Structural and Biosynthetic Studies of the Granule Membrane Protein, GMP-140, from Human Platelets and Endothelial Cells

Selectins-The Two Dr. Jekyll and Mr. Hyde Faces of Adhesion Molecules-A Review

Selectins belong to a group of adhesion molecules that fulfill an essential role in immune and inflammatory responses and tissue healing. Selectins are glycoproteins that decode the information carried by glycan structures, and non-covalent interactions of selectins with these glycan structures mediate biological processes. The sialylated and fucosylated tetrasaccharide sLe^x is an essential glycan recognized by selectins. Several glycosyltransferases are responsible for the biosynthesis of the sLe^x tetrasaccharide. Selectins are involved in a sequence of interactions of circulated leukocytes with endothelial cells in the blood called the adhesion cascade. Recently, it has become evident that cancer cells utilize a similar adhesion cascade to promote metastases. However, like Dr. Jekyll and Mr. Hyde’s two faces, selectins also contribute to tissue destruction during some infections and inflammatory diseases. The most prominent function of selectins is associated with the initial stage of the leukocyte adhesion cascade, in which selectin binding enables tethering and rolling. The first adhesive event occurs through specific non-covalent interactions between selectins and their ligands, with glycans functioning as an interface between leukocytes or cancer cells and the endothelium. Targeting these interactions remains a principal strategy aimed at developing new therapies for the treatment of immune and inflammatory disorders and cancer. In this review, we will survey the significant contributions to and the current status of the understanding of the structure of selectins and the role of selectins in various biological processes. The potential of selectins and their ligands as therapeutic targets in chronic and acute inflammatory diseases and cancer will also be discussed. We will emphasize the structural characteristic of selectins and the catalytic mechanisms of glycosyltransferases involved in the biosynthesis of glycan recognition determinants. Furthermore, recent achievements in the synthesis of selectin inhibitors will be reviewed with a focus on the various strategies used for the development of glycosyltransferase inhibitors, including substrate analog inhibitors and transition state analog inhibitors, which are based on knowledge of the catalytic mechanism.

Influencing factors in quantitative measurement using activated platelet levels and platelet-activating capacity for the assessment of thrombosis in pre-metabolic syndrome and type 2 diabetes mellitus

Activated platelet levels and platelet-activating capacity are well recognized as useful index parameters for the physiological and pharmacological prediction of thrombotic events. Recently, quantitative measurements for platelet functions using a flow cytometer have been increasing gradually. However, the relation of physiological factors, such as sex, aging, and laboratory tests, to platelet functions has not been well documented. We conducted a blood analysis of people with normal/pre-metabolic syndrome and patients with type 2 diabetes mellitus to clarify the pathological factors. The levels of basal (non-stimulated)-activated, platelet-expressed P-selectin and activated platelet stimulated by agonists were measured by a flow cytometer, and ratios of platelet-activating capacity were also calculated. Statistical analyses indicated significantly high basal-activated platelet in pre-metabolic syndrome, and basal-activated platelet was positively associated with hyperlipidemia and hepatic damage. Platelet-activating capacity was significantly low in aging and hyperlipidemia, but high in hyperglycemia, and was negatively associated with hyperlipidemia and hepatic damage. Aging and high nutrient condition impaired platelet functions. Quantitative measurements of basal-activated platelet and platelet-activating capacity are precise parameters for the prediction of thrombotic events.

Platelets in patients with aspirin-exacerbated respiratory disease

Aspirin-exacerbated respiratory disease (AERD) is a chronic inflammatory disease characterized clinically by the triad of asthma, nasal polyposis, and pathognomonic respiratory reactions after ingestion of aspirin. It is a distinct syndrome associated with eosinophilic infiltration of respiratory tissues and excessive production of cysteinyl leukotrienes. Despite the consistent clinical phenotype of the respiratory disease, the underlying pathogenesis of the disease remains unclear. In addition to their role in hemostasis, platelets have the capacity to influence the activation state and function of other immune cells during inflammation and to facilitate granulocyte recruitment into the tissues. Platelets also possess a repertoire of potent preformed mediators of inflammation that are released on activation and are a rich source of newly synthesized lipid mediators that alter vascular permeability and smooth muscle tone. Accordingly, platelet activity has been linked to diverse inflammatory diseases, including asthma. Both human and animal studies strongly suggest that platelet activity is uniquely associated with the pathophysiology of AERD. This article summarizes the evidence supporting an effector role for platelets in asthmatic patients in general and in patients with AERD in particular and considers the potential therapeutic implications.

Glycosylation inhibitors efficiently inhibit P-selectin-mediated cell adhesion to endothelial cells

Adhesion molecules play a critical role in the adhesive interactions of multiple cell types in sickle cell disease (SCD). We previously showed that anti-P-selectin aptamer efficiently inhibits cell adhesion to endothelial cells (ECs) and permits SCD mice to survive hypoxic stress. In an effort to discover new mechanisms with which to inhibit P-selectin, we examined the role of glycosylation. P-selectin is a 90 kDa protein but was found to migrate as 90 and 140 kDa bands on gel electrophoresis. When P-selectin isolated from ECs was digested with peptide N-glycosidase F, but not O-glycosidase, the 140 kDa band was lost and the 90 kDa band was enhanced. Treatment of ECs with tunicamycin, an N-glycosylation inhibitor, suppressed CD62P (P-selectin) expression on the cell surface as well as the 140 kDa form in the cytoplasm. These results indicate that the 140 kDa band is N-glycosylated and glycosylation is critical for cell surface expression of P-selectin in ECs. Thrombin, which stimulates P-selectin expression on ECs, induced AKT phosphorylation, whereas tunicamycin inhibited AKT phosphorylation, suggesting that AKT signaling is involved in the tunicamycin-mediated inhibition of P-selectin expression. Importantly, the adhesion of sickle red blood cells (sRBCs) and leukocytes to ECs induced by thrombin or hypoxia was markedly inhibited by two structurally distinct glycosylation inhibitors; the levels of which were comparable to that of a P-selectin monoclonal antibody which most strongly inhibited cell adhesion in vivo. Knockdown studies of P-selectin using short-hairpin RNAs in ECs suppressed sRBC adhesion, indicating a legitimate role for P-selectin in sRBC adhesion. Together, these results demonstrate that P-selectin expression on ECs is regulated in part by glycosylation mechanisms and that glycosylation inhibitors efficiently reduce the adhesion of sRBCs and leukocytes to ECs. Glycosylation inhibitors may lead to a novel therapy which inhibits cell adhesion in SCD.

Simultaneous assay of activated platelet count and platelet-activating capacity by P-selectin detection using K2-EDTA-treated whole blood for antiplatelet agents

INTRODUCTION

It is well recognized that examinations of activated platelets (aPLTs) and platelet-activating capacity are very important to observe and prevent embolic diseases (events) such as ischemic stroke and myocardial infarction. Previously, we reported an appropriate measurement technique of aPLT for clinical assay. In this paper, we investigated stable conditions for measurement of activating capacity of platelets.

