A dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN)-related protein is highly expressed on human liver sinusoidal endothelial cells and promotes HIV-1 infection

The discovery of dendritic cell (DC)-specific intercellular adhesion molecule (ICAM)-3-grabbing nonintegrin (DC-SIGN) as a DC-specific ICAM-3 binding receptor that enhances HIV-1 infection of T cells in trans has indicated a potentially important role for adhesion molecules in AIDS pathogenesis. A related molecule called DC-SIGNR exhibits 77% amino acid sequence identity with DC-SIGN. The DC-SIGN and DC-SIGNR genes map within a 30-kb region on chromosome 19p13.2-3. Their strong homology and close physical location indicate a recent duplication of the original gene. Messenger RNA and protein expression patterns demonstrate that the DC-SIGN-related molecule is highly expressed on liver sinusoidal cells and in the lymph node but not on DCs, in contrast to DC-SIGN. Therefore, we suggest that a more appropriate name for the DC-SIGN-related molecule is L-SIGN, liver/lymph node-specific ICAM-3-grabbing nonintegrin. We show that in the liver, L-SIGN is expressed by sinusoidal endothelial cells. Functional studies indicate that L-SIGN behaves similarly to DC-SIGN in that it has a high affinity for ICAM-3, captures HIV-1 through gp120 binding, and enhances HIV-1 infection of T cells in trans. We propose that L-SIGN may play an important role in the interaction between liver sinusoidal endothelium and trafficking lymphocytes, as well as function in the pathogenesis of HIV-1.

Dipeptidase-1 Is an Adhesion Receptor for Neutrophil Recruitment in Lungs and Liver

A hallmark feature of inflammation is the orchestrated recruitment of neutrophils from the bloodstream into inflamed tissue. Although selectins and integrins mediate recruitment in many tissues, they have a minimal role in the lungs and liver. Exploiting an unbiased in vivo functional screen, we identified a lung and liver homing peptide that functionally abrogates neutrophil recruitment to these organs. Using biochemical, genetic, and confocal intravital imaging approaches, we identified dipeptidase-1 (DPEP1) as the target and established its role as a physical adhesion receptor for neutrophil sequestration independent of its enzymatic activity. Importantly, genetic ablation or functional peptide blocking of DPEP1 significantly reduced neutrophil recruitment to the lungs and liver and provided improved survival in models of endotoxemia. Our data establish DPEP1 as a major adhesion receptor on the lung and liver endothelium and identify a therapeutic target for neutrophil-driven inflammatory diseases of the lungs.

Integrin alpha9beta1 mediates enhanced cell migration through nitric oxide synthase activity regulated by Src tyrosine kinase

Integrins are important mediators of cell adhesion and migration, which in turn are essential for diverse biological functions, including wound healing and cancer metastasis. The integrin alpha9beta1 is expressed on numerous mammalian tissues and can mediate accelerated cell migration. As the molecular signaling mechanisms that transduce this effect are poorly defined, we investigated the pathways by which activated integrin alpha9beta1 signals migration. We found for the first time that specific ligation of integrin alpha9beta1 rapidly activates Src tyrosine kinase, with concomitant tyrosine phosphorylation of p130Cas and activation of Rac-1. Furthermore, activation of integrin alpha9beta1 also enhanced NO production through activation of inducible nitric oxide synthase (iNOS). Inhibition of Src tyrosine kinase or NOS decreased integrin-alpha9beta1-dependent cell migration. Src appeared to function most proximal in the signaling cascade, in a FAK-independent manner to facilitate iNOS activation and NO-dependent cell migration. The cytoplasmic domain of integrin alpha9 was crucial for integrin-alpha9beta1-induced Src activation, subsequent signaling events and cell migration. When taken together, our results describe a novel and unique mechanism of coordinated interactions of the integrin alpha9 cytoplasmic domain, Src tyrosine kinase and iNOS to transduce integrin-alpha9beta1-mediated cell migration.

