The protein-tyrosine phosphatase SHP-2 associates with tyrosine-phosphorylated adhesion molecule PECAM-1 (CD31)

Aggregation of many cell-surface receptors results in tyrosine phosphorylation of numerous proteins. We previously observed the tyrosine phosphorylation of the platelet/endothelial cell adhesion molecule, PECAM-1 (CD31), after FcepsilonRI stimulation in rat basophilic leukemia RBL-2H3 cells. Here we found that PECAM-1 was also transiently tyrosine-phosphoryated after adherence of these cells to fibronectin. Similarly aggregation of the T cell receptor on Jurkat cells also induced this tyrosine phosphorylation. The protein-tyrosine phosphatase SHP-2 is a widely expressed cytosolic enzyme with two Src homology 2 (SH2) domains. SHP-2, but not the related protein-tyrosine phosphatase SHP-1, associated with PECAM-1. This association of the two proteins correlated with the extent of the tyrosine phosphorylation of PECAM-1. A fusion protein containing the two SH2 domains of SHP-2 precipitated PECAM-1 from cell lysates and also directly bound to phosphorylated PECAM-1. In immune precipitate phosphatase assays, there was tyrosine dephosphorylation of PECAM-1. Therefore, integrin and immune receptor activation results in tyrosine phosphorylation of PECAM-1 and the binding of the protein-tyrosine phosphatase SHP-2, which could regulate receptor-mediated signaling in cells.

PECAM-1/CD31, an endothelial receptor for binding Plasmodium falciparum-infected erythrocytes

Excessive binding of Plasmodium falciparum-infected red blood cells (pRBCs) to the vascular endothelium (cytoadherence) and to uninfected erythrocytes (rosetting) may lead to occlusion of the microvasculature and thereby contribute directly to the acute pathology of severe human malaria. A number of endothelial receptors have been identified as targets for the pRBCs, including CD36, intercellular adhesion molecule-1 (ICAM-1) and chondroitin-4-sulfate (CSA). In vitro, CD36 is the most frequent target of strains from patients with mild as well as severe P. falciparum malaria, but is expressed at low levels on the cerebral microvasculature and therefore seems unlikely to be involved in the evolution of cerebral disease. Strains of P. falciparum that form rosettes are associated both with the occurrence of cerebral malaria and severe anemia. Here we report that malaria-infected RBCs adhere to platelet/endothelial cell adhesion molecule-1 (PECAM-1/CD31) on the vascular endothelium. pRBCs bind to endothelial cells, to PECAM-1/CD31 transfected cells, and directly to recombinant PECAM-1/CD31 absorbed onto plastic. Soluble PECAM-1/CD31 and monoclonal antibodies specific for the amino-terminal segment of PECAM-1/CD31 (domains 1-4) blocked the binding. Interferon-gamma (IFN-gamma)-essential for the development of cerebral malaria in the mouse-was found to augment adhesion of human pRBCs to PECAM-1/CD31 on endothelial cell monolayers. Our results suggest that PECAM-1/CD31 is a virulence-associated endothelial receptor of P. falciparum-infected RBCs.

Platelet/endothelial cell adhesion molecule-1 (PECAM-1) is localized over the entire plasma membrane of endothelial cells

The subcellular localization of PECAM-1 in endothelial cells was examined by using advanced morphological techniques, such as confocal scanning microscopy and immunolabeling procedures for electron microscopy. The localization of PECAM-1 was studied immunohistochemically with five specific monoclonal antibodies and one polyclonal antibody (all anti-human) in human and rabbit myocardium and in isolated endothelial cells. In vivo, PECAM-1 was localized uniformly on the plasma membrane of all vascular endothelial cells, predominantly on the luminal side of vessels. No specific increase in labeling was found at sites of cell-to-cell contact. In vitro, primary isolated cells (human umbilical vein endothelial cells) showed continuous labeling of the entire cell membrane. Cells of higher passages were labeled in a manner similar to freshly isolated cells. Our findings refute the commonly accepted hypothesis that PECAM-1 is localized only at cell-to-cell contacts. Further, we have not been able to confirm the hypothesis regarding the important mechanical role of PECAM-1 in stabilizing the endothelial monolayer. Since PECAM-1 is also expressed on platelets and is known to bind to itself, the way in which PECAM-1-positive endothelial cells are protected against binding of PECAM-1-positive platelets remains unclear. In view of these findings, the role of PECAM-1 in the leukocyte migration cascade needs to be re-evaluated.

Putative control of angiogenesis in hemangioblastomas by the von Hippel-Lindau tumor suppressor gene

The hypoxia-inducible endothelial cell-specific mitogen vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) is expressed in low amounts in adult human brain, but is highly upregulated in the perinecrotic palisading cells of glioblastomas. We observed high VEGF expression in cerebellar hemangioblastomas, which are highly vascular, nonnecrotic and presumably nonhypoxic tumors, and hypothesized that a mechanism other than hypoxia leads to VEGF upregulation. Because hemangioblastomas develop in patients with von Hippel-Lindau disease, and mutations of the von Hippel-Lindau tumor suppressor (VHL) gene have also been reported in sporadic hemangioblastomas, we investigated VHL expression in normal cerebellum and in hemangioblastomas and tested the hypothesis that mutations in the VHL gene lead to upregulation of VEGE We observed constitutive expression of VHL mRNA, but downregulation of VEGF mRNA in the postnatal cerebellum. In the adult cerebellum, VHL is predominantly expressed in neuronal cells. In hemangioblastomas, VHL expression appears to be restricted to stromal cells, suggesting that the neoplastic component is the stromal cell. VHL-deficient renal cell carcinoma cells (786-0) produced significantly higher levels of VEGF mRNA and protein compared with 786-0/ wt10 cells, which were stably transfected with the wild-type VHL gene. Our observations suggest that VHL mutations affect stromal cells in hemangioblastomas and that VEGF is upregulated in stromal cells as a consequence of mutations in the VHL gene.

Characterization of phosphotyrosine binding motifs in the cytoplasmic domain of platelet/endothelial cell adhesion molecule-1 (PECAM-1) that are required for the cellular association and activation of the protein-tyrosine phosphatase, SHP-2

Recent studies have shown that the Src homology-2 (SH2) domain-containing protein-tyrosine phosphatase, SHP-2, associates with the cytoplasmic domain of PECAM-1 as it becomes tyrosine-phosphorylated during platelet aggregation: a process that can be mimicked in part by small synthetic phosphopeptides corresponding to the cytoplasmic domain of PECAM-1 encompassing tyrosine residues Tyr-663 or Tyr-686. To further examine the molecular requirements for PECAM-1/SHP-2 interactions, we generated human embryonic kidney (HEK)-293 cell lines that stably expressed mutant forms of PECAM-1 harboring tyrosine to phenylalanine (Tyr --> Phe) mutations in the cytoplasmic domain. Y663F and Y686F forms of PECAM-1 were tyrosine-phosphorylated to a somewhat lesser extent than wild-type PECAM-1, and a doubly substituted Y663,686F form of PECAM-1 failed to become tyrosine-phosphorylated, suggesting that the PECAM-1 cytoplasmic domain tyrosine residues 596, 636 and 701 do not serve as substrates for cellular kinases. Interestingly, SHP-2 binding was lost when either Tyr-663 or Tyr-686 were changed to phenylalanine, indicating that both residues are required for SHP-2/PECAM-1 association. Although PECAM-1 phosphopeptides NSDVQpY663TEVQV and DTETVpY686SEVRK stimulated the catalytic activity of the phosphatase to a similar extent, surface plasmon resonance studies revealed that the Tyr-663-containing peptide had approximately 10-fold higher affinity for SHP-2 than did the Tyr-686 peptide. Finally, peptido-precipitation analysis showed that the NH2-terminal SH2 domain of SHP-2 reacted preferentially with the Tyr-663 PECAM-1 phosphopeptide, while the Tyr-686 phosphopeptide associated only with the COOH-terminal SH2 domain of the phosphatase. Together, these data provide a molecular model for PECAM-1/SHP-2 interactions that may shed light on the downstream events that follow PECAM-1-mediated interactions of vascular cells.

