A low ratio of high molecular weight adiponectin to total adiponectin associates with periodontal status in middle-aged men

BACKGROUND

Periodontitis has been reported to relate closely to systemic diseases. However, a biomarker for periodontal status has not been established.

METHODS

A cross-sectional study was conducted using oral and systemic health checkup data of 151 middle-aged men. The serum levels of adiponectin and its subfractions were also analysed.

RESULTS

The ratio of high molecular weight adiponectin to total adiponectin was significantly lower in subjects with periodontal pockets. Moreover, this ratio independently associated with periodontal condition.

CONCLUSIONS

The ratio of HMW adiponectin to total adiponectin could be a novel biomarker for evaluation of periodontal health in middle-aged men.

Cardioprotection by regular ethanol consumption: potential mechanisms and clinical application

Epidemiological studies demonstrate that excessive drinking is associated with hypertension, cerebral bleeding and loss of cardiac contractility. Conversely, studies have shown that mortality rates for people who regularly drink ethanol in moderation are lower than in abstainers, primarily due to decreased fatal ischemic heart disease. Further, moderate ethanol consumers have lower rates of myocardial infarction compared with abstainers. These beneficial cardiac effects may be due to pleiotropic effects of ethanol on lipids, platelets, and fibrinolytic activity. During the past decade, studies conducted in several animal models have revealed that light to moderate regular ethanol consumption renders hearts more tolerant to myocardial ischemia-reperfusion injury; to a degree similar to cardiac ischemic preconditioning (brief episodes of ischemia dramatically limit infarct size following prolonged ischemia). Recent clinical evidence suggests that light to moderate ethanol consumption in the year prior to myocardial infarction is associated with reduced mortality following myocardial infarction. These findings suggest that light to moderate ethanol consumption not only prevents myocardial infarction but also improves survival after myocardial infarction. Proposed mechanisms of cardioprotection by regular ethanol consumption include activation of adenosine A1 receptors, alpha(1)-adrenoceptors, protein kinase C-delta and epsilon, adenosine triphosphate-dependent potassium (K(ATP)) channels, nitric oxide synthase and reduced leukocyte-endothelial cell adhesive interactions. In this review, we focus on the recent progress in elucidating the endogenous myocyte signaling mediating cardioprotection by light to moderate ethanol consumption.

Transfer of Fas (CD95) protein from the cell surface to the surface of polystyrene beads coated with anti-Fas antibody clone CH-11

Mouse monoclonal anti-Fas (CD95) antibody clone CH-11 has been widely used in research on apoptosis. CH-11 has the ability to bind to Fas protein on cell surface and induce apoptosis. Here, we used polystyrene beads coated with CH-11 to investigate the role of lipid rafts in Fas-mediated apoptosis in SKW6.4 cells. Unexpectedly, by treatment of the cells with CH-11-coated beads Fas protein was detached from cell surface and transferred to the surface of CH-11-coated beads. Western blot analysis showed that Fas protein containing both extracellular and intracellular domains was attached to the beads. Fas protein was not transferred from the cells to the surface of the beads coated with other anti-Fas antibodies or Fas ligand. Similar phenomenon was observed in Jurkat T cells. Furthermore, CH-11-induced apoptosis was suppressed by pretreatment with CH-11-coated beads in Jurkat cells. These results suggest that CH-11 might possess distinct properties on Fas protein compared with other anti-Fas antibodies or Fas ligand, and also suggest that caution should be needed to use polystyrene beads coated with antibodies such as CH-11.

Enamel matrix derivative protein stimulated wound healing via phosphoinositide 3-kinase

BACKGROUND

Enamel matrix derivative (EMD) protein has been clinically used for periodontal regeneration, but the molecular mechanisms are not clear. Previous studies suggested that the activation of phosphoinositide 3-kinase (PI 3-kinase) plays a key role in facilitating cell migration. Given that the migration of osteoblasts is one of the key steps in the wound-healing processes, we hypothesized that EMD protein would stimulate osteoblast migration by activating PI 3-kinase. In this study, we tested this hypothesis using MG-63 cells as model systems to evaluate mechanisms of migration by stimulation with EMD protein.

METHODS

Confluent MG-63 cells were mechanically scratched using a sterilized 1-mm pipette tip that removed the cells within a circular area. The wells were incubated for 24 hours in various stimulation conditions (25, 50, or 100 microg/ml EMD protein) with or without the PI 3-kinase inhibitor wortmannin (1, 10, and 100 nM) or LY294002 (1, 10, and 100 microM). Migrated cells in the wound section were counted by randomly selecting three areas from one well. The activation of PI 3-kinase by EMD protein was evaluated by the phosphorylation of Akt using Western blot analysis.

RESULTS

Although EMD protein did not affect proliferation, it enhanced migration into wounds on MG-63 cells. We showed that EMD protein enhanced the phosphorylation of Akt in a dose-dependent manner. We demonstrated that the PI 3-kinase inhibitors wortmannin and LY294002 blocked migration into wounds and the phosphorylation of Akt enhanced by EMD protein in MG-63 cells.

CONCLUSION

These results demonstrated that the activation of PI 3-kinase plays a key role in the EMD protein-stimulated migration of osteoblasts.

Emdogain stimulates matrix degradation by osteoblasts

Emdogain has been used clinically for periodontal regeneration, although the underlying molecular mechanisms are not clear at present. In this study, we hypothesized that Emdogain stimulated degradation of type I collagen via osteoblasts. We showed that Emdogain enhanced cell-mediated degradation of type I collagen in an MMP-dependent manner. Although MG-63 cells spontaneously produced a zymogen form of MMP-1, treatment with Emdogain significantly induced the generation of the active form of this enzyme. We demonstrated that MMP-3 was produced from MG63 cells in response to Emdogain in a MEK1/2-dependent manner. Concomitantly, blocking of MEK1/2 activation by U0126 significantly inhibited the generation of the active form of MMP-1 without affecting the total production of this collagenase. These results suggest that Emdogain facilitates tissue regeneration through the activation of the collagenase, MMP-1, that degrades matrix proteins in bone tissue microenvironments.

Release of cytochrome c from mitochondria precedes Bax translocation/activation in Triton X-100-induced apoptosis

The precise mechanisms by which sublytic concentrations of detergents induce apoptosis remain unclear. Recent studies reported the ability of nonionic detergents such as Triton X-100 to induce conformational change of Bax to the active form in vitro. Here we investigated whether activation of Bax might play a role in Triton X-100-induced apoptosis in cells. Although Bax translocation/activation was inhibited by caspase inhibitors, cytochrome c release from mitochondria was not affected in Triton X-100-induced apoptosis in U-937 cells. These results demonstrate that translocation/activation of Bax occurs downstream of cytochrome c release and caspase activation in Triton X-100-induced apoptosis.

P-selectin glycoprotein ligand-1 mediates L-selectin-independent leukocyte rolling in high endothelial venules of peripheral lymph nodes

Lymphocyte homing to peripheral lymph nodes (LNs) requires L-selectin. Previous studies, however, suggest that there are L-selectin-independent mechanisms of lymphocyte homing. P-selectin glycoprotein ligand-1 (PSGL-1) is a major ligand for P-selectin expressed in a selectin-binding form on myeloid cells and subsets of lymphoid cells. To discover whether PSGL-1 plays a role in lymphocyte homing, we examined leukocyte rolling and adhesion in the high endothelial venules (HEVs) of the subiliac LNs of wild-type and PSGL-1-deficient mice by intravital microscopy. There were no significant differences in blood velocity or wall shear stress between wild-type and PSGL-1-deficient mice. Although the leukocyte rolling fraction was not altered in PSGL-1-deficient mice, infusion of an anti-L-selectin mAb into these mice completely abolished leukocyte rolling, while the same treatment in wild-type mice inhibited 90% of the leukocyte rolling. This residual rolling in wild-type mice appears to depend on the PSGL-1-P-selectin interaction, since infusion of an anti-L-selectin mAb together with an anti-PSGL-1 mAb or anti-P-selectin mAb almost completely abolished the rolling. PSGL-1 deficiency also led to a higher rolling velocity, suggesting that PSGL-1 mediates leukocyte rolling at low velocities. P-selectin was found to be expressed on the HEVs of subiliac LNs under the conditions of intravital microscopy. Taken together, these results indicate that the interaction of PSGL-1 with P-selectin constitutes a second mechanism of leukocyte rolling in the HEVs of peripheral LNs.

