The E-selectin-ligand ESL-1 is located in the Golgi as well as on microvilli on the cell surface

Ancient eukaryotic protein interactions illuminate modern genetic traits and disorders

All eukaryotes share a common ancestor from roughly 1.5 - 1.8 billion years ago, a single-celled, swimming microbe known as LECA, the Last Eukaryotic Common Ancestor. Nearly half of the genes in modern eukaryotes were present in LECA, and many current genetic diseases and traits stem from these ancient molecular systems. To better understand these systems, we compared genes across modern organisms and identified a core set of 10,092 shared protein-coding gene families likely present in LECA, a quarter of which are uncharacterized. We then integrated >26,000 mass spectrometry proteomics analyses from 31 species to infer how these proteins interact in higher-order complexes. The resulting interactome describes the biochemical organization of LECA, revealing both known and new assemblies. We analyzed these ancient protein interactions to find new human gene-disease relationships for bone density and congenital birth defects, demonstrating the value of ancestral protein interactions for guiding functional genetics today.

Antitumor effect of memantine is related to the formation of the splicing isoform of GLG1, a decoy FGF‑binding protein

Drug repositioning is a strategy for repurposing the approved or investigational drugs that are outside the scope of the original medical indication. Memantine is used as a non‑competitive N‑methyl‑D‑aspartate receptor antagonist to prevent glutamate‑mediated excitotoxicity in Alzheimer's disease, and is one of the promising agents which is utilized for the purpose of cancer therapy. However, the association between memantine and Golgi glycoprotein 1 (GLG1), an intracellular fibroblast growth factor receptor, in cancers has not yet been clarified. The present study analyzed the expression and location of GLG1 in tumor cells treated with memantine. Memantine was found to suppress the growth of malignant glioma and breast cancer cells in a concentration‑dependent manner. The mRNA expression of GLG1 was upregulated in a concentration‑dependent manner, and the splicing variant profiles were altered in all cell lines examined. The results of western blot analysis revealed an increase in the full‑length and truncated forms of GLG1. Moreover, GLG1 spread in the cytosol of memantine‑treated cells, whereas it localized in the Golgi apparatus in control cells. Since GLG1 functions as a decoy FGF receptor, the modulation of GLG1 may prove to be one of the mechanisms underlying the cancer‑suppressive effects of memantine.

Immunological insights of selectins in human disease mechanism

Selectin enzymes are glycoproteins and are an important adhesion molecule in the mammalian immune system, especially in the inflammatory response and the healing process of tissues. Selectins play an important role in a variety of biological processes, including the rolling of leukocytes in endothelial cells, a process known as the adhesion cascade. It has recently been discovered and reported that the selectin mechanism plays a role in cancer and thrombosis disease. This process begins with non-covalent interactions-based selectin-ligand binding and the glycans play a role as a connector between cancer cells and the endothelium in this process. The selectin mechanism is critical for the immune system, but it is also involved in disease mechanisms, earning the selectins the nickname "Selectins-The Two Dr. Jekyll and Mr. Hyde Faces". As a result, the drug for selectins should have a multifaceted role and be a dynamic molecule that targets the disease mechanism specifically. This chapter explores the role of selectins in the disease mechanism at the mechanism level that provides the impact for identifying the selectin inhibitors. Overall, this chapter provides the molecular level insights on selectins, their ligands, involvement in normal and disease mechanisms.

Interaction networks of Weibel-Palade body regulators syntaxin-3 and syntaxin binding protein 5 in endothelial cells

The endothelium stores the hemostatic protein Von Willebrand factor (VWF) in endothelial storage organelles called Weibel-Palade bodies (WPBs). During maturation, WPBs recruit a complex of Rab GTPases and effectors that associate with components of the SNARE machinery that control WPB exocytosis. Recent genome wide association studies have found links between genetic variations in the SNAREs syntaxin-2 (STX2) and syntaxin binding protein 5 (STXBP5) and VWF plasma levels, suggesting a role for SNARE proteins in regulating VWF release. Moreover, we have previously identified the SNARE proteins syntaxin-3 and STXBP1 as regulators of WPB release. In this study we used an unbiased iterative interactomic approach to identify new components of the WPB exocytotic machinery. An interactome screen of syntaxin-3 identifies a number of SNAREs and SNARE associated proteins (STXBP2, STXBP5, SNAP23, NAPA and NSF). We show that the VAMP-like domain (VLD) of STXBP5 is indispensable for the interaction with SNARE proteins and this capacity of the VLD could be exploited to identify an extended set of novel endothelial SNARE interactors of STXBP5. In addition, an STXBP5 variant with an N436S substitution, which is linked to lower VWF plasma levels, does not show a difference in interactome when compared with WT STXBP5. SIGNIFICANCE: The hemostatic protein Von Willebrand factor plays a pivotal role in vascular health: quantitative or qualitative deficiencies of VWF can lead to bleeding, while elevated levels of VWF are associated with increased risk of thrombosis. Tight regulation of VWF secretion from WPBs is therefore essential to maintain vascular homeostasis. We used an unbiased proteomic screen to identify new components of the regulatory machinery that controls WPB exocytosis. Our data expand the endothelial SNARE protein network and provide a set of novel candidate WPB regulators that may contribute to regulation of VWF plasma levels and vascular health.

Notable Aspects of Glycan-Protein Interactions

This mini review highlights several interesting aspects of glycan-mediated interactions that are common between cells, bacteria, and viruses. Glycans are ubiquitously found on all living cells, and in the extracellular milieu of multicellular organisms. They are known to mediate initial binding and recognition events of both immune cells and pathogens with their target cells or tissues. The host target tissues are hidden under a layer of secreted glycosylated decoy targets. In addition, pathogens can utilize and display host glycans to prevent identification as foreign by the host’s immune system (molecular mimicry). Both the host and pathogens continually evolve. The host evolves to prevent infection and the pathogens evolve to evade host defenses. Many pathogens express both glycan-binding proteins and glycosidases. Interestingly, these proteins are often located at the tip of elongated protrusions in bacteria, or in the leading edge of the cell. Glycan-protein interactions have low affinity and, as a result, multivalent interactions are often required to achieve biologically relevant binding. These enable dynamic forms of adhesion mechanisms, reviewed here, and include rolling (cells), stick and roll (bacteria) or surfacing (viruses).

The Garz Sec7 domain guanine nucleotide exchange factor for Arf regulates salivary gland development in Drosophila

Surface delivery of proteins involved in cell-cell and cell-matrix interactions in cultured mammalian cells requires the GBF1 guanine nucleotide exchange factor. However, the role of GBF1 in delivery of adhesion proteins during organogenesis in intact animals has not been characterized. Here, we report the function of the fly GBF1 homolog, Gartenzwerg (Garz) in the development of the salivary gland in Drosophila melanogaster. We used the GAL4/UAS system to selectively deplete Garz from salivary gland cells. We show that depletion of Garz disrupts the secretory pathway as evidenced by the collapse of Golgi-localized Lava lamp (Lva) and the TGN-localized γ subunit of the clathrin-adaptor protein complex (AP-1). Additionally, Garz depletion inhibits trafficking of cell-cell adhesion proteins cadherin (DE-cad) and Flamingo to the cell surface. Disregulation of trafficking correlates with mistargeting of the tumor suppressor protein Discs large involved in epithelial polarity determination. Garz-depleted salivary cells are smaller and lack well-defined plasma membrane domains. Garz depletion also inhibits normal elongation and positioning of epithelial cells, resulting in a disorganized salivary gland that lacks a well defined luminal duct. Our findings suggest that Garz is essential for establishment of epithelial structures and demonstrate an absolute requirement for Garz during Drosophila development.