METHODS

Blood samples were taken from healthy volunteers using anticoagulants of 2K-EDTA, sodium citrate and heparin, and platelets were stimulated with adenosine diphosphate (ADP) or collagen. We demonstrated platelet-activating capacity by detection of scattering light, absorbance, microscopic observation, and P-selectin (CD62P) expression. We also performed basic experiments in seven healthy volunteers to test the clinical application of these assays with monitoring aspirin therapy.

RESULTS

We judged that samples of whole blood with 2K-EDTA were suitable for CD62P expression assay as functional assessments of platelet activity, because platelets treated with anticoagulants such as sodium citrate and heparin were extremely damaged after stimulation, and it was difficult to measure the CD62P expression by flow cytometry. For optimal results, samples should be tested within 1 h after the drawing of blood and stimulated with ADP or collagen for 10 min. The CD62P-positive platelet value of blood from volunteers who had taken aspirin was decreased, and platelet activation was inhibited as well.

CONCLUSION

The simultaneous assay of aPLT and platelet-activating capacity by CD62P detection using whole blood treated with the K2-EDTA anticoagulant was useful for the monitoring of antiplatelet drugs.

Development of an immunopredictor for the evaluation of the risk of cardiovascular diseases based on the level of soluble P-selectin

Due to its physiologic role in modulating adhesive interactions between blood cells and the endothelium during inflammatory processes or at injury sites, the adhesion molecule P-selectin is of great interest. The level of soluble P-selectin in plasma or serum can be detected and used as a clinical predictor for adverse cardiovascular events, leading to the presumption that it is secreted, shed or cleaved from the cell membrane during the process of diseases. Increased levels of soluble P-selectin in the plasma have been shown to be associated with a range of cardiovascular disorders, including coronary artery disease, hypertension and atrial fibrillation. Therefore, it is of huge significance to develop simple, rapid and sensitive methods for the detection of such pathological predictors, not only for facilitating the surveillance of cardiovascular mortality/sudden cardiac death, but also for effectively monitoring the drug potency on platelets based on measurement of P-selectin performed on fixed blood samples following platelet stimulation in whole blood in a remote setting. We herein developed a simple, yet novel and sensitive electrochemical sandwich immunosensor for the detection of P-selectin; it operates through covalent linkage of anti-P-selectin antibody on CNT@GNB nanocomposites-modified disposable screen-printed electrode as the detection platform, with the potassium ferrocyanide-encapsulated, anti-P-selectin-tagged liposomal biolabels as the electrochemical signal probes. The immunorecognition of the sample P-selectin by the liposomal biolabels occurred on the surface of the electrodes; the release of potassium ferrocyanide from the bound liposomal biolabels extensively contributed to the increase in electrochemical signal, which was acquired in HCl solution at +0.32V in square wave voltammetry mode. The resulting sigmoidally shaped dose-response curves possessed a linear dynamic working range from 1×10(-13) to 1×10(-5)g/mL. This liposome-based electrochemical immunoassay provides an amplification approach for detecting P-selectin at trace levels, leading to a detection limit as low as 4.3fg (equivalent to 5μL of 0.85pg/mL solution). A commercially available ELISA kit was used as a reference method to validate the newly-developed assay through the analysis of mouse serum samples. A strong correlation was observed between the two data sets as the R-squared value of 0.997 from the linear regression line. This electrochemical immunosensor will be useful for the detection of P-selectin in biological fluids and tissue extracts.

Pleiotropic platelet defects in mice with disrupted FOG1-NuRD interaction

Understanding platelet biology has been aided by studies of mice with mutations in key megakaryocytic transcription factors. We have shown that point mutations in the GATA1 cofactor FOG1 that disrupt binding to the nucleosome remodeling and deacetylase (NuRD) complex have erythroid and megakaryocyte lineages defects. Mice that are homozygous for a FOG1 point mutation (ki/ki), which ablates FOG1-NuRD interactions, have platelets that display a gray platelet syndrome (GPS)-like macrothrombocytopenia. These platelets have few α-granules and an increased number of lysosomal-like vacuoles on electron microscopy, reminiscent of the platelet in patients with GATA1-related X-linked GPS. Here we further characterized the platelet defect in ki/ki mice. We found markedly deficient levels of P-selectin protein limited to megakaryocytes and platelets. Other α-granule proteins were expressed at normal levels and were appropriately localized to α-granule-like structures. Treatment of ki/ki platelets with thrombin failed to stimulate Akt phosphorylation, resulting in poor granule secretion and platelet aggregation. These studies show that disruption of the GATA1/FOG1/NuRD transcriptional system results in a complex, pleiotropic platelet defect beyond GPS-like macrothrombocytopenia and suggest that this transcriptional complex regulates not only megakaryopoiesis but also α-granule generation and signaling pathways required for granule secretion.

Cytoplasmic domain of P-selectin glycoprotein ligand-1 facilitates dimerization and export from the endoplasmic reticulum

P-selectin glycoprotein ligand-1 (PSGL-1) is a homodimeric transmembrane mucin on leukocytes. During inflammation, reversible interactions of PSGL-1 with selectins mediate leukocyte rolling on vascular surfaces. The transmembrane domain of PSGL-1 is required for dimerization, and the cytoplasmic domain propagates signals that activate β(2) integrins to slow rolling on integrin ligands. Leukocytes from knock-in "ΔCD" mice express a truncated PSGL-1 that lacks the cytoplasmic domain. Unexpectedly, they have 10-fold less PSGL-1 on their surfaces than WT leukocytes. Using glycosidases, proteases, Western blotting, confocal microscopy, cell-surface cross-linking, FRET, and pulse-chase metabolic labeling, we demonstrate that deleting the cytoplasmic domain impaired dimerization and delayed export of PSGL-1 from the endoplasmic reticulum (ER), markedly increasing a monomeric precursor in the ER and decreasing mature PSGL-1 on the cell surface. A monomeric full-length PSGL-1 made by substituting the transmembrane domain with that of CD43 exited the ER normally, revealing that dimerization was not required for ER export. Thus, the transmembrane and cytoplasmic domains cooperate to promote dimerization of PSGL-1. Furthermore, the cytoplasmic domain provides a key signal to export precursors of PSGL-1 from the ER to the Golgi apparatus en route to the cell surface.