Matrix metalloproteinase-1 produced by human CXCL12-stimulated natural killer cells

Natural killer (NK) cells play a key role in inflammation and tumor regression through their ability to migrate into tissues. CXCL12 is a chemokine that promotes lymphocyte invasion and migration into tissues; however, the mechanism for this process remains incompletely understood. In this study, we show that CXCL12 significantly enhanced CD16(+)CD56(+) human peripheral NK-cell invasion into type I collagen by the catalytic activity of matrix metalloproteinase-1 (MMP-1). Confocal immunofluorescence and co-immunoprecipitation studies suggest that MMP-1 colocalized with alpha(2)beta(1) integrin on CXCL-12-stimulated NK-cell surface. The binding of pro-MMP-1 with alpha(2)beta(1) integrin required activation of G(i)-coupled pathway. However, the production of MMP-1 from CXCL12-stimulated NK cells was mediated by p38 and mitogen-activated or extracellular signal-regulation protein kinase kinase 1/2 in a manner independent of the G(i)-coupled pathway. These results suggest that CXCL12/CXCR4 interaction transduces the two signaling pathways to promote NK-cell invasion, which stimulates pericellular degradation of extracellular matrix proteins by membrane-associated MMP-1. The mechanisms would thus play a role in facilitating lymphocyte trafficking and accumulation in tissues during physiological and pathological processes.

Role of membrane sphingomyelin and ceramide in platform formation for Fas-mediated apoptosis

Engagement of the Fas receptor (CD95) initiates multiple signaling pathways that lead to apoptosis, such as the formation of death-inducing signaling complex (DISC), activation of caspase cascades, and the generation of the lipid messenger, ceramide. Sphingomyelin (SM) is a major component of lipid rafts, which are specialized structures that enhance the efficiency of membrane receptor signaling and are a main source of ceramide. However, the functions of SM in Fas-mediated apoptosis have yet to be clearly defined, as the responsible genes have not been identified. After cloning a gene responsible for SM synthesis, SMS1, we established SM synthase–defective WR19L cells transfected with the human Fas gene (WR/Fas-SM(−)), and cells that have been functionally restored by transfection with SMS1 (WR/Fas-SMS1). We show that expression of membrane SM enhances Fas-mediated apoptosis through increasing DISC formation, activation of caspases, efficient translocation of Fas into lipid rafts, and subsequent Fas clustering. Furthermore, WR/Fas-SMS1 cells, but not WR/Fas-SM(−) cells, showed a considerable increase in ceramide generation within lipid rafts upon Fas stimulation. These data suggest that a membrane SM is important for Fas clustering through aggregation of lipid rafts, leading to Fas-mediated apoptosis.

Current Status and Perspectives in Ceramide-Targeting Molecular Medicine

Ceramide is not only structurally but also functionally a key molecule in diverse kinds of sphingolipids. In the past decade, ceramide has been shown to be of crucial significance in several cell functions including apoptosis, cell growth, senescence, and cell cycle control. Among them, the role of ceramide in apoptosis induction has extensively been studied, and ceramide-targeting molecular medicine for apoptosis-based diseases such as malignant tumors, atherosclerosis and neurodegenerative disorders appears to come out to the clinical field. We here describe the recent advances in research of ceramide-mediated apoptosis signaling. We also show the relation of ceramide level through regulation of ceramide-related enzymes (sphingomyelinase, ceramidase, sphingomyelin synthase and glucosylceramide synthase) with diseases such as cancer, leukemia, bacterial infections, AIDS, Alzheimer's disease, atherosclerosis, diabetes mellitus and atopic dermatitis. The strategies to construct the ceramide-targeting medicine for intractable diseases such as cancer and leukemia are discussed.

Reduced expression of Bax in ceramide-resistant HL-60 subline

Ceramide, the backbone of sphingolipids, has been reported to be involved in various cellular responses including apoptosis. We recently established and characterized a C2-ceramide-resistant HL-60 subline designated HL-CR. HL-CR cells were resistant to not only ceramide but also anti-cancer drugs including daunorubicin, etoposide, and cytosine arabinoside. To elucidate the mechanisms by which HL-CR cells became resistant to various apoptosis-inducing stimuli, the levels of Bcl-2 family proteins, which play crucial roles in drug-induced apoptosis, were compared between HL-CR and parental HL-60 cells. Among Bcl-2 family members, Bax, a pro-apoptotic Bcl-2 family protein, was highly expressed in HL-60 but was hardly detected in HL-CR cells. Transient transfection of bax-expressing plasmid, but not the vector alone, induced apoptosis in HL-CR cells. These results suggest that reduced expression of Bax might play a role in resistance to various apoptosis-inducing stimuli in HL-CR cells.

Increase of Nuclear Ceramide through Caspase-3-Dependent Regulation of the “Sphingomyelin Cycle” in Fas-Induced Apoptosis

Regardless of the existence of ceramide-related molecules, such as sphingomyelin (SM), neutral sphingomyelinase (nSMase), and SM synthase, in the nucleus, the regulation of ceramide in the nucleus is poorly understood in stress-induced apoptosis. In Fas-induced Jurkat T-cell apoptosis, we found a time- and dose-dependent increase of ceramide content in the nuclear and microsomal fractions. Fas-induced increase of ceramide content in the nucleus also was detected by confocal microscopy using anticeramide antibody. Activation of nSMase and inhibition of SM synthase were evident in the nuclear fraction after Fas cross-linking, whereas nSMase was activated, but SM synthase was not affected, in the microsomal fraction. Pretreatment with D-609, a putative SM synthase inhibitor, enhanced Fas-induced increase of ceramide in the nucleus and induction of apoptosis along with increase of Fas-induced inhibition of nuclear SM synthase. Fas-induced activation of caspase-3 was detected in the nuclear fraction and in whole cell lysate. A caspase-3 inhibitor, acetyl-Asp-Glu-Val-Asp-chloromethyl ketone, blocked not only Fas-induced increases of apoptosis and ceramide content but also Fas-induced activation of nSMase and inhibition of SM synthase in the nuclear fraction. Taken together, it is suggested that the nucleus is a site for ceramide increase and caspase-3 activation in Fas-induced Jurkat T-cell apoptosis and that caspase-3-dependent regulation of the "SM cycle" consisting of nSMase and SM synthase plays a role in Fas-induced ceramide increase in the nucleus.

