Characterization of protein kinase C activity in interferon gamma treated murine peritoneal macrophages

Macrophage activation for tumoricidal and microbicidal functions can be achieved in part by treatment with recombinant interferon gamma (IFN gamma) in vitro. We have previously demonstrated that IFN gamma treatment of murine peritoneal macrophages results in a two- to five-fold increase in the activity of Ca++, phospholipid dependent protein kinase C (Hamilton et al., J. Biol. Chem., 260:1378, 1985). We now report that this effect was not dependent upon continuing protein synthesis since treatment with cycloheximide under conditions where normal protein synthesis was inhibited by greater than 95% had no effect upon the development of increased enzyme activity. Examination of Ca++ and phospholipid requirements revealed no differences between enzyme isolated from control or IFN gamma treated cells. Similarly, protein kinase C from control and IFN gamma-treated cells could not be distinguished in terms of the diacylglycerol (DG) or phorbol diester (PMA) concentration required for stimulation of activity. Kinetic analysis of the ATP (as substrate) concentration dependence revealed that both control and treated enzyme preparations (either basal or stimulated) had comparable Km values. Maximum velocity (Vmax) was increased both by IFN gamma treatment and also by stimulation with DG or PMA. The major difference which could be discerned between protein kinase C derived from control versus IFN gamma-treated macrophages was the magnitude of the response to DG or PMA; IFN gamma treatment increased the stimulation index (i.e., ratio of basal to stimulated activity) by a factor of two to four fold. These results suggest that IFN gamma treatment leads to reversible modulation of existing protein kinase C resulting in increased catalytic efficiency when exposed to an appropriate stimulant.     

Involvement of protein kinase C in platelet-activating factor-stimulated diacylglycerol accumulation in murine peritoneal macrophages

Incubation of murine peritoneal macrophages with platelet-activating factor (PAF; 1-O-alkyl(C16 + C18)-2-acetyl-sn-glycerol-3-phosphorylcholine) results in the rapid accumulation of [3H]inositol phosphates and sn-1,2-diacylglycerol (DAG) and mobilization of intracellular calcium (Prpic, V., Uhing, R. J., Weiel, J. E., Jakoi, L., Gawdi, G., Herman, B., and Adams, D. O. (1988) J. Cell Biol. 107, 363-372). We have further investigated the relationship of phosphoinositide metabolism to accumulation of DAG and the possible involvement of protein kinase C in the accumulation of DAG in response to PAF. DAG accumulation proceeds at a slower rate than the accumulation of either [3H] inositol 1,4,5-trisphosphate or total [3H]inositol phosphates. Accumulation of DAG from additional precursors is suggested from both an estimation of the mass of total inositol phosphates produced and the accumulation of [3H]choline in response in PAF. Down-regulation of protein kinase C by prolonged pretreatment with phorbol ester or inhibition of the enzyme with sphingosine inhibited the PAF-generated accumulation of DAG at 10 min by approximately 80%. Under the same conditions, no inhibition of PAF-stimulated generation of [3H]inositol 1,4,5-trisphosphate was observed. Similar inhibition was observed when 10 microM ionomycin or 0.1 microM phorbol 12-myristate 13-acetate were used to stimulate accumulation of DAG. The results suggest that PAF stimulates the accumulation of DAG from source other than phosphatidylinositol metabolism in peritoneal macrophages and that this occurs subsequent to the activation of protein kinase C.     

Elevated levels of protein kinase C activity and alpha-isoenzyme expression in murine peritoneal B cells