Class I myosins in B-cell physiology: functions in spreading, immune synapses, motility, and vesicular traffic

Myosins comprise a family of motor proteins whose role in muscle contraction and motility in a large range of eukaryotic cells has been widely studied. Although these proteins have been characterized extensively and much is known about their function in different cellular compartments, little is known about these molecules in hematopoietic cells. Myosins expressed by cells from the immune response are involved in maintaining plasma membrane tension, moving and secreting vesicles, endo- and exocytotic processes, and promoting the adhesion and motility of cells. Herein, we summarize our current understanding of class I myosins in B cells, with an emphasis on the emerging roles of these molecular motors in immune functions.

Platelet-leukocyte crosstalk: Linking proinflammatory responses to procoagulant state

Platelet activation is known to be associated with the release of a vast array of chemokines and proinflammatory lipids which induce pleiotropic effects on a wide variety of tissues and cells, including leukocytes. During thrombosis, the recruitment of leukocytes to activated platelets is considered an important step which not only links thrombosis to inflammatory responses but may also enhance procoagulant state. This phenomenon is highly regulated and influenced by precise mutual interactions between the cells at site of vascular injury and thrombi formation. Platelet-leukocyte interaction involves a variety of mediators including adhesion molecules, chemokines and chemoattractant molecules, shed proteins, various proinflammatory lipids and other materials. The current review addresses the detailed mechanisms underlying platelet-leukocyte crosstalk. This includes their adhesive interactions, transcellular metabolisms, induced tissue factor activity and neutrophil extracellular traps formation as well as the impacts of these phenomena in modulation of the proinflammatory and procoagulant functions in a reciprocal manner that enhances the physiological responses.

Haploinsufficiency of E-selectin ligand-1 is associated with reduced atherosclerotic plaque macrophage content while complete deficiency leads to early embryonic lethality in mice

E-selectin-1 (ESL-1), also known as golgi complex-localized glycoprotein-1 (GLG1), homocysteine-rich fibroblast growth factor receptor (CGR-1), and latent transforming growth factor-β complex protein 1 (LTCP-1), is a multifunctional protein with widespread tissue distribution. To determine the functional consequences of ESL-1 deficiency, mice were generated carrying an ESL-1 gene trap. After backcrossing to C57BL6/J for 6 generations, mice heterozygous for the gene trap (ESL-1(+/-)) were intercrossed to produce ESL-1(-/-) mice, however ESL-1(-/-) mice were not viable, even at embryonic day E10.5. To determine the effect of heterozygous ESL-1 deficiency on atherosclerosis, apolipoprotein E deficient (ApoE(-/-)), ESL-1(+/-) mice were generated and fed western diet. Compared to ApoE(-/-), ESL-1(+)(/)(+) mice, atherosclerotic lesions from ApoE(-/-), ESL-1(+/-) contained more collagen and fewer macrophages, suggesting increased plaque stability. In conclusion, heterozygous deficiency of ESL-1 is associated with features of increased atherosclerotic plaque stability while complete deficiency of ESL-1 leads to embryonic lethality.

E-selectin ligands as mechanosensitive receptors on neutrophils in health and disease

Application of mechanical force to bonds between selectins and their ligands is a requirement for these adhesion receptors to optimally perform functions that include leukocyte tethering and activation of stable adhesion. Although all three selectins are reported to signal from the outside-in subsequent to ligand binding, E-selectin is unique in its capacity to bind multiple sialyl Lewis x presenting ligands and mediate slow rolling on the order of a micron per second. A diverse set of ligands are recognized by E-selectin in the mouse, including ESL-1, CD44 (HCELL), and PSGL-1 which are critical in transition from slow rolling to arrest and for efficient transendothelial migration. The molecular recognition process is different in humans as L-selectin is a major ligand, which along with glycolipids constitute more than half of the E-selectin receptors on human polymorphonuclear neutrophils (PMN). In addition, E-selectin is most efficient at raising the affinity and avidity of CD18 integrins that supports PMN deceleration and trafficking to sites of acute inflammation. The mechanism is only partially understood but known to involve a rise in cytosolic calcium and tyrosine phosphorylation that activates p38 MAP kinase and Syk kinase, both of which transduce signals from clustered E-selectin ligands. In this review we highlight the molecular recognition and mechanical requirements of this process to reveal how E-selectin confers selectivity and efficiency of signaling for extravasation at sites of inflammation and the mechanism of action of a new glycomimetic antagonist targeted to the lectin domain that has shown efficacy in blocking neutrophil activation and adhesion on inflamed endothelium.

Neutrophil function in small animals

Neutrophils are highly mobile phagocytes that serve as the initial effectors against pathogens and are actively recruited to sites of inflammation. Chemoattractants guide them toward the inflammation, and their interaction with endothelial cells directs them through postcapillary venules and into the tissues. Once they have reached their destination, they can efficiently kill many microbes via phagocytosis, extracellular release of granule contents, and the formation of NETs. They also actively produce cytokines and other mediators to promote or suppress inflammation, repair tissues, and modulate the immune response. The importance of neutrophil function in host health is emphasized through discussion of inherited disorders of neutrophil function such as leukocyte adhesion deficiency and cyclic hematopoiesis.

Retention in the Golgi apparatus and expression on the cell surface of Cfr/Esl-1/Glg-1/MG-160 are regulated by two distinct mechanisms

Cfr (cysteine-rich fibroblast growth factor receptor) is an Fgf (fibroblast growth factor)-binding protein without a tyrosine kinase. We have shown previously that Cfr is involved in Fgf18 signalling via Fgf receptor 3c. However, as Cfr is also known as Glg (Golgi apparatus protein)-1 or MG-160 and occurs in the Golgi apparatus, it remains unknown how the distribution of Cfr is regulated. In the present study, we performed a mutagenic analysis of Cfr to show that two distinct regions contribute to its distribution and stability. First, the C-terminal region retains Cfr in the Golgi apparatus. Secondly, the Cfr repeats in the extracellular juxtamembrane region destabilizes Cfr passed through the Golgi apparatus. This destabilization does not depend on the cleavage and secretion of the extracellular domain of Cfr. Furthermore, we found that Cfr with a GPI (glycosylphosphatidylinositol) anchor was predominantly expressed on the cell surface in Ba/F3 cells and affected Fgf18 signalling in a similar manner to the full-length Cfr, indicating that the interaction of Cfr with Fgfs on the cell surface is important for its function in Fgf signalling. These results suggest that the expression of Cfr in the Golgi apparatus and on the plasma membrane is finely tuned through two distinct mechanisms for exhibiting different functions.