Characterization of C2-ceramide-resistant HL-60 subline (HL-CR): involvement of PKC delta in C2-ceramide resistance

We have established a C2-ceramide-resistant HL-60 subline (HL-CR). HL-CR cells were resistant not only to C2-ceramide but also to various anticancer drugs. HL-CR cells did not respond to differentiation-inducing reagents including 1alpha,25-dihydroxyvitamin D(3), retinoic acid, and 12-O-tetradecanoylphorbol-13-acetate (TPA). TPA induced apoptosis in HL-CR cells much slower than in parental HL-60 cells. As it was reported that PKC isozymes were involved in C2-ceramide-induced apoptosis, we investigated the role of PKC isozymes in C2-ceramide resistance in HL-CR cells. The protein level of PKC delta was lower in HL-CR cells than in parental HL-60 cells, whereas the levels of PKC alpha, betaI, epsilon, and zeta were rather higher in HL-CR cells than in parental cells. Translocation of PKC delta from membrane to cytosol was induced by C2-ceramide in HL-CR cells as well as in wild-type HL-60 cells. Furthermore, overexpression of PKC delta in HL-CR cells potentiated C2-ceramide- and TPA-induced apoptosis and growth inhibition. These results suggest a role for ceramide in apoptosis and differentiation in HL-60 cells, and also suggest that PKC delta might be involved in ceramide- and TPA-induced apoptosis.

Phospholipase C activation is required for cardioprotection by ethanol consumption

Regular alcohol consumption decreases the incidence of myocardial infarction (MI) and improves post-MI survival. It has previously been reported that chronic ethanol exposure induces long-term protection against cardiac ischemia/reperfusion injury, which improves myocardial recovery after MI. Chronic cardioprotection by ethanol requires the activation of myocyte adenosine A1 receptors and sustained intramyocyte translocation of epsilon protein kinase C. A1 receptors activate phospholipase C (PLC). In the present paper, the role of PLC in mediating ethanol's protective effect against ischemia/reperfusion injury is investigated. Isolated hearts from guinea pigs fed 2.5% ethanol in their water for four months were subjected to ischemia/reperfusion. Hearts from ethanol-treated animals showed improved recovery of left ventricular developed pressure compared with controls (61% versus 38% of baseline, respectively; P<0.05) and decreased necrosis, assessed by the release of creatine kinase (263+/-18 U/mL x g dry weight versus 360+/-24 U/mL x g dry weight, respectively; P<0.05). Ethanol protection was abolished by the PLC antagonist, U-73122 (50 nM). These findings suggest that PLC activation is required for ethanol cardioprotection against ischemia/reperfusion injury.

Membrane-bound form of fractalkine induces IFN-gamma production by NK cells

Natural killer (NK) cells participate in both innate and adaptive immunity, in part by their prompt secretion of cytokines including IFN-gamma, a pro-inflammatory cytokine with an important role in Th1 polarization. To assess the involvement of fractalkine in inflammatory processes, we examined the effect of fractalkine on IFN-gamma production by NK cells. Although soluble chemokines, including MCP-1 and RANTES as well as fractalkine, had a negligible effect on IFN-gamma production, immobilized fractalkine markedly induced IFN-gamma production by NK cells in a dose-dependent manner. Pretreatment of NK cells with the phosphatidylinositol 3-kinase (PI 3-K) inhibitor, wortmannin, completely inhibited the production of IFN-gamma induced by fractalkine, and pretreatment with the protein tyrosine kinase inhibitor, herbimycin A, partially suppressed the response, suggesting that augmentation of IFN-gamma production in response to fractalkine treatment of NK cells involves signaling through PI 3-K and protein tyrosine kinases. Furthermore, co-culture of NK cells with fractalkine-transfected 293E cells markedly enhanced IFN-gamma production by NK cells compared with co-culture with control 293E cells. These findings may indicate a paracrine feedback loop system in which endothelial cells may be activated to produce more fractalkine, and also suggest a role for fractalkine expressed on endothelial cells in Th1 polarization through the stimulation of IFN-gamma production by NK cells.

Lipid rafts as the signaling scaffold for NK cell activation: tyrosine phosphorylation and association of LAT with phosphatidylinositol 3-kinase and phospholipase C-gamma following CD2 stimulation

Natural killer (NK) cells participate in both innate and adaptive immunity through the prompt secretion of cytokines and ability to lyse virally infected cells or tumor cells. Although it has been well understood that lipid rafts (rafts) and a raft-associated linker for activation of T cells (LAT) plays a central role in TCR signal transduction, there are still great gaps in our knowledge of the molecular events involved in NK cell activation. We show here that CD2 and rafts became polarized to the site of NK cell activation by CD2 cross-linking or target cell binding using confocal microscopy, and LAT and a significant amount of CD2 colocalized in raft fractions of sucrose-density gradient from an NK cell line, NK3.3. CD2 cross-linking strongly induced tyrosine phosphorylation of LAT, resulting in increased association with phosphatidylinositol 3-kinase (PI 3-K) and phospholipase C-gamma1 (PLC-gamma1). In vitro binding studies using glutathione S-transferase fusion proteins demonstrated that a large portion of the association between LAT and PI 3-K or PLC-gamma1 was mediated through their SH2 domains in tyrosine phosphorylation-dependent manner. Furthermore, disruption of lipid rafts by cholesterol depletion from cell membranes using methyl-beta-cyclodextrin markedly reduced LAT tyrosine phosphorylation and NK cell functions, including cytotoxicity and granule exocytosis. These results document that modulation of raft integrity by aggregation of NK cell activating receptors, which leads to the formation of complexes of LAT with PI 3-K and PLC-gamma1, is essential for the NK cell lytic mechanisms.

Sphingosine-induced c-jun expression: differences between sphingosine- and C2-ceramide-mediated signaling pathways

Sphingolipids such as ceramide and sphingosine are putative intracellular signal mediators in cell differentiation, growth inhibition and apoptosis. Previously, we reported that C2-ceramide induced c-jun expression in apoptosis of human leukemia HL-60 cells. Here we report that sphingosine also induced c-jun expression in apoptosis of HL-60 cells. Sphingosine-induced c-jun expression was stimulated by H-89, a protein kinase A inhibitor, whereas C2-ceramide-induced c-jun expression was inhibited by protein kinase C inhibitors. Furthermore, H-89 potentiated sphingosine-induced but not C2-ceramide-induced growth inhibition. These results suggest that sphingosine and C2-ceramide might induce c-jun expression and apoptosis in distinct signaling pathways.

Control of ceramide-induced apoptosis by IGF-1: involvement of PI-3 kinase, caspase-3 and catalase

Insulin-like growth factor-1 (IGF-1) inhibited N-acetylsphingosine (C2-ceramide)-induced HL-60 cell apoptosis via relieving oxidative damage. This inhibitory action of IGF-1 was blocked by a phosphatidylinositol-3 (PI-3) kinase inhibitor wortmannin and enhanced by overexpression of the p110 catalytic subunit of PI-3 kinase. Either IGF-1 pretreatment or PI-3 kinase overexpression restored ceramide-depleted catalase function, and this restoration was inhibited by wortmannin. A catalase inhibitor 3-amino-1h-1, 2, 4-triazole (ATZ) blocked the inhibitory action of IGF-1 on ceramide-induced apoptosis, whereas exogenous purified catalase enhanced it. Ceramide-activated caspase-3 was inhibited by IGF-1/PI-3 kinase and enhanced by wortmannin, while the addition of a specific caspase-3 inhibitor DMQD-CHO significantly enhanced the restoration by IGF-1 of ceramide-depleted catalase function. Moreover, IGF-1 inhibited C2-ceramide-induced decrease of mitochondrial membrane potential, and increase of cytochrome c release, caspase-3 cleavage and caspase-3 activity as judged by PhiPhiLux cleaving method. In summary, these results suggest that IGF-1/PI-3 kinase inhibited C2-ceramide-induced apoptosis due to relieving oxidative damage, which resulted from the inhibition of catalase by activated caspase-3.

