Regulation of protein kinase C activity by gangliosides

Functions of sphingolipids and sphingolipid breakdown products in cellular regulation

The discovery that breakdown products of cellular sphingolipids are biologically active has generated interest in the role of these molecules in cell physiology and pathology. Sphingolipid breakdown products, sphingosine and lysosphingolipids, inhibit protein kinase C, a pivotal enzyme in cell regulation and signal transduction. Sphingolipids and lysosphingolipids affect significant cellular responses and exhibit antitumor promoter activities in various mammalian cells. These molecules may function as endogenous modulators of cell function and possibly as second messengers.

Regulation of proliferation by the cholera toxin B subunit in FRTL-5 cells may involve a mechanism independent from the modulation of membrane receptor function

In quiescent rat thyroid (FRTL-5) cells, the B subunit of cholera toxin, which binds to cell surface ganglioside GM1 specifically, alone induced DNA synthesis and markedly enhanced that induced by insulin in serum-free medium. On the other hand, the B subunit inhibited DNA synthesis induced by thyrotropin (TSH). The B subunit did not activate adenylate cyclase and had no effect on the TSH-induced cyclic adenosine 3',5'-monophosphate (cAMP) production. Moreover, the B subunit inhibited DNA synthesis induced by dibutyryl cAMP (Bt2cAMP) or phorbol-12-myristate-13-acetate (PMA). These data demonstrate that the B subunit has both stimulatory and inhibitory effects on DNA synthesis in FRTL-5 cells depending on the presence of other growth factors and that these effects on cell proliferation by the interaction of the B subunit, possibly with cell surface ganglioside GM1, may involve a mechanism independent from the modulation of membrane receptor function through interaction with growth factor receptor.

Gangliosides modulate Schwann cell proliferation and morphology

We examined the effect of gangliosides on Schwann cell cultures isolated from neonatal rat sciatic nerves. Addition of gangliosides (GM1, GM3, and ganglioside mixture) at concentrations between 0.25 and 2 mg/ml significantly diminished both the baseline rate of proliferation of the Schwann cells and their response to two types of mitogens, the axolemmal fragments and derivatives of adenosine 3'-5'-monophosphate (cAMP). Gangliosides, the sialic acid residue of which had been removed, were highly toxic to the Schwann cells, which went to indicate that sialic acid is necessary to produce the inhibitory effects. Gangliosides also produced prominent changes in the morphological appearance of the Schwann cells. Most of the Schwann cells treated with gangliosides had an elongated shape with long processes and an alignment of end-to-end or side-by-side cell adhesion. These effects of gangliosides apparently were not mediated by cAMP, since intracellular cyclic adenosine monophosphate (cAMP) of Schwann cells at a basal- and forskolin-stimulated level was not altered by the exogenous gangliosides. These findings indicate that the direct effect of gangliosides on Schwann cells should also be considered as a background mechanism of ganglioside-induced facilitation of neuronal regeneration.

Sphingosine and psychosine, suggested inhibitors of protein kinase C, inhibit LH effects in rat luteal cells

The possible involvement of protein kinase C on luteinizing hormone (LH) effects in dispersed rat luteal cells was investigated using two substances that have been reported to be protein kinase C inhibitors, sphingosine and psychosine. Sphingosine efficiently inhibited protein kinase C activity both in brain and luteal cytosol fractions. Both substances inhibited LH-stimulated cyclic adenosine monophosphate (cAMP) accumulation in a dose-dependent fashion with an LD50 at 3-7 microM (sphingosine) and 40 microM (psychosine). LH-stimulated progesterone production was also inhibited with an ID50 at 6-10 microM (sphingosine) and 40-100 microM (psychosine). The inhibition was not due to an increased phosphodiesterase activity since IBMX (3-isobutyl-1-methylxanthine, 0.1 mM) and RO 20-1724 (4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone, 0.1 mM) did not abolish the inhibitory effect of sphingosine. To study the mode of action of sphingosine, forskolin and cAMP analogues were tested. The effect of these substances on steroidogenesis was inhibited, as well as the forskolin-induced cAMP accumulation, by sphingosine. This study demonstrates a clear inhibition of LH-stimulated effects by sphingosine and psychosine. LH action in rat luteal cells is discussed in relation to protein kinase C and the possible mode of sphingosine action.