Orally active αvβ3 integrin inhibitor MK-0429 reduces melanoma metastasis

Melanoma remains one of the most aggressive types of cancer with a historically low survival rate. The αvβ3 integrin is involved in the progression of malignant melanoma. In the present study, the efficacy of MK-0429, a selective inhibitor of the αvβ3 integrin, was evaluated for its potential in the prevention of melanoma metastasis. Female B6D2F1 mice injected via the tail vein with murine B16F10 melanoma developed lung metastases within ~10 days. In the first experiment, the prevention of lung metastasis was assessed in the model treated with either vehicle, MK-0429 at 100 and 300 mg/kg orally twice daily or cyclophosphamide at 300 mg/kg, i.p. once daily. Study endpoints included determination of the study time period to achieve metastasis in lungs in this model, evaluation of the health effects on the study animals, the total number of lung colonies identified and lung tumor area. Unlike cyclophosphamide, the MK-0429 treatment did not lead to a significant weight reduction in mice. MK-0429 at 100 and 300 mg/kg reduced the number of metastatic tumor colonies by 64 and 57%, respectively, and the high dose also reduced the tumor area by 60% as compared to the vehicle. The second experiment employed B16F10 luciferase-expressing cells to examine the de novo progression of melanoma metastasis over 15 days with bioluminescent imaging of mice treated with MK-0429 at 300 mg/kg as compared to the vehicle. Tumor burden progressively advanced in the lungs of the B16F10-treated animals. However, MK-0429 reduced the progression of ventral and dorsal lung metastases by 22 and 38%, respectively, as compared to the vehicle, by study completion. Quantification of ex vivo tumor burden showed a 30-40% reduction in lung colonies by MK-0429. The two studies collectively demonstrated that MK-0429 was safe and efficacious in significantly decreasing melanoma metastasis in the lungs. The results emphasized the potential of MK-0429 as a novel, therapeutic agent for the prevention of metastatic melanoma.

Identification of a unique filamin A binding region within the cytoplasmic domain of glycoprotein Ibalpha

Binding of the platelet GPIb/V/IX (glycoprotein Ib/V/IX) receptor to von Willebrand factor is critical for platelet adhesion and aggregation under conditions of rapid blood flow. The adhesive function of GPIbalpha is regulated by its anchorage to the membrane skeleton through a specific interaction with filamin A. In the present study, we examined the amino acid residues within the cytoplasmic tail of GPIbalpha, which are critical for association with filamin A, using a series of 25-mer synthetic peptides that mimic the cytoplasmic tail sequences of wild-type and mutant forms of GPIbalpha. Peptide binding studies of purified human filamin A have demonstrated a major role for the conserved hydrophobic stretch L567FLWV571 in mediating this interaction. Progressive alanine substitutions of triple, double and single amino acid residues within the Pro561-Arg572 region suggested an important role for Trp570 and Phe568 in promoting GPIbalpha binding to filamin A. The importance of these two residues in promoting filamin A binding to GPIbalpha in vivo was confirmed from the study of Chinese-hamster ovary cells expressing GPIbalpha Trp570-->Ala and Phe568-->Ala substitutions. Phenotypic analysis of these cell lines in flow-based adhesion studies revealed a critical role for these residues in maintaining receptor anchorage to the membrane skeleton and in maintaining cell adhesion to a von Willebrand factor matrix under high-shear conditions. These studies demonstrate a novel filamin A binding motif in the cytoplasmic tail of GPIbalpha, which is critically dependent on both Trp570 and Phe568.

Critical role of platelet glycoprotein ibα in arterial remodeling

OBJECTIVE

Arteriogenesis is strongly dependent on the recruitment of leukocytes, especially monocytes, into the perivascular space of growing collateral vessels. On the basis of previous findings that platelets are central players in inflammatory processes and mediate the recruitment of leukocytes, the aim of this study was to assess the role of platelets in a model of arterial remodeling.