Vesnarinone causes oxidative damage by inhibiting catalase function through ceramide action in myeloid cell apoptosis

Vesnarinone is an effective inotropic agent for treating congestive heart failure, but its clinical usage is restricted because of the severe side effect of agranulocytosis. In myeloid HL-60 cells, vesnarinone increased the intracellular content of a proapoptotic lipid mediator, ceramide, in a time- and dose-dependent manner. Vesnarinone-induced apoptosis was significantly enhanced by simultaneous treatment with a cell-permeable N-acetyl sphingosine (C2-ceramide). Treatment with neither vesnarinone, C2-ceramide, nor simultaneously with vesnarinone and C2-ceramide caused a marked increase of reactive oxygen intermediates (ROI) generation measured by the 2',7'-dichlorofluorescin method. However, oxidative damage judged by the production of lipid peroxidates and the nitroblue tetrazolium-reducing ability were enhanced more significantly by simultaneous treatment with vesnarinone and C2-ceramide than by vesnarinone alone. Moreover, vesnarinone inhibited catalase function both at the protein and activity level, and this inhibition was synergistically enhanced by C2-ceramide, and vesnarinone-induced oxidative damage and apoptosis were significantly suppressed by treatment of HL-60 cells with purified catalase. C2-ceramide enhanced vesnarinone-induced inhibition of the ROI-scavenging enzyme catalase at the levels of protein and activity in HL-60 cells; in contrast, however, vesnarinone did not induce ceramide generation, oxidative damage, or catalase depletion in HL-60/ves cells, where vesnarinone could not induce apoptosis. Taken together, the results suggest that vesnarinone induces myeloid cell apoptosis by increasing oxidative damage via ceramide-induced inhibition of catalase function.

Role for adapter proteins in costimulatory signals of CD2 and IL-2 on NK cell activation

Natural killer (NK) cells participate in both innate and adaptive immunity through the prompt secretion of cytokines and ability to lyse virally infected cells or tumor cells. Triggering of NK cells requires aggregation of surface receptors such as CD2 and CD16, and NK cell activity can be augmented in vitro by stimulation with IL-2. In this study, we examined the role of adapter proteins in the increased NK activation following CD2 crosslinking and IL-2 stimulation of NK3.3 cells. NK3.3 cells lysed NK-sensitive K562 cells in a CD2-dependent manner, and IL-2 markedly enhanced lytic activity in a 4h cytotoxic assay. IL-2 also enhanced spontaneous and CD2-mediated granule exocytosis from NK3.3 cells. CD2 crosslinking markedly induced tyrosine phosphorylation of Cbl associated with Grb2 or CrkL, Shc and LAT, compared with IL-2 stimulation. However, costimulation of IL-2 with CD2 crosslinking remarkably enhanced associations of Grb2-Shc and CrkL-Cbl, compared to IL-2 stimulation or CD2 crosslinking alone. In vitro binding studies using GST-fusion proteins revealed that interactions of Grb2-Shc and CrkL-Cbl were mediated through each SH2 domain in tyrosine phosphorylation-dependent manner. Furthermore, CD2 crosslinking, but not IL-2 stimulation, markedly induced tyrosine phosphorylation of LAT. Thus, tyrosine phosphorylation of different adapter proteins and consequent interactions between signaling molecules described here may explain the molecular mechanisms of the additive effects of IL-2 stimulation and CD2 crosslinking on NK cell activation.

Oxygen radicals mediate ultrastructural and metabolic protection of preconditioning in vivo in pig hearts

Ischemic preconditioning (PC) preserves myocardial high-energy phosphate metabolites and intracellular pH during subsequent sustained ischemia. Generation of reactive oxygen species may be required to mediate PC, as seen in vitro. In the present study, the effects of inhibiting reactive oxygen species generation during a PC protocol in vivo using an open-chest porcine model were examined. Myocyte ultrastructural changes assessed by electron microscopy were correlated with phosphorus nuclear magnetic resonance spectroscopy data. Open-chest pigs underwent 60 min of left anterior descending coronary artery occlusion. PC was elicited by a single episode of 5 min occlusion and 5 min reperfusion. The cell-diffusible hydroxyl radical and superoxide radical scavenger, N-2-mercapto-propionyl glycine (MPG, 20 mg/kg), or placebo saline were infused for 40 min, starting 30 min before PC (PC plus MPG group, n=10; and PC group, n=9). After PC, ATP and intracellular pH were significantly preserved through 25 min of ischemia (control versus PC, 46+/-3% versus 55+/-5% of baseline [P<0.05]; and control versus PC, 6.18+/-0.08 versus 6.42+/-0.03 [P<0.05], respectively). Phosphocreatine was significantly preserved through 20 min of ischemia (control versus PC, 0+/-0% versus 7+/-2% of baseline [P<0.05]). The preservation of high-energy phosphate metabolites and intracellular pH was abolished by inhibiting the generation of reactive oxygen species with MPG. Preservation of high-energy phosphate metabolites with PC was associated with reduced ultrastructural damage, as seen by electron microscopy, including less myocyte swelling, myofibrillar disruption and nuclear chromatin margination. The present study demonstrates the importance of reactive oxygen species generation in mediating PC preservation of myocyte ultrastructure and high-energy phosphate metabolites during prolonged ischemia in vivo.

Fractalkine and vascular injury

The vascular endothelium plays a central role in the recruitment and migration of circulating effector cells into sites of inflammation and immune responses. The unique CX(3)C-chemokine, fractalkine, is expressed on activated endothelial cells, and its receptor, CX(3)CR1, is expressed on natural killer cells, monocytes and some CD8+ T cells, all of which possess cytolytic function. Accumulating evidence that fractalkine is expressed on endothelial cells during glomerulonephritis and cardiac allograft rejection, as well as on cardiac endothelial cells activated by pro-inflammatory cytokines, might provide insight into the pathogenesis of vascular injury. Here, we propose a model in which fractalkine mediates vascular injury through the accumulation and activation of killer cells.

Fractalkine, a CX3C-chemokine, functions predominantly as an adhesion molecule in monocytic cell line THP-1

A newly identified CX3C-chemokine, fractalkine, expressed on activated endothelial cells plays an important role in leucocyte adhesion and migration. Co-immobilized fractalkine with fibronectin or intercellular adhesion molecule-1 enhanced adhesion of THP-1 cells, which express the fractalkine receptor (CX3CR1), compared with that observed for each alone. That adherence was fractalkine-dependent and was confirmed in blocking studies. However, soluble fractalkine induced little chemotaxis in THP-1 cells in comparison to monocyte chemotactic protein-1 (MCP-1), which induced a strong chemotactic response. Moreover, the membrane form of fractalkine expressed on ECV304 cells reduced MCP-1 mediated chemotaxis of THP-1 cells. These results indicate that fractalkine may function as an adhesion molecule between monocytes and endothelial cells rather than as a chemotactic factor.

Identification of ISC1 (YER019w) as inositol phosphosphingolipid phospholipase C in Saccharomyces cerevisiae

Sphingolipids have emerged as novel bioactive mediators in eukaryotic cells including yeast. It has been proposed that sphingomyelin (SM) hydrolysis and the concomitant generation of ceramide are involved in various stress responses in mammalian cells. The yeast Saccharomyces cerevisiae has inositol phosphosphingolipids (IPS) instead of SM and glycolipids, and synthesis of IPS is indispensable to its growth. Although the genes responsible for the synthesis of IPS have been identified, the gene(s) for the degradation of IPS has not been reported. Here we show that ISC1 (YER019w), which has homology to bacterial neutral sphingomyelinase (SMase), encodes IPS phospholipase C (IPS-PLC). First, we observed that overexpression of ISC1 greatly increased neutral SMase activity, and this activity was dependent on the presence of phosphatidylserine. Cells deleted in ISC1 demonstrated negligible neutral SMase activity. Because yeast cells have IPS instead of SM, we investigated whether IPS are the physiologic substrates of this enzyme. Lysates of ISC1-overexpressing cells demonstrated very high PLC activities on IPS. Deletion of ISC1 eliminated endogenous IPS-PLC activities. Labeling yeast cells with [(3)H]dihydrosphingosine showed that IPS were increased in the deletion mutant cells. This study identifies the first enzyme involved in catabolism of complex sphingolipids in S. cerevisiae.

