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Y Asaoka

Publications and source records attributed to Y Asaoka.

At least 37 records · Page 2Linked to original sources
PubMed1992

Platelet activation by simultaneous actions of diacylglycerol and unsaturated fatty acids.

Several cis-unsaturated fatty acids such as oleic, linoleic, linolenic, eicosapentaenoic, and docosahexaenoic acids added directly to intact human platelets greatly enhance protein kinase C activation as judged by the phosphorylation of its specific endogenous substrate, a 47-kDa protein. This enhancement absolutely requires the presence of a membrane-permeant diacylglycerol, 1,2-dioctanoylglycerol, or a tumor-promoting phorbol ester, phorbol 12-myristate 13-acetate. In the presence of ionomycin and either 1,2-dioctanoylglycerol or phorbol 12-myristate 13-acetate, the release of serotonin from the platelets is also remarkably increased by cis-unsaturated fatty acids. The effect of these fatty acids is observed at concentrations less than 50 microM. Saturated fatty acids and trans-unsaturated fatty acids are inactive. Titration of ionomycin to induce a release reaction and measurement of the intracellular Ca2+ level by the fura-2 procedure indicate that cis-unsaturated fatty acids increase an apparent sensitivity of the platelet response to Ca2+. The results suggest that cis-unsaturated fatty acids, which are presumably produced from phosphatidylcholine by signal-dependent activation of phospholipase A2, may take part directly in cell signaling through the protein kinase C pathway.

Diglycerides↗
PubMed1992

Role of lysophosphatidylcholine in T-lymphocyte activation: involvement of phospholipase A2 in signal transduction through protein kinase C.

2-Lysophosphatidylcholine (lysoPtdCho), a product of the hydrolysis of phosphatidylcholine catalyzed by phospholipase A2, greatly potentiates the activation of human resting T lymphocytes that is induced by a membrane-permeant diacylglycerol plus a calcium ionophore, as determined by the expression of the alpha subunit of the interleukin 2 receptor and thymidine incorporation into DNA. LysoPtdCho per se is inactive unless both diacylglycerol and a calcium ionophore are present. This effect of lysoPtdCho is also observed when diacylglycerol is replaced by a tumor-promoting phorbol ester. Other lysophosphatides including lysophosphatidylserine, lysophosphatidylinositol, and lysophosphatidic acid are inert except for lysophosphatidylethanolamine, which is far less effective than lysoPtdCho. Tracer experiments with radioactive choline indicate that, when T lymphocytes are stimulated with an antigenic signal, lysoPtdCho is indeed produced in a time-dependent fashion, although the concentration of this lysophospholipid accumulated remains to be quantitated. It suggests that phospholipase A2 is directly involved in the signal transduction pathway through protein kinase C to induce long-term cellular responses.

Calcium↗
PubMed1992

The signal-induced phospholipid degradation cascade and protein kinase C activation.

Acting in synergy with diacylglycerol, unsaturated free fatty acids such as arachidonic, oleic, linoleic, linolenic and docosahexaenoic acids dramatically activate some members of the protein kinase C family at the basal level of Ca2+ concentration. It is plausible that phospholipase C and phospholipase A2, and possibly phospholipase D as well, are involved in the activation of protein kinase C. Presumably, this enzyme activation is integrated into the signal-induced membrane phospholipid degradation cascade, prolonging the activation of protein kinase C. The sustained activity of this enzyme appears to be of importance for long-term cellular responses such as development of neuronal plasticity and gene activation.

Animals↗
PubMed1992

Protein kinase C, calcium and phospholipid degradation.

In most cells, calcium signals are transient, while the resulting physiological responses often persist longer. The sustained activation of protein kinase C has been postulated to be essential for maintaining such cellular responses. It is becoming clear that an elaborate network involving protein kinase C, calcium and degradation of membrane phospholipids may generate several molecules that are necessary for sustaining the activation of protein kinase C itself. Multiple members of the protein kinase C family show distinct responses to calcium and the phospholipid degradation products, suggesting their unique functions in cell signalling.