Gangliosides in the blood plasma: levels of ganglio-series gangliosides in the plasma after administration of brain gangliosides

The temporal change in the levels of the gangliotetraose-series gangliosides, i.e., GMla, GDla, GD1b, GT1b, in the blood plasma after intramuscular administration of bovine brain gangliosides (5 mg/kg) to beagle dogs (11.3-12.2 kg) was determined with high sensitivity by a recently developed thin-layer chromatography/enzyme-immunostaining method (Hirabayashi, Y., Koketsu, K., Higashi, H., Suzuki, Y., Matsumoto, M., Sugimoto, M. and Ogawa, T. (1986) Biochim. Biophys. Acta 876, 178-182). The amounts of GMla, GDla, GD1b, GT1b and their combined total in the plasma of beagle dogs before administration of gangliosides were 21 +/- 1, 36 +/- 7, 15 +/- 2, 16 +/- 2 and 88 +/- 6 pmol/ml of blood plasma, respectively. Trapezoidal calculation showed that the times of the maximum levels of GMla, GDla, GDlb, GTlb and the total of the their levels in the plasma were 8.0 +/- 1.2, 8.7 +/- 0.7, 6.3 +/- 2.0, 17.0 +/- 7.0 and 8.7 +/- 0.7 h after the administration of gangliosides, and their maximum concentrations were 517 +/- 37, 654 +/- 53, 160 +/- 5, 184 +/- 20 and 1383 +/- 74 pmol/ml, respectively. The maximum level of each ganglioside decreased gradually, reaching the normal level after 10 days. The half-maximum level of each ganglioside occurred 2-3 days after the administration. Asialo GM1 (GA1) was not detected plasma at any of the test times.

Effect of exogenous gangliosides on the lipid composition of chick neurons in culture

When exogenous gangliosides are added to the growth medium of neuronal cell cultures they are inserted into their plasma membranes and are afterwards metabolized in the cytoplasmic interior. The action of exogenous gangliosides brings important morphological and biochemical changes to neurons in culture. The present report shows that the treatment with exogenous gangliosides of a primary culture of chick neurons modified the distribution of fatty acids in phosphatidylinositol (PI), mainly that of arachidonic acid and the fatty acids of the (n - 3) series without affecting the other phospholipids. The composition of neutral lipids did not change but their content was increased up to 2-3-fold depending upon the concentration of gangliosides. The change of the growth medium from one containing fetal calf serum to a chemically defined one reduced dramatically the content of free fatty acids while the addition of gangliosides raised this content to normal levels. The increase in the amount of diacylglycerol (DG) confirmed the finding that gangliosides stimulate phosphoinositide degradation. Finally the fatty acid composition of DG suggests indirectly that this compound might be produced also by degradation of phosphatidylcholine and not only of PI.

Dexamethasone-induced alterations in the glycosphingolipids of rat kidney

To determine whether glucocorticoids would influence the glycosphingolipid composition of the rat kidney, male albino rats of the Sherman strain were subcutaneously administered dexamethasone (100 micrograms/100 g body wt/day) or diluent for four days. The compositions of ceramide and of acidic and neutral glycosphingolipids of the kidneys of these animals were then examined and compared. The results demonstrated that dexamethasone administration: 1) increased the content of ceramide and of acidic and neutral glycosphingolipids in kidney; 2) increased the relative percentage of globotriaosyl- and globotetraosyl-ceramide, but decreased the relative percentages of glucosylceramide; 3) decreased the relative percentages of GM3 and increased other gangliosides; 4) increased the relative percentages of N-glycolylneuraminic acid in GM3; 5) did not appear to influence significantly the long-chain bases of the major glycosphingolipids; and 6) altered the relative percentages and chain length of the hydroxy and nonhydroxy fatty acids of the major acidic and neutral glycosphingolipids in this tissue. The data show that dexamethasone administration induces quantitative and qualitative changes in the glycosphingolipids of the rat kidney.