Differential interaction of Cbl with Grb2 and CrkL in CD2-mediated NK cell activation

Natural killer (NK) cells participate in both innate and adoptive immunity by their prompt secretion of cytokines and by their ability to lyse virally infected cells or tumor cells. CD2 is surface glycoprotein receptors and crucial for NK cell activation. However, molecular events involved in CD2-mediated NK cell activation have not been fully elucidated. Cbl-Grb2 and Cbl-CrkL interactions have been implicated in T cell and B cell receptor, and cytokine receptor signaling. Here we analyzed tyrosine phosphorylation and interactions of Cbl with adapter proteins, Grb2 and CrkL, in NK3.3 cells. CD2 crosslinking results in the marked tyrosine phosphorylation of Cbl in an antibody concentration- and time-dependent manner. Immunodepletion studies reveal that Grb2-associated tyrosine phosphorylated p120 kDa protein is Cbl. In vitro binding studies using GST-fusion proteins demonstrate that Cbl constitutively associates with the SH3 domains of Grb2, with a preference for the amino-terminal domain. In addition, we demonstrate that CrkL associates with a large portion of tyrosine phosphorylated Cbl after CD2 stimulation of NK3.3 cells. In contrast to constitutive Cbl association with Grb2, tyrosine phosphorylated Cbl interacts with CrkL via its SH2 domain only after CD2 stimulation. Although the precise roles of interactions of Cbl with Grb2 and CrkL in NK cell activation remains to be elucidated, their tyrosine phosphorylation, in addition to the multiple protein interactions described here, strongly suggest that interactions of Cbl with Grb2 and CrkL may play pivotal roles in CD2-mediated NK cell activation.

CX3C-chemokine, fractalkine-enhanced adhesion of THP-1 cells to endothelial cells through integrin-dependent and -independent mechanisms

Leukocyte adhesion and trafficking at the endothelium requires both cellular adhesion molecules and chemotactic factors. A newly identified CX3C chemokine, fractalkine, expressed on activated endothelial cells, plays an important role in leukocyte adhesion and migration. We examined the functional effects of fractalkine on beta1 and beta2 integrin-mediated adhesion using a macrophage-like cell line, THP-1 cells. In this study, we report that THP-1 cells express mRNA encoding a receptor for fractalkine, CX3CR1, determined by Northern blotting. Scatchard analysis using fractalkine-SEAP (secreted form of placental alkaline phosphatase) chimeric proteins revealed that THP-1 cells express a single class of CX3CR1 with a dissociation constant of 30 pM and a mean expression of 440 sites per cell. THP-1 cells efficiently adhered, in a fractalkine-dependent manner, to full-length of fractalkine immobilized onto plastic and to the membrane-bound form of fractalkine expressed on ECV304 cells or TNF-alpha-activated HUVECs. Moreover, soluble-fractalkine enhanced adhesion of THP-1 cells to fibronectin and ICAM-1 in a dose-dependent manner. Pertussis toxin, an inhibitor of Gi, inhibited the fractalkine-mediated enhancement of THP-1 cell adhesion to fibronectin and ICAM-1. Finally, we found that soluble-fractalkine also enhanced adhesion of freshly separated monocytes to fibronectin and ICAM-1. These results indicate that fractalkine may induce firm adhesion between monocytes and endothelial cells not only through an intrinsic adhesion function itself, but also through activation of integrin avidity for their ligands.

Fractalkine-mediated endothelial cell injury by NK cells

Endothelial cells (ECs) are primary targets of immunological attack, and their injury can lead to vasculopathy and organ dysfunction in vascular leak syndrome and in rejection of allografts or xenografts. A newly identified CX3C-chemokine, fractalkine, expressed on activated ECs plays an important role in leukocyte adhesion and migration. In this study we examined the functional roles of fractalkine on NK cell activity and NK cell-mediated endothelial cell injury. Freshly separated NK cells expressed the fractalkine receptor (CX3CR1) determined by FACS analysis and efficiently adhered to immobilized full-length fractalkine, but not to the truncated forms of the chemokine domain or mucin domain, suggesting that fractalkine functions as an adhesion molecule on the interaction between NK cells and ECs. Soluble fractalkine enhanced NK cell cytolytic activity against K562 target cells in a dose- and time-dependent manner. This enhancement correlated well with increased granular exocytosis from NK cells, which was completely inhibited by the G protein inhibitor, pertussis toxin. Transfection of fractalkine cDNA into ECV304 cells or HUVECs resulted in increased adhesion of NK cells and susceptibility to NK cell-mediated cytolysis compared with control transfection. Moreover, both enhanced adhesion and susceptibility of fractalkine-transfected cells were markedly suppressed by soluble fractalkine or anti-CX3CR1 Ab. Our results suggest that fractalkine plays an important role not only in the binding of NK cells to endothelial cells, but also in NK cell-mediated endothelium damage, which may result in vascular injury.

Suppression of heat shock protein-70 by ceramide in heat shock-induced HL-60 cell apoptosis

Ceramide has emerged as a mediator of cell growth, differentiation, and apoptosis in many biological systems. Many kinds of stresses are reported to induce apoptosis with an increase of ceramide generation. Here we showed that the intracellular ceramide levels increased in parallel with heat shock (HS)-induced apoptosis in an intensity- and time-dependent manner, and synthetic N-acetylsphingosine (C(2)-ceramide) synergistically enhanced HS-induced apoptosis in HL-60 cells. In order to know the role of ceramide generation in HS-induced apoptosis, we examined the effects of C(2)-ceramide on the levels of mRNA and protein of heat shock proteins (HSPs). The increase of HSP-70 mRNA levels 1-2 h after HS at 42 degrees C for 30 min was suppressed by C(2)-ceramide in a dose-dependent manner. In comparison with HSP-70, the levels of HSP-60 and -90 mRNAs were faintly suppressed by C(2)-ceramide. Similarly, the increase in the protein levels of HSP-70 was significantly suppressed 4-8 h after HS by C(2)-ceramide in a dose-dependent manner. Additionally, in 293 cells, which are constitutively overexpressing HSP-70 gene, the levels of HSP-70 mRNA were suppressed by C(2)-ceramide in parallel with the increase of apoptotic cells. We next examined the mechanisms by which C(2)-ceramide suppressed HS-increased HSP-70 expression. The treatment with C(2)-ceramide did not affect both an activation of a nuclear transcription factor for HSP-70, heat shock factor-1, and an increased transcriptional rate of HSP-70 by HS, but increased the rates of HSP-70 mRNA degradation. In summary, ceramide may efficiently induce HS-induced apoptosis by suppressing anti-apoptotic HSP-70 through a post-transcriptional regulation.