Animals↗
PubMed1992

The family of protein kinase C in transmembrane signalling for cellular regulation.

Signal-induced hydrolysis of inositol phospholipid produces two second messengers, diacylglycerol and inositol trisphosphate. Diacylglycerol activates protein kinase C, whereas inositol trisphosphate mobilizes Ca2+ from its internal store. Analogously, signal-induced hydrolysis of choline phospholipid generates two second messengers, unsaturated free fatty acid and lysophosphatidylcholine. The free fatty acid synergizes with diacylglycerol to activate protein kinase C and causes full activation of the enzyme even at the basal level of Ca2+. On the other hand, lysophosphatidylcholine dramatically enhances cellular responses such as cell proliferation and differentiation under the conditions where diacylglycerol and Ca2+ are available. It is likely that all of the immediate products of signal-induced degradation of inositol and choline phospholipids are involved directly in concert in the transmembrane control of cellular functions.

Animals↗
PubMed1991

Sustained activation of protein kinase C is essential to HL-60 cell differentiation to macrophage.

Although a single dose of phorbol 12-myristate 13-acetate (PMA) allowed HL-60 cells to differentiate to macrophages, a single dose of membrane-permeant diacylglycerol (DAG), 1,2-dioctanoylglycerol (1,2-DiC8), was normally insufficient to differentiate these cells. These cells metabolized 1,2-DiC8 very rapidly, and 1,2-DiC8 available to protein kinase C (PKC) activation was removed from the incubation medium at a rate proportional to cell density. However, increasing the duration of exposure of HL-60 cells to this DAG either by its repeated addition or by decreasing the cell density greatly enhanced their differentiation to macrophages as measured by CD11b expression. During this differentiation induced by DAG, neither measurable translocation nor depletion (down-regulation) of PKC was observed. When the cells were exposed to PMA, on the other hand, some PKC subspecies were instantaneously translocated to membranes and subsequently disappeared very quickly, whereas the alpha-subspecies was decreased to the level of approximately 60% of the resting cell, but thereafter its activity was maintained at a nearly constant level in membranes. After approximately 4 hr, the PKC subspecies, once depleted, reappeared gradually in the membrane fraction. The results suggest that sustained activation of PKC is essential to differentiation of HL-60 cells to macrophages, and depletion of the enzyme is not needed. Perhaps translocation of PKC represents an extreme state of the active form of the enzyme, which may result from PMA action, and the alpha-subspecies presumably plays a key role in HL-60 cell differentiation.

Biological Transport↗
PubMed1991

Metabolic rate of membrane-permeant diacylglycerol and its relation to human resting T-lymphocyte activation.

DL-1,2-Dioctanoylglycerol (1,2-DiC8) added to human peripheral resting T lymphocytes was rapidly metabolized to produce octanoic acid and further to small molecules, probably by the action of diacylglycerol lipase and/or nonspecific esterase. Only a small portion was converted to the corresponding phosphatidic acid or was isomerized to 1,3-DiC8 before being metabolized. The uptake of 1,2-DiC8 by the cell was apparently fast, and the rate of disappearance of 1,2-DiC8 was dependent on the cell densities; at a higher density of T lymphocytes 1,2-DiC8 was removed quickly, whereas at a lower cell density 1,2-DiC8 remained for a longer period of time. With a fixed amount of 1,2-DiC8 added, the extent of interleukin 2 receptor alpha-subunit (IL-2R alpha) expression was inversely related to the cell density and proportional to the duration of exposure of the cells to 1,2-DiC8. Repeated doses of 1,2-DiC8 potentiated IL-2R alpha expression. In contrast, a single dose of phorbol 12-myristate 13-acetate caused T-lymphocyte activation to similar extents irrespective of the cell density, probably because the phorbol ester was not metabolized and remained in membranes. The available evidence supports a proposal made in a previous paper and indicates that the sustained activation of protein kinase C for at least the first 3-4 hr is essential for the activation of resting T lymphocytes.