Development of an improved assay system for activated platelet counts and evaluation by aspirin monitoring

Platelets represent a linkage among inflammation, thrombosis, and atherogenesis, and enhanced platelet activation is regarded as a risk for thrombotic disorders. The level of P-selectin expressed (CD62P) on the platelet surface is a useful marker of activated platelets (aPLT). Although CD62P has been measured briefly by flow cytometry using an anti-CD62P antibody, the assay remains imprecise and we tried to establish stable conditions for its measurement. The levels of aPLT are increased significantly by many factors, such as meals, sampling and keeping conditions, centrifugation, and the timing of fixation. For optimal results, sampling should be performed quickly in a K(2)-ethylenediaminetetraacetic acid (EDTA) containing a sample tube, and whole blood should be fixed with 666 mmol/L formaldehyde plus 167 mmol/L glyoxal for 5 min. After washing with phosphate buffered saline (PBS), the fixed platelets were reacted with anti-CD62P antibody for 20 min and measured by flow-cytometric detection for aPLT. The coefficient of variation of our aPLT assay was 10.4%. We also examined basic experiments to test the clinical application of our aPLT assay by monitoring aspirin therapy. The levels of aPLT after the administration of aspirin for 3 days were significantly lower than those in the group that did not receive aspirin. These results suggest that the aPLT assay is an effective analytical procedure for measuring platelet reactivity.

P-selectin-dependent platelet aggregation and apoptosis may explain the decrease in platelet count during Helicobacter pylori infection

P-selectin expression has been shown in Helicobacter pylori-infected persons, an infection that has been clinically associated with platelet-related diseases, such as idiopathic thrombocytopenic purpura. However, the role of P-selectin expression during H pylori infection remains unclear. In this study, we hypothesized that P-selectin expression was associated with platelet aggregation during H pylori infection. Using flow cytometry, we examined the levels of adhesion between H pylori and platelets as well as the levels of P-selectin expression and platelet phosphatidylserine (PS) expression during H pylori infection. Significantly high levels of adhesion between pro-aggregatory bacteria and platelets were observed. We identified that H pylori IgG is required for bacteria to induce P-selectin expression and that a significant release of P-selectin is essential for H pylori to induce aggregation. In addition, cellular apoptotic signs, such as membrane blebbing, were observed in platelet aggregates. PS expression was also detected in platelets during infection with both pro-aggrogatory and nonaggregatory strains of H pylori. These results suggest that the decrease in platelet counts seen during H pylori infection is the result of P-selection-dependent platelet aggregation and PS expression induced by the bacteria.

Dimerization of P-selectin in platelets and endothelial cells

P-selectin is a leukocyte adhesion receptor stored in platelets and endothelial cells and is translocated to the surface upon cell activation. Purified P-selectin is oligomeric and has increased avidity for its ligand relative to the monomeric form, but whether P-selectin self-associates in the membrane of intact cells is not known. A chemical cross-linking approach was used to show that P-selectin is present as noncovalent dimers in resting platelets, human umbilical vein endothelial cells, and heterologous RIN5F cells expressing P-selectin. The results of 2-dimensional isoelectric focusing are consistent in showing P-selectin dimers as homodimers, but they are composed of a more basic subset of P-selectin than the monomers. This suggests that the dimers are a biochemically distinct subset of P-selectin. P-selectin dimers form in the endoplasmic reticulum and Golgi compartments of human umbilical vein endothelial cells only after synthesis of the mature P-selectin subunit, and are not preferentially stored in Weibel-Palade bodies as compared with the monomeric form. Platelet activation with thrombin receptor–activating peptide leads to the presence of P-selectin monomers and homodimers on the cell surface as well as P-selectin heterodimers, which are composed of P-selectin and an unidentified protein of approximately 81 kd molecular weight. In summary, these studies demonstrate that P-selectin is homodimeric in situ and that platelet activation leads to the formation of an additional activation-specific heterodimeric species. In addition, the homodimer has unique biochemical characteristics compared with the monomeric form, and dimerization occurs in the endoplasmic reticulum and Golgi compartments of endothelial cells.

Dimerization of P-selectin in platelets and endothelial cells

P-selectin is a leukocyte adhesion receptor stored in platelets and endothelial cells and is translocated to the surface upon cell activation. Purified P-selectin is oligomeric and has increased avidity for its ligand relative to the monomeric form, but whether P-selectin self-associates in the membrane of intact cells is not known. A chemical cross-linking approach was used to show that P-selectin is present as noncovalent dimers in resting platelets, human umbilical vein endothelial cells, and heterologous RIN5F cells expressing P-selectin. The results of 2-dimensional isoelectric focusing are consistent in showing P-selectin dimers as homodimers, but they are composed of a more basic subset of P-selectin than the monomers. This suggests that the dimers are a biochemically distinct subset of P-selectin. P-selectin dimers form in the endoplasmic reticulum and Golgi compartments of human umbilical vein endothelial cells only after synthesis of the mature P-selectin subunit, and are not preferentially stored in Weibel-Palade bodies as compared with the monomeric form. Platelet activation with thrombin receptor–activating peptide leads to the presence of P-selectin monomers and homodimers on the cell surface as well as P-selectin heterodimers, which are composed of P-selectin and an unidentified protein of approximately 81 kd molecular weight. In summary, these studies demonstrate that P-selectin is homodimeric in situ and that platelet activation leads to the formation of an additional activation-specific heterodimeric species. In addition, the homodimer has unique biochemical characteristics compared with the monomeric form, and dimerization occurs in the endoplasmic reticulum and Golgi compartments of endothelial cells.

A concise synthesis of the 6-O- and 6'-O-sulfated analogues of the sialyl Lewis X tetrasaccharide

The octyl glycoside of the sialyl Lewis X tetrasaccharide and its 6-O-sulfated and 6'-O-sulfated analogues were chemically synthesized in a concise manner starting from readily accessible monosaccharide intermediates. The synthesis involved formation of an orthogonally protected tetrasaccharide intermediate from which all three materials were prepared. A selective catalytic hydrogenolysis of four O-benzyl ethers in presence of a 4,6-O-benzylidene group was the key step in the synthetic scheme.

Density-dependent induction of TNF-alpha release from human monocytes by immobilized P-selectin

P-selectin purified from human platelets, when immobilized on a solid surface, induced monocytes to release tumor necrosis factor-alpha (TNF-alpha). The induction of TNF-alpha release was dependent on the concentration of P-selectin used for the immobilization, and the maximal stimulation was observed when the plate was coated with 0.3 microgram/ml of P-selectin. Use of either a higher or a lower concentration of P-selectin for the plate-coating was found to elicit less TNF-alpha release, although the higher concentration of P-selectin caused a stronger adhesion of HL-60 leukemic cells. The expression of mRNA for TNF-alpha roughly paralleled the TNF-alpha secretion, as assessed by RT-PCR. These results indicate that monocytes are activated by immobilized P-selectin in a density-dependent manner.