Expression of matrix metalloprotease-9 in vascular pericytes in human breast cancer

Matrix metalloprotease-9 (MMP-9; 92-kd type IV collagenase, gelatinase B) is regarded as important for degradation of the basement membrane and extracellular matrix during cancer invasion and other tissue-remodeling events. Expression of MMP-9 was analyzed in 22 cases of human ductal breast cancer by immunohistochemistry and in 8 of these cases also by in situ hybridization. For immunohistochemistry we used affinity-purified polyclonal antibodies as well as a MMP-9-specific monoclonal antibody (clone 6-6B). Three different stromal cell types with a positive MMP-9 immunoreaction were identified morphologically: neutrophils and macrophage-like cells in all cases and vascular cells in 16 of 22 cases. Double immunofluorescence with antibodies to CD68 conclusively demonstrated MMP-9 expression in macrophages. To identify the positive vascular cells, we employed antibodies to von Willebrand factor and PAL-E for identification of endothelial cells, high molecular weight melanoma-associated antigen for pericytes, and alpha-smooth muscle actin for vascular smooth muscle cells. Using conventional and confocal double immunofluorescence microscopy, colocalization of MMP-9 was seen with high molecular weight melanoma-associated antigen, the pericyte marker, whereas little or no coexpression was seen with alpha-smooth muscle actin. Virtually no coexpression was seen with the endothelial cell markers PAL-E and von Willebrand factor. In situ hybridization showed that MMP-9 mRNA colocalized with MMP-9 immunoreactivity in macrophages and vascular structures, whereas no MMP-9 mRNA was detected in neutrophils. No MMP-9 immunostaining or in situ hybridization signal was detected in cancer cells in any of the cases. Based on these results, it is concluded that MMP-9 in human breast cancer is located in tumor-infiltrating stromal cells, including neutrophils, macrophages, and vascular pericytes, and that the latter two cell types also produce this metalloprotease. We suggest that the MMP-9 produced in pericytes may play a role in extracellular matrix degradation during tumor angiogenesis.

Tyrosine residue in exon 14 of the cytoplasmic domain of platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31) regulates ligand binding specificity

Platelet/endothelial cell adhesion molecule (PECAM-1) is a cell adhesion molecule of the immunoglobulin superfamily that plays a role in a number of vascular processes including leukocyte transmigration through endothelium. The presence of a specific 19- amino acid exon within the cytoplasmic domain of PECAM-1 regulates the binding specificity of the molecule; specifically, isoforms containing exon 14 mediate heterophilic cell-cell aggregation while those variants missing exon 14 mediate homophilic cell-cell aggregation. To more precisely identify the region of exon 14 responsible for ligand specificity, a series of deletion mutants were created in which smaller regions of exon 14 were removed. After transfection into L cells, they were tested for their ability to mediate aggregation. For heterophilic aggregation to occur, a conserved 5-amino acid region (VYSEI in the murine sequence or VYSEV in the human sequence) in the mid-portion of the exon was required. A final construct, in which this tyrosine was mutated into a phenylalanine, aggregated in a homophilic manner when transfected into L cells. Inhibition of phosphatase activity by exposure of cells expressing wild type or mutant forms of PECAM-1 to sodium orthovanadate resulted in high levels of cytoplasmic tyrosine phosphorylation and led to a switch from heterophilic to homophilic aggregation. Our data thus indicate either loss of this tyrosine from exon 14 or its phosphorylation results in a change in ligand specificity from heterophilic to homophilic binding. Vascular cells could thus determine whether PECAM-1 functions as a heterophilic or homophilic adhesion molecule by processes such as alternative splicing or by regulation of the balance between tyrosine phosphorylation or dephosphorylation. Defining the conditions under which these changes occur will be important in understanding the biology of PECAM-1 in transmigration, angiogenesis, development, and other processes in which this molecule plays a role.

Characterisation of cellular infiltration and adhesion molecule expression in CBA/CaH-kdkd mice with tubulointerstitial renal disease

CBA/CaH-kdkd mice develop a spontaneous and chronic tubulointerstitial renal disease which is characterised by mononuclear cell infiltration, tubular collapse and cystic dilatation of tubules. The pathogenic mechanisms of renal injury have not been fully elucidated in this model. We have analysed the nature of infiltrating cells and the expression of MHC class II antigens, cytokines and adhesion molecules in CBA/CaH-kdkd kidneys at various disease stages. Using immunohistochemical techniques we found that kdkd kidneys are characterised by abundant macrophage and dendritic cell infiltration with fewer T cells with CD4+ and CD8+ phenotypes. Interestingly, MHC class II antigens were not induced on renal tubules. The proinflammatory cytokine, TNF-alpha, was markedly enhanced in kdkd kidney (up to fourfold), whereas the T cell-specific cytokine, IFN-gamma, increased less (less than twofold). ICAM-1 and VCAM-1 were markedly overexpressed by injured proximal tubules. ICAM-2 and PECAM-1 were constitutively expressed on glomerular capillaries and vascular endothelium in normal kidneys and did not change in CBA/CaH-kdkd mice. In conclusion, tubulointerstitial nephritis in CBA/CaH-kdkd mice is characterised by prominent macrophage infiltration and abundant expression of ICAM-1 and VCAM-1 on injured renal tubules. The lack of MHC class II antigens on injured tubules suggests that the kd gene defect could generate a secondary renal inflammatory response which is characterised by prominent macrophage infiltration and a relative scarcity of T cells.

Up-regulation of flk-1/vascular endothelial growth factor receptor 2 by its ligand in a cerebral slice culture system

Vascular endothelial growth factor (VEGF) and its tyrosine kinase receptors VEGFR-1 (flt-1) and VEGFR-2 (flk-1/KDR) are key mediators of physiological and pathological angiogenesis. They are expressed in most tissues during embryonic development but are down-regulated in the adult, when angiogenesis ceases. Up-regulation of VEGFR-2 and of VEGF are observed in many pathological conditions under which angiogenesis is reinduced. A major regulator of VEGF expression is hypoxia. Although the temporal expression pattern of VEGFR-2 parallels VEGF expression to a high extent, little is known about its regulation. Here, we show that VEGFR-2 is highly expressed in early postnatal mouse brain but is down-regulated commencing at postnatal day 15 (P15) of mouse brain development and is hardly detectable in P30 mouse brain. Using P30 mouse brain slices, we observed that hypoxia up-regulates VEGFR-2 in the slices but not in human umbilical vein endothelial cells, suggesting the presence of a hypoxia-inducible factor in the murine neuroectoderm that up-regulates VEGFR-2. To identify the factors involved, normoxic P30 cerebral slices were cultured with growth factors that are either hypoxia-inducible (e.g., PDGF-BB, erythropoietin, and VEGF) and/or are known to act on endothelial cells (e.g., PDGF-BB, VEGF, and PIGF). Exogenously added recombinant VEGF led to an up-regulation of VEGFR-2 expression, which could be inhibited by preincubation with a neutralizing anti-VEGF antibody. Addition of PDGF-BB, PIGF, and erythropoietin had no effect on VEGFR-2 expression. Our results suggest a differential but synergistic regulation by hypoxia of VEGF and VEGFR-2: a direct induction of VEGF that subsequently up-regulates VEGFR-2 in endothelial cells. This autoenhancing system may represent an important mechanism of tumor angiogenesis.

Glucosaminylmuramyl dipeptide (GMDP) modulates endothelial cell activities in vitro but has no effect on angiogenesis in vivo

OBJECTIVE AND DESIGN

The aim of the study was to evaluate the effects of GMDP on angiogenesis in vivo and as a modulator of human umbilical vein endothelial cell proliferation, cell surface antigen expression and cell adhesion in vitro.

MATERIALS

Human umbilical vein endothelial cells (HUVEC), fertilized white leghorn chicken eggs, antibodies against adhesion molecules and glucosaminylmuramyl dipeptide (GMDP).

TREATMENT

GMDP [0.01-100 micrograms/ml] applied to cell cultures for 6-72 h and to the chick chorioallantoic membrane (CAM) for four days.