Phosphatidylglycerol-modulated protein kinase activity from human spleen. I. Enzyme purification and properties

Protein kinase P (PK-P) is a phospholipid-modulated protein kinase activity previously described in human and murine cells. This paper details the 3300-fold, high yield purification to electrophoretic homogeneity of protein kinase P from human spleen by a three-step chromatographic process. Physical characterization disclosed a protein of Mr 27,000 (by electrophoresis) or 31,700 (by gel filtration and sedimentation) and pI 5.09. Protein kinase P activity was stimulated by phosphatidylglycerol or phosphatidylinositol, with maximal stimulation observed between 200 and 400 micrograms/ml phospholipid. No stimulation was noted using phosphatidic acid or phosphatidylserine. Histone H2B was the best substrate for demonstrating the protein kinase P phospholipid stimulation. Histone H1 was phosphorylated in a phospholipid independent manner. Vinculin and actin were not substrates. Optimum enzyme activity was observed at approximately 35 degrees C and pH 6.95. PK-P was relatively insensitive to the calmodulin and protein kinase C inhibitors W7 and H7, and to the cAMP-dependent protein kinase inhibitor. Kinetic analysis disclosed complex patterns including optimal rather than Michaelis-Menton kinetics for histone and phospholipid concentration, and a steep activation threshold with respect to histone concentration in the presence of phospholipid. Biphasic kinetics for Mg2+-ATP were observed, with the major stimulatory effect of phospholipid being on Vmax rather than Km. These data suggest a model for the mechanism of activation of protein kinase P by phospholipid entailing a direct three-way interaction between substrate, enzyme, and phospholipid micelles rather than allosteric activation by phospholipid.

Differential actions of neurotrophic factors on lesion-induced damage of the serotonergic neurons projecting to the hippocampus

The changes induced by nerve growth factor (NGF) and by GM1-ganglioside administration on serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and tryptophan content and on choline acetyltransferase activity, were studied in the central nervous system of rats undergoing electrolytic damage of a mesencephalic area, located near the nucleus interpeduncularis. This lesion selectively reduced the content of 5-HT and 5-HIAA in the ipsilateral hippocampus. Daily intraperitoneal injection of GM1-ganglioside (30 mg/kg/day for 6-14 days) significantly reduced the injury-induced loss of hippocampal 5-HT and 5-HIAA content. On the contrary NGF, administered at a dose (10 micrograms/rat i.c.v. twice a week for 2 weeks) which was able to increase, in the same animals, the cortical choline acetyltransferase activity, failed to affect the lesion-induced reduction of 5-HT and of 5-HIAA in the hippocampus.

Regulation of protein kinase C activity by various lipids

Protein kinase C has recently attracted considerable attention because of its importance in the control of cell division, cell differentiation, and signal transduction across the cell membrane. The activity of this enzyme is altered by several lipids such as diacylglycerol, free fatty acids, lipoxins, gangliosides, and sulfatides. These lipids may interact with protein kinase C either directly or through calcium ions and produce their regulatory effect (activation or inhibition) on the activities of the enzymes phosphorylated by this kinase. These processes widen our perspective of the regulation of intercellular and intracellular communication.

Synthetic sialyl compounds as well as natural gangliosides induce neuritogenesis in a mouse neuroblastoma cell line (Neuro2a)

Amphipathic compounds containing N-acetylneuraminic acid (sialic acid) [for example, D-N-acetylneuraminyl-(alpha 2-1)-2S,3R,4E-2-N-tetracosanoyl sphingenine, sialyl alkyl glycerol ethers, and sialyl cholesterols] induced neuritogenesis in a neuroblastoma cell line (Neuro2a). The sialic acid in the hydrophilic moiety of the compounds is specifically required for neuritogenesis. The requirement for molecular specificity of the hydrophobic moiety, however, is rather low. Regarding the hydrophobic moiety, no preference for cholesterol, alkyl glycerol ether, or ceramide residues was observed as to their neuritogenic activity. Sialyl compounds with alpha-ketosidic sialyl linkages were more active than the corresponding beta-anomers. These sialyl compounds induced the growth of only one neurite, but a long one, from the cell body. This type of neuritogenes is completely different from that induced by compounds capable of elevating the concentration of intracellular cyclic AMP, which induced the appearance of many neurites from a single cell body. Besides this morphological change, the active sialyl compounds also caused a change in the carbohydrate composition of the cell surface. Sialyl compound treatment drastically increased the concentration of peanut agglutinin binding sites.