Biosynthesis and post-translational processing of lectin-like oxidized low density lipoprotein receptor-1 (LOX-1). N-linked glycosylation affects cell-surface expression and ligand binding

LOX-1 (lectin-like oxidized low density lipoprotein receptor-1) is a type II membrane protein belonging to the C-type lectin family that can act as a cell-surface receptor for atherogenic oxidized low density lipoprotein (Ox-LDL) and may play crucial roles in atherogenesis. In this study, we show, by pulse-chase labeling and glycosidase digestion, that LOX-1 is synthesized as a 40-kDa precursor protein with N-linked high mannose carbohydrate chains (pre-LOX-1), which is subsequently further glycosylated and processed into the 48-kDa mature form within 40 min. Furthermore, when treated with an N-glycosylation inhibitor, tunicamycin, both tumor necrosis factor-alpha-activated bovine aortic endothelial cells and CHO-K1 cells stably expressing bovine LOX-1 (BLOX-1-CHO) exclusively produced a 32-kDa deglycosylated form of LOX-1. Cell enzyme-linked immunosorbent assay, flow cytometry, and immunofluorescence confocal microscopy demonstrated that the deglycosylated form of LOX-1 is not efficiently transported to the cell surface, but is retained in the endoplasmic reticulum or Golgi apparatus in tumor necrosis factor-alpha-activated bovine aortic endothelial cells, but not in BLOX-1-CHO cells. Radiolabeled Ox-LDL binding studies revealed that the deglycosylated form of LOX-1 expressed on the cell surface of BLOX-1-CHO cells has a reduced affinity for Ox-LDL binding. Taken together, N-linked glycosylation appears to play key roles in the cell-surface expression and ligand binding of LOX-1.

Leukocyte-leukocyte interactions mediated by platelet microparticles under flow

Platelet microparticles (PMPs) are released from activated platelets and express functional adhesion receptors, including P-selectin, on their surface. PMP concentrations are elevated in many disorders, and their role in accelerating coagulation has been studied. However, their role in leukocyte aggregation has not been defined. We hypothesized that P-selectin–expressing PMPs bridge leukocytes that express P-selectin glycoprotein ligand-1 (PSGL-1), thereby allowing them to interact under flow conditions. PMPs were isolated from platelet-rich plasma or were generated by activating washed platelets with calcium ionophore. PMPs increased transient adhesion of flowing HL-60 cells or neutrophils to HL-60 cells or neutrophils prebound to the surface of a parallel plate flow chamber. Homotypic neutrophil interactions are initiated by the binding of L-selectin to PSGL-1. However, even when L-selectin function was blocked, PMPs allowed flowing neutrophils to aggregate and to interact with PSGL-1–expressing cells prebound to the surface of the flow chamber. The microparticle-mediated cell interactions occurred at lower shear stresses than those mediated by L-selectin. PMPs may enhance leukocyte aggregation and leukocyte accumulation on selectin-expressing substrates, especially in diseases where the concentration of the particles is elevated.

Effects of methionine-induced hyperhomocysteinemia on endothelium-dependent vasodilation and oxidative status in healthy adults

BACKGROUND

Homocysteine-mediated endothelial dysfunction has been proposed to occur via oxidative stress mechanisms in humans. However, there is controversy regarding the effects of homocysteine on endothelial function and oxidative status, which may in part result from age discrepancy across the studies. The present study was designed to investigate the aging effect on the relationship between endothelium-dependent vasodilation and oxidative status in methionine-induced hyperhomocysteinemia.

METHODS AND RESULTS

Plasma homocysteine, phosphatidylcholine hydroperoxide (PCOOH), P-selectin levels, and brachial artery flow-mediated vasodilation were measured at baseline and 4 hours after an oral methionine load (0.1 g/kg) in 15 younger (21 to 40 years) and 15 older (55 to 70 years) healthy adults. Homocysteine increased from 7.3+/-1.3 micromol/L at baseline to 22.7+/-5.2 micromol/L at 4 hours in younger (P<0.001) and from 7. 4+/-1.4 to 24.3+/-4.5 micromol/L in older adults (P<0.001). PCOOH levels were not significantly different between baseline and 4 hours in both groups (P=0.10 in young; P=0.14 in old). P-selectin, which is expected to increase during oxidative stress, was not changed in older (P=0.08) but decreased in younger adults (P=0.037) at 4 hours. Flow-mediated vasodilation was preserved from 13.1+/-2.1% at baseline to 13.5+/-2.8% at 4 hours in younger (P=0.49) and decreased from 12.8+/-2.4% to 8.5+/-2.8% in older adults (P<0.001).

CONCLUSIONS

The present study demonstrates that endothelial dysfunction caused by methionine-induced hyperhomocysteinemia is age-related and is mediated through impaired nitric oxide activity without change of oxidative status. Our data do not support previous hypotheses that endothelial damage by homocysteine is via oxidative stress mechanism in humans.

Radiation-induced normal tissue injury: role of adhesion molecules in leukocyte-endothelial cell interactions

The late onset of necrosis and fibrosis in normal tissues can be a serious consequence of radiotherapy in cancer patients. Because radiation-induced vascular injury precedes the tissue damage, vascular injury is regarded as crucial in the pathogenesis of tissue damage. An understanding of the processes responsible is essential to develop strategies for the amelioration of radiation-induced normal tissue damage. Leukocyte infiltration is commonly observed at sites of irradiation and is likely to lead to the acceleration and/or induction of parenchymal atrophy, fibrosis and necrosis in normal tissues following radiotherapy. The molecular mechanisms mediating leukocyte infiltration of tissues during inflammation have been studied extensively. It is now well established that cell adhesion molecules (CAMs) expressed on leukocytes and endothelial cells control the trafficking of leukocytes from the blood vessel lumen in these conditions. CAMs including E (endothelial), P (platelet) and L (leukocyte)-selectins, intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), beta1 and beta2 integrins and CD31 are involved in the cascade of events resulting in rolling, arrest and transmigration of leukocytes through the inflamed endothelium. Whether a similar sequence of molecular events induces leukocyte sequestration in irradiated normal tissues is not known. This review is focussed on the role of CAMs in radiation-induced leukocyte infiltration of normal tissues and the therapeutic implications of these findings.

P-Selectin Expression by Endothelial Cells Is Decreased in Neonatal Rats and Human Premature Infants

Decreased adhesion of neutrophils to endothelial cells and delayed transendothelial cell migration of neutrophils have been consistently reported in neonatal animals and humans and contribute to their susceptibility to infection. The delayed transmigration of neutrophils is especially prevalent in premature neonates. To define the nature of this defect, we used an in vivo animal model of inflammation and found that radiolabeled leukocytes from adult rats transmigrated into the peritoneum of other adult rats 5 times more efficiently than they did in neonatal rats (P = .05). This indicated that defects in neonatal neutrophils could not completely account for the delayed transmigration. Delayed transmigration in the neonatal rats correlated with a defect in the expression of P-selectin on the surface of their endothelial cells. We found a similar P-selectin deficiency in endothelial cells lining mesenteric venules and umbilical veins of human premature infants when compared with term human infants. The decreased P-selectin in premature infants was associated with decreased numbers of P-selectin storage granules and decreased P-selectin transcription. Decreased P-selectin expression on the surface of endothelial cells in preterm infants may contribute to delayed neutrophil transmigration and increased susceptibility to infection.

