The E-selectin-ligand ESL-1 is a variant of a receptor for fibroblast growth factor

Sialyl Lewis X Defines an Activated and Functional Regulatory T Cell Subpopulation in Mice

Attempts have been made to elucidate the functional markers of regulatory T cells (Tregs), CD4+Foxp3+ T cells with an immunosuppressive function. Sialyl Lewis X (sLex), a tetrasaccharide Ag, is involved in leukocyte trafficking as selectin ligands and is a marker of highly differentiated Tregs in humans. However, the importance of sLex in murine Tregs remains unknown. In this study, we report that sLex defines the activated and functional subset of murine Tregs. The contact hypersensitivity model showed that murine Tregs strongly express sLex upon activation, accompanied by functional Treg marker elevation, such as Foxp3, CD25, CD103, CD39, and granzyme B. RNA sequencing analysis revealed sLex-positive (sLex+) Tregs expressed genes involved in Treg function at a higher level than sLex-negative (sLex-) Tregs. Using an in vitro suppression assay, we found that sLex+ Tregs could more efficiently suppress naive CD4+ T cell proliferation than sLex- Tregs. In the murine contact hypersensitivity elicitation model, the topical sLex+ Treg injection into the ears suppressed ear inflammation more efficiently than that of sLex- Tregs. Our results indicate that sLex could serve as a unique surface marker of activated and functional Tregs with immunosuppressive functions in mice.

Neuroimmunomodulatory properties of polysialic acid

Polymeric sialic acid (polysialic acid, polySia) is a remarkable posttranslational modification of only few select proteins. The major, and most prominent polySia protein carrier is the neural cell adhesion molecule NCAM. Here, the key functions of polySia are to regulate interactions of NCAM and to balance cellular interactions in brain development and plasticity. During recent years, however, increasing evidence points towards a role of polySia in the modulation of immune responses. These immunomodulatory functions can be mediated by polySia on proteins other than NCAM, presented either on the cell surface or released into the extracellular space. This perspective review summarizes our current knowledge and addresses major open questions on polySia and polySia receptors in modulating innate immune responses in the brain.

Cell-adhesion Molecules as Key Mechanisms of Tumor Invasion: The Case of Breast Cancer

Cancer is a major health problem worldwide and the second leading cause of death following cardiovascular diseases. Breast cancer is the leading cause of mortality and morbidity among women and one of the most common malignant neoplasms prompt to metastatic disease. In the present review, the mechanisms of the major cell adhesion molecules involved in tumor invasion are discussed, focusing on the case of breast cancer. A non-systematic updated revision of the literature was performed in order to assemble information regarding the expression of the adhesion cell molecules associated with metastasis.

N-Glycosylation and Inflammation; the Not-So-Sweet Relation

Chronic inflammation is the main feature of many long-term inflammatory diseases such as autoimmune diseases, metabolic disorders, and cancer. There is a growing number of studies in which alterations of N-glycosylation have been observed in many pathophysiological conditions, yet studies of the underlying mechanisms that precede N-glycome changes are still sparse. Proinflammatory cytokines have been shown to alter the substrate synthesis pathways as well as the expression of glycosyltransferases required for the biosynthesis of N-glycans. The resulting N-glycosylation changes can further contribute to disease pathogenesis through modulation of various aspects of immune cell processes, including those relevant to pathogen recognition and fine-tuning the inflammatory response. This review summarizes our current knowledge of inflammation-induced N-glycosylation changes, with a particular focus on specific subsets of immune cells of innate and adaptive immunity and how these changes affect their effector functions, cell interactions, and signal transduction.

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.

Polysialic Acid in the Immune System

Polysialic acid (polySia) is a highly regulated polymer of sialic acid (Sia) with such potent biophysical characteristics that when expressed drastically influences the interaction properties of cells. Although much of what is known of polySia in mammals has been elucidated from the study of its role in the central nervous system (CNS), polySia is also expressed in other tissues, including the immune system where it presents dynamic changes during differentiation, maturation, and activation of different types of immune cells of the innate and adaptive response, being involved in key regulatory mechanisms. At least six polySia protein carriers (CCR7, ESL-1, NCAM, NRP2, ST8Sia 2, and ST8Sia 4) are expressed in different types of immune cells, but there is still much to be explored in regard not only to the regulatory mechanisms that determine their expression and the structure of polySia chains but also to the identification of the cis- and trans- ligands of polySia that establish signaling networks. This review summarizes the current knowledge on polySia in the immune system, addressing its biosynthesis, its tools for identification and structural characterization, and its functional roles and therapeutic implications.

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.

Green Biocompatible Method for the Synthesis of Collagen/Chitin Composites to Study Their Composition and Assembly Influence on Fibroblasts Growth

A green biocompatible route for the deposition and simultaneous assembly, by pH increment, of collagen/chitin composites was proposed. Both assembled and unassembled samples with different collagen/chitin ratios were synthesized, maintaining the β-chitin polymorph. The first set showed a microfibrous organization with compositional submicron homogeneity. The second set presented a nanohomogeneous composition based on collagen nanoaggregates and chitin nanofibrils. The sets were tested as scaffolds for fibroblast growth (NIH-3T3) to study the influence of composition and assembly. In the unassembled scaffolds, the positive influence of collagen on cell growth mostly worn out in 48 h, while the addition of chitin enhanced this effect for over 72 h. The assembled samples showed higher viability at 24 h but a less positive effect on viability along the time. This work highlighted critical aspects of the influence that composition and assembly has on fibroblast growth, a knowledge worth exploiting in scaffold design and preparation.

Targeting E-selectin to Tackle Cancer Using Uproleselan

E-selectin is a vascular adhesion molecule expressed mainly on endothelium, and its primary role is to facilitate leukocyte cell trafficking by recognizing ligand surface proteins. E-selectin gained a new role since it was demonstrated to be involved in cancer cell trafficking, stem-like properties and therapy resistance. Therefore, being expressed in the tumor microenvironment, E-selectin can potentially be used to eradicate cancer. Uproleselan (also known as GMI-1271), a specific E-selectin antagonist, has been tested on leukemia, myeloma, pancreatic, colon and breast cancer cells, most of which involve the bone marrow as a primary or as a metastatic tumor site. This novel therapy disrupts the tumor microenvironment by affecting the two main steps of metastasis-extravasation and adhesion-thus blocking E-selectin reduces tumor dissemination. Additionally, uproleselan mobilized cancer cells from the protective vascular niche into the circulation, making them more susceptible to chemotherapy. Several preclinical and clinical studies summarized herein demonstrate that uproleselan has favorable safety and pharmacokinetics and is a tumor microenvironment-disrupting agent that improves the efficacy of chemotherapy