A rapid stimulation of phosphatidylinositol metabolism in rabbit leukocytes by pseudomonal leukocidin

Interaction of the hemolytic lectin CEL-III from the marine invertebrate Cucumaria echinata with the erythrocyte membrane

CEL-III is one of four Ca(2+)-dependent galactose/N-acetylgalactosamine (GalNAc)-binding lectins from the marine invertebrate Cucumaria echinata which exhibits hemolytic activity, especially toward rabbit and human erythrocytes. The hemolytic activity of CEL-III was also Ca(2+)-dependent and was found to be inhibited by galactose or GalNAc-containing carbohydrates, suggesting that the hemolysis was caused by CEL-III binding to specific carbohydrates on the erythrocyte membrane by Ca(2+)-dependent lectin activity, followed by partial destruction of the membrane. The activity of CEL-III was highest at 10 degrees C and decreased markedly with increasing temperature, unlike usual enzymatic reactions. The hemolytic activity of CEL-III increased with increasing pH from neutral to 10, but almost no hemolysis was observed below pH 6.5. Immunoblotting analysis of proteins from the erythrocyte membrane after treatment with CEL-III indicated that CEL-III aggregates were irreversibly bound to the membrane. When erythrocytes were incubated with CEL-III in the presence of dextran with molecular masses greater than 4 kDa, lysis was impeded considerably, while a concomitant release of ATP was detected from these osmotically protected cells. It was found that CEL-III released carboxyfluorescein from artificial globoside-containing lipid vesicles, and it is suggested that CEL-III is a novel pore-forming protein with the characteristics of a Ca(2+)-dependent lectin, which may act as a toxic protein to foreign microorganisms.

Enhanced protein phosphorylation, IL-2 receptor expression, and IL-2 production precede cellular proliferation in lymphocytes oxidized by periodic acid

Increased rates of protein phosphorylation, IL-2 receptor (IL-2R) expression, IL-2 production and DNA synthesis were quantified in rat lymphocytes oxidized by periodic acid (H5IO6). Enhanced phosphorylation of 97, 59 and 37 to 29 kDa proteins in lymphocytes was detected at 18 and 36 hrs post-oxidation, whereas IL-2R expression and IL-2 elaboration were at their maximum by 24 hrs. The number of oxidized cells entering the S-phase of the cell cycle and their thymidine incorporation rates reached their maximum at 72 hrs. These results indicate that H5IO6-induced blastogenesis elicits a progression of responses temporally similar to those of lymphocytes stimulated by lectins.

Phosphoinositide breakdown and superoxide anion release in formyl-peptide-stimulated human alveolar macrophages. Comparison between quiescent and activated cells

Human alveolar macrophages (AMs) from allergic asthmatics (AAs) showed continuous Li+-sensitive production of IP1, indicating that the cells were continuously activated. Furthermore, whereas the accumulation of IP1, IP2 and IP3 rapidly increased by as much as 125-175% in chemotactic-factor-stimulated AMs from healthy subjects, stimulation of cells from AAs increased these inositol phosphates only slightly. This moderate production could be due to a permanent state of activation leading to a depleted pool of polyphosphoinositides, corroborating the greater capacity of these cells to generate superoxide anion after stimulation by a chemoattractant. The activation state could be due to the action of priming agents, which are known to be released into the inflammatory sites.

Inhibition of macrophage activation by isoquinolinesulfonamides, phenothiazines, and a napthalenesulfonamide

The influence of isoquinolinesulfonamides (H-7 and H-8), phenothiazines(trifluoperazine and fluphenazine), and a naphthalenesulfonamide (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) on stimulated superoxide anion production and phosphatidyl inositol (PI) cycle activity was investigated in the guinea pig alveolar macrophage. All five drugs were able to inhibit superoxide anion production stimulated by n-formyl-nel-leu-phe (FNLP), leukotriene B4 (LTB4), and phorbol-12,13-dibutyrate (PDB). The order of potency was trifluoperazine greater than or equal to fluphenazine greater than H-7 = W-7 greater than H-8. The dose response curves could be shifted to less efficacy by increasing extracellular calcium. By itself, W-7 markedly stimulated 45Ca+2 efflux, fluphenazine and trifluoperazine slightly stimulated 45Ca+2 efflux, while H-7 and H-8 had no effect on 45Ca+2 efflux from macrophages preloaded with 45Ca+2. Consistent with these results, W-7 markedly stimulated PI cycle activity, fluphenazine and trifluoperazine slightly stimulated PI cycle activity, while H-7 and H-8 had no significant effects on PI cycle activity. In addition, W-7 by itself was able to stimulate a weak and short-lived "burst" of superoxide anion production. In order to evaluate whether a site of action of the inhibitors was at protein kinase C and whether protein kinase C was involved in terminating the normally short-lived FNLP- and LTB4-stimulated macrophage activation, fluphenazine and H-7 were used to evaluate the duration of FNLP- and LTB4-stimulated PI cycle activity, at concentrations of the inhibitors that significantly blocked stimulated superoxide anion production. In all cases, FNLP and LTB4 still stimulated PI cycle activity, which still terminated even though protein kinase C was inhibited. These results suggest that all five drugs block protein kinase C, but H-7 was the most specific in its action at protein kinase C, while the phenothiazines and W-7 have multiple sites of action. In addition, these results suggest that protein kinase C may not function to cause the termination of FNLP- and LTB4-stimulated PI cycle activity and subsequent superoxide anion production.