P-Selectin Expression by Endothelial Cells Is Decreased in Neonatal Rats and Human Premature Infants

Decreased adhesion of neutrophils to endothelial cells and delayed transendothelial cell migration of neutrophils have been consistently reported in neonatal animals and humans and contribute to their susceptibility to infection. The delayed transmigration of neutrophils is especially prevalent in premature neonates. To define the nature of this defect, we used an in vivo animal model of inflammation and found that radiolabeled leukocytes from adult rats transmigrated into the peritoneum of other adult rats 5 times more efficiently than they did in neonatal rats (P = .05). This indicated that defects in neonatal neutrophils could not completely account for the delayed transmigration. Delayed transmigration in the neonatal rats correlated with a defect in the expression of P-selectin on the surface of their endothelial cells. We found a similar P-selectin deficiency in endothelial cells lining mesenteric venules and umbilical veins of human premature infants when compared with term human infants. The decreased P-selectin in premature infants was associated with decreased numbers of P-selectin storage granules and decreased P-selectin transcription. Decreased P-selectin expression on the surface of endothelial cells in preterm infants may contribute to delayed neutrophil transmigration and increased susceptibility to infection.

Biomechanics of cell interactions in shear fields

Cellular interactions play a key role in diverse biological processes within the cardiovascular system. Targeting of leukocytes to sites of inflammation is viewed as a multistage process of sequential involvement of distinct adhesion molecules on the leukocyte and endothelial cell (EC) surface that is dictated by the local fluid dynamic environment. For neutrophils, the initial contact and rolling along the vessel wall are mediated primarily by selecting. Subsequent firm adhesion requires activation of neutrophil P, integrins and binding to their ligand ICAM-1 on the EC surface. The final step of this cascade of events includes neutrophil transmigration to extravascular tissue space. The neutrophil model of emigration in inflammation has been extended and refined to account for monocyte and T cell interactions with ECs. Platelet adhesion to thrombogenic surfaces (i.e. immobilized von Willebrand factor) under flow follows the general principles of leukocyte extravasation. More specifically, platelet glycoprotein (GP) Ib alpha appears to mediate an initial selectin-like tethering platelet-vWf interaction, followed by alpha II beta beta 3 integrin activation and firm adhesion. Some of the signaling mechanisms associated with cellular interactions in inflammatory and thrombotic processes are discussed. These basic principles are also discussed in the context of tissue engineering research.

An atypical sorting determinant in the cytoplasmic domain of P-selectin mediates endosomal sorting

We previously identified the 11 amino acid C1 region of the cytoplasmic domain of P-selectin as essential for an endosomal sorting event that confers rapid turnover on P-selectin. The amino acid sequence of this region has no obvious similarity to other known sorting motifs. We have analyzed the sequence requirements for endosomal sorting by measuring the effects of site-specific mutations on the turnover of P-selectin and of the chimeric protein LLP, containing the lumenal and transmembrane domains of the low density lipoprotein receptor and the cytoplasmic domain of P-selectin. Endosomal sorting activity was remarkably tolerant of alanine substitutions within the C1 region. The activity was eliminated by alanine substitution of only one amino acid residue, leucine 768, where substitution with several other large side chains, hydrophobic and polar, maintained the sorting activity. The results indicate that the endosomal sorting determinant is not structurally related to previously reported sorting determinants. Rather, the results suggest that the structure of the sorting determinant is dependent on the tertiary structure of the cytoplasmic domain.

The transmembrane domain enhances granular targeting of P-selectin

P-selectin is an integral membrane glycoprotein that is stored in granules of endothelial cells and platelets. The cytoplasmic domain of P-selectin is known to contain at least part of the signal that directs the protein to storage granules. In order to more fully understand how P-selectin is targeted to the regulated secretory pathway, we have expressed chimeric constructs between P- and E-selectin, a protein which is expressed on the cell surface, in a rat insulinoma cell line. Immunofluorescence studies indicated that replacing the cytoplasmic domain of E-selectin with that of P-selectin resulted in low-level granular expression. In contrast, when both the transmembrane and cytoplasmic domains of E-selectin were replaced with the analogous domains of P-selectin, the granular localization appeared greatly increased. This was confirmed by immunoelectron microscopy which demonstrated a three- to fourfold improvement in granular targeting, i.e. similar to wild-type P-selectin. The transmembrane domain had to be in the context of the P-selectin cytoplasmic domain as this membrane-spanning region could not induce granular targeting on its own. These results describe a novel function for the transmembrane domain of P-selectin in enhancing the efficiency of granular targeting and further implicate protein transmembrane domains in intracellular trafficking.

Tyrosine phosphorylation of platelet endothelial cell adhesion molecule-1 induced by lysophosphatidylcholine in cultured endothelial cells

Lysophosphatidylcholine (lyso-PC), a biologically active phospholipid, appears to modulate various endothelial cell functions through tyrosine kinase-dependent signaling pathways. In cultured bovine aortic endothelial cells (BAEC), we have found that a 130 kDa protein (p130) was rapidly tyrosine phosphorylated within 2 min and sustained for, at least, 1 hr in response to 10 mumol/L of lyso-PC but not to phorbol myristate acetate (PMA). Prolonged preexposure to PMA did not affect lyso-PC-induced p130 tyrosine phosphorylation, suggesting that mechanisms independent of protein kinase C may be involved. Fractionation of the cell lysates revealed that p130 was detectable in the membrane fraction but not in the cytosolic fraction. Immunoprecipitation followed by immunoblotting of lyso-PC-treated BAEC identified p130 as bovine PECAM-1. Tyrosine phosphorylation of PECAM-1 appears to be one of the earliest events elicited by lyso-PC, and may play a role in lyso-PC-induced modulation of endothelial functions.