METHODS

Angiogenic activity of GMDP in vivo was assessed using the CAM assay; HUVEC proliferation was measured by tritiated thymidine incorporation and cell cycle studies; cell surface antigen expression by indirect immunofluorescence and flow cytometry; cell adhesion by quantification of [3H]-thymidine labeled leukocyte adherence to HUVEC monolayers. Statistical analysis was performed using one-way ANOVA and if necessary was followed by Duncan's multiple range test for variables.

RESULTS

GMDP induced [3H]-thymidine incorporation in a concentration- and time-dependent manner (p < 0.003) and significantly increased the porportion of cells in the S phase of the cell cycle (p < 0.03). It weakly augmented the expression of ICAM-1 and CD31 but not adhesion of leukocytes to HUVEC monolayers GMDP was not angiogenic in the CAM assay.

CONCLUSIONS

GMDP can modulate endothelial cell activity without the induction of angiogenesis in vivo which may have implications for its use as a therapeutic agent.

Oxidant stress-induced transendothelial migration of monocytes is linked to phosphorylation of PECAM-1

Reactive oxygen species (ROS) are believed to cause vascular injury in the pathophysiology of atherosclerosis, diabetes, and vasoocclusion in sickle cell disease. Studies have shown that ROS causes increased adhesion of monocytes and neutrophils to the endothelium. We investigated the effects of tert-butylhydroperoxide (t-BuOOH), an inducer of oxidant stress, to determine the cellular signaling pathway leading to the transendothelial migration of polymorphonuclear leukocytes. Our studies revealed that signaling by t-BuOOH in human umbilical vein endothelial cells (HUVECs) causes a twofold increase in the transendothelial migration of monocyte-like HL-60 cells and a fivefold increase in platelet endothelial cell adhesion molecule-1 (PECAM-1) phosphorylation. The transmigration induced by t-BuOOH was inhibited by an antibody to PECAM-1. These events were inhibited by antioxidants and inhibitors of protein kinase C, p21ras and glutathione synthesis. However, treatment of HUVECs with the phosphatase inhibitor calyculin A augmented the t-BuOOH-mediated transendothelial migration of monocytes and PECAM-1 phosphorylation. Our results suggest that oxidative stress can induce the transendothelial migration of monocytes as a result of phosphorylation of PECAM-1, a crucial event in the diapedesis of leukocytes during pathophysiology of vascular diseases.

The association between tumour progression and vascularity in the oral mucosa

Tumourigenesis in experimental models is associated with the formation of new blood vessels (angiogenesis). Recent studies have suggested that tumour angiogenic activity may be inferred in histological sections by measuring the density of the vasculature. The purpose of this study was to determine whether the transition from normal to dysplastic and neoplastic tissue in the oral mucosa is accompanied by quantitative or qualitative changes in the vascularity of the tissue, and how the estimate of vascularity is influenced by the vessel marker and method of assessment. A total of 100 specimens of normal oral mucosa, dysplastic lesions, and squamous cell carcinomas were examined. Sections were immunostained with the pan-endothelial antibodies to von Willebrand Factor (vWF) and CD31, or with an antibody to the alpha v beta 3 integrin, previously reported to be a marker of angiogenic vessels. Vascularity was quantitated by two different methods: highest microvascular density (h-MVD) and microvascular volume, as determined by point counting (MVV). The results showed that vascularity, measured by the MVV method using antibodies to either vWF or CD31, increased significantly (P < 0.0001) with disease progression from normal oral mucosa, through mild, moderate, and severe dysplasia to early and late carcinoma (76 paraffin-embedded tissues examined). In contrast, h-MVD did not discriminate between dysplastic lesions and carcinoma. A similar percentage of the total vessel volume (MVV) and density (h-MVD) were positive for alpha v beta 3 in 24 frozen tissues examined, including normal oral mucosa. It is concluded that there is a close association between vascularity and tumour progression in the oral mucosa. Morphometric analysis reflecting microvascular volume is more informative than the currently popular analysis of microvascular density. The expression of alpha v beta 3 in the vasculature of oral tissues does not necessarily reflect the presence of angiogenic vessels.

Effects of aminoguanidine on adhesion molecule expression of human endothelial cells

The effect of aminoguanidine (AG) on the expression of adhesion molecules on nonactivated human umbilical vein endothelial cells (HUVEC) was investigated in vitro. Nonactivated HUVEC cultivated on long-term glycated fibronectin (FN) as compared to native FN showed a significant upregulation of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and CD31 which could be further promoted by long-term glycated bovine serum albumin. AG, at a concentration of 0.01 mol/l, caused an upregulation of ICAM-1 of 48 +/- 17.4% in HUVEC cultivated on gelatin. In contrast, VCAM-1 and E-selectin remained unaffected. At this concentration, formation of advanced glycation end products (AGE) was inhibited by 57%, as determined immunologically, and by 50%, as verified by AGE-specific fluorescence. A hypothesis concerning the upregulation of ICAM-1 by AG as compared to VCAM-1 is proposed relating to its relative redox insensitivity. Our results demonstrate that the beneficial effect of AG in reducing the risk of accelerated development of atherosclerosis in diabetic patients by inhibiting formation of AGE on matrix proteins such as FN might be hampered by its tendency to upregulate ICAM-1 on endothelial cells.

Identification and characterization of functional cation coordination sites in platelet endothelial cell adhesion molecule-1

We have employed 45CaCl2 binding studies, terbium (Tb3+) luminescence spectroscopy, and electrospray mass spectroscopy (ESI-MS) to identify divalent metal binding properties of soluble recombinant human PECAM-1 (srPECAM-1), and to define unique cation binding domains using short, linear peptide sequences from the protein. PECAM-1 was found to directly interact with 45CaCl2, binding 2.3 nmol of Ca2+/nmol of srPECAM-1 with a Kd of 1.17 nM. PECAM-1 was found to contain high-affinity cation binding sites involving amino acids Asp443, Asp444, and Glu446 of Ig-domain 5 and residues Glu487, Glu490, Asp491, Glu538, Glu540, and Glu542 of Ig-domain 6. The PECAM cation binding sites demonstrated broad specificity for all divalent cations, with Mn2+ having a higher affinity than Ca2+ or Mg2+. Direct binding of Tb3+ to these PECAM peptides was confirmed by ESI-MS. Modeling studies predict that the six cation binding residues within Ig-domain 6 are proximal to each other in three-dimensional space, and may form a single cation coordination site. The identification of cation binding sites in PECAM-1 will direct further work in examining its cation-dependent roles in cellular signaling.

Epithelioid angiosarcoma of bone

Angiosarcoma of bone is a rare, high-grade sarcoma of vascular origin. This article describes an epithelioid angiosarcoma in the humerus of a 48-year-old man. A multilocular osteolytic lesion with undefined margins and destroyed cortical and medullary bone, associated with a large soft tissue mass was demonstrated radiologically in the proximal metaphysis of the right humerus. The tumor, resected by amputation, was composed mostly of proliferating malignant cells with an epithelioid morphology. It had a predominantly sheet-like growth pattern, and an occasional pseudoglandular or alveolar arrangement, mimicking an adenocarcinoma. The dilated anastomotic vascular spaces lined by epithelioid endothelial cells and the intracytoplasmic lumina/vacuoles that sometimes contained erythrocytes suggested focal endothelial differentiation. On immunohistochemical investigation, many neoplastic cells expressed cytokeratin and endothelial markers: factor-VIII related antigen, CD31, and UEA-I. The ultrastructure of the tumor was consistent with that of an angiosarcoma. Our patient died of disease shortly after the diagnosis, implying an aggressive clinical course. Awareness of the existence of skeletal epithelioid angiosarcoma, combined with the identification of intracytoplasmic lumina, or at least small vasoformative foci, and immunohistochemical positivity for endothelial markers provide the best guide for distinguishing this tumor from metastatic carcinomas.