Leukocyte ligands for endothelial selectins: specialized glycoconjugates that mediate rolling and signaling under flow

Reversible interactions of glycoconjugates on leukocytes with P- and E-selectin on endothelial cells mediate tethering and rolling of leukocytes in inflamed vascular beds, the first step in their recruitment to sites of injury. Although selectin ligands on hematopoietic precursors have been identified, here we review evidence that PSGL-1, CD44, and ESL-1 on mature leukocytes are physiologic glycoprotein ligands for endothelial selectins. Each ligand has specialized adhesive functions during tethering and rolling. Furthermore, PSGL-1 and CD44 induce signals that activate the β2 integrin LFA-1 and promote slow rolling, whereas ESL-1 induces signals that activate the β2 integrin Mac-1 in adherent neutrophils. We also review evidence for glycolipids, CD43, L-selectin, and other glycoconjugates as potential physiologic ligands for endothelial selectins on neutrophils or lymphocytes. Although the physiologic characterization of these ligands has been obtained in mice, we also note reported similarities and differences with human selectin ligands.

Myosin 1c participates in B cell cytoskeleton rearrangements, is recruited to the immunologic synapse, and contributes to antigen presentation

Myosin 1c (Myo1c) is a member of the unconventional class I myosins of vertebrates, which directly link the plasma membrane with the microfilament cortical web. Although this molecular motor has been implicated in cell functions such as cytoskeleton organization, cell motility, nuclear transcription, and endocytosis, its role in hematopoietic cells is largely unknown. In this study, we show that Myo1c is abundantly expressed in murine B lymphocytes and is preferentially located at the plasma membrane, especially in peripheral processes such as microvilli. We observed that this motor concentrates at the growing membrane protrusions generated during B cell spreading and that it is actively recruited to the immune synapse. Interestingly, Myo1c was detected in lipid rafts of B cells and showed strong colocalization with MHC-II, particularly after cross-linking of these molecules. By transfection of a dominant negative form of Myo1c or specific siRNA, we also detected alterations in the spreading and Ag-presenting ability of these cells. The data suggest that Myo1c is involved in the cytoskeleton dynamics and membrane protein anchoring or sorting in B lymphocytes.

Global gene disruption in human cells to assign genes to phenotypes by deep sequencing

Insertional mutagenesis in a haploid background can lead to complete disruption of gene function¹. Here we generate a population of human cells that contain insertions in >98% of their expressed genes. We established Phenotypic Interrogation via Tag Sequencing (PhITSeq) as a method to examine millions of mutant alleles through selection and parallel sequencing. Analysis of pools of selected cells rather than individual clones provides a rapid assessment of the spectrum of genes involved in phenotypes under study. This facilitates comparative screens as illustrated here for the family of cytolethal distending toxins (CDTs). CDTs are virulence factors secreted by a variety of pathogenic gram-negative bacteria that cause tissue damage at distinct anatomical sites². We identified 743 mutations distributed over 12 human genes important for intoxication by four different CDTs. While related CDTs may share host factors, they also exploit unique host factors yielding a characteristic profile for each CDT.

Dysregulated neutrophil--endothelial interaction in antineutrophil cytoplasmic autoantibody (ANCA)-associated vasculitides: implications for pathogenesis and disease intervention

The interplay between neutrophils and endothelial cells allows ANCA to become pathogenic and results in uncontrolled inflammation in the vessel wall. This review presents an overall view on neutrophil-endothelial interaction during inflammation with a focus on ANCA-associated vasculitis, and summarizes the effector mechanisms which cause vascular damage in AAV. In addition, potential elements for disease intervention based on this process are discussed.

Neutrophils, from marrow to microbes

Neutrophils are produced in the bone marrow from stem cells that proliferate and differentiate to mature neutrophils fully equipped with an armory of granules. These contain proteins that enable the neutrophil to deliver lethal hits against microorganisms, but also to cause great tissue damage. Neutrophils circulate in the blood as dormant cells. At sites of infection, endothelial cells capture bypassing neutrophils and guide them through the endothelial cell lining whereby the neutrophils are activated and tuned for the subsequent interaction with microbes. Once in tissues, neutrophils kill microorganisms by microbicidal agents liberated from granules or generated by metabolic activation. As a final act, neutrophils can extrude stands of DNA with bactericidal proteins attached that act as extracellular traps for microorganisms.

Identification of host factors involved in coronavirus replication by quantitative proteomics analysis

In this study, we applied a quantitative proteomic approach, based on SILAC, to investigate the interactions of coronaviruses with the secretory pathway of the host cell, with the aim to identify host factors involved in coronavirus replication. Comparison of the protein profiles of Golgi‐enriched fractions of cells that were either mock infected or infected with mouse hepatitis virus revealed the significant depletion or enrichment of 116 proteins. Although ribosomal/nucleic acid binding proteins were enriched in the Golgi‐fractions of mouse hepatitis virus‐infected cells, proteins annotated to localize to several organelles of the secretory pathway were overrepresented among the proteins that were depleted from these fractions upon infection. We hypothesized that proteins, of which the abundance or distribution is affected by infection, are likely to be involved in the virus life cycle. Indeed, depletion of a small subset of the affected proteins by using small interfering RNAs identified several host factors involved in coronavirus infection. Transfection of small interfering RNAs targeting either C11orf59 or Golgi apparatus glycoprotein 1 resulted in increased virus replication, whereas depletion of vesicle‐trafficking protein vesicle‐trafficking protein sec22b enhanced the release of infectious progeny virus. Overexpression of these proteins, on the other hand, had a negative effect on virus replication. Overall, our study shows that the SILAC approach is a suitable tool to study host–pathogen interactions and to identify host proteins involved in virus replication.

Core 1-derived O-glycans are essential E-selectin ligands on neutrophils

Neutrophils roll on E-selectin in inflamed venules through interactions with cell-surface glycoconjugates. The identification of physiologic E-selectin ligands on neutrophils has been elusive. Current evidence suggests that P-selectin glycoprotein ligand-1 (PSGL-1), E-selectin ligand-1 (ESL-1), and CD44 encompass all glycoprotein ligands for E-selectin; that ESL-1 and CD44 use N-glycans to bind to E-selectin; and that neutrophils lacking core 2 O-glycans have partially defective interactions with E-selectin. These data imply that N-glycans on ESL-1 and CD44 and O-glycans on PSGL-1 constitute all E-selectin ligands, with neither glycan subset having a dominant role. The enzyme T-synthase transfers Gal to GalNAcalpha1-Ser/Thr to form the core 1 structure Galbeta1-3GalNAcalpha1-Ser/Thr, a precursor for core 2 and extended core 1 O-glycans that might serve as selectin ligands. Here, using mice lacking T-synthase in endothelial and hematopoietic cells, we found that E-selectin bound to CD44 and ESL-1 in lysates of T-synthase-deficient neutrophils. However, the cells exhibited markedly impaired rolling on E-selectin in vitro and in vivo, failed to activate beta2 integrins while rolling, and did not emigrate into inflamed tissues. These defects were more severe than those of neutrophils lacking PSGL-1, CD44, and the mucin CD43. Our results demonstrate that core 1-derived O-glycans are essential E-selectin ligands; that some of these O-glycans are on protein(s) other than PSGL-1, CD44, and CD43; and that PSGL-1, CD44, and ESL-1 do not constitute all glycoprotein ligands for E-selectin.