Biological Transport↗
PubMed1991

Lysophosphatidylcholine as a possible second messenger synergistic to diacylglycerol and calcium ion for T-lymphocyte activation.

An immediate reaction product of phosphatidylcholine hydrolysis catalyzed by phospholipase A2, lysophosphatidylcholine (lysoPC), synergizes with a membrane-permeable diacylglycerol, 1,2-dioctanoylglycerol, and ionomycin to activate resting T-lymphocytes as measured by interleukin-2 alpha-receptor expression. It is suggestive that both phospholipase C and phospholipase A2 are directly involved in signal transduction in a synergistic fashion and that lysoPC acts as an additional second messenger for cellular regulation, probably for long-term responses such as cell proliferation and differentiation.

Calcium↗
PubMed1991

Synergistic action of diacylglycerol and unsaturated fatty acid for protein kinase C activation: its possible implications.

Kinetic properties of the purified alpha, beta, and gamma subspecies of protein kinase C (PKC) to respond to diacylglycerol, phosphatidylserine (PtdSer), and Ca2+ were reinvestigated in the presence of several fatty acids. Although responses of these enzyme subspecies to the lipids slightly differed from one another, the reaction velocity of these subspecies was significantly enhanced by synergistic action of diacylglycerol and a cis-unsaturated fatty acid. Arachidonic, oleic, linoleic, linolenic, and docosahexaenoic acids were active in this role, whereas saturated fatty acids such as palmitic and stearic acids were inactive. Elaidic acid was also inactive. In the presence of both PtdSer and diacylglycerol, the cis-unsaturated fatty acids increased further an apparent affinity of PKC to Ca2+ and allowed the enzyme to exhibit almost full activation at nearly basal levels of Ca2+ concentration. The concentration of fatty acid giving rise to the maximum activation of enzyme was approximately 20-50 microM. The result presented herein implies that the receptor-mediated release of unsaturated fatty acids from phospholipids may take part, in synergy with diacylglycerol, in the activation of PKC even when the Ca2+ concentration is low. A possibility arises, then, that the activation of PKC is an integral part of the signal-induced degradation cascade of various membrane phospholipids, which is initiated by the actions of phospholipase C and phospholipase A2.

Arachidonic Acid↗
PubMed1989

Phosphatidylinositol turnover in human monocyte-derived macrophages by native and acetyl LDL.

Monocyte-derived macrophages play a key role in pathogenesis of atherosclerosis. However, the mechanism of activating macrophages in atheromatous lesions has not been fully investigated. This report describes the contribution of phosphatidylinositol turnover to the uptake of low density lipoproteins (LDL) by macrophages. Both native and acetyl LDL stimulated inositol 1,4,5-triphosphate (IP3) formation in a dose-dependent manner at concentrations of 0-70 micrograms/ml. The potency of IP3 formation by acetyl LDL (0.44 nmol/mg protein) was 2-fold higher than that by native LDL (0.21 nmol/mg protein). Time course studies showed that a maximal effect of IP3 formation by acetyl LDL at concentrations of 30 micrograms/ml was observed at 3 min. Longer incubation diminished IP3 formation. Oxidized LDL also stimulated IP3 formation with a similar efficiency to acetyl LDL. It was indicated that chemically modified LDL which were taken up through the scavenger receptor pathway activated the macrophages by mediating the phosphatidylinositol hydrolysis and IP3 formation.

Cells, Cultured↗
PubMed1989

Distinct effects of phosphatidylethanol on three types of rat brain protein kinase C.