Diabetic RBC-induced oxidant stress leads to transendothelial migration of monocyte-like HL-60 cells

Red blood cells (RBC) from patients with diabetes mellitus exhibit an increased propensity to adhere to cultured human umbilical vein endothelial cells (HUVEC) as a result of interaction of advanced glycation end products with their counter receptors, contributing to the pathogenesis of vascular complications. We determined whether the interaction of diabetic RBC with HUVEC induced cellular oxidant stress that would culminate in adherence and diapedesis of monocytes, these being initiating events in endothelial injury and atherogenesis. We show that the adherence of diabetic RBC (2% hematocrit), but not normal RBC, to HUVEC results in a fourfold increase in the production of lipid peroxides. Furthermore, diabetic RBC-induced oxidant stress causes a sixfold increase in platelet endothelial cell adhesion molecule-1 (PECAM-1) phosphorylation and doubles transendothelial migration of monocyte-like HL-60 cells; both are blocked by antioxidants and protein kinase C (PKC) inhibitors. Our results show that the adherence of diabetic RBC to endothelial cells initiates a cascade of cellular events resulting in PKC activation, causing PECAM-1 phosphorylation and concomitant transendothelial migration of monocytes. The increased diapedesis of monocytes, brought about by the interaction of diabetic RBC across vascular endothelium, may play an important role in accelerated atherosclerosis and cardiovascular disease in diabetics.

The influence of lesion length on intimal hyperplasia after Fogarty balloon injury in the rabbit carotid artery: role of endothelium

After balloon angioplasty, retarded endothelial cell recoverage of the injured segment may lead to enhanced intimal hyperplasia. We tested the hypothesis that long lesions result in more intimal hyperplasia than short lesions due to a prolonged time to complete endothelial cell recoverage. A 2-french Fogarty balloon was used to create 2.5- and 5-cm-long lesions in the rabbit carotid artery. After termination, the injured arteries (n = 9 for all groups) were serially processed for histochemistry. Endothelial cell coverage was assessed with an antibody to CD31 and cell proliferation with a monoclonal antibody to Ki-67 nuclear antigen. The intimal hyperplasia cross-sectional area was measured morphometrically. All data are mean +/- SEM. At 21 days, endothelial cell recoverage was almost complete in the 2.5-cm lesions. In the 5-cm lesions, endothelial cell recoverage was 66 +/- 6% in the middle segments (p = 0.04, 2.5 vs. 5 cm) and 100% at the cranial and caudal ends of the lesion. At 42 days, endothelial cell coverage had increased to 81 +/- 7% in the middle segments of the 5-cm lesions. The intimal hyperplasia area was similar in the 2.5- and the 5-cm lesions both at 21 days (0.19 +/- 0.02 and 0.20 +/- 0.01 mm2, respectively) and 42 days (0.27 +/- 0.02 and 0.26 +/- 0.03 mm2, respectively). The increase in intimal hyperplasia from 21 to 42 days was significant for both lesion lengths (p = 0.004). At 21 days, intimal proliferation was similar for the 2.5- and 5-cm lesions. After 42 days postinjury, intimal proliferation had decreased (p < 0.001) equally for both lesion lengths. Earlier recoverage by endothelium in the 2.5-cm lesions did not inhibit intimal hyperplasia compared to the 5-cm lesions which were still incompletely reendothelialized. We conclude that in the rabbit, rapid endothelial cell recoverage of Fogarty balloon-injured arteries may not limit intimal hyperplasia in the center of the lesion. It is conceivable that the inability of regenerated endothelium to inhibit intimal hyperplasia is due to its initially dedifferentiated and possibly dysfunctional phenotype.

Distribution of adhesion molecules on HeLa cells, platelets and endothelium in an in vitro model mimicking the early phase of metastasis. An immunogold electron microscopic study

The aim of the present study was to obtain information about the distribution of various adhesion molecules within and on the surface of HeLa cells, platelets and endothelial cells in an in vitro model mimicking the early phase of metastasis. Suspensions of HeLa cells and human platelets, added to a medium of cultured human umbilical-vein endothelial cells, were stimulated by the addition of thrombin. Hirudin was added before thrombin in some experiments, and in other experiments the endothelium was pretreated with 0.5 mM acetylsalicylic acid (ASA). The distribution of platelet-endothelial cell adhesion molecule (PECAM), P-selectin, von Willebrand factor (vWf), fibrinogen (FG) and thrombospondin (TSP) was investigated on fixed material from the three experimental settings by using an immunogold electron-microscopic technique on frozen thin sections. Cells that had not been exposed to thrombin or any other type of stimulation were used as controls. PECAM was the only adhesion molecule detected on HeLa cells. It outlined the membrane on tumour cells that were not adherent to platelets in both basic and hirudin experiments. However, tumour cells in close proximity to activated platelets were unlabelled. In contrast, PECAM was detected on both platelets and endothelium in all experimental settings and in controls. P-selectin was only demonstrable on platelets in basic experiments. vWf was found both in endothelium and in platelets in controls and in all experimental settings. FG and TSP were found on platelets only, in a manner similar to that seen with vWf. Thus, among the adhesive factors examined in our experimental model, PECAM is the only one demonstrated on HeLa cells. This suggests that PECAM on tumour cells may play a role as adhesion molecule in the early stage of metastasis. P-selectin, vWf, FG and TSP were also consistently expressed. Therefore, these factors may contribute to the adhesive reactions involved in early metastasis.

Numerous vessels detected by CD34 in the villous stroma of complete hydatidiform moles

It has been considered that the villous stroma of complete hydatidiform moles (CHMs) is usually avascular. Vessels would normally form if embryogenesis had occurred. But judging by the structural maturity of molar villi, it was suspected that they must contain a considerable number of blood vessels and an attempt was made to demonstrate their presence. It has been shown previously that the vascular endothelial cell markers factor VIII related antigen (FVIII-RAg), Ulex europaeus 1 agglutinin (UEA-1) and CD31 were of no use in demonstrating the vessels in molar villi. A monoclonal antibody, QBEND/10, raised against the CD34 antigen in human endothelial cell membranes and hemopoietic progenitor cells, was selected to test its use as a marker of villous vascular endothelial cells in CHMs. On immunohistochemical analysis, numerous blood vessels were found using CD34 antibody in the stroma of CHMs, and the numbers corresponded to those found in normal villi of gestational age 8-12 weeks. Moreover, the luminal free surface of all vascular endothelial cells was so specifically delineated that it permitted the identification of vessels not apparent on hematoxylin- and eosin-stained sections; other stromal cells and trophoblast were not labeled.

Differential modulation of IL-1-induced endothelial adhesion molecules and transendothelial migration of granulocytes by G-CSF

Granulocyte colony stimulating factor (G-CSF) is widely used for mobilization of haemopoietic stem cells into the peripheral blood. However, little is known about the mechanisms involved in mobilization and the immune modulatory effects of this growth factor. In this report we show that G-CSF down-regulated intercellular adhesion molecule 1 (ICAM-1) induced by Interleukin-1 (IL-1) on human endothelial cells. Interestingly, the G-CSF-mediated down-modulation of IL-1-induced ICAM-1 appeared to be biphasic. In pharmacological concentrations (> 300 ng/ml), and in dose ranges of plasma G-CSF levels above that of nonfebrile healthy individuals (30 pg/ml), a significant decrease in surface ICAM-1 could be observed. This could be explained, at least in part, by an increased autocrine G-CSF production by endothelial cells in response to IL-1 and exogenous G-CSF. In contrast to ICAM-1, IL-1-triggered VCAM-1 expression was superinduced by G-CSF with the optimal concentration of 30 pg/ml. To evaluate the functional significance of these findings, 51Cr adhesion assays with peripheral blood mononuclear cells (PBMC) or granulocytes known to lack the VCAM-1 counter-receptor very late antigen 4 (VLA-4) and IL-1-stimulated endothelial cells, in the presence or absence of G-CSF, were performed. G-CSF could not inhibit the IL-1-induced adhesion of PBMC to endothelial cells, which may be due to the differential adhesion molecule modulation. In contrast, granulocyte adhesion induced by IL-1 could effectively be blocked by co-incubation with G-CSF. Finally, G-CSF also inhibited transendothelial migration of granulocytes through IL-1-activated endothelial cells in a concentration-dependent manner.

CD31 (JC70) expression in plasma cells: an immunohistochemical analysis of reactive and neoplastic plasma cells

AIMS

To investigate the immunohistochemical expression of CD31 (JC70) in normal and neoplastic plasma cells.