Elevated serum concentrations of soluble selectin and immunoglobulin type adhesion molecules in patients with inflammatory bowel disease

Adhesion molecules mediate the extravasation of leukocytes and their accumulation in inflamed tissues. In the present study, serum concentrations of the selectin (sP- and sE-selectin) and immunoglobulin supergene family (sICAM-1 and sVCAM-1) of adhesion molecules were measured in 93 patients with inflammatory bowel disease (Crohn's disease, n = 65; ulcerative colitis, n = 28) and 58 age-matched normal controls. sP-selectin serum concentrations (mean +/- SEM ng/ml) of patients with Crohn's disease (399 +/- 33 ng/ml) and ulcerative colitis (385 +/- 42 ng/ml) were increased (P = 0.0067 and P = 0.0193, respectively) compared to controls (251 +/- 33 ng/ml). In contrast, E-selectin serum levels of patients with Crohn's disease (58 +/- 5 ng/ml) and ulcerative colitis (64 +/- 12 ng/ml) were not significantly higher than those of controls (53 +/- 5 ng/ml). sICAM-1 serum concentrations of patients with Crohn's disease (420 +/- 19 ng/ml) and those with ulcerative colitis (375 +/- 40 ng/ml) were elevated (P = 0.0001 and P = 0.0473, respectively) compared to controls (297 +/- 8 ng/ml). Further, sVCAM-1 levels of patients with Crohn's disease (664 +/- 43 ng/ml) and ulcerative colitis (963 +/- 162 ng/ml) were increased (P = 0.0222 and P = 0.0121, respectively) compared to controls (510 +/- 31 ng/ml). With few exceptions, serum levels of soluble adhesion molecules were not significantly correlated to disease activity indices or disease localization. Elevated circulating selectin and immunoglobulin supergene type adhesion molecules may compete with membrane-bound forms for their cognate ligands and thereby limit the rolling and stable adhesion of leukocytes.

Expression of a P-selectin ligand in zona pellucida of porcine oocytes and P-selectin on acrosomal membrane of porcine sperm cells. Potential implications for their involvement in sperm-egg interactions

The selectin family of cell adhesion molecules mediates initial leukocyte adhesion to vascular endothelial cells at sites of inflammation. O-glycan structural similarities between oligosaccharides from human leukocyte P-selectin glycoprotein ligand-1 (PSGL-1) and from zona pellucida glycoproteins of porcine oocytes indicate the possible existence of a P-selectin ligand in the zona pellucida. Here, using biochemical as well as morphological approaches, we demonstrate that a P-selectin ligand is expressed in the porcine zona pellucida. In addition, a search for a specific receptor for this ligand leads to the identification of P-selectin on the acrosomal membrane of porcine sperm cells. In vitro binding of porcine acrosome-reacted sperm cells to oocytes was found to be Ca2+ dependent and inhibitable with either P-selectin, P-selectin receptor-globulin, or leukocyte adhesion blocking antibodies against P-selectin and PSGL-1. Moreover, porcine sperm cells were found to be capable of binding to human promyeloid cell line HL-60. Taken together, our findings implicate a potential role for the oocyte P-selectin ligand and the sperm P-selectin in porcine sperm-egg interactions.

Molecular Pathogenesis of Type I Congenital Plasminogen Deficiency: Expression of Recombinant Human Mutant Plasminogens in Mammalian Cells

We previously reported the genetic abnormality in a Japanese family with type I congenital plasminogen deficiency caused by a Ser572 to Pro572 mutation. To characterize the molecular pathogenesis of the disease in this family, we expressed recombinant human wild-type and mutant (rS572P) plasminogens in COS-1 cells. Activation-resistant wild-type and mutant plasminogen stable transfectants in CHO-K1 cells also were established. Transient transfection and metabolic labeling experiments followed by immunoprecipitation analysis showed that the mutant plasminogen was secreted from COS-1 cells in reduced amounts, compared with the wild type. Endo H digestion of the wild-type and mutant plasminogen showed no shift in their migrations on sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, indicating that both contain complex type oligosaccharide structures and could therefore be secreted. Furthermore, the secretion of activation-resistant mutant plasminogen was significantly reduced. Pulse-chase experiments and Northern blot analysis showed that the impaired secretion of the mutant plasminogen was the consequence of the accumulation of the mutant protein inside the cells but not of reduced plasminogen mRNA. Immunocytochemical staining of stable transfectants also revealed that CHO-K1 cells expressing the activation-resistant mutant plasminogen stained mainly in the perinuclear area, suggesting delayed processing of the mutant protein in the intracellular transport pathway. We conclude that the impaired secretion of mutant plasminogen, due to intracellular accumulation, is the molecular pathogenesis of type I congenital plasminogen deficiency caused by a Ser572 to Pro572 mutation.

Molecular Pathogenesis of Type I Congenital Plasminogen Deficiency: Expression of Recombinant Human Mutant Plasminogens in Mammalian Cells

We previously reported the genetic abnormality in a Japanese family with type I congenital plasminogen deficiency caused by a Ser572 to Pro572 mutation. To characterize the molecular pathogenesis of the disease in this family, we expressed recombinant human wild-type and mutant (rS572P) plasminogens in COS-1 cells. Activation-resistant wild-type and mutant plasminogen stable transfectants in CHO-K1 cells also were established. Transient transfection and metabolic labeling experiments followed by immunoprecipitation analysis showed that the mutant plasminogen was secreted from COS-1 cells in reduced amounts, compared with the wild type. Endo H digestion of the wild-type and mutant plasminogen showed no shift in their migrations on sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, indicating that both contain complex type oligosaccharide structures and could therefore be secreted. Furthermore, the secretion of activation-resistant mutant plasminogen was significantly reduced. Pulse-chase experiments and Northern blot analysis showed that the impaired secretion of the mutant plasminogen was the consequence of the accumulation of the mutant protein inside the cells but not of reduced plasminogen mRNA. Immunocytochemical staining of stable transfectants also revealed that CHO-K1 cells expressing the activation-resistant mutant plasminogen stained mainly in the perinuclear area, suggesting delayed processing of the mutant protein in the intracellular transport pathway. We conclude that the impaired secretion of mutant plasminogen, due to intracellular accumulation, is the molecular pathogenesis of type I congenital plasminogen deficiency caused by a Ser572 to Pro572 mutation.

P-selectin is upregulated early in the course of hyperoxic lung injury in mice

While treatment with supplemental oxygen is often essential in patients with lung disease, prolonged therapy may cause lung injury by itself. Although the mechanisms responsible for initiating hyperoxic lung damage almost certainly involve primary oxidative transformations, the possible contributions of inflammation to the tissue injury have been attracting increasing research activity. Increases in intercellular adhesion molecule-1 (ICAM-1) coincide with the inflammation, but in other models of inflammation transient adhesion mediated by members of the Selectin gene family was found to be essential before ICAM-1/beta 2 interactions could occur. We, therefore, wondered whether a similar sequence of initial transient adhesion followed by subsequent responses would be observed in hyperoxic lung inflammation. We, therefore, determined the effects of hyperoxia exposure on lung mRNA for P- and E-Selectin in mouse lungs. We found that there was no detectable mRNA for E-Selectin through 72 h of hyperoxia exposure by Northern blotting, but that mRNA for P-Selectin was detectable as early as 48 h after initiation of hyperoxia. To determine the location of P-Selectin upregulation we examined hyperoxia-exposed mouse lungs by in situ hybridization and found that the upregulation of P-Selectin at 48 h was localized to large muscularized vessels, at 72 h expression was detected in some medium size muscularized vessels, and at 96 h abundant expression was observed also on nonmuscularized small vessels. In conclusion, increases in mRNA for P-Selectin early in the course of hyperoxia exposure suggest that P-Selectin expression in hyperoxic lungs increases in parallel with upregulation of ICAM-1, leading to the accumulation of neutrophils in hyperoxic lungs, and that interventions targeting these two adhesion molecules may lead to a diminution in hyperoxic lung inflammation and lung injury.