Neutrophil microdomains: linking heterocellular interactions with vascular injury

PURPOSE OF REVIEW

Neutrophil infiltration is an important feature in inflammatory scenarios. Before these cells infiltrate tissues, however, they contribute to crucial intravascular events in which neutrophil microdomains mediate heterotypic interactions with endothelial cells, red blood cells and/or platelets. In vascular diseases, this can result in exacerbated neutrophil activation, subsequent vascular injury and obstruction of microcirculatory blood flow. This review discusses recent advances in elucidating these neutrophil domains and their associated functions in cell adhesion.

RECENT FINDINGS

Neutrophil recruitment is mediated by sequential interactions with the endothelium, termed rolling, adhesion and extravasation. Evidence points to novel signaling pathways induced during the rolling phase resulting in the transition to leukocyte adhesion, which appear to contribute to chemokine mediated activation. In addition, specific neutrophil microdomains are important for interactions with other hematopoietic cells inducing reductions in microvascular flow and injury.

SUMMARY

Neutrophils integrate signals received from the endothelium to act as linkers between the vessel wall and a variety of vascular components (i.e. endothelial cells, platelets, red blood cells) in acute and chronic inflammatory conditions to mediate interactions that can result in vascular injury and vasoocclusion.

Glycosylation in immune cell trafficking

Leukocyte recruitment encompasses cell adhesion and activation steps that enable circulating leukocytes to roll, arrest, and firmly adhere on the endothelial surface before they extravasate into distinct tissue locations. This complex sequence of events relies on adhesive interactions between surface structures on leukocytes and endothelial cells and also on signals generated during the cell-cell contacts. Cell surface glycans play a crucial role in leukocyte recruitment. Several glycosyltransferases such as alpha1,3 fucosyltransferases, alpha2,3 sialyltransferases, core 2 N-acetylglucosaminlytransferases, beta1,4 galactosyltransferases, and polypeptide N-acetylgalactosaminyltransferases have been implicated in the generation of functional selectin ligands that mediate leukocyte rolling via binding to selectins. Recent evidence also suggests a role of alpha2,3 sialylated carbohydrate determinants in triggering chemokine-mediated leukocyte arrest and influencing beta1 integrin function. The recent discovery of galectin- and siglec-dependent processes further emphasizes the significant role of glycans for the successful recruitment of leukocytes into tissues. Advancing the knowledge on glycan function into appropriate pathology models is likely to suggest interesting new therapeutic strategies in the treatment of immune- and inflammation-mediated diseases.

Proteomic characterization of HIV-modulated membrane receptors, kinases and signaling proteins involved in novel angiogenic pathways

Background

Kaposi's sarcoma (KS), hemangioma, and other angioproliferative diseases are highly prevalent in HIV-infected individuals. While KS is etiologically linked to the human herpesvirus-8 (HHV8) infection, HIV-patients without HHV-8 and those infected with unrelated viruses also develop angiopathies. Further, HIV-Tat can activate protein-tyrosine-kinase (PTK-activity) of the vascular endothelial growth factor receptor involved in stimulating angiogenic processes. However, Tat by itself or HHV8-genes alone cannot induce angiogenesis in vivo unless specific proteins/enzymes are produced synchronously by different cell-types. We therefore tested a hypothesis that chronic HIV-replication in non-endothelial cells may produce novel factors that provoke angiogenic pathways.

Methods

Genome-wide proteins from HIV-infected and uninfected T-lymphocytes were tested by subtractive proteomics analyses at various stages of virus and cell growth in vitro over a period of two years. Several thousand differentially regulated proteins were identified by mass spectrometry (MS) and >200 proteins were confirmed in multiple gels. Each protein was scrutinized extensively by protein-interaction-pathways, bioinformatics, and statistical analyses.

Results

By functional categorization, 31 proteins were identified to be associated with various signaling events involved in angiogenesis. 88% proteins were located in the plasma membrane or extracellular matrix and >90% were found to be essential for regeneration, neovascularization and angiogenic processes during embryonic development.

Conclusion

Chronic HIV-infection of T-cells produces membrane receptor-PTKs, serine-threonine kinases, growth factors, adhesion molecules and many diffusible signaling proteins that have not been previously reported in HIV-infected cells. Each protein has been associated with endothelial cell-growth, morphogenesis, sprouting, microvessel-formation and other biological processes involved in angiogenesis (p = 10^-4 to 10^-12). Bioinformatics analyses suggest that overproduction of PTKs and other kinases in HIV-infected cells has suppressed VEGF/VEGFR-PTK expression and promoted VEGFR-independent pathways. This unique mechanism is similar to that observed in neovascularization and angiogenesis during embryogenesis. Validation of clinically relevant proteins by gene-silencing and translational studies in vivo would identify specific targets that can be used for early diagnosis of angiogenic disorders and future development of inhibitors of angiopathies. This is the first comprehensive study to demonstrate that HIV-infection alone, without any co-infection or treatment, can induce numerous "embryonic" proteins and kinases capable of generating novel VEGF-independent angiogenic pathways.

Dissecting the role of the ARF guanine nucleotide exchange factor GBF1 in Golgi biogenesis and protein trafficking

COPI recruitment to membranes appears to be essential for the biogenesis of the Golgi and for secretory trafficking. Preventing COPI recruitment by expressing inactive forms of the ADP-ribosylation factor (ARF) or the ARF-activating guanine nucleotide exchange factor GBF1, or by treating cells with brefeldin A (BFA), causes the collapse of the Golgi into the endoplasmic reticulum (ER) and arrests trafficking of soluble and transmembrane proteins at the ER. Here, we assess COPI function in Golgi biogenesis and protein trafficking by preventing COPI recruitment to membranes by removing GBF1. We report that siRNA-mediated depletion of GBF1 causes COPI dispersal but does not lead to collapse of the Golgi. Instead, it causes extensive tubulation of the cis-Golgi. The Golgi-derived tubules target to peripheral ER-Golgi intermediate compartment (ERGIC) sites and create dynamic continuities between the ERGIC and the cis-Golgi compartment. COPI dispersal in GBF1-depleted cells causes dramatic inhibition of the trafficking of transmembrane proteins. Unexpectedly, soluble proteins continue to be secreted from GBF1-depleted cells. Our findings suggest that a secretory pathway capable of trafficking soluble proteins can be maintained in cells in which COPI recruitment is compromised by GBF1 depletion. However, the trafficking of transmembrane proteins through the existing pathway requires GBF1-mediated ARF activation and COPI recruitment.