Conventional murine splenic B cells are stimulated to initiate DNA synthesis by the combination of a phorbol ester protein kinase C (PKC) agonist, and a calcium ionophore; in contrast, recent work from this laboratory has shown that peritoneal B cells, enriched for the Ly-1+ B cell subset, differ in that they proliferate in response to the single signal provided by phorbol ester, acting alone. To elucidate the mechanism responsible for the abbreviated signaling requirement of peritoneal B cells, studies of intracellular Ca2+ and PKC were carried out. Measurements using the calcium sensitive dye, Indo-1, showed that base line levels of intracellular Ca2+ in peritoneal B cells were similar to those of splenic B cells, and that there was no change as a result of phorbol ester treatment. However, measurements of PKC based on the phosphorylation of histone showed enzymatic activity in peritoneal B cells to be about 60% greater than that of splenic B cells on a per microgram protein basis. Furthermore, this difference was accentuated by phorbol ester treatment, so that after 4 h, membrane and cytosol fractions from peritoneal B cells contained more than 5 times the PKC activity of the corresponding splenic B cell fractions because the down-regulation of PKC was relatively delayed in peritoneal B cells. This could not be accounted for by the onset of new PKC synthesis, but may relate to the finding that peritoneal B cells express more of the alpha-isoenzyme of PKC than splenic B cells, as shown by immunoblot analysis. Together with data from experiments using the PKC inhibitor 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride(H7), these results suggest that PKC activity remaining hours after phorbol ester treatment may contribute to the unusual phorbol ester responsiveness of peritoneal B cells, and indicate that B cells from separate anatomic locations differ in terms of several parameters relating to the activity and behavior of PKC.     

Fc-receptor mediated protein phosphorylation in murine peritoneal macrophages

The effect of Fc receptor engagement on protein phosphorylation in murine peritoneal macrophages has been investigated. Treatment of macrophage cultures with insoluble immune complexes resulted in enhanced phosphorylation of six proteins at 73, 66, 53, 37, 31 and 25 kD. Comparison of the protein phosphorylation patterns induced by immune complexes with those induced by agents which mimic the actions of well known intracellular second messengers (i.e., A23187, dibutyryl cAMP, or phorbol myristate acetate) revealed substantial similarity between Fc receptor induced events and those induced in response to phorbol diesters. There were, however, two phosphorylated proteins which were only seen following stimulation with immune complexes. Thus, more than one kind of protein kinase activity appears to be involved in Fc receptor mediated stimulation of macrophage function.     

Regulation of prostaglandin synthesis by protein kinase C in mouse peritoneal macrophages.

Resident mouse peritoneal macrophages synthesized and released prostaglandins (PGs) when challenged with 12-O-tetradecanoylphorbol 13-acetate (TPA) or 1,2-dioctanoyl-sn-glycerol (DiC8). Both stimuli were found to activate Ca2+/phospholipid-dependent protein kinase C (PKC). 1-(5-Isoquinolinesulphonyl)-2-methylpiperazine ('H-7') and D-sphingosine, known to inhibit PKC by different mechanisms, were able to decrease the PKC activity of macrophages in a dose-dependent manner. Addition of either PKC inhibitor decreased PG synthesis and also the release of arachidonic acid (AA) from phospholipids induced by TPA or DiC8. Simultaneously TPA or DiC8 also decreased incorporation of free AA into membrane phospholipids of macrophages. AA incorporation could be restored, however, by pretreatment with the PKC inhibitors. Our results demonstrate an involvement of PKC in the regulation of PG synthesis in mouse peritoneal macrophages and provide further evidence that reacylation of released fatty acids may be an important regulatory step.     

Serum amyloid A, an acute-phase protein, modulates proteoglycan synthesis in cultured murine peritoneal macrophages.

Cultured peritoneal macrophages obtained from azocasein-injected mice were found to produce several fold more cell-associated and medium proteoglycans than peritoneal macrophages from untreated mice. Since serum amyloid A (an acute-phase protein) is also upregulated following injections of azocasein, we questioned whether its production was the immediate agent stimulating proteoglycan formation. Cultured peritoneal macrophages from untreated mice were then incubated with varying concentrations of SAA, resulting in a similar dose-dependent several fold increase in proteoglycan production. Of particular note was a disproportionate increase in cell-associated heparan sulfate proteoglycans in both experimental groups and of dermatan sulfate and chondroitin sulfate proteoglycans when cells were incubated in the presence of SAA in the culture medium. These results indicate a potentially important function of SAA in directing specific modifications in inflammatory conditions where increase in macrophage proteoglycans may play direct roles.     

Possible involvement of protein kinase C in interleukin-1 production by mouse peritoneal macrophages

Both lipopolysaccharide (LPS) and phorbol-12,13-dibutyrate (PDBu), a protein kinase C-activating phorbol ester, induced interleukin-1 (IL-1) production in mouse peritoneal macrophages. Prolonged treatment of the cells with PDBu led to the down-regulation and complete disappearance of protein kinase C. In these cells, PDBu did not increase IL-1 production, but LPS still stimulated IL-1 production although the maximum level was slightly reduced. These results suggest that protein kinase C and another unknown signal pathway are involved in LPS-induced IL-1 production.     