METHODS

Plasma cells in bone marrow biopsies and extramedullary locations were examined. All extramedullary biopsies were formalin fixed and paraffin embedded. The bone marrow biopsies were fixed in formal acetic acid and embedded in paraffin wax. Twenty multiple myelomas (12 bone marrow and eight extramedullary deposits), 10 extramedullary plasmacytomas, and 30 biopsies with reactive plasma cells (10 bone marrow, 20 extramedullary biopsies) were stained with anti-CD31 (JC70) using the streptavidin-biotin detection system with diaminobenzidine as a chromogen. Antigen retrieval in bone marrow biopsies was achieved by pressure cooking. In all other biopsies, antigen retrieval was achieved by microwave pretreatment.

RESULTS

All 20 extramedullary cases with reactive plasma cells showed intense membrane staining. Focal staining was detected in reactive plasma cells in bone marrow biopsies. Five of 10 plasmacytomas showed membrane staining. None of the cases of multiple myeloma, either medullary or extramedullary, showed any immunoreactivity for CD31.

CONCLUSIONS

CD31, a member of the immunoglobulin supergene family of cell adhesion molecules, is strongly expressed in extramedullary reactive plasma cells, focally in bone marrow reactive plasma cells, and occasionally in extramedullary plasmacytomas.

Expression of functional VCAM-1 by cultured nasal polyp-derived microvascular endothelium

Induction of endothelial vascular cell adhesion molecule-1 (VCAM-1) by interleukin (IL)-4 is believed to exert a major impact on the extravasation of leukocyte subsets in allergic disease. This notion has recently been challenged because cultured microvascular endothelial cells (ECs) derived from various organs are unable to express VCAM-1 after exposure to IL-4. In this study, we have established a method for isolation and culture of nasal polyp-derived microvascular ECs and report their cytokine-regulated VCAM-1 expression. With a combination of cell enzyme-linked immunosorbent assay, flow cytometry, and reverse transcription polymerase chain reaction, such expression was shown to be induced in a dose- and time-dependent manner not only by IL-1 beta and tumor necrosis factor-alpha but also by IL-4 and IL-13. Therefore, the response of nasal microvascular ECs did not harmonize with that of counterparts from several other tissues. IL-4 or IL-13 combined with submaximal concentrations of IL-1 beta or tumor necrosis factor-alpha increased VCAM-1 expression in a synergistic manner. VCAM-1 was functional as shown by antibody-mediated inhibition of leukocyte adhesion. Taken together, our results supported the notion that selective VCAM-1 induction by IL-4 and IL-13 plays an important role for the preferential recruitment of eosinophils and T lymphocytes seen in human airways affected by allergy.

Platelet endothelial cell adhesion molecule-1 is phosphorylatable by c-Src, binds Src-Src homology 2 domain, and exhibits immunoreceptor tyrosine-based activation motif-like properties

Platelet endothelial cell adhesion molecule-1 (PECAM-1) is 130-kDa member of the immunoglobulin gene superfamily that localizes to cell-cell borders of confluent endothelial cells and has been shown to play a role in the control of endothelial sheet migration and leukocyte transmigration through the endothelium. The cytoplasmic tail plays an important role in the modulation of PECAM-1 function. Mutation of tyrosine 663 or 686 in the cytoplasmic tail reduces phosphorylation and mutation of 686 is associated with a reduction in PECAM-1-mediated inhibition of cell migration (1). We have previously noted that these two tyrosine residues are surrounded by consensus sequences for Src homology 2 (SH2) domain binding (1, 2), and the experiments presented explore the potential for PECAM-1-Src and PECAM-1-SH2 domain interactions. PECAM-1 is more highly phosphorylated in endothelial cells overexpressing c-Src, and in in vitro kinase assays, c-Src can phosphorylate a glutathione S-transferase (GST)-PECAM cytoplasmic tail fusion protein. The phosphorylated fusion protein associates with the bead-bound c-Src. This association appears to be mediated by Src-SH2 domain, because PECAM-1 can be precipitated by a GST-Src-SH2 affinity matrix. The binding to the GST-Src-SH2 affinity matrix correlates directly with the level of PECAM-1 phosphorylation, because more PECAM-1 is precipitated from c-Src overexpressors and from wild-type rather than Tyr663 --> Phe and Tyr686 --> Phe mutant PECAM-1 expressors. Yet unidentified phosphoproteins can also be coimmunoprecipitated with wild-type but not mutant PECAM-1. Finally, we note the similarity of the PECAM-1 cytoplasmic domain sequence to the immunoreceptor tyrosine-based activation motif. Our data begin to delineate how tyrosines 663 and 686 may play a role in mediating PECAM-1 signal transduction.

Platelet endothelial cell adhesion molecule-1 is a major SH-PTP2 binding protein in vascular endothelial cells

Platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) is rapidly tyrosine phosphorylated in mechanically stimulated vascular endothelial cells (ECs). A 65-kDa protein from ECs specifically bound to the c-Src phosphorylated PECAM-1 cytoplasmic domain and was identified as a protein tyrosine phosphatase SH-PTP2 (SHP2, Syp). PECAM-1 was coimmunoprecipitated by anti-SH-PTP2 from EC extracts as a major binding protein, and the level of association increased when PECAM-1 was tyrosine phosphorylated. This association was mediated by SH2 domains of SH-PTP2. A rapid translocation of SH-PTP2 into cell-cell adhesion sites, where PECAM-1 was localized, occurred in mechanically stimulated cells. Our results suggest that PECAM-1 is a component of a mechanosensing machinery acting upstream of SH-PTP2.

Aggregation of the high affinity IgE receptor results in the tyrosine phosphorylation of the surface adhesion protein PECAM-1 (CD31)

One of the earliest events after aggregation of the high affinity receptor for IgE (FcepsilonRI) on mast cells is the activation of protein tyrosine kinases resulting in tyrosine phosphorylation of numerous proteins. Using a monoclonal antibody raised against the rat basophilic leukemia RBL-2H3 cells, we identified that platelet/endothelial cell adhesion molecule 1 (PECAM-1 or CD31) was tyrosine phosphorylated in these cells. Aggregation of PECAM-1 did not induce a detectable increase in its tyrosine phosphorylation, nor did it result in degranulation. However, the minimal tyrosine phosphorylation of PECAM-1 in nonstimulated cells was dramatically increased after FcepsilonRI aggregation. This receptor-induced tyrosine phosphorylation of PECAM-1 was an early event, independent of Ca2+ influx or of the activation of protein kinase C and of cell adhesion. PECAM-1 is an adhesion molecule that is required for the transmigration of leukocytes across the endothelium into sites of inflammation. Therefore tyrosine phosphorylation of PECAM-1 may modulate its interaction with other molecules, thereby regulating the migration of basophils into inflammatory sites.

An angiogenic role for the neurokines midkine and pleiotrophin in tumorigenesis

Recent analysis of bladder tumors has correlated expression of the neurokine midkine (MK) with poor patient survival. To examine a role for MK and the related pleiotrophin (PTN) in tumorigenesis, they were overexpressed in MCF-7 breast carcinoma cells. Expression had no effect on in vitro growth but conferred a growth advantage in vivo. Enhanced tumor growth correlated with increased vascular density and endothelial proliferation, implicating an angiogenic role for MK and PTN. Angiogenic activity of MK and PTN was confirmed in the rabbit corneal assay. Our data therefore identify two novel targets for antiangiogenic drug development.

Angiosarcoma at unusual sites. A report of two cases with aspiration cytology and diagnostic pitfalls

BACKGROUND

Angiosarcomas are uncommon soft tissue neoplasms with a predilection for skin and superficial soft tissues.

CASES

Two cases of angiosarcoma occurred at unusual sites, the parotid gland and lung. The parotid lesion was characterized by malignant cells present singly, in loose groups, in tight three-dimensional aggregates and in acinar formation initially misinterpreted as an adenocarcinoma. The lung mass showed malignant cells in association with vascular endothelium, suggestive of angiosarcoma. Both cases were negative for Ulex europaeus and Factor VIII-related protein but demonstrated strong immunopositivity for CD31, a highly specific endothelial marker.