Residues throughout the cytoplasmic domain affect the internalization efficiency of P-selectin

The cytoplasmic domains of many membrane proteins have short sequences, usually including a tyrosine or a di-leucine, that function as sorting signals. P-selectin is an adhesion receptor for leukocytes that is expressed on activated platelets and endothelial cells. Its 35-residue cytoplasmic domain contains signals for sorting into regulated secretory granules, for endocytosis, and for movement from endosomes to lysosomes. The domain has a membrane-distal sequence, YGVFTNAAF, that resembles some tyrosine-based signals. We studied the effects of deletions and mutations in the cytoplasmic tail of human P-selectin on its internalization in clathrin-coated pits of transfected Chinese hamster ovary cells. Mutations and deletions in the putative tyrosine-based motif did not clearly implicate these residues as critical components of a short internalization signal. Indeed, a construct containing a truncated 18-residue cytoplasmic domain with a single substitution (K761A/H773Stop) was internalized nearly three times as fast as wild-type P-selectin; this construct contained no di-leucine, tyrosine, or other known sorting motif. Substitution of residues throughout the cytoplasmic domain affected the internalization rate of P-selectin. Furthermore, the cytoplasmic domain of P-selectin mediated faster internalization when attached to the extracellular and transmembrane domains of the low density lipoprotein receptor than when attached to the corresponding domains of P-selectin. Thus, we were unable to identify a short internalization signal in the cytoplasmic tail of P-selectin. Residues throughout the cytoplasmic domain, and perhaps the transmembrane sequence to which the domain is attached, affect the efficiency of internalization.

Characterization of canine platelet P-selectin (CD 62) and its utility in flow cytometry platelet studies

1. P-selectin (PADGEM, GMP140, or CD62) a member of lectin-like adhesive proteins is expressed on the surface of activated degranulated canine platelets and is the calcium-dependent receptor for leukocyte adhesion. 2. The electrophoretic mobility of P-selectin, by Western blot analysis and immunoprecipitation from radiolabeled membranes of canine and human platelets, was similar or identical and immunocytochemical studies localized P-selectin in internal vesicles similar to the alpha granule localization in human platelets. 3. Two antibodies to human P-selectin KC4.1 and AC1.2 crossreacted with canine platelets whose surface binding, in response to agonists thrombin, calcium ionophore (A23187), phorbol esters and ADP, was similar. 4. Anti-P-selectin antibodies in conjunction with crossreacting anti-GPIIb/IIIa antibodies (A2A9, 7E3, RUU-PL7F12) enables the analysis of activated platelets, platelet-derived microparticles and platelet-leukocyte interactions in canine models by flow cytometry.

Production of a monoclonal antibody against canine GMP-140 (P-selectin) and studies of its vascular distribution in canine tissues

Rapid upregulation of the adhesion molecule GMP-140 (P-selectin) on endothelial cells is believed to play an important role in the initial binding of leukocytes to endothelium, a very early step in the inflammatory response. Activated platelets that are involved in the coagulation system and in inflammatory processes also express GMP-140 on their surfaces. The objectives of the present study were to develop a monoclonal antibody against this adhesion molecule in the dog and to use this antibody to study platelet-neutrophil interactions in whole blood and to characterize the in vivo localization of GMP-140 in canine tissues. Five Balb/c mice were immunized with thrombin-stimulated dog platelets, and clones were screened using an enzyme-linked immunosorbent assay. The clone MD3 (IgG1) showed preferential binding to activated as compared with resting platelets. Flow cytometric analysis using MD3 revealed that 27% of circulating neutrophils in unstimulated blood had platelets bound to their surfaces; stimulation with platelet activating factor increased this percentage to 85%. Immunoblot analysis of solubilized dog platelets resolved by sodium dodecyl sulfate polyacrylamide gel electrophoresis indicated that the antibody MD3 recognized an approximately 140-kd protein. Immunohistochemical study of normal dog tissues with MD3 revealed that the antigen was present in endothelial cells of arteries, capillaries, and veins, depending on the specific tissue examined. Blood vessels staining positively with MD3 were most abundant in the digestive system (liver, stomach, small and large intestines), moderate in the lungs, kidneys, spleen, lymph nodes, and endocrine glands, and minimal in the brain, myocardium, skeletal system, and skin. Based on its presence on stimulated but not resting platelets, its molecular weight, and its vascular distribution, the antigen recognized by MD3 appears to be the selectin GMP-140 of the dog. This study documents that the cellular and tissue distribution of GMP-140 in dogs is very similar to that in human beings.

Thrombin receptor 14-amino acid peptide mediates endothelial hyperadhesivity and neutrophil adhesion by P-selectin-dependent mechanism

Thrombin cleaves its receptor at arginine-41, resulting in the generation of a new receptor NH2-terminus with the sequence SFLLRNPNDKYEPF. This peptide (TRP-14) may signal a variety of thrombin's responses. We examined the effects of TRP-14 in inducing endothelial cell hyperadhesivity and neutrophil (PMN) adhesion to endothelial cell monolayers. Human umbilical vein endothelial cells (HUVECs) challenged with TRP-14 (10(-4) to 10(-5) M) produced concentration-dependent increases in endothelial adhesivity to PMN. In contrast, position 1 to 2 inverted peptide (FSLLRNPNDKYEPF) did not induce the response. The adhesion response was transient; that is, PMN adhesion increased within 15 minutes and decreased by 75 minutes after TRP-14 challenge of HUVECs. The transient endothelial adhesiveness paralleled the time course of P-selectin expression. TRP-14-induced release of P-selectin from intracellular stores may be a critical determinant of the response since treatment of endothelial cells with anti-P-selectin monoclonal antibody (mAb) G1 prevented the increase in PMN adhesion. Control nonneutralizing anti-P-selectin mAb S12 and mAb RR1/1 directed against intercellular adhesion molecule-1 (ICAM-1) on HUVECs were ineffective. The results indicate that the "tethered ligand" of the thrombin receptor created by the proteolytic action of thrombin on its receptor (i.e., TRP-14) signals increased endothelial adhesiveness by a P-selectin-dependent mechanism. Thrombin-induced PMN adhesion may involve formation of a new NH2-terminus of the endothelial thrombin receptor with the sequence SFLLRNPNDKYEPF followed by activation of endothelial second messenger pathways and the transient expression of P-selectin.