Role of c-jun expression increased by heat shock- and ceramide-activated caspase-3 in HL-60 cell apoptosis. Possible involvement of ceramide in heat shock-induced apoptosis

Ceramide has emerged as a lipid mediator in apoptosis induced by a variety of stresses. As we previously showed that the activation of AP-1, a nuclear transcription factor was indispensable to ceramide-induced apoptosis in human leukemia HL-60 cells (Sawai, H., Okazaki, T., Yamamoto, H., Okano, H., Takeda, Y., Tashima, M., Sawada, H., Okuma, M., Ishikura, H., Umehara, H., and Domae, N. (1995) J. Biol. Chem. 270, 27326-27331), the role and mechanism of heat shock (HS)-increased c-jun expression in apoptosis was here investigated. HS increased morphological changes compatible with apoptosis in human leukemia HL-60 cells, and induced ceramide generation and sphingomyelin hydrolysis with an increase of neutral magnesium-dependent sphingomyelinase activity. When HS failed to induce apoptosis in HS-resistant HL-60 cells, ceramide generation was not detected, suggesting that ceramide was involved in downstream signals required for HS-induced apoptosis. Both HS and N-acetylsphingosine (C(2)-ceramide) increased the expression of c-jun/c-fos mRNAs with the peak 2 h after treatment. When we examined whether the inhibition of c-jun expression by its antisense oligodeoxynucleotides (AS) blocked HS- or C(2)-ceramide-induced apoptosis, AS of c-jun gene inhibited apoptotic morphological changes and DNA fragmentation whereas did not sense oligodeoxynucleotides. Moreover, a synthetic tetrapeptide, acetyl-Asp-Met-Gln-Asp-aldehyde (DMQD-CHO), which inhibited the formation of active form of caspase-3 more efficiently than those of caspase-4, -6, -7, and -8, blocked both caspase-3 like activity, c-jun expression and apoptosis induced by HS or C(2)-ceramide, although DMQD-CHO did not affect HS-induced ceramide generation. These results suggested that the ceramide was generated through sphingomyelin hydrolysis by HS-activated neutral, magnesium-dependent sphingomyelinase and that subsequent c-jun expression through activation of caspase-3 played a role in HS-induced HL-60 cell apoptosis.

Function of the cloned putative neutral sphingomyelinase as lyso-platelet activating factor-phospholipase C

Sphingolipids such as ceramide and sphingosine have been regarded as novel signal mediators in cells. However, the mechanisms of generation of these lipids upon various stimulation remain to be elucidated. Neutral sphingomyelinase (N-SMase) is one of the key enzymes in the generation of ceramide, and recently the cloning of a putative N-SMase was reported. Because the function of the protein was unclear in the previous report, we investigated the role it plays in cells. N-SMase activity in cells overexpressing the protein with hexa-histidine tag was immunoprecipitated with anti-hexa-histidine antibody. The metabolism of ceramide and SM was not apparently affected in overexpressing cells. Radiolabeling experiments using [(3)H]palmitic acid or [(3)H]hexadecanol demonstrated an accumulation of 1-O-alkyl-sn-glycerol and a corresponding decrease of 1-alkyl-2-acyl-sn-glycero-3-phosphocholine in overexpressing cells. In vitro studies showed that both 1-acyl-2-lyso-sn-glycero-3-phosphocholine (lyso-PC) and 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine (lyso-platelet activating factor (lyso-PAF)) are good substrates of the protein. In further radiolabeling experiments, 1-acyl-lyso-PC was predominantly and equally metabolized into diacyl-PC in both vector and overexpressing cells. On the other hand, 1-O-alkyl-lyso-PC (lyso-PAF) was metabolized into both diradyl-PC and 1-O-alkyl-glycerol in overexpressing cells but only into diradyl-PC in vector cells. These results suggest that the protein acts as lyso-PAF-PLC rather than lyso-PC-PLC or N-SMase in cells.

[Endothelial injury by oxidized LDL]

Recent progress in the research of oxidized LDL has revealed that this lipoprotein causes not only foam cell transformation of macrophages but also several endothelial dysfunction, and the effects on endothelial cells are also involved with the process of atherogenesis. Receptors for oxidized LDL on endothelial cells, such as LOX-1 and SREC, have been cloned and their characteristics are now under investigation. In addition to lowering plasma cholesterol level, it is expected that new strategies to prevent atherosclerosis is established by focusing on the endothelial injury caused by oxidized LDL.

Beta2-integrin, LFA-1, and TCR/CD3 synergistically induce tyrosine phosphorylation of focal adhesion kinase (pp125(FAK)) in PHA-activated T cells

Complete T cell activation requires not only a first signal via TCR/CD3 engagement but also a costimulatory signal through accessory receptors such as CD2, CD28, or integrins. Focal adhesion kinase, pp125(FAK) (FAK), was previously shown to be localized in focal adhesions in fibroblasts and to be involved in integrin-mediated cellular activation. Although signaling through beta1- or beta3-integrins induces tyrosine phosphorylation of FAK, there has been no evidence that activation of T cells through the beta2-integrin, LFA-1, involves FAK. We report here that crosslinking of LFA-1 induces tyrosine phosphorylation of FAK in PHA-activated T cells. Moreover, cocrosslinking with anti-LFA-1 mAb and suboptimal concentration of anti-CD3 mAb markedly increases tyrosine phosphorylation of FAK in an antibody-concentration-dependent and time-kinetics-dependent manner compared with stimulation through CD3 alone, which correlates well with enhanced proliferation of PHA-activated T cells. Furthermore, LFA-1beta costimulation with CD3 induces tyrosine phosphorylation of Syk associated with FAK. These results indicate, for the first time, that signals mediated by LFA-1 can regulate FAK, suggesting that LFA-1-mediated T cell costimulation may be involved in T cell activation at least partially through FAK.

Beta 2-integrin, LFA-1-mediated p125FAK activation

Accumulation of T cells at inflammatory sites is one of the characteristic features of infection, autoimmune and chronic inflammatory diseases. Optimal activation of T cells requires the binding of the MHC/Ag complex with T cell receptor, as well as a secondary signal initiated by costimulatory molecules such as CD2, CD28 or integrins. Focal adhesion kinase, pp125FAK (FAK) has been previously shown to be localized in focal adhesions in fibroblasts and to be involved in integrin-mediated cellular activation. Although signaling through beta 1- or beta 3-integrins induces tyrosine phosphorylation of FAK, there has been no evidence that activation of T cells through the beta 2-integrin, lymphocyte function-associated antigen (LFA)-1, involves FAK. We report here that crosslinking of LFA-1 induces tyrosine phosphorylation of FAK in PHA-activated T cells. Moreover, co-crosslinking with anti-LFA-1 monoclonal antibody (mAb) and suboptimal concentration of anti-CD3 mAb markedly increases tyrosine phosphorylation of FAK in an antibody-concentration and time-dependent manner compared with stimulation through CD3 alone. Furthermore this increased phosphorylation correlates well with the enhanced proliferation of PHA-activated T cells. Results indicate that signals mediated by LFA-1 can regulate FAK, suggesting that LFA-1-mediated T cell costimulation may be involved in T cell activation at least partially through FAK.

Co-stimulation of T cells with CD2 augments TCR-CD3-mediated activation of protein tyrosine kinase p72syk, resulting in increased tyrosine phosphorylation of adapter proteins, Shc and Cbl

Complete T cell activation requires not only the first signal via TCR-CD3 engagement, but also a co-stimulatory signal through accessory receptors such as CD2, LFA-1 and CD28. However, the pathway of co-stimulatory signaling through accessory receptors is incompletely understood. We report here that CD2 provides a co-stimulus for activation of CD3-mediated syk/ZAP-70 family kinase, p72Syk (Syk), in Jurkat T cells. Although cross-linking of CD2 alone or any combination of CD2 with LFA-1alpha, LFA-1beta or CD28 did not induce tyrosine phosphorylation of Syk, co-cross-linking of CD2 with CD3 enhanced CD3-mediated tyrosine phosphorylation of Syk. Enhancement of tyrosine phosphorylation of Syk by CD2 co-stimulation was CD2 antibody concentration-dependent, and time course studies showed that CD2 co-stimulation enhanced Syk tyrosine phosphorylation by 30 s and through 5 min stimulation compared with the control. In vitro kinase assay revealed that co-cross-linking of CD2 with CD3 augmented Syk kinase activity using myelin basic protein as a substrate. Furthermore, CD2 co-stimulation with CD3 resulted in enhanced tyrosine phosphorylation of adapter proteins, such as Shc and Cbl, in an antibody concentration-dependent manner. Finally, CD2 provided a co-stimulatory signals for synthesis of IL-2 in Jurkat cells and phytohemagglutinin (PHA)-activated T cells and for proliferation of PHA-activated T cells. Taken together, these results indicate that CD2 is an important co-stimulatory receptor for CD3-mediated T cell activation and functions in concert with CD3.