Complete identification of E-selectin ligands on neutrophils reveals distinct functions of PSGL-1, ESL-1, and CD44

The selectins and their ligands are required for leukocyte extravasation during inflammation. Several glycoproteins have been suggested to bind to E-selectin in vitro, but the complete identification of its physiological ligands has remained elusive. Here, we showed that E-selectin ligand-1 (ESL-1), P-selectin glycoprotein ligand-1 (PSGL-1), and CD44 encompassed all endothelial-selectin ligand activity on neutrophils by using gene- and RNA-targeted loss of function. PSGL-1 played a major role in the initial leukocyte capture, whereas ESL-1 was critical for converting initial tethers into steady slow rolling. CD44 controlled rolling velocity and mediated E-selectin-dependent redistribution of PSGL-1 and L-selectin to a major pole on slowly rolling leukocytes through p38 signaling. These results suggest distinct and dynamic contributions of these three glycoproteins in selectin-mediated neutrophil adhesion and signaling.

Midbody and primary cilium of neural progenitors release extracellular membrane particles enriched in the stem cell marker prominin-1

Expansion of the neocortex requires symmetric divisions of neuroepithelial cells, the primary progenitor cells of the developing mammalian central nervous system. Symmetrically dividing neuroepithelial cells are known to form a midbody at their apical (rather than lateral) surface. We show that apical midbodies of neuroepithelial cells concentrate prominin-1 (CD133), a somatic stem cell marker and defining constituent of a specific plasma membrane microdomain. Moreover, these apical midbodies are released, as a whole or in part, into the extracellular space, yielding the prominin-1–enriched membrane particles found in the neural tube fluid. The primary cilium of neuroepithelial cells also concentrates prominin-1 and appears to be a second source of the prominin-1–bearing extracellular membrane particles. Our data reveal novel origins of extracellular membrane traffic that enable neural stem and progenitor cells to avoid the asymmetric inheritance of the midbody observed for other cells and, by releasing a stem cell membrane microdomain, to potentially influence the balance of their proliferation versus differentiation.

Protein Markers of Ischemic Insult in Brain Endothelial Cells Identified Using 2D Gel Electrophoresis and ICAT-Based Quantitative Proteomics

The blood-brain barrier (BBB) is formed by endothelial cells of cerebral microvessels sealed by tight junctions. Ischemic brain injury is known to initiate a series of biochemical and molecular processes that lead to the disruption of the BBB, development of vascular inflammation, and subsequent neurovascular remodeling including angiogenesis. Molecular effectors of these changes are multiple and are regulated in a dynamic fashion. The current study was designed to analyze changes in cellular and secreted proteins in rat brain endothelial cells (BEC) exposed to ischemic insult in vitro using two complementary quantitative proteomic approaches: two-dimensional gel electrophoresis (2DE) and isotope-coded affinity tag (ICAT)-based proteomics. We show a comprehensive qualitative and quantitative comparison between the two proteomic methods applied to the same experimental system with respect to their reproducibility, specificity, and the type of proteins identified. In total, >160 proteins showed differential expression in response to the ischemic insult, with 38 identified by 2DE and 138 by ICAT. Only 15 proteins were commonly identified. ICAT showed superior reproducibility over 2DE and was more suitable for detecting small, large, basic, hydrophobic, and secreted proteins than 2DE. However, positive identification of proteins by MS/MS was more reliably done using a 2DE-based method compared to ICAT. Changes in proteins involved in nucleic acid, protein, and carbohydrate metabolism, signal transduction, cell structure, adhesion and motility, immunity and defense, cell cycle, and apoptosis were observed. The functional significance of observed protein changes was evaluated through a multifaceted protein classification and validation process, which included literature mining and comparative evaluation of protein changes in analogous in vitro and in vivo ischemia models. The comparative analyses of protein changes between the in vitro and in vivo models demonstrated a significant correlative relationship, emphasizing the 'translational' value of in vitro endothelial models in neurovascular research.

CD43 functions as a ligand for E-Selectin on activated T cells

E-selectin, an inducible cell adhesion molecule expressed on endothelial cells, mediates the rolling on endothelium of leukocytes expressing E-selectin ligands, such as neutrophils and activated T cells. Although previous studies using mice lacking P-selectin glycoprotein ligand-1 (PSGL-1) have indicated that PSGL-1 on Th1 cells functions as an E-selectin ligand, the molecular nature of E-selectin ligands other than PSGL-1 remains unknown. In this study, we show that a 130-kDa glycoprotein was precipitated by an E-selectin-IgG chimera from mouse Th1 cells. This protein was cleaved by O-sialoglycoprotein endopeptidase and required sialic acid for E-selectin binding. The mAb 1B11, which recognizes the 130-kDa glycoform of CD43, recognized the 130-kDa band in the E-selectin-IgG precipitate. In addition, immunoprecipitation of the E-selectin-IgG precipitate with 1B11 depleted the 130-kDa protein, further confirming its identity as CD43. CD43 was also precipitated with E-selectin-IgG from cultured human T cells. E-selectin-dependent cell rolling on CD43 was observed under flow conditions using a CD43-IgG chimera generated in Chinese hamster ovary cells expressing alpha-1,3-fucosyltransferase VII and a core 2 beta-1,6-N-acetylglucosaminyltransferase. These results suggest that CD43, when modified by a specific set of glycosyltranferases, can function as an E-selectin ligand and therefore potentially mediate activated T cell migration into inflamed sites.

Identification of leukocyte E-selectin ligands, P-selectin glycoprotein ligand-1 and E-selectin ligand-1, on human metastatic prostate tumor cells

Prostate tumor cells, which characteristically metastasize to bone, initiate binding interactions with bone marrow endothelium under blood flow conditions through binding interactions with E-selectin. We hypothesized that E-selectin ligands on prostate tumor cells are directly associated with bone-metastatic potential. In this report, we elucidate the identity of E-selectin ligands on human metastatic prostate tumor cells and examine their association with prostate tumor progression and metastasis in vivo. To our surprise, we found that the E-selectin-binding form of P-selectin glycoprotein ligand-1 (PSGL-1) is expressed on the human bone-metastatic prostate tumor MDA PCa 2b cell line. Interestingly, we also found that human prostate tumor cells derived from bone, lymph node, and brain metastases expressed another leukocyte E-selectin ligand, E-selectin ligand-1 (ESL-1). Immunohistochemical analysis of PSGL-1 and ESL-1 in normal prostate tissue and in localized and metastatic prostate tumors revealed that ESL-1 was principally localized to intracellular cell membrane and expressed on all normal and malignant prostate tissue, whereas PSGL-1 was notably detected on the surfaces of bone-metastatic prostate tumor cells. These findings implicate a functional role of PSGL-1 in the bone tropism of prostate tumor cells and establish a new perspective into the molecular mechanism of human prostate tumor metastasis.