A monoclonal antibody-based enzyme immunoassay for human GMP-140/P-selectin

Two hybridoma cell lines producing monoclonal antibodies WGA-1 and PL7-6, reactive only with thrombin-stimulated human platelet have been established. Both these antibodies were investigated for their specific reactivity against GMP-140, based on the amino acid composition analysis of immunopurified antigen and N terminal amino acid sequencing of its protease fragments. A two-site enzyme immunoassay for quantification of human GMP-140 was developed using WGA-1 monoclonal antibody immobilized on 96-well microplates and horseradish peroxidase-labeled PL7-6 monoclonal antibody as detector. The assay was able to measure GMP-140 in serum and plasma with a sensitivity of about 5 ng/ml and a precision better than 10%. This assay will be useful for the detection of GMP-140 derived from platelets or endothelium in biological fluids and tissue extracts.

GMP-140: a receptor for neutrophils and monocytes on activated platelets and endothelium

GMP-140 is a membrane glycoprotein located in secretory granules of platelets and endothelium. When these cells are activated by agonists such as thrombin, GMP-140 is rapidly translocated to the plasma membrane. GMP-140, along with ELAM-1 and the peripheral lymph node homing receptor, defines the selectin family of structurally related molecules that regulate interactions of leukocytes with the blood vessel wall. Each of these molecules contains an N-terminal lectin-like domain, followed by an EGF-like region, a series of consensus repeats related to those in complement-binding proteins, a transmembrane domain, and a short cytoplasmic tail. The genomic structures of the selectins suggest that they arose by duplication and modification of exons encoding specific structural domains. GMP-140 is a receptor for neutrophils and monocytes when it is expressed on activated platelets and endothelium. This property facilitates rapid adhesion of leukocytes to endothelium at regions of tissue injury as well as platelet-leukocyte interactions at sites of inflammation and hemorrhage. Like other leukocyte adhesion molecules, GMP-140 may also participate in pathologic inflammation, thrombosis, and tumor metastasis. Confirmation of such pathologic roles may lead to design of new drugs that block adhesive receptor function in human disease.

Endothelium specific Weibel-Palade bodies in a continuous human cell line, EA.hy926

Weibel-Palade bodies are ultrastructurally defined organelles found only in vascular endothelial cells. Because endothelium in corpo is very dispersed, isolation and further characterization of this organelle has been dependent on increasing the number of cells in culture. However, primary isolates of endothelial cells have a limited replication potential and tend to senesce in culture. In this report, EA.hy926, a continuously replicating cell line derived from human endothelium, is shown to contain Weibel-Palade bodies. Electron micrographs demonstrate the ultrastructural characteristics of these tissue-specific organelles and their cytoplasmic distribution in EA.hy926 cells. Von Willebrand factor, which has been shown to exist in Weibel Palade bodies, is demonstrated by immunofluorescence in discrete rod-shaped organelles whose size, shape, and distribution are consistent with that of Weibel-Palade bodies in primary endothelial cell cultures. Rapid release of von Willebrand factor can be induced by calcium ionophore, and large multimeric forms of the protein are found in EA.hy926 cells. These two properties are consistent with the function currently ascribed to Weibel Palade bodies: storage of multimerized von Willebrand factor. Thus ultrastructural, immunologic, and functional data establish the existence of this as yet poorly understood tissue-specific organelle in a continuous, vigorously replicating human cell line.

A possible pathogenesis for Blackfoot disease--effects of trivalent arsenic (As2O3) on cultured human umbilical vein endothelial cells

Blackfoot disease (BFD) is an endemic peripheral vascular occlusive disease found among the inhabitants of the southwest coast of Taiwan. The clinical features of BFD are similar to those of Buerger's disease. Pathology shows arteriosclerosis obliterans and thromboangiitis obliterans. The high arsenic content of artesian well water in the area is regarded as the main causal factor of this disease. Therefore, the purpose of this study was to observe the toxic effects of various arsenic concentrations on cultured human umbilical vein endothelial cells (HUV-EC). The methods of this study included cell growth assay, 51Cr-release assay, and staining of Factor VIII related antigen (FVIII-RAg) and Ulex europaeus agglutinin I (UEA-I) binding sites of HUV-EC. The following data were obtained: 1) no obvious cytotoxicity in 51Cr-release assay; 2) inhibition of the synthesis of both FVIII-RAg and UEA-I binding sites when the arsenic concentration was above 100 ng/ml; 3) dose-dependent inhibition of growth of HUV-EC by any concentration of arsenic. At a higher concentration of more than 100 ng/ml, arsenic inhibited endothelial cell proliferation and glycoprotein synthesis, whereas it only inhibited the proliferation at a lower concentration of less than 50 ng/ml. It is suggested that arsenic, at both higher and lower concentrations, may damage endothelial cells. Such damage may play an important role in the pathogenesis of BFD.

Prevention of activated neutrophil adhesion to endothelium by soluble adhesion protein GMP140

Neutrophils and monocytes, but not lymphocytes, adhered strongly to plastic surfaces coated with GMP140, a protein of endothelial cells and platelets. This adhesion of neutrophils was mediated by GMP140 and not by the CD18 integrin complex. By contrast, GMP140 in solution inhibited the CD18-dependent adhesion of tumor necrosis factor-alpha-activated neutrophils to plastic surfaces and resting endothelium, but not of resting neutrophils to tumor necrosis factor-alpha-activated endothelium. Thus, the binding of a soluble form of an adhesion protein selectively inhibited another set of adhesive events. Soluble GMP140 may be important in maintaining the nonadhesiveness of neutrophils in the circulation and may serve to limit inflammatory reactions.

Rapid neutrophil adhesion to activated endothelium mediated by GMP-140

Granule membrane protein-140 (GMP-140), a membrane glycoprotein of platelet and endothelial cell secretory granules, is rapidly redistributed to the plasma membrane during cellular activation and degranulation. Also known as PADGEM protein, GMP-140 is structurally related to two molecules involved in leukocyte adhesion to vascular endothelium: ELAM-1, a cytokine-inducible endothelial cell receptor for neutrophils, and the MEL-14 lymphocyte homing receptor. These three proteins define a new gene family, termed selectins, each of which contains an N-terminal lectin domain, followed by an epidermal growth factor-like module, a variable number of repeating units related to those in complement-binding proteins, a transmembrane domain, and a short cytoplasmic tail. Here we demonstrate that GMP-140 can mediate leukocyte adhesion, thus establishing a functional similarity with the other selectins. Human neutrophils and promyelocytic HL-60 cells bind specifically to COS cells transfected with GMP-140 complementary DNA and to microtitre wells coated with purified GMP-140. Cell binding does not require active neutrophil metabolism but is dependent on extracellular Ca2+. Within minutes after stimulation with phorbol esters or histamine, human endothelial cells become adhesive for neutrophils; this interaction is inhibited by antibodies to GMP-140. Thus, GMP-140 expressed by activated endothelium might promote rapid neutrophil targeting to sites of acute inflammation.