The relationship between the bilayer to hexagonal phase transition temperature in membranes and protein kinase C activity

A number of substances affect the activity of protein kinase C. Among uncharged and zwitterionic compounds, those which activate protein kinase C also lower the bilayer to hexagonal phase transition temperature of dielaidoylphosphatidylethanolamine while substances which inhibit protein kinase C raise this transition temperature. Using this criteria, we have identified 3 beta-chloro-5-cholestene, 5 beta-cholan-24-ol and eicosane as new protein kinase C activators and have shown that Z-Ser-Leu-NH2, Z-Gly-Leu-NH2, Z-Tyr-Leu-NH2, cyclosporin A and cholestan-3 beta, 5 alpha, 6 beta-triol are protein kinase C inhibitors.

Substrate-specific stimulation of protein kinase C by polyvalent anion

The activity of protein kinase C (PKC) toward arginine-rich substrates was greatly stimulated by sulfate and phosphate, but not by monovalent anions. This stimulation did not require phospholipid, calcium, or diacylglycerol, and appeared to mimic the stimulation by phospholipid. Anionic proteins such as bovine serum albumin also promoted PKC activity toward certain substrates that were characterized by either high arginine or high lysine content. The mechanism of both of these stimulations appeared to be related to formation of a substrate-PKC complex which is essential to phosphorylation by PKC. Polyvalent anions bind the cationic substrate and, together with PKC, form an aggregate which allows phosphorylation. Potential physiological relevance of this stimulation is discussed.

Inhibition of protein kinase C from polymorphonuclear neutrophils by long chain acyl coenzyme A and counteraction by Mg-ATP

The Ca2+- and phospholipid-dependent protein kinase (protein kinase C) from bovine polymorphonuclear neutrophils was inhibited by micromolar amounts of long chain acyl-CoAs. The extent of inhibition at a given concentration of the acyl-CoAs depended on the length of the chain. A chain length of at least 12C was required for inhibition. Inhibition of protein kinase C activity was counteracted specifically by Mg-ATP.

Modified ganglioside as a possible modulator of transmembrane signaling mechanism through growth factor receptors: a preliminary note

Two types of modified GM3 strongly alter EGF-dependent phosphorylation of the EGF receptor in opposite directions, i.e., de-N-acetyl-GM3 (amino-GM3; NeuNH2 alpha 2----3Gal beta 1----4Glc beta 1----1 Ceramide) strongly promotes tyrosine phosphorylation of the EGF receptor of A431 cells, while lyso-GM3 (NeuNAc alpha 2----3Gal beta 1----4 Glc beta----1 Sphingosine) as well as GM3 inhibit tyrosine phosphorylation of the EGF receptor in the same cells under the same conditions. A hypothesis is proposed that de-N-acylation of gangliosides, in either the sialic acid or ceramide moiety, is a crucial event in triggering a positive or negative transmembrane signal.

Role of substrate in determining the phospholipid specificity of protein kinase C activation

The phospholipid selectivity of protein kinase C (PKC) activation was examined by using two substrates, histone and a random copolymer of lysine and serine [poly(lysine, serine)] (PLS), plus phospholipids provided as vesicles or as Triton-mixed micelle preparations. The results indicated that substrate-phospholipid interaction was an essential component of PKC activation and that many in vitro properties of PKC activation are attributable to this interaction. The substrate histone interacted with phospholipid-Triton mixed micelles containing phosphatidylserine (PS), but not with those containing phosphatidylinositol (PI) or phosphatidylglycerol (PG). In direct correlation, only PS-Triton mixed micelles were effective in supporting PKC activity. Also, the minimum PS composition (4 mol % in Triton) required to induce significant histone-PS interaction coincided with the minimum composition required for phosphorylation of histones. Moreover, the PS composition required for maximum activity varied with the histone concentration of the reaction. In contrast to histone, PLS interacted with phospholipid-Triton mixed micelles containing either PS, PI, or PG, and all these mixed micelles supported the phosphorylation of PLS. In fact, by selection of appropriate experimental conditions (e.g., concentration of substrate and phospholipid), any of the three mixed micelles could appear the most effective in supporting PKC activity. Phospholipid vesicles containing PS, PG, or PI were found to interact with both histone and PLS and to support the activity of PKC. Physical properties of the solution and conditions used for preparation of phospholipid vesicles had considerable influence on PKC activation. At high phospholipid concentrations, vesicles containing PS, PI, or PG supported the activity of PKC to essentially the same level, provided that the physical differences among the phospholipid vesicles were minimized.(ABSTRACT TRUNCATED AT 250 WORDS)