A novel isoform of human Golgi complex-localized glycoprotein-1 (also known as E-selectin ligand-1, MG-160 and cysteine-rich fibroblast growth factor receptor) targets differential subcellular localization

The initial step in trafficking of leukocytes through the vascular endothelium is mediated by an adhesive interaction between molecules of the selectin family and their cognate receptors. Previously, a putative murine E-selectin ligand-1 (ESL-1) was identified and found to be identical to Golgi complex-localized glycoprotein-1 (GLG1), also known as MG-160, and to a previously identified basic fibroblast growth factor (bFGF)-binding protein known as cysteine-rich FGF receptor (CFR). We report here a novel variant of the human GLG1 gene product that we call GLG2, cloned from a human monocyte cDNA library. GLG2 encodes a polypeptide identical to GLG1 except with a unique 24-amino-acid extension at the C-terminus of its cytoplasmic domain. Transfection of chimeric constructs into human embryonic kidney epithelial 293 cells revealed that the cytoplasmic domains of GLG1 and GLG2 targeted the expression of each chimeric protein differentially, GLG1 to the cell surface and GLG2 to the Golgi. Genetic analysis suggests that GLG1 and GLG2 are the products of a single gene, the mRNA of which can be processed by alternative splicing to generate two different transcripts encoding either GLG1 or GLG2. Northern blot analysis showed that the relative amounts of the mRNAs for either isoform differ in a cell- and species-specific manner. These data suggest that alternative splicing of the GLG1 gene transcript might regulate the function of its product.

Selectins-an emerging target for drug delivery

Selectins are multifunctional adhesion molecules that mediate the initial interactions between circulating leukocytes and cells of the endothelium. First identified over a decade ago, selectins have provided insight into areas as diverse as normal lymphocyte homing, leukocyte recruitment during inflammatory responses, carbohydrate ligand biosynthesis and adhesion-mediated signalling. Of late, selectins were introduced as targets for drug delivery in the development of new anti-inflammatory therapeutics and in anti-cancer therapy. This review will examine the selectins and their ligands with a focus on recent findings on their role in physiology and pathophysiology as well as the emerging role of selectins as targets in controlled drug delivery.

Adhesion to E-selectin promotes growth inhibition and apoptosis of human and murine hematopoietic progenitor cells independent of PSGL-1

Although both P- and E-selectin are constitutively expressed on bone marrow endothelial cells, their role in the regulation of hematopoiesis has only recently been investigated. We have previously shown that P-selectin glycoprotein ligand-l (PSGL-1/CD162) is expressed by primitive human bone marrow CD34+ cells, mediates their adhesion to P-selectin, and, more importantly, inhibits their proliferation. We now demonstrate that adhesion to E-selectin inhibits the proliferation of human CD34+ cells isolated either from human umbilical cord blood, adult mobilized blood, or steady-state bone marrow. Furthermore, a subpopulation, which does not contain the most primitive hematopoietic progenitor cells, undergoes apoptosis following E-selectin-mediated adhesion. The same phenomenon was observed in cells isolated from mouse bone marrow. Using lineage-negative Sca-1+ c-KIT+ bone marrow cells from PSGL-1(-/-) and wild-type mice, we establish that PSGL-1 is not the ligand involved in E-selectin-mediated growth inhibition and apoptosis. Moreover, stable transfection of the human myeloid cell line K562 (which does not express PSGL-1) with alpha(1,3) fucosyltransferase VII alone was sufficient to recapitulate the E-selectin-mediated growth inhibition and apoptosis observed in hematopoietic progenitor cells. These data demonstrate that an E-selectin ligand(s) other than PSGL-1 transduces growth inhibitory and proapoptotic signals and requires posttranslational fucosylation to be functional.

IL-12, STAT4-dependent up-regulation of CD4(+) T cell core 2 beta-1,6-n-acetylglucosaminyltransferase, an enzyme essential for biosynthesis of P-selectin ligands

TCR activation of naive T cells in the presence of IL-12 drives polarization toward a Th1 phenotype and synthesis of P- and E-selectin ligands. Fucosyltransferase VII (Fuc-T VII) and core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT) are critical for biosynthesis of selectin ligands. P-selectin glycoprotein ligand-1 is the best characterized ligand for P-selectin and also binds E-selectin. The contributions of TCR and cytokine signaling pathways to up-regulate Fuc-T VII and C2GnT during biosynthesis of E- and P-selectin ligands, such as P-selectin glycoprotein ligand 1, are unknown. IL-12 signals via the STAT4 pathway. Here, naive DO11.10 TCR transgenic and STAT4(-/-) TCR transgenic CD4(+) T cells were stimulated with Ag and IL-12 (Th1 condition), IL-4 (Th2), or neutralizing anti-IL-4 mAb only (Th0). The levels of Fuc-T VII and C2GnT mRNA in these cells were compared with their adhesive interactions with P- and E-selectin in vitro under flow. The data show IL-12/STAT4 signaling is necessary for induction of C2GnT, but not Fuc-TVII mRNA, and that STAT4(-/-) Th1 cells do not traffic normally to sites of inflammation in vivo, do not interact with P-selectin, and exhibit a partial reduction of E-selectin interactions under shear stress in vitro. Ag-specific TCR activation in CD4(+) T cells was sufficient to trigger induction of Fuc-TVII, but not C2GnT, mRNA and expression of E-selectin, but not P-selectin, ligands. Thus, Fuc-T VII and C2GnT are regulated by different signals during Th cell differentiation, and both cytokine and TCR signals are necessary for the expression of E- and P-selectin ligands.

L-selectin shedding is independent of its subsurface structures and topographic distribution

L-selectin (CD62L), a lectin-like adhesion molecule, mediates lymphocyte homing and leukocyte accumulation at sites of inflammation. Its transmembrane (TM) and intracellular (IC) domains confer clustering of L-selectin on microvilli of resting leukocytes, which is important for L-selectin function. Following activation of protein kinase C (PKC) or calmodulin inhibition, the wild-type (WT) protein is rapidly cleaved in its membrane-proximal ectodomain. To examine whether L-selectin topography or TM/IC domains are involved in this shedding process, we used stable transfectants expressing WT L-selectin (on microvilli) or chimeric molecules consisting of the L-selectin ectodomain linked to the TM/IC domains of CD44 (excluded from microvilli) or CD31 (randomly distributed). PKC activation by PMA altered the cells' surface morphology, but did not induce a redistribution of L-selectin ectodomains. All cell lines shed ectodomains upon PMA activation in a dose-dependent fashion and with similar kinetics. Calmodulin inhibition by trifluoperazine induced shedding in both WT and chimera transfectants. At high trifluoperazine concentrations, shedding of WT L-selectin was significantly more pronounced than that of chimeric molecules. Regardless of the activating stimulus, shedding was blocked by a hydroxamate-based metalloprotease inhibitor, suggesting that ectodomain down-regulation occurred through proteolytic cleavage by identical protease(s). These results show that the recognition site(s) for PKC-induced L-selectin shedding is exclusively contained within the ectodomain; the nature of subsurface structures and surface topography are irrelevant. Shedding induced by calmodulin inhibition has two components: one requires the L-selectin TM/IC domain, and the other is independent of it.