CONCLUSION

In the absence of vasoformative structures, important diagnostic pitfalls are pseudovascular adenoid squamous cell carcinoma, poorly differentiated adenocarcinoma, melanoma and lymphoma. Immunocytochemical studies and clinical history are essential to the correct diagnosis.

Platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) tyrosine phosphorylation state changes during vasculogenesis in the murine conceptus

Vasculogenesis, the differentiation of mesodermal cells to angioblasts and the subsequent formation of blood islands and blood vessels by angioblasts in the conceptus, is a dynamic process modulated, in part, by cell-extracellular matrix and cell-cell interactions in the presence of a variety of growth factors and morphogens. In this report we demonstrate differential tyrosine phosphorylation of platelet-endothelial cell adhesion molecule-1 (PECAM-1) during the formation of blood islands and vessels from clusters of extraembryonic and embryonic angioblasts in the murine conceptus. In addition, we identify the phosphorylation of a particular tyrosine residue in the PECAM-1 cytoplasmic domain, Tyr686, which has the potential of mediating binding to Src homology 2 domain-containing proteins, affecting PECAM-1 cellular localization and endothelial cell migration.

Human cytotrophoblasts adopt a vascular phenotype as they differentiate. A strategy for successful endovascular invasion?

Establishment of the human placenta requires that fetal cytotrophoblast stem cells in anchoring chorionic villi become invasive. These cytotrophoblasts aggregate into cell columns and invade both the uterine interstitium and vasculature, anchoring the fetus to the mother and establishing blood flow to the placenta. Cytotrophoblasts colonizing spiral arterioles replace maternal endothelium as far as the first third of the myometrium. We show here that differentiating cytotrophoblasts transform their adhesion receptor phenotype so as to resemble the endothelial cells they replace. Cytotrophoblasts in cell columns show reduced E-cadherin staining and express VE-(endothelial) cadherin, platelet-endothelial adhesion molecule-1, vascular endothelial adhesion molecule-1, and alpha-4-integrins. Cytotrophoblasts in the uterine interstitium and maternal vasculature continue to express these receptors, and, like endothelial cells during angiogenesis, also stain for alphaVbeta3. In functional studies, alphaVbeta3 and VE-cadherin enhance, while E-cadherin restrains, cytotrophoblast invasiveness. Cytotrophoblasts expressing alpha4 integrins bound immobilized VCAM-1 in vitro, suggesting that this receptor-pair could mediate cytotrophoblast-endothelium or cytotrophoblast-cytotrophoblast interactions in vivo, during endovascular invasion. In the pregnancy disorder preeclampsia, in which endovascular invasion remains superficial, cytotrophoblasts fail to express most of these endothelial markers (Zhou et al., 1997. J. Clin. Invest. 99:2152-2164.), suggesting that this adhesion phenotype switch is required for successful endovascular invasion and normal placentation.

Fibrin(ogen) and von Willebrand factor deposition are associated with intimal thickening after balloon angioplasty of the rabbit carotid artery

The aim of the study was to assess the contribution of thrombus incorporation into neointimal thickening in the rabbit carotid artery after deep vascular injury induced by balloon angioplasty compared with superficial vascular injury induced by a perivascular collar. Besides CD 31 (PECAM 1), vimentin, alpha-smooth muscle actin, rabbit anti-macrophage monoclonal antibody and proliferating cell nuclear antigen, fibrin(ogen) and von Willebrand factor (vWF) deposition was assessed immunohistochemically. Angioplasty was performed in 47 rabbits and evaluated immediately (n = 7), after 6 hours (n = 4), and after 1 (n = 7), 2 (n = 9), or 3 (n = 20) weeks. A collar was placed in 29 rabbits and evaluated immediately (n = 5), after 6 hours (n = 5), and after 1 (n = 7), 2 (n = 10), or 3 (n = 2) weeks. After dilatation, the arteries were extensively denuded of endothelium, the internal elastic membrane was ruptured and blood-filled clefts were present in the media, pointing to deep vascular (type III) injury. Six hours later, mural fibrin(ogen) thrombi were formed, specially at sites with severe damage. This fibrin(ogen) matrix became infiltrated by phagocytes and smooth muscle cells. A luminal cap covered by regenerating endothelium was formed, demonstrating increased immunoreactivity to vWF. vWF was deposited in the extracellular neointimal spaces. Fibrin(ogen) thrombus deposition and incorporation appeared to be protracted phenomena for at least 2 weeks. After collar placement, minimal endothelial denudation was documented, pointing to focal superficial (type I) vascular injury. In subsequent weeks, neointimal thickening was associated with vWF deposition but not with fibrin(ogen) thrombus incorporation. In conclusion, mural fibrin(ogen) thrombus formation and incorporation contribute to neointima formation after deep vascular injury and seem to occur for several weeks after the initial insult.

Expression of endothelial adhesion molecules and recruitment of neutrophils after traumatic brain injury in rats

Traumatic brain injury (TBI) is often accompanied by an acute inflammatory reaction mediated initially by neutrophils. Adhesion molecules expressed on vascular endothelium are requisite elements during recruitment of leukocytes at sites of inflammation. In a rat model of TBI the induction and persistent expression of E-selectin (CD62E) on cerebrovascular endothelium ipsilateral, but not contralateral, to the site of contusion was demonstrated (P < 0.05 at 4 and 48 h posttrauma). In addition, these studies confirmed up-regulation and prolonged expression of ICAM-1 (CD54) on endothelium in the traumatized hemisphere (P < 0.05 at 4, 24, 48, and 72 h posttrauma). It is of interest that increased expression of CD54 was noted on blood vessels in the contralateral, non-traumatized hemisphere 48 h posttrauma. Expression of a third endothelial adhesion molecule, PECAM-1 (CD31), was unchanged following trauma. Administration of a murine monoclonal antibody (TM-8) that inhibits the adhesive function of CD54 blocked a significant portion (37.9%) of neutrophil recruitment 24 h posttrauma (P = 0.04). Employing immunocytochemistry and a monoclonal antibody specific for rat neutrophils (RP-3), peak infiltration of neutrophils was shown to occur 48 h after trauma. In contrast to emigration of neutrophils from blood vessels within the contusion, however, entry of neutrophils occurred from the surrounding leptomeninges and choroidal vessels. These studies demonstrate the relevance of CD54 (ICAM-1) in recruitment of neutrophils following TBI. However, the majority of neutrophil influx relies on endothelial adhesion molecules other than CD54. Because emigration of neutrophils was shown to occur predominantly from vessels within the leptomeninges and choroid plexus, intrathecal delivery of agents that inhibit the adhesive interactions between neutrophils, endothelial CD54, and other endothelial adhesion molecules to be defined may offer a novel form of therapy to prevent the acute inflammatory response that follows TBI.

Tyrosine phosphorylation of platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) in mechanically stimulated vascular endothelial cells

Fluid flow triggers signal transducing events, modulates gene expression, and remodels cytoskeletal structures in vascular endothelial cells (ECs). However, the primary steps of mechanoreception are still unknown. We have recently reported that a glycoprotein is rapidly tyrosine-phosphorylated in bovine ECs exposed to fluid flow or osmotic shock. Here were cloned a 3.4 kb cDNA encoding this protein and found that this was bovine PECAM-1. The tyrosine-phosphorylation level of PECAM-1 immunoprecipitated from mechanically stimulated bovine or human ECs increased. The PECAM-1 phosphorylation was not induced by reagents that triggered Ca2+ mobilization in ECs. An autophosphorylatable band comigrating with c-Src was co-immunoprecipitated with anti-PECAM-1, and c-Src phosphorylated and bound to a GST fusion protein containing the PECAM-1 cytoplasmic domain. A spliced mRNA form lacking amino acid residues 703-721 in the cytoplasmic domain was also expressed in bovine ECs, c-Src neither phosphorylated nor bound to the fusion protein containing the spliced PECAM-1 cytoplasmic domain which lacked one (Tyr 713) of the six tyrosine residues in the PECAM-1 cytoplasmic domain. These results suggest that the YSEI motif containing Tyr 713 is the Src phosphorylation/binding site. Our study is the first demonstration of inducible tyrosine phosphorylation of PECAM-1 and suggests involvement of PECAM-1 and Src family kinases in the sensing/signal transduction of mechanical stimuli in ECs.