Involvement of protein tyrosine kinase p72syk and phosphatidylinositol 3-kinase in CD2-mediated granular exocytosis in the natural killer cell line, NK3.3

The granular exocytosis pathway is one mechanism by which NK cells and CTLs induce cytolysis of target cells. Triggering through adhesion molecules such as CD2 and LFA-1 as well as Fc gammaRIII (CD16) can invoke this pathway. CD2 is a cell surface glycoprotein present on CTLs and NK cells that plays an important role in both cellular adhesion and signal transduction. Here we report that cross-linking of CD2 as well as CD16 by immobilized Abs enhances granular exocytosis in an NK cell line, NK3.3. Herbimycin, a protein tyrosine kinase (PTK) inhibitor, or wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI 3-K), inhibited completely or almost completely CD2- or CD16-mediated granular exocytosis, suggesting the involvement of protein tyrosine kinases and PI 3-K in both CD2- and CD16-mediated granular exocytosis. We also observed that cross-linking of CD2 as well as CD16 enhances p72syk tyrosine kinase activity, and this enhancement correlated well with the increased tyrosine phosphorylation of several cellular proteins, including the adapter protein Shc. Furthermore, we have observed that cross-linking of CD2 as well as CD16 enhances the PI 3-K activity associated with the tyrosine-phosphorylated cellular proteins and Shc. These results provide insight into the signaling pathways by which triggering of CD2 and CD16 on NK cells leads to cytolysis of target cells.

Involvement of protein tyrosine kinase p72syk and phosphatidylinositol 3-kinase in CD2-mediated granular exocytosis in the natural killer cell line, NK3.3

The granular exocytosis pathway is one mechanism by which NK cells and CTLs induce cytolysis of target cells. Triggering through adhesion molecules such as CD2 and LFA-1 as well as Fc gammaRIII (CD16) can invoke this pathway. CD2 is a cell surface glycoprotein present on CTLs and NK cells that plays an important role in both cellular adhesion and signal transduction. Here we report that cross-linking of CD2 as well as CD16 by immobilized Abs enhances granular exocytosis in an NK cell line, NK3.3. Herbimycin, a protein tyrosine kinase (PTK) inhibitor, or wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI 3-K), inhibited completely or almost completely CD2- or CD16-mediated granular exocytosis, suggesting the involvement of protein tyrosine kinases and PI 3-K in both CD2- and CD16-mediated granular exocytosis. We also observed that cross-linking of CD2 as well as CD16 enhances p72syk tyrosine kinase activity, and this enhancement correlated well with the increased tyrosine phosphorylation of several cellular proteins, including the adapter protein Shc. Furthermore, we have observed that cross-linking of CD2 as well as CD16 enhances the PI 3-K activity associated with the tyrosine-phosphorylated cellular proteins and Shc. These results provide insight into the signaling pathways by which triggering of CD2 and CD16 on NK cells leads to cytolysis of target cells.

Identification of domains on the extrinsic 33-kDa protein possibly involved in electrostatic interaction with photosystem II complex by means of chemical modification

The extrinsic 33-kDa protein of photosystem II (PSII) was modified with various reagents, and the resulting proteins were checked for the ability to rebind to PSII and to reactivate oxygen evolution. While modification of more than eight carboxyl groups of aspartyl and glutamyl residues with glycine methyl ester did not affect the rebinding and reactivating capabilities, modification of amino groups of lysyl residues with either N-succinimidyl propionate or 2, 4,6-trinitrobenzene sulfonic acid or modification of guanidino groups of arginyl residues with 2,3-butanedione resulted in a loss of rebinding and reactivating capabilities of the 33-kDa protein. Moreover, the number of lysyl and arginyl residues susceptible to modification was significantly decreased when the protein was bound to PSII as compared with when it was free in solution, whereas the number of carboxyl groups modified was little affected. These results suggested that positive charges are important for the electrostatic interaction between the extrinsic 33-kDa protein and PSII intrinsic proteins, whereas negative charges on the protein do not contribute to such interaction. By a combination of protease digestion and mass spectroscopic analysis, the domains of lysyl residues accessible to N-succinimidyl propionate or 2,4, 6-trinitrobenzene sulfonic acid modification only when the 33-kDa protein is free in solution were determined to be Lys4, Lys20, Lys66-Lys76, Lys101, Lys105, Lys130, Lys159, Lys186, and Lys230-Lys236. These domains include those previously reported accessible to N-hydroxysuccinimidobiotin only in solution (Frankel and Bricker (1995) Biochemistry 34, 7492-7497), and may be important for the interaction of the 33-kDa protein with PSII intrinsic proteins.

Ceramide-induced translocation of protein kinase C-delta and -epsilon to the cytosol. Implications in apoptosis

Ceramide is now recognized as an intracellular lipid signal mediator, which induces various kinds of cell functions including apoptosis. Ceramide-induced apoptosis was reported to be blocked by 12-O-tetradecanoylphorbol 13-acetate, a protein kinase C (PKC) activator, but its mechanism remained unclear. Therefore, we investigated whether ceramide has any effects on PKC in the induction of apoptosis. We here report that N-acetylsphingosine (synthetic membrane-permeable ceramide) induced translocation of PKC-delta and -epsilon isozymes from the membrane to the cytosol within 5 min in human leukemia cell lines. Treatment with sphingomyelinase, tumor necrosis factor-alpha, or anti-Fas antibody, all of which can induce apoptosis by generating natural ceramide, similarly induced cytosolic translocation of PKC-delta and -epsilon. In Fas-resistant cells anti-Fas antibody did not induce cytosolic translocation of PKC-delta and -epsilon because of no generation of ceramide, whereas N-acetylsphingosine induced apoptosis with cytosolic translocation of PKC-delta and -epsilon. Furthermore, both 12-O-tetradecanoylphorbol 13-acetate and a nonspecific kinase inhibitor, staurosporine, prevented ceramide-induced apoptosis by inhibiting cytosolic translocation of PKC-delta and -epsilon. These data suggest that cytosolic translocation of PKC-delta and -epsilon plays an important role in ceramide-mediated apoptosis.

[Ceramide: a lipid mediator of apoptotic signal transduction]

Ceramide, the backbone of sphingolipids, is now recognized as an intracellular signal mediator of various cellular responses including cell differentiation and apoptosis. Tumor necrosis factor-alpha, anti-Fas antibody, anticancer drugs, radiation or heat shock induce apoptosis through generation of ceramide by activation of sphingomyelinase or ceramide synthase. The mechanism by which ceramide mediates apoptosis is unclear. We have found that ceramide induces the transcription of c-jun gene and increases the DNA binding activity of transcription factor AP-1 in human myelogenous leukemia HL-60 cells, and that activation of c-jun/AP-1 by ceramide(presumably through activation of Jun N-terminal kinase/stress-activated protein kinase) may be involved in the signaling pathway leading to apoptosis.