LPS regulation of specific protein synthesis in murine peritoneal macrophages

Two-dimensional polyacrylamide gel electrophoresis (2D PAGE) analysis of biosynthetically labeled proteins of murine peritoneal macrophages elicited by inflammatory and activating stimuli indicated that the accumulation of a small number of cell-associated proteins was altered after in vitro treatment with bacterial lipopolysaccharide (LPS). Both increases and decreases in the accumulation of specific proteins were observed after LPS stimulation. Proteins of approximately 87, 43, 37, 30, and 28 Kd were similarly regulated by LPS in proteose peptone-, P. acnes-, and M. bovis BCG-elicited macrophages. Thioglycollate-elicited and resident peritoneal macrophages showed very few changes in the pattern of proteins synthesized after LPS treatment. Many of the proteins whose accumulation was increased by LPS in the elicited macrophages (proteins of approximately 87, 52, 43, 37, and 28 Kd) were already synthesized at high levels in resident macrophages. LPS stimulation also altered the accumulation of many of the same proteins in bone marrow-derived macrophages, indicating the lack of T lymphocyte influence on the LPS-induced changes in macrophages. LPS stimulation of highly purified B cells caused changes in the accumulation of several proteins of 70 and 78 Kd, which were different from those regulated by LPS in peritoneal macrophages.     

A possible role of protein kinase C in regulating prostaglandin synthesis of mouse peritoneal macrophages

The addition of the analogue of diacylglycerol, 1-oleoyl-2-acetylglycerol (OAG), to resident macrophages isolated from the peritoneal cavity of mice led to a dose and time dependent increase in the synthesis of prostaglandin E. This was likely due to an enhanced amount of arachidonic acid available for eicosanoid synthesis as OAG suppressed the incorporation of arachidonic acid into cellular phospholipids by inhibiting acyl-CoA:lysophosphatide acyltransferase. Since OAG has been shown to activate protein kinase C in various cells, these data lead us to suggest that synthesis of eicosanoids in peritoneal macrophages is mediated by the activation of protein kinase C.     

Characterization of Ca2+-activated, phospholipid-dependent protein kinase C/protein kinase M in guinea pig peritoneal exudate macrophages

Protein kinase C (C-kinase) is shown to be present in the cytosolic and particulate fractions of mineral oil induced peritoneal macrophages of guinea pigs. By omission or use of a high concentration of leupeptin, three forms of the enzyme were obtained: stimulant/Ca2+/phospholipid-dependent C-kinase, eluted from DEAE 52 cellulose at 0.08-0.16 M NaCl; stimulant/Ca2+/phospholipid-independent protein kinase M (M-kinase), and Ca2+-inhibited & stimulant/phospholipid-dependent form of protein kinase, both eluted from DEAE 52 cellulose at 0.18-0.22 M NaCl. Phorbol ester or 1,2-diacylglycerol were used as stimulants. It is suggested that Ca2+-inhibited & stimulant/phospholipid-dependent protein kinase represents the in vivo form of the M-kinase in intact cells.     

Activation of the stem cell-derived tyrosine kinase/RON receptor tyrosine kinase by macrophage-stimulating protein results in the induction of arginase activity in murine peritoneal macrophages.

Regulation of macrophage activities in response to inflammatory stimuli must be finely tuned to promote an effective immune response while, at the same time, preventing damage to the host. Our lab and others have previously shown that macrophage-stimulating protein (MSP), through activation of its receptor RON, negatively regulates NO production in response to IFN-gamma and LPS by inhibiting the expression of inducible NO synthase (iNOS). Furthermore, activated macrophages from mice harboring targeted mutations in RON produce increased levels of NO both in vitro and in vivo, rendering them more susceptible to LPS-induced endotoxic shock. In this study, we demonstrate that stimulation of murine peritoneal macrophages with MSP results in the RON-dependent up-regulation of arginase, an enzyme associated with alternative activation that competes with iNOS for the substrate L-arginine, the products of which are involved in cell proliferation and matrix synthesis. Expression of other genes associated with alternative activation, including scavenger receptor A and IL-1R antagonist, is also up-regulated in MSP-stimulated murine macrophages. Stimulation of cells with IFN-gamma and LPS blocks the ability of MSP to induce arginase activity. However, pretreatment of cells with MSP results in the up-regulation of arginase and inhibits their ability to produce NO in response to IFN-gamma and LPS, even in the presence of excess substrate, suggesting that the inhibition of NO by MSP occurs primarily through its ability to regulate iNOS expression.     