Expression of platelet-endothelial cell adhesion molecule-1 (PECAM) by macaque trophoblast cells during invasion of the spiral arteries

BACKGROUND

Placental development in higher primates is characterized by the invasion of uterine blood vessels by trophoblast cells. These cells proceed to migrate within uterine spiral arteries, opposite to the direction of normal blood flow. Observations indicate adhesion of intra-arterial trophoblast to endothelium as well as to adjacent trophoblast cells.

METHODS

Macaque placenta and endometrial tissues were collected from day 15 of pregnancy (implantation begins on day 9) to term. Standard indirect immunoperoxidase methods were used to identify platelet-endothelial cell adhesion molecule-1 (PECAM), cytokeratins, and factor VIII-related antigen.

RESULTS

In early specimens arterioles were often nearly occluded by cytokeratin-labeled trophoblast cells. Adjacent sections revealed the presence of PECAM on these trophoblast cells and on the endothelium. After day 30 the invaded arteries usually contained a re-formed lumen, and trophoblast cells were increasingly evident in the modified walls of arteries, where PECAM labeling was often reduced on cells distant from the lumen. Endothelium of both invaded and uninvaded uterine vessels retained PECAM reactivity throughout gestation. Trophoblast cells of the cell columns, cytotrophoblastic shell, and mid- to late-gestation chorionic plate were also reactive for PECAM. Villous cytotrophoblast cells did not express PECAM, but a dense border of PECAM was consistently present on the apical surfaces of syncytial trophoblast.

CONCLUSIONS

Because PECAM functions as a counter-ligand for PECAM via homophilic binding, we conclude that this molecule is directly involved in adhesion of trophoblast cells to arterial endothelium in addition to maintaining cohesion between some subpopulations of cytotrophoblast cells.

Hypoxia induces PECAM-1 phosphorylation and transendothelial migration of monocytes

Polymorphonuclear neutrophils (PMN) adhere to the vascular endothelium under hypoxic conditions, causing microvascular injury. The molecular mechanism of hypoxia-induced adhesion of PMN to and diapedesis through the vascular endothelium is poorly understood. We examined the effects of hypoxia on the transendothelial migration of monocytes. Exposure of human umbilical vein endothelial cells (HUVEC) cultured in Transwell chambers under low oxygen tension (3% O2 compared with 21% O2) resulted in an increased rate of migration of both monocyte-like HL-60 cells and human peripheral blood monocytes. Migration was inhibited by addition of an antibody to platelet endothelial cell adhesion molecule-1 (PECAM-1), a protein kinase C (PKC) inhibitor, or a platelet-activating factor (PAF)-receptor antagonist. In HUVEC, hypoxic conditions (1, 3, 5, and 14% O2) increased the phosphorylation of PECAM-1. The extent of phosphorylation of PECAM-1 was inversely related to the concentration of oxygen to which HUVEC were exposed. Hypoxia-induced phosphorylation of PECAM-1 was inhibited by either a PKC inhibitor or a PAF-receptor antagonist, indicating the involvement of hypoxia-induced release of PAF in both PKC activation and the concomitant phosphorylation of PECAM-1. These results were substantiated by the findings that treatment of HUVEC with 100 nM PAF under normoxic conditions augmented 11.8-fold the phosphorylation of PECAM-1 and twofold increase in the transendothelial migration of monocyte-like HL-60 cells. We conclude that PAF, produced by cultured endothelial cells in response to hypoxia, acts in an autocrine fashion to activate PKC, causing PECAM-1 phosphorylation and thus the transendothelial migration of monocytes.

Integrin engagement mediates tyrosine dephosphorylation on platelet-endothelial cell adhesion molecule 1

Platelet-endothelial cell adhesion molecule 1 (PECAM-1, CD31) is a 130-kDa member of the immunoglobulin gene superfamily expressed on endothelial cells, platelets, neutrophils, and monocytes and plays a role during endothelial cell migration. Phosphoamino acid analysis and Western blot analysis with anti-phosphotyrosine antibody show that endothelial PECAM-1 is tyrosine-phosphorylated. Phosphorylation is decreased with endothelial cell migration on fibronectin and collagen and with cell spreading on fibronectin but not on plastic. Cell adhesion on anti-integrin antibodies is also able to specifically induce PECAM-1 dephosphorylation while concurrently inducing pp125 focal adhesion kinase phosphorylation. Inhibition of dephosphorylation with sodium orthovanadate suggests that this effect is at least partially mediated by phosphatase activity. Tyr-663 and Tyr-686 are identified as potential phosphorylation sites and mutated to phenylalanine. When expressed, both mutants show reduced PECAM-1 phosphorylation but Phe-686 mutants also show significant reversal of PECAM-1-mediated inhibition of cell migration and do not localize PECAM-1 to cell borders. Our results suggest that beta 1-integrin engagement can signal to dephosphorylate PECAM-1 and that this signaling pathway may play a role during endothelial cell migration.

Glucose-induced transmigration of monocytes is linked to phosphorylation of PECAM-1 in cultured endothelial cells

The adherence of circulating monocytes to the endothelium, their migration into the subendothelium, and the subsequent formation of foam cells are initial events in the pathogenesis of atherosclerosis. However, the effect of hyperglycemia on the transendothelial migration of monocytes is not known. Exposure of human umbilical vein endothelial cells (HUVEC) cultured in a Transwell chamber to 25 mM D-glucose (a concentration representing a hyperglycemic state) for 2 h resulted in a twofold increase in the migration of vitamin D3-differentiated monocyte-like HL-60 cells. The migration was inhibited by addition of either an antibody to platelet-endothelial cell adhesion molecule-1 (PECAM-1) or a protein kinase C inhibitor, GF-109203X. In HUVEC, high concentrations of D-glucose (25 mM), but not of other sugars such as L-glucose, 2-deoxyglucose, D-galactose, or D-mannitol, caused a sevenfold increase in the phosphorylation of PECAM-1 as a result of activation of protein kinase C. The 25 mM D-glucose-induced PECAM-1 phosphorylation and transmigration of monocyte-like HL-60 cells were further increased by treatment of HUVEC with the phosphatase inhibitor calyculin A. These results suggest that direct phosphorylation of PECAM-1 in response to elevated glucose promotes transendothelial migration of monocytes, contributing to accelerated atherogenesis in diabetics.

L1 adhesion molecule on human lymphocytes and monocytes: expression and involvement in binding to alpha v beta 3 integrin

The L1 adhesion molecule is a member of the immunoglobulin (Ig) superfamily initially identified in the nervous system which contains six Ig-like domains. Besides the known L1-L1 homotypic interaction, L1 was recently shown to bind to very late antigen (VLA)-5 in the mouse and alpha v beta 3 in the human. The sixth Ig domain is critical for this function. We now demonstrate that human CD4+ peripheral blood T lymphocytes, monocytes and B lymphocytes, but not CD8+ T lymphocytes, express L1. When compared to the expression of CD31, another ligand for alpha v beta 3 on T lymphocytes, only a small proportion of cells were CD31+L1+ double positive. L1 was also detected on the surface of human monocytic and lymphoid tumor lines and was shown to have a molecular mass of approximately 220 kDa, similar to the molecule present on neuroblastoma cells. The function of the sixth Ig domain of human L1 as an integrin ligand was also investigated. Using an RGD-containing peptide derived from the sixth Ig domain as well as a fusion protein of the sixth Ig domain of L1 and the Fc portion of human IgG1 (6.L1-Fc), we demonstrated the binding of human MED-B1 (alpha v beta 3hi, alpha 5 beta 1lo) tumor cells and this binding was blocked by alpha v-specific mAb. In contrast, human Nalm-6 cells (alpha v beta 3lo, alpha 5 beta 1hi) did not bind to the 6.L1-Fc fusion protein. MED-B1 cells could also be stained with the 6.L1-Fc fusion protein. Our results suggest that human L1 binds predominantly to alpha v beta 3 and that its presence on leukocytes could be important for adhesion and migration.