Increased processing of lymphocyte function-associated antigen-1 in human natural killer cells stimulated with IL-2

Previously we reported that surface expression of lymphocyte function-associated antigen-1 (LFA-1), the primary leukocyte integrin on human natural killer (NK) and lymphokine-activated killer (LAK) cells, does not differ between NK and LAK cells. In contrast to surface expression, we now report that much higher levels of both precursor and mature forms of LFA-1 molecules were found relative to MHC class I, another membrane glycoprotein, with metabolic labeling of IL-2-stimulated LAK cells compared with native NK cells. An 85-90 kDa glycoprotein, found in much higher quantities in LAK compared with NK cells, appeared to be a precursor of the 95 kDa beta chain of the beta 2 integrin family in human LAK cells because: (i) pulse-chase experiments using LAK cells demonstrated decreased 35S-labeling of the 85-90 kDa molecule with a concomitant increase in the radioactivity of the mature 95 kDa LFA-1 beta chain, (ii) results of protease treatment revealed that the two molecules share virtually identical peptide maps, and (iii) endoglycosaminidase F treatment of LAK cell lysates immunoprecipitated with antibody against LFA-1 beta resulted in the disappearance of both the 85-90 and 96 kDa LFA-1 beta signals, and appearance of a signal at approximately 76 kDa. Digestion of the same immunoprecipitates with neuraminidase resulted in the disappearance of the 95 kDa signal and revealed a single molecular weight signal corresponding to 85-90 kDa. These data suggest that a core protein of approximately 76 kDa becomes N-glycosylated, perhaps terminally with sialic acid residues, to mature into the 95 kDa form. Moreover, the rate of maturation of LFA-1 was more rapid in LAK than NK cells, with half times of 0.8 versus 1.5 h for the alpha chain and 3.7 versus 4.9 h for the beta chain for LAK versus NK cells respectively. IL-2 treatment of NK cells therefore alters the processing of LFA-1 molecules during the transition to LAK cells, providing a larger intracellular reservoir with which to replenish the surface molecule. Together with our previous observation that LFA-1 is phosphorylated and transduces signal more effectively in LAK than NK cells, the findings support the notion that adhesion molecules contribute to the increased function of LAK cells.

Characteristics and partial purification of a novel cytosolic, magnesium-independent, neutral sphingomyelinase activated in the early signal transduction of 1 alpha,25-dihydroxyvitamin D3-induced HL-60 cell differentiation

Treatment of HL-60 cells with a 1 alpha,25-dihydroxyvitamin D3 induces activation of a neutral sphingomyelinase (SMase), resulting in a decrease in sphingomyelin (SM) levels and an increase in ceramide levels in a proposed "sphingomyelin cycle" of cell regulation (Okazaki, T., Bell, R., and Hannun, Y. (1989) J. Biol. Chem. 264, 19076-19080). Cell-permeable synthetic ceramides induce HL-60 cell differentiation toward a monocytic lineage without conversion to sphingosine, suggesting that ceramide is a lipid mediator of cell differentiation (Okazaki, T., Bielawska, A., Bell, R., and Hannun, Y. (1990) J. Biol. Chem. 265, 15823-15831). In this study, we investigated a novel SMase that was activated 2-2.5 h after treatment of cells with 1 alpha,25-dihydroxyvitamin D3. The activated SMase was localized to the cytosolic fraction. It was inhibited by copper, ferric iron, and zinc and showed optimal activity at pH 7.5. A mixed micellar assay was developed for the enzyme, with optimal activity achieved at 12 mol% SM in Triton X-100 mixed micelles and at 20 mol% SM in deoxycholate micelles. The activity was modestly enhanced by phosphatidic acid, phosphatidylserine, or phosphatidylinositol, but not by other major phospholipids. Purification was performed by chromatography on DEAE anion-exchange, Q-Sepharose Fast Flow, hydroxylapatite, sphingosylphosphocholine affinity, and Superose 12 gel filtration columns. Two peaks of activity with molecular masses of 45 and 95 kDa were resolved by gel filtration chromatography on Superose 12. The specific activities of the purified 45- and 95-kDa enzymes were 2780 and 2790 nmol/mg/h, respectively. These data identify a novel cytosolic, magnesium-independent, neutral SMase(s) that is activated during cell differentiation.

Evaluation of oral aclarubicin treatment for tumors of the gastrointestinal track

Aclarubicin (ACR), a drug useful for the treatment not only of tumors of the hematopoietic system but also of those of the gastrointestinal tract, has been administered invariably by the intravenous route. We attempted oral administration of ACR to increase its specificity in the treatment of gastrointestinal tumors. Oral administration resulted in a much higher intratumor concentration but lower peripheral blood cell or bone marrow cell concentration of the drug as compared with intravenous administration. The reduced peripheral cell inhibition and bone marrow suppression permits the administration of the drug in higher doses, and the absence of the drug in the plasma suggests a reduced likelihood of myocardial cell injury and hepatocyte impairment. These favorable findings are considered to warrant early clinical trial of the treatment.

[Five cases of hematological disorders associated with acute myocardial infarction in thrombocytopenia]

Case of hematological disorders associated with acute myocardial infarction had been found in five of forty five autopsy cases which had hematological disorders during the past seven years. The five cases of hematological disorders consisted of two cases of myelodysplastic syndrome, a case of aplastic anemia, a case of primary myelofibrosis in blast transformation, and a case of acute myelogenous leukemia. All the patients were over 60 years old. Four patients had coronary artery stenosis and extensive myocardial infarction. Fibrinogen degradation products were elevated in four patients. DIC was recognized in two and suspected in two others. In all cases, platelet counts markedly decreased to less than 2.5 x 10(10)/L. Since no chest pain was noted by any patient, it was difficult to diagnose acute myocardial infarction without autopsy, except in one case. It is important to recognize the possibility of severe cardiac dysfunction due to myocardial infarction in thrombocytopenia, especially in the aged with DIC.

[Idiopathic plasmacytic lymphadenopathy with polyclonal hyperimmunoglobulinemia (IPL) accompanied with severe thrombocytopenia and interstitial pneumonitis]

A case of generalized lymphadenopathy with severe thrombocytopenia and marked polyclonal hypergammaglobulinemia is reported. A 51-year-old man was admitted to the hospital because of nasal bleeding and generalized lymphadenopathy. Laboratory examination revealed a platelet count of 6,000/microliters, a total protein level of 11.6 g/dl, and a gammaglobulin level of 8.7 g/dl including 6,726 mg/dl IgG, 1,119 mg/dl IgA, 265 mg/dl IgM, 265 mg/dl IgD and 226 IU/ml IgE. Neither definite evidence suggesting viral infection nor an autoimmune disease was found except slightly elevated titers of anti-microsome and anti-thyroglobulin antibodies. The chest X-ray revealed diffuse reticular shadowing suggesting interstitial pneumonitis. The cervical lymph node biopsy revealed massive infiltration by IgG-, IgA-, and IgM-positive plasmocytoid cells in the paracortical T cell areas, but no destruction of normal architecture of lymph node. The treatment with prednisolone resulted in a decrease in the severity of the lymphadenopathy, thrombocytopenia and polyclonal hypergammopathy. He is still well; however, interstitial pneumonitis, mild thrombocytopenia, and polyclonal hypergammopathy have persisted for 4 years. The histological findings in this case are similar to those in the case of Castleman lymphoma of a plasma cell type. Thus, considering the clinical data and clinical course, the diagnosis in this case is likely to be idiopathic plasmacytic lymphadenopathy with polyclonal hyperglobulinemia as a subtype of the plasma cell type of Castleman lymphoma. However, the accompanying interstitial pneumonitis and the severe thrombocytopenia, which was caused by excessive platelet destruction or by the suppression of megakaryocytes by proliferated plasma cells, are unique and are not found in any of the previously reported cases.