4,7,10,13,16,19-docosahexaenoic activity of protein kinase C and support the binding of [3H]phorbol 12,13-dibutyrate, both to approximately 50% of the level supported by phosphatidylserine. In the presence of phosphatidylserine, the omega-3 fatty acids reduce catalytic activity and [3H]phorbol 12,13-dibutyrate binding by about one-half. The effects of the omega-3 fatty acids on enzyme activity suggest that fish oils act as partial agonists competitively with phosphatidylserine. EPA, DCHA, and arachidonate (but not a variety of saturated fatty acids) inhibit the cAMP-dependent protein kinase. Thus dietary fish oils and cellular fatty acids mobilized by the action of phospholipase A2 may differentially modulate the activities of protein kinase C and cAMP-dependent protein kinase. These data suggest means by which unsaturated fatty acids mobilized within cells may act as second messengers.

Action of organic solvents on protein kinase C

The action of organic solvents on the biochemical and biophysical properties of protein kinase C (PKC) was measured in a defined lipid vesicle system. Chloroform, benzyl alcohol and ethanol all partially activated PKC. They had no effect on the Ca(2+)- or anionic phospholipid-, phosphatidylserine-dependence. Their ability to activate PKC correlated with their lipid perturbing effect as measured by the decrease in fluorescence anisotropy. Chloroform was the most potent activator stimulating PKC phosphotransferase activity up to a level 40% of that obtained by the endogenous activator, diacylglycerol. The three fluidizers induced a more hydrophobic environment for at least one PKC tryptophan residue. This may have been due to insertion of an additional or different region of protein kinase C into the lipid bilayer as demonstrated by a blue shift in tryptophan fluorescence, providing an explanation for their inability to act as competitors of PKC binding of phorbol esters. Higher concentrations of the organic solvents resulted in a lipid bilayer that was too fluid to support membrane activity. This study demonstrates that these anesthetics and alcohols modulate lipid structure which subsequently induces PKC to undergo a different protein-lipid interaction in comparison to the endogenous activator, diacylglycerol. This supports the proposal that the biophysical state of the membrane plays a significant role in modulating PKC activity.

Antisense DNA downregulates protein kinase C isozymes (beta and alpha) and insulin-stimulated 2-deoxyglucose uptake in rat adipocytes

Rat adipocytes were treated with antisense dimethoxytrityl pentadecadeoxynucleotides, complementary to mRNA initiation codon regions for alpha and beta isozymes of protein kinase C (PKC). This antisense treatment provoked 50-70% decreases in PKC and insulin-stimulated 2-deoxyglucose uptake, but did not inhibit insulin-stimulated diacylglycerol synthesis. Sense or nonsense oligodeoxynucleotides were without effect on PKC and 2-deoxyglucose uptake. These results suggest that: (i) PKC-alpha and PKC-beta isozymes can be specifically downregulated in rat adipocytes by antisense oligodeoxynucleotides, and (ii) insulin-stimulated glucose transport requires PKC.

Protein kinase C immunoreactivity in kitten visual cortex is developmentally regulated and input-dependent

Immunocytochemistry with polyclonal antibodies directed against protein kinase C (PKC) was utilized to investigate the development of the kinase in kitten visual cortex neurons. The immunoreaction product was found at postsynaptic sites at all ages studied. However, PKC was localized in presynaptic terminals only during the first few weeks of postnatal life, during the period when the cortex is most susceptible to visual experience. The overall level of PKC immunoreactivity was high at early postnatal ages (up to 6 weeks) and declined afterwards till adulthood. This decline in reactivity was not equal across the cortex and was particularly marked in the middle cortical layers, especially layer IV. The reduction of PKC immunoreactivity in all cortical layers but layer IV was abolished by isolating a portion of cortex from its neuronal inputs early in life. Indirect evidence points to the lateral geniculate nucleus as the source of input that is required for input-dependent maturational changes in the kinase level. The results reported here suggest that the expression of PKC in kitten visual cortex in not only developmentally regulated but is also use-dependent.