Desmoplakin expression and organization at human umbilical vein endothelial cell-to-cell junctions

Desmoplakin is an intracellular component of desmosomes which plays a role in the anchorage of intermediate filaments to these structures. We report here that, despite the absence of desmosomes, cultured endothelial cells from human umbilical vein express desmoplakin I and II both at mRNA and protein level. Desmoplakin I/II are found only in the detergent insoluble fraction suggesting that most of the protein is linked to the cytoskeleton. Desmoplakin I/II could be detected by western blot only in long confluent cells even if desmoplakin mRNA levels are unchanged by cell confluency. This suggests that desmoplakin might be stabilized at protein level by its association with junctional components. Immunofluorescence confocal microscopy showed that desmoplakin codistributes with VE-cadherin and plakoglobin along the lateral cell membrane. In contrast, desmoplakin localization was distinct from that of PECAM, an endothelial specific junctional protein localized outside adherence junctions. Endothelial cells do not have keratins but they express vimentin. In confluent cells vimentin forms peripheral filaments which attach to the cell membrane in areas at desmoplakin localization. These data suggest that desmoplakin may participate in the molecular organization of interendothelial junctions by interacting with VE-cadherin and promoting vimentin anchorage. This new type of intercellular junction seems to correspond to the “complexus adhaerentes' described in vivo in lymphatic endothelium.

Comparison of changes in endothelial adhesion molecule expression following UVB irradiation of skin and a human dermal microvascular cell line (HMEC-1)

We have assessed the pattern of dermal endothelial adhesion molecule expression following broadband UVB irradiation in vivo and in vitro. Skin biopsies were taken from 4 human volunteers at baseline and at 4, 8 and 24 h post-irradiation with 2.5 minimal erythema doses of UVB. Sections were stained immunohistochemically for E-selectin, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1). CD31 and neutrophil elastase. The effect of direct UVB irradiation on E-selectin, ICAM-1 and VCAM-1 was examined in a human dermal microvascular endothelial cell line, HMEC-1. Cultured HMEC-1 were irradiated with 2.5-40 mJ/cm2 of UVB, and assessed for adhesion molecule expression by immunofluorescence microscopy and fluorescence-activated cell sorter analysis. In vivo, E-selectin was minimally expressed on EC at baseline and was induced by 4 h following irradiation, P < 0.01. ICAM-1 was moderately expressed at baseline and appeared mildly induced at 24 h, although this did not reach statistical significance. VCAM-1 was weakly expressed in unirradiated skin while CD31 was moderately expressed, but neither was induced by UVB irradiation. A significant neutrophilic infiltrate appeared by 8 h and was maximal at 24 h, P < 0.05. Neutrophil infiltration correlated with E-selectin expression, r = 0.96. In HMEC-1, ICAM-1 was upregulated at 24 h post-irradiation, with an increase in mean channel fluorescence from 100% at baseline to 145 (SD12)% at 24 h, P < 0.05. No change was seen in expression of E-selectin, VCAM-1 or CD31. These studies support the involvement of endothelial adhesion molecules E-selectin and ICAM-1 in UVB-induced inflammation. Whereas ICAM-1 is upregulated by direct irradiation of endothelial cells, E-selectin stimulation appears to be an indirect effect.

Leucocyte/endothelial cell adhesion receptors in muscle biopsies from patients with idiopathic inflammatory myopathies (IIM)

Interactions between leucocytes and endothelial cells through specific adhesion receptors play an increasingly recognized crucial role in the development of inflammatory infiltrates in chronic inflammatory diseases. In this study we investigated adhesion molecule expression in muscle biopsies from 18 dermatomyositis, six polymyositis, five inclusion-body myositis patients and from eight normal controls. Immunohistochemical detection of leucocyte integrins LFA-1 and VLA-4, their endothelial counter-receptors intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), and the endothelial cell markers CD31 and von Willebrand factor-related antigen (vWFAg) was performed using specific MoAbs and an alkaline phosphatase anti-alkaline phosphatase technique. ICAM-1 expression was up-regulated and VCAM-1 induced in muscle capillaries of dermatomyositis samples. In both dermatomyositis and polymyositis, endothelial cells from vessels surrounded by inflammatory infiltrates strongly expressed ICAM-1 and VCAM-1. Infiltrating leucocytes were intensively LFA-1- and VLA-4-positive. These data suggest that leucocyte/endothelial cell interactions mediated by the receptor/ligand pairs LFA-1/ICAM-1 and VLA-4/VCAM-1 actively participate in the development of muscle inflammatory infiltrates in the major inflammatory myopathies. In addition, ICAM-1 and VCAM-1 over-expression by capillary endothelial cells in dermatomyositis supports the hypothesis that capillary activation and/or injury is a major feature in this disease.

Cigarette smoke condensate-induced adhesion molecule expression and transendothelial migration of monocytes

Cigarette smoking is clearly linked with increased incidence of atherosclerosis and cardiovascular disease. The adherence of blood monocytes to the endothelium, followed by their migration beneath the endothelium, are initiating events in the formation of foam cells, promoting atherogenesis. We show that cigarette smoke condensate (CSC)-induced surface expression of a subset of cell adhesion molecules (CAM) [intercellular adhesion molecule 1 (ICAM-1), endothelial leukocyte adhesion molecule 1 (ELAM-1), and vascular cell adhesion molecule 1 (VCAM-1)] in human umbilical vein endothelial cells (HUVEC) is associated with an increase in the binding activity of nuclear transcription factor NF-kappa B to the consensus motif common to the CAM genes. Furthermore, CSC (25 microgram/ml) both increases the rate of transendothelial migration of vitamin D3-differentiated monocyte-like cells across the HUVEC monolayer by 200% and causes an approximately 10-fold increases in the phosphorylation of platelet endothelial CAM (PECAM-1), an adhesion molecule located at intercellular junctions and involved in endothelial cell-cell adhesion. Our results show that CSC-induced activation of protein kinase C in endothelial cells initiates a signaling pathways, leading to heightened binding of NF-kappa B to specific DNA sequences, which in turn increases surface expression of the subset of CAMs. Furthermore, our studies demonstrate a link between the phosphorylation of PECAM-1 and the migration of blood monocytes across vascular endothelium.

PECAM-1 expression in human mesothelial cells: an in vitro study

Mesothelial cells are actively involved in inflammatory processes by expressing a set of cell adhesion molecules (CAMs). Transmigration of leukocytes into inflamed tissues requires a chemotactic stimulus and engagement of platelet-endothelial cell adhesion molecule-1 (PECAM-1). To investigate the kinetics involved in peritonitis, pure cultures of mesothelial cells are necessary. In previous studies, we have found that human mesothelial cells (HOMES) show a weak constitutive expression of PECAM-1, which cannot be further stimulated by cytokines. It is known that all serous cavities and body fluids contain numerous macrophages which strongly express this adhesion molecule. To identify the cells responsible for the expression of PECAM-1, mesothelial cells freshly obtained from omental tissue were isolated using PECAM-1-conjugated magnetic beads by cell sorting. For these studies, the negative as well as the positive fraction of isolated cells were used. As a control, freshly isolated monocytes were studied. Cell cultures were characterized by light and electron microscopy, as well as immunocytochemistry. The negative cell fraction was cultivated and stimulated for different times with tumor necrosis factor-alpha (30 and 300 U/ml), interleukin-1 beta (10 and 100 U/ml) and interferon-gamma (500 U/ml) and PECAM-1 expression was analyzed by a comparative quantitative cell enzyme immunoassay (EIA). The positive cell fraction was treated in the same manner. Both fractions of isolated cells showed strong positivity for cytokeratins 8, 18, 7 and 19, as well as vimentin. CD68, a monocyte marker, was not detected on mesothelial cells. In addition, EIA analysis confirmed the constitutive expression of PECAM-1 obtained from previous studies. This expression on HOMES was not inducible, irrespective of the type and concentration of cytokine studied. These data confirm PECAM-1 expression on mesothelial cells obtained from human omental tissue and suggest a critical role in transmigration of leukocytes during peritoneal inflammation.