Affinity, kinetics, and thermodynamics of E-selectin binding to E-selectin ligand-1

E-selectin is an endothelial adhesion molecule, which mediates the tethering and rolling of leukocytes on vascular endothelium. It recognizes the glycoprotein E-selectin ligand-1 (ESL-1) as a major binding partner on mouse myeloid cells. Using surface plasmon resonance, we measured the kinetics and affinity of binding of monomeric E-selectin to ESL-1 isolated from mouse bone marrow cells. E-selectin bound to ESL-1 with a fast dissociation rate constant of 4.6 s(-1) and a calculated association rate constant of 7.4 x 10(4) m(-1) s(-1). We determined a dissociation constant (K(d)) of 62 microm, which resembles the affinity of L-selectin binding to glycosylation-dependent cell adhesion molecule-1. The affinity of the E-selectin-ESL-1 interaction did not change significantly when the temperature was varied from 5 degrees C to 37 degrees C, indicating that the enthalpic contribution to the binding is small at physiological temperatures, and that, in contrast to typical protein-carbohydrate interactions, binding is driven primarily by favorable entropic changes. Interestingly, surface plasmon resonance experiments with recombinant ESL-1 from alpha 1,3-fucosyltransferase IV-expressing Chinese hamster ovary cells showed a very similar K(d) of 66 microm, suggesting that this fucosyltransferase is sufficient to produce fully functional recombinant ESL-1. Following the recent description of the affinity and kinetics of the selectin-ligand pairs L-selectin-glycosylation-dependent cell adhesion molecule-1 and P-selectin-P-selectin glycoprotein ligand-1, this is the first determination of the parameters of E-selectin binding to one of its naturally occurring ligands.

A novel proliferation-associated variant of CFR-1 defined by a human monoclonal antibody

The germline coded human monoclonal IgM antibody 103/51 was isolated from a gastric carcinoma patient. This antibody binds to a 130-kd membrane molecule and has a mitotic effect on tumor cells in vitro. To characterize the target, we sequenced the protein and showed that the antibody binds to the cysteine-rich fibroblast growth factor receptor (CFR)-1, which is highly homologous to MG-160 and the E-selectin-ligand (ESL)-1. The epitope was determined by glycosidase-digestion experiments to be an N-linked carbohydrate side chain. Immunohistochemistry was used to investigate the tissue distribution of CFR-1. Different healthy tissues were tested and only the collecting tubes of the kidney, the Golgi apparatus, and the glomerular and fascicular zones of the adrenal gland stained positive. However, on malignant tissue the receptor is overexpressed in nearly all tested stomach cancers (12 of 15) and other tested carcinomas (13 of 15). Most interestingly, the receptor is also present in Helicobacter pylori gastritis and gastric dysplasia, but absent on uninflamed stomach mucosa. This restricted tissue pattern indicates that antibody 103/51 reacts with a membrane-bound variant of CFR-1, which is mainly expressed on transformed cells and precursor lesions and is essential for proliferation processes. The possible activity of antibody 103/51 as an activating ligand in these proliferative changes of gastric epithelial mucosa is discussed.

P-selectin glycoprotein ligand-1 and E-selectin ligand-1 are differentially modified by fucosyltransferases Fuc-TIV and Fuc-TVII in mouse neutrophils

P-selectin glycoprotein ligand-1 (PSGL-1) and E-selectin ligand-1 (ESL-1) are the two major selectin ligands on mouse neutrophils. Transfection experiments demonstrate that each ligand requires alpha1,3-fucosylation for selectin-binding. However, the relative contributions made by the two known myeloid alpha1, 3-fucosyltransferases Fuc-TVII or Fuc-TIV to this alpha1, 3-fucosylation are not yet clear. To address this issue, we have used mice deficient in Fuc-TIV and/or Fuc-TVII to examine how these enzymes generate selectin-binding glycoforms of PSGL-1 and ESL-1 in mouse neutrophils. Selectin binding was analyzed by affinity isolation experiments using recombinant, antibody-like forms of the respective endothelial selectins. We observe essentially normal binding of E- or P-selectin to PSGL-1 expressed by Fuc-TIV-deficient neutrophils but find that PSGL-1 expressed by Fuc-TVII-deficient neutrophils is not bound by E- or P-selectin. By contrast, E-selectin binds with normal efficiency to ESL-1 on Fuc-TVII-deficient neutrophils but exhibits an 80% reduction in its ability to bind ESL-1 isolated from Fuc-TIV-deficient neutrophils. The same specificity with which Fuc-TVII and Fuc-TIV generate selectin-binding forms of PSGL-1 and ESL-1 was found in transfection experiments with CHO-Pro(-)5 cells. In contrast, each fucosyltransferase alone could generate selectin-binding glycoforms of each of the two ligands in CHO-DUKX-B1 cells. Our data imply that in mouse neutrophils and their precursors, Fuc-TVII exclusively directs expression of PSGL-1 glycoforms bound with high affinity by P-selectin. By contrast, Fuc-TIV preferentially directs expression of ESL-1 glycoforms that exhibit high affinity for E-selectin. This substrate specificity can be mimicked in CHO-Pro(-)5 cells.

Cysteine-rich fibroblast growth factor receptor alters secretion and intracellular routing of fibroblast growth factor 3

Expression of the cysteine-rich fibroblast growth factor (FGF) receptor (CFR) in COS-1 cells strongly inhibits the secretion of co-expressed FGF3. By using a column retention assay and affinity chromatography, we demonstrate that at physiological salt concentrations FGF3 binds with strong affinity to CFR in vivo and in vitro. Furthermore, to show that FGF3 binds to CFR in vivo, truncation mutants of CFR with changed subcellular distributions were shown to cause a similar redistribution of FGF3. Although CFR is a 150-kDa integral membrane glycoprotein that is primarily located in the Golgi apparatus, we show here that in COS-1 cells a substantial proportion of CFR is secreted. This is due to a carboxyl-terminal proteolytic cleavage that releases the intraluminal portion of the protein for secretion. However, the apparent size of the integral membrane and secreted CFR appears similar, since the loss of protein mass is balanced by a gain of complex carbohydrates. The released CFR is associated with the extracellular matrix through its affinity for glycosaminoglycans. These findings show that CFR can modulate the secretion of FGF3 and may control its biological activity by regulating its secretion.

L-selectin-mediated leukocyte adhesion in vivo: microvillous distribution determines tethering efficiency, but not rolling velocity

Adhesion receptors that are known to initiate contact (tethering) between blood-borne leukocytes and their endothelial counterreceptors are frequently concentrated on the microvilli of leukocytes. Other adhesion molecules are displayed either randomly or preferentially on the planar cell body. To determine whether ultrastructural distribution plays a role during tethering in vivo, we used pre-B cell transfectants expressing L- or E-selectin ectodomains linked to transmembrane/intracellular domains that mediated different surface distribution patterns. We analyzed the frequency and velocity of transfectant rolling in high endothelial venules of peripheral lymph nodes using an intravital microscopy model. Ectodomains on microvilli conferred a higher efficiency at initiating rolling than random distribution which, in turn, was more efficient than preferential expression on the cell body. The role of microvillous presentation was less accentuated in venules below 20 micrometers in diameter than in larger venules. In the narrow venules, tethering of cells with cell body expression may have been aided by forced margination through collision with erythrocytes. L-selectin transfected cells rolled 10-fold faster than E-selectin transfectants. Interestingly, rolling velocity histograms of cell lines expressing equivalent copy numbers of the same ectodomain were always similar, irrespective of the topographic distribution. Our data indicate that the distribution of adhesion receptors has a dramatic impact on contact initiation between leukocytes and endothelial cells, but does not play a role once rolling has been established.