Modulation of protein kinase C activity by NaF in bone marrow derived macrophages

Stimulation of murine bone marrow derived macrophages with NaF, prelabeled with [1-¹⁴C]oleate and [³H]inositol, increased the production of inositol phosphates and the release of 1,2-[¹⁴C]diacylglycerol (DAG). Moreover, NaF also induced activation of protein kinase C. These results indicate that bone marrow derived macrophages exhibit a phosphatidyl-4,5-bisphosphate phospholipase C activity, sensitive to NaF, which might be modulated by G-proteins. Activation of protein kinase C could have been mediated by NaF-induced release of DAG.     

Recombinant granulocyte-macrophage colony-stimulating factor increases adenylate cyclase activity in murine peritoneal macrophages

Granulocyte-macrophage colony stimulating factor (GM-CSF) is a pleiotrophic cytokine which stimulates the function and proliferation of macrophage populations. Although the effects of GM-CSF are diverse and GM-CSF has entered into clinical trials, relatively little is known about signal transduction pathways utilized by GM-CSF. In view of previous studies which have suggested that some of the effects of GM-CSF on monocyte-macrophages can be mimicked by agents which increase intracellular cAMP, we investigated the effect of rGM-CSF on adenylate cyclase (AC) activity in murine peritoneal macrophages. Adenylate cyclase activity was quantitated in macrophage membrane preparations and in intact cells. In seven separate experiments, GM-CSF (50 U/ml) increased AC activity by 61(6)% relative to macrophages treated with carrier medium alone. A dose-dependent increase in AC activity was observed (10 to 100 U/ml) which peaked within 1 to 5 min after the addition of GM-CSF and returned to basal levels by 10 to 20 min. Lineweaver-Burk analysis revealed that the Vmax of macrophage AC was increased from 0.40 to 0.52 pmoles cAMP/min by GM-CSF but the Km was unchanged. Intracellular cAMP was increased by GM-CSF to 129(27)% of control values by 1 min of treatment (n = 6). Under similar experimental conditions, GM-CSF did not increase the activity of PK C (n = 14) or phospholipase A2 (n = 3) in peritoneal macrophages. These data show that macrophage adenylate cyclase activity is rapidly stimulated by GM-CSF. Moreover, these findings support further study of the role of cAMP in transmitting the intracellular signals initiated by GM-CSF in tissue macrophages.     

Enhanced leukotriene C4 synthase activity in thioglycollate-elicited peritoneal macrophages

The utilization of LTA4 by peritoneal macrophages (MO) obtained from untreated rats (control) as well as by those elicited from rats was investigated at designated intervals (on days 3, 7, and 14) following the intraperitoneal injection of thioglycollate (TG). On day 7 following the injection the elicited MO converted LTA4 to LTC4 at the highest rate while the resident MO showed the lowest rate. The conversion of LTA4 to LTC4 and LTB4 was next examined by using each MO lysate. The apparent LTC4 synthase activity was significantly higher in the MO lysate both on day 3 and day 7, with the latter being the highest value obtained. The GSH S-transferase activity in each lysate using as the substrate, DNCB was significantly lower on day 3 but significantly higher on day 7 as compared to control values. However, this elevated activity was less variable than that observed with LTC4 synthase. The possible implication for these observations is discussed.     

Palmitoylcarnitine modulates interaction protein kinase C delta-GAP-43

Palmitoylcarnitine, reported previously to promote neuronal differentiation, was observed to affect distribution of protein kinase C (PKC) isoforms in neuroblastoma NB-2a cells, leading to retardation in cytoplasm of high molecular weight species of PKCbeta and delta. Growth cone protein-GAP-43, a PKC substrate, was co-immunoprecipitated with all the conventional and novel PKCs: palmitoylcarnitine, however, decreased its amount exclusively in the complex with PKCdelta. Administration of palmitoylcarnitine, although did not change the subcellular distribution of GAP-43, decreased its phosphorylation, which could regulate other signal transduction pathways (calmodulin and G(0)-dependent).     

Phosphorylation by calcium calmodulin-dependent protein kinase II and protein kinase C modulates the activity of nitric oxide synthase.

Nitric oxide synthase purified from rat brain, which is Ca2+ and calmodulin dependent, was phosphorylated by calcium calmodulin-dependent protein kinase II as well as protein kinase C. Phosphorylation by calcium calmodulin-dependent protein kinase II resulted in a marked decrease in enzyme activity (33% of control) without changing the co-factor requirements, whereas a moderate increase in enzyme activity (140% of control) was observed after phosphorylation by protein kinase C. These findings indicate that brain nitric oxide synthase activity may be regulated not only by Ca2+/calmodulin and several co-factors, but also by phosphorylation.     

Ligation of Fc receptor of macrophages stimulates protein kinase C and antileishmanial activity

Fc receptors are known to express on the surface of mature monocytes macrophages and lymphocytes. In this study a ligand e.g. liposomal IgG (human IgG coupled to PE-liposome via carbodimide reaction) was developed to ligate the Fc receptor of macrophages. When liposomal IgG was incubated with macrophages at 37°C for 5 min, it induced the macrophage activation which suppress the parasite burden approximatley to an extent of 60%, 50% and 45%, when macrophages were infected with UR6, AG83 and GE1 strains of L-donovani respectively. Superior efficacy of liposomal IgG were achieved compared to the treatment with free IgG and free liposomes. The activity of protein kinase C (PKC) has been found to be higher in the Fc receptor targeted macrophage membrane fraction, suggesting its translocation from the cytosol. Staurosporine, a potent inhibitor of the enzyme protein kinase C (PKC) has been found to protect the parasite inside the macrophage indicating the role of PKC in the signaling process. The liposomal IgG treatment has been found to induce the generation of significant amount of superoxide and hydrogen peroxide which helped to suppress the parasite burden. Further when liposomal IgG were incubated with IFN- primed, LPS activated macrophages, a significant amount of NO release was also noticed, indicating its role in parasite killing. The above results suggest that Fc receptor mediated activation by liposomal IgG may be used as an alternative approach to kill parasites intracellularly.     

Cyclooxygenase-1-dependent prostaglandin synthesis modulates tumor necrosis factor-alpha secretion in lipopolysaccharide-challenged murine resident peritoneal macrophages

Comprehensive studies of prostaglandin (PG) synthesis in murine resident peritoneal macrophages (RPM) responding to bacterial lipopolysaccharide (LPS) revealed that the primary PGs produced by RPM were prostacyclin and PGE(2). Detectable increases in net PG formation occurred within the first hour, and maximal PG formation had occurred by 6-10 h after LPS addition. Free arachidonic acid levels rose and peaked at 1-2 h after LPS addition and then returned to baseline. Cyclooxygenase-2 (COX-2) and microsomal PGE synthase levels markedly increased upon exposure of RPM to LPS, with the most rapid increases in protein expression occurring 2-6 h after addition of the stimulus. RPM constitutively expressed high levels of COX-1. Studies using isoform-selective inhibitors and RPM from mice bearing targeted deletions of ptgs-1 and ptgs-2 demonstrated that COX-1 contributes significantly to PG synthesis in RPM, especially during the initial 1-2 h after LPS addition. Selective inhibition of either COX isoform resulted in increased secretion of tumor necrosis factor-alpha (TNF-alpha); however, this effect was much greater with the COX-1 than with the COX-2 inhibitor. These results demonstrate autocrine regulation of TNF-alpha secretion by endogenous PGs synthesized primarily by COX-1 in RPM and suggest that COX-1 may play a significant role in the regulation of the early response to endotoxemia.     

The role of protein kinase C in the induction of nitric oxide synthesis by murine macrophages.

The role of protein kinase C (PKC) in the induction of nitric oxide synthesis by interferon-gamma (IFN-gamma) was investigated using two murine macrophage cell lines, J774 and RAW 264.7. Nitric oxide (NO) production was markedly reduced by a PKC inhibitor, Ro31-8220 in a dose-dependent manner. Incubation of cells with IFN-gamma resulted in translocation of PKC to the cell membrane. Prolonged incubation of cells with a high concentration of phorbol ester, which down-regulated PKC activity, also reduced nitric oxide production. These findings provide evidence that PKC is involved in the induction of nitric oxide synthesis by IFN-gamma.