Protein kinase C plays a crucial role in signal transduction for activating cellular function. Phosphatidylserine and Ca2+ are essential for the activation of protein kinase C, and diacylglycerol which is produced in the receptor-mediated hydrolysis of inositol phospholipids, increases the affinity of this enzyme for phosphatidylserine and Ca2+. In brain tissues, protein kinase C has been shown to be separated into three fractions, Type I, II, and III by hydroxyapatite column chromatography, and cDNA analysis has revealed that they correspond to gamma-, beta I-, beta II-, and alpha-cDNA, respectively. Phospholipase D has been known to catalyze the transphosphatidyl reaction between various membrane phospholipids and alcohols. In fact, phosphatidylethanol has been found in many tissues including brain of ethanol-treated rats. This report describes the different responses of three distinct forms of protein kinase C to phosphatidylethanol. Phosphatidylethanol can replace phosphatidylserine at high Ca2+ concentrations for the activation of Type I, II, and III protein kinase C. However, phosphatidylethanol can activate only Type I enzyme at physiological Ca2+ concentrations, which is expressed exclusively in the central nervous tissue. Consideration of these results suggests the possibility that ethanol may exert some effect on the signal transduction in neuronal tissue, via changes in protein phosphorylation.

Animals↗
PubMed1988

Properties of protein kinase C subspecies in human platelets.

Protein kinase C (PKC) from human platelets was resolved into two fractions by hydroxyapatite column chromatography. One of the enzymes was indistinguishable from the brain type III PKC having alpha-sequence in its kinetic and immunological properties. The other enzyme was kinetically different from any of the brain PKC subspecies so far isolated, although it resembled the brain type II PKC having beta-sequence. With H1 histone as substrate, this platelet enzyme was not very sensitive to Ca2+, and activated partly by phosphatidylserine plus diacylglycerol or by free arachidonic acid. Both platelet enzymes could phosphorylate the P47 protein in vitro, but the enzyme physiologically responsible for the P47 protein phosphorylation in the activated platelets remains to be identified.

Amino Acid Sequence↗
PubMed1988

Activation of a brain-specific protein kinase C subspecies in the presence of phosphatidylethanol.

Protein kinase C (PKC) is normally activated by diacylglycerol in the presence of Ca2+ and phosphatidylserine. At physiological concentrations of Ca2+, however, phosphatidylethanol, a product of the phospholipase D-catalyzed transphosphatidylation reaction between membrane phospholipids and ethanol, can replace phosphatidylserine, and activate PKC. This mode of activation is most effective for the gamma-subspecies, which is expressed only in central nervous tissue. Phosphatidylmethanol is also effective to some extent. Consideration of these results suggests the possibility that ethanol may exert some effect on signal transduction in this tissue via changes in protein phosphorylation.

Animals↗
PubMed1987

The common structure and activities of four subspecies of rat brain protein kinase C family.

Elucidation of the complete sequences of four cDNA clones (alpha, beta I, beta II, and gamma) of the rat brain protein kinase C family has revealed their common structure composed of a single polypeptide chain with four constant (C1-C4) and five variable (V1-V5) regions. Although these sequences are highly homologous and closely related to one another V3-, V4-, and V5-regions of gamma-subspecies are slightly bigger than the corresponding regions of the other three subspecies. The first constant region, C1, contains a tandem repeat of cysteine-rich sequence (6, total 12 cysteine residues). The third constant region, C3, has an ATP-binding sequence which is found in many protein kinases. In adult rat whole brain, the relative activities of alpha-, beta I-, beta II-, and gamma-subspecies are roughly 16, 8, 55, and 21%, respectively. gamma-Subspecies is expressed after birth apparently only in the central nervous tissue, implying its role in the regulation of specific neuronal functions.

Amino Acid Sequence↗
PubMed1987

Identification of the structures of multiple subspecies of protein kinase C expressed in rat brain.

Rat brain protein kinase C purified to apparent homogeneity [(1986) Biochem. Biophys. Res. Commun. 135, 636-643] was resolved into three distinct fractions, type I, II and III, upon chromatography on a hydroxyapatite column connected to high-performance liquid chromatography. Comparison of each fraction with the four subspecies of protein kinase C, that were separately expressed in COS cells transfected by the respective cDNAs, alpha, beta I, beta II and d gamma, identified the primary structures of these three fractions of protein kinase C. Type I corresponded to the enzyme encoded by the gamma-sequence; type II was a mixture of the two subspecies determined by the beta I- and beta II-sequences; and type III had the structure encoded by the alpha-sequence. The structures and properties of these subspecies of protein kinase C were similar to each other.

Animals↗