APPROACH AND RESULTS

C57Bl6 wild-type mice, IL4-R/Iba mice lacking the extracellular domain of the glycoprotein Ibα (GPIbα) receptor, and mice treated with antibodies to block GPIbα or deplete circulating platelets were studied in peripheral arteriogenesis. Using a novel model of intravital 2-photon and epifluorescence imaging, we visualized and quantified the interaction of platelets with leukocytes and the vascular endothelium in vivo. We found that transient platelet adhesion to the endothelium of collateral vessels was a major event during arteriogenesis and depended on GPIbα. Furthermore, leukocyte recruitment was obviously affected in animals with defective platelet GPIbα function. In IL4-R/Iba mice, transient and firm leukocyte adhesion to the endothelium of collateral vessels, as well as leukocyte accumulation in the perivascular space, were significantly reduced. Furthermore, we detected platelet-leukocyte aggregates within the circulation, which were significantly reduced in IL4-R/Iba animals. Finally, platelet depletion and loss of GPIbα function resulted in poor reperfusion recovery as determined by laser Doppler imaging.

CONCLUSIONS

Thus, GPIbα-mediated interactions between platelets and endothelial cells, as well as leukocytes, support innate immune cell recruitment and promote arteriogenesis-establishing platelets as critical players in this process.

Structurally Robust and Functionally Highly Versatile-C-Type Lectin (-Related) Proteins in Snake Venoms

Snake venoms contain an astounding variety of different proteins. Among them are numerous C-type lectin family members, which are grouped into classical Ca²⁺- and sugar-binding lectins and the non-sugar-binding snake venom C-type lectin-related proteins (SV-CLRPs), also called snaclecs. Both groups share the robust C-type lectin domain (CTLD) fold but differ in a long loop, which either contributes to a sugar-binding site or is expanded into a loop-swapping heterodimerization domain between two CLRP subunits. Most C-type lectin (-related) proteins assemble in ordered supramolecular complexes with a high versatility of subunit numbers and geometric arrays. Similarly versatile is their ability to inhibit or block their target molecules as well as to agonistically stimulate or antagonistically blunt a cellular reaction triggered by their target receptor. By utilizing distinct interaction sites differentially, SV-CLRPs target a plethora of molecules, such as distinct coagulation factors and receptors of platelets and endothelial cells that are involved in hemostasis, thrombus formation, inflammation and hematogenous metastasis. Because of their robust structure and their high affinity towards their clinically relevant targets, SV-CLRPs are and will potentially be valuable prototypes to develop new diagnostic and therapeutic tools in medicine, provided that the molecular mechanisms underlying their versatility are disclosed.

Secretory component mediates Candida albicans binding to epithelial cells

OBJECTIVES

Candida albicans attaches to oral surfaces via a number of mechanisms including adherence mediated by salivary components adsorbed to the C. albicans cell surface. Our goal was to identify the salivary molecules involved.

MATERIALS AND METHODS

Biotinylated salivary polypeptides that were bound by C. albicans were detected in extracts from washed, saliva-treated yeast cells by polyacrylamide gel electrophoresis and electroblot or immunoblot transfer analysis and purified by electroelution. Purified material was tested for the ability to promote the adherence of radiolabelled C. albicans yeast cells to cultured epithelial monolayers.

RESULTS

Three of the polypeptides bound by C. albicans cells were identified as components of secretory IgA, including secretory component. Using non-denaturing polyacrylamide gel electrophoresis, we demonstrated that secretory component could be detected in its free form in saliva, and was bound by yeast cells. Secretory component which was purified by electroelution from non-denaturing PAGE-separated saliva, without detectable complete IgA, promoted adherence of yeast cells to cultured epithelial monolayers in a dose-dependent fashion.

CONCLUSION

These results indicate that despite the inhibitory effect on adherence of IgA specific to C. albicans, IgA components, in particular secretory component, also promote binding to cultured epithelial monolayers.

Platelet Dysfunction During Mechanical Circulatory Support: Elevated Shear Stress Promotes Downregulation of αIIbβ3 and GPIb via Microparticle Shedding Decreasing Platelet Aggregability

[Figure: see text].