Mechanisms that regulate the function of the selectins and their ligands

Selectins are a family of three cell adhesion molecules (L-, E-, and P-selectin) specialized in capturing leukocytes from the bloodstream to the blood vessel wall. This initial cell contact is followed by the selectin-mediated rolling of leukocytes on the endothelial cell surface. This represents the first step in a cascade of molecular interactions that lead to leukocyte extravasation, enabling the processes of lymphocyte recirculation and leukocyte migration into inflamed tissue. The central importance of the selectins in these processes has been well documented in vivo by the use of adhesion-blocking antibodies as well as by studies on selectin gene-deficient mice. This review focuses on the molecular mechanisms that regulate expression and function(s) of the selectins and their ligands. Cell-surface expression of the selectins is regulated by a variety of different mechanisms. The selectins bind to carbohydrate structures on glycoproteins, glycolipids, and proteoglycans. Glycoproteins are the most likely candidates for physiologically relevant ligands. Only a few glycoproteins are appropriately glycosylated to allow strong binding to the selectins. Recently, more knowledge about the structure and the regulated expression of some of the carbohydrates on these ligands necessary for selectin binding has been accumulated. For at least one of these ligands, the physiological function is now well established. A novel and exciting aspect is the signaling function of the selectins and their ligands. Especially in the last two years, convincing data have been published supporting the idea that selectins and glycoprotein ligands of the selectins participate in the activation of leukocyte integrins.

Core 2 oligosaccharide biosynthesis distinguishes between selectin ligands essential for leukocyte homing and inflammation

Mammalian serine/threonine-linked oligosaccharides (O-glycans) are commonly synthesized with the Golgi enzyme core 2 beta-1,6-N-acetylglucosaminyltransferase (C2 GlcNAcT). Core 2 O-glycans have been hypothesized to be essential for mucin production and selectin ligand biosynthesis. We report that mice lacking C2 GlcNAcT exhibit a restricted phenotype with neutrophilia and a partial deficiency of selectin ligands. Loss of core 2 oligosaccharides reduces neutrophil rolling on substrata bearing E-, L-, and P-selectins and neutrophil recruitment to sites of inflammation. However, the diminished presence of L-selectin ligands on lymph node high endothelial venules does not affect lymphocyte homing. These studies indicate that core 2 oligosaccharide biosynthesis segregates the physiologic roles of selectins and reveal a function for the C2 GlcNAcT in myeloid homeostasis and inflammation.

Fibroblast growth factors as multifunctional signaling factors

The fibroblast growth factor (FGF) family consists of at least 15 structurally related polypeptide growth factors. Their expression is controlled at the levels of transcription, mRNA stability, and translation. The bioavailability of FGFs is further modulated by posttranslational processing and regulated protein trafficking. FGFs bind to receptor tyrosine kinases (FGFRs), heparan sulfate proteoglycans (HSPG), and a cysteine-rich FGF receptor (CFR). FGFRs are required for most biological activities of FGFs. HSPGs alter FGF-FGFR interactions and CFR participates in FGF intracellular transport. FGF signaling pathways are intricate and are intertwined with insulin-like growth factor, transforming growth factor-beta, bone morphogenetic protein, and vertebrate homologs of Drosophila wingless activated pathways. FGFs are major regulators of embryonic development: They influence the formation of the primary body axis, neural axis, limbs, and other structures. The activities of FGFs depend on their coordination of fundamental cellular functions, such as survival, replication, differentiation, adhesion, and motility, through effects on gene expression and the cytoskeleton.

Truncations of the C-terminal cytoplasmic domain of MG160, a medial Golgi sialoglycoprotein, result in its partial transport to the plasma membrane and filopodia

MG160, a type I cysteine-rich membrane sialoglycoprotein residing in the medial cisternae of the rat Golgi apparatus, is highly homologous to CFR, a fibroblast growth factor receptor, and ESL-1, an E-selectin ligand located at the cell surface of mouse myeloid cells and recently detected in the Golgi apparatus as well. The mechanism for the transport of MG160 from the Golgi apparatus to the cell surface is unknown. In this study we found that differential processing of the carboxy-terminal cytoplasmic domain (CD), consisting of amino acids Arg1159 Ile Thr Lys Arg Val Thr Arg Glu Leu Lys Asp Arg1171, resulted in the partial transport of the protein to the plasma membrane and filopodia. In Chinese hamster ovary cells (CHO), stably transfected with the entire cDNA encoding MG160, the protein was localized in the Golgi apparatus. However, when the terminal Arg1171 or up to nine distal amino acids were deleted, the protein was distributed to the plasma membrane and filopodia as well as the Golgi apparatus. This report shows that the CD of an endogenous type I Golgi protein is important for its efficient retention and identifies a unique residue preference in this process. Cleavage within the CD of MG160 may constitute a regulatory mechanism for the partial export of the protein from the Golgi apparatus to the plasma membrane and filopodia.

Transcytosis and surface presentation of IL-8 by venular endothelial cells

Chemokines have been convincingly implicated in actuating inflammatory leukocyte emigration. To affect the circulating leukocytes, tissue-derived chemokines have to traverse the endothelial cells (ECs). This was thought to be accomplished by chemokine diffusion through the intercellular gaps. On the contrary, we show by electron microscopy that the prototype chemokine IL-8 is internalized by venular ECs abluminally and transcytosed to the luminal surface. Here, it is presented to the adherent leukocytes on the EC membrane, predominantly in association with the EC projections. The intact C terminus of IL-8, the molecule's "immobilization" domain, is required for the EC binding, transcytosis, and consequently, the in vivo proemigratory activity of IL-8, indicating that the described subcellular interactions of IL-8 with the ECs are functionally relevant.

The P-Selectin Glycoprotein Ligand-1 Is Important for Recruitment of Neutrophils Into Inflamed Mouse Peritoneum

The P-selectin glycoprotein ligand-1 (PSGL-1) is a high-affinity ligand of P-selectin on myeloid cells and certain subsets of lymphoid cells. We generated the rat monoclonal antibody (MoAb) 2PH1 that recognizes an epitope within the first 19 amino acids at the N-terminus of the processed form of mouse PSGL-1. This antibody blocks attachment of mouse myeloid cells to P-selectin under both static and flow conditions. Intravenous administration of saturating amounts of 2PH1 reduced the number of rolling leukocytes in venules of the acutely exposed mouse cremaster muscle by 79% (±5.7%), whereas an anti–P-selectin MoAb reduced it completely. Examining the effect of the MoAb 2PH1 on the recruitment of neutrophils into chemically inflamed mouse peritoneum showed that blocking PSGL-1 inhibited neutrophil accumulation in the peritoneum by 82% (±7%) at 2 hours and by 59% (±7.9%) at 4 hours after stimulation. A similar effect was seen with the MoAb against P-selectin. Simultaneous administration of both antibodies at the 4-hour time point blocked neutrophil accumulation by 86% (±4.2%), arguing for an additional partner molecule for PSGL-1 besides P-selectin. This is the first demonstration of the importance of PSGL-1 in the recruitment of mouse neutrophils into inflamed tissue.