Periodic acid-induced blastogenesis of lymphocytes is independent of phosphoinositide turnover

The blastogenic transformation of lymphocytes by periodic acid was investigated to determine if blastogenesis induced by this mitogen was preceded by phosphoinositide turnover as previously shown for the lectins. Although periodate oxidation stimulated nucleic acid synthesis and interleukin-2 production, no changes in phosphoinositide turnover could be detected when compared to control lymphocyte cultures. These data indicate that increased phosphoinositide turnover is not an absolute prerequisite for lymphocyte proliferation.

Action of a cytotoxin from Pseudomonas aeruginosa on human leukemic cell lines. Increase in cell permeability to Ca2+ and Mn2+ and lack of stimulation of inositol lipid turnover

Quin2 loaded human leukemic, JURKAT and K562 cells, were exposed to various doses of Pseudomonas aeruginosa cytotoxin. This cytotoxin induced an increase in quin2 fluorescence indicating an increase in the cytoplasmic free Ca2+ concentration. The rate of the fluorescence increase and the lag time before the response were dependent on the doses of the cytotoxin. Addition of MnCl2 to the cytotoxin-treated cells induced a decrease in the quin2 fluorescence at rates dependent on the doses of the cytotoxin. The cytotoxin did not stimulate the inositol lipid turnover in JURKAT cells, which was determined by the accumulation of [3H]inositol phosphates in myo-[2-3H]inositol-prelabeled cells in the presence of LiCl. These results indicate that the cytotoxin increases cell permeability to both Ca2+ and Mn2+ by direct breakdown of the permeability barrier of the plasma membrane.

Calcium regulation of phosphatidyl inositol turnover in macrophage activation by formyl peptides

Stimulation by the tripeptide N-formyl norleucyl leucyl phenylalanine (FNLLP) of the guinea pig alveolar macrophage gives rise to transient production of superoxide anion (O2-). Components of the phosphatidyl inositol (PI) cycle (phosphatidic acid (PA), phosphatidyl inositol-4,5-bisphosphate (TPI) and phosphatidyl inositol-4-phosphate (DPI) were monitored using 32P in order to examine the possible association of this cycle with the FNLLP-stimulated production of O2-. Macrophage stimulation by FNLLP led to an increased flux of metabolites through the PI cycle. The level of 32P label in both TPI and DPI rapidly decreased upon exposure to FNLLP, followed by a 5-min period during which the 32P label in TPI and DPI approached prestimulated levels. During this period, there was a fivefold increase in 32P-PA. It is suggested that diacylglycerol (DAG) is the O2- -activating intermediate in the stimulated mechanism, as evidenced by the buildup of PA (for which DAG is the precursor) in parallel with the time course of O2- production. The importance of continued cycling of PI in the stimulated mechanism is demonstrated by the inhibition by LiCl of the extent, but not the initial rate, of both O2- production and the formation of 32P-PA upon peptide stimulation after 1-h preincubation with 10 mM LiCl. The influence of calcium on this mechanism was also examined. It has previously been demonstrated that intracellular availability of calcium can influence the rate and extent of O2- production. In cells preloaded with quin-2, which acts as a high-affinity sink for calcium in the cytosol, the initial rate of FNLLP-stimulated O2- production is inhibited in low (10 microM) extracellular calcium medium. High extracellular calcium (1 mM) completely reverses this inhibition and also significantly extends the time course of O2- production in both quin-2 and control cells (Stickle et al., 1984). In parallel with these effects on O2- production, varying calcium conditions is demonstrated to influence the rate and extent of PA formation. These same calcium conditions were found to have little or no effect on the initial unstimulated levels of TPI, DPI, and PA. These results indicate that the influence of an intracellular pool of calcium on O2- production may be via its influence on stimulated PI turnover.

Binding of pseudomonal leukocidin to rabbit polymorphonuclear leukocytes

The leukocytotoxic toxin pseudomonal leukocidin, produced by Pseudomonas aeruginosa, was radioiodinated with chloramine-T reagent. Binding of [125I]leukocidin to rabbit polymorphonuclear leukocytes was found to be concentration dependent at 37 degrees C. A Scatchard plot of binding data was linear, indicating that leukocidin binds to a single population of sites. The dissociation constant, KD, was calculated from the Scatchard plot to be 2.5 X 10(-7) M, and the number of binding sites per leukocyte was approximately 4.4 X 10(5). Unlabeled leukocidin or antileukocidin antibody reduced the binding of [125I]leukocidin to the leukocytes. A leukocidin-binding protein was extracted from rabbit polymorphonuclear leukocytes with Triton X-100 and purified by leukocidin-Sepharose 4B affinity column chromatography. Approximately 60 micrograms of binding protein was obtained from 8.1 mg of material extracted from the leukocytes. The binding protein had a molecular weight of about 50,000 as shown by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis and staining with silver nitrate. Under nondenaturing conditions, its molecular weight was also about 50,000, as shown by gel filtration-Sephadex G-200 chromatography. The 50,000-dalton protein purified in this way from rabbit polymorphonuclear leukocytes competitively inhibited the binding of leukocidin to leukocytes and inactivated leukocidin activity. With equimolar amounts of the 50,000-dalton protein and leukocidin, up to 90% inactivation of leukocidin was observed.

Inositol trisphosphate, a novel second messenger in cellular signal transduction

There has recently been rapid progress in understanding receptors that generate intracellular signals from inositol lipids. One of these lipids, phosphatidylinositol 4,5-bisphosphate, is hydrolysed to diacylglycerol and inositol trisphosphate as part of a signal transduction mechanism for controlling a variety of cellular processes including secretion, metabolism, phototransduction and cell proliferation. Diacylglycerol operates within the plane of the membrane to activate protein kinase C, whereas inositol trisphosphate is released into the cytoplasm to function as a second messenger for mobilizing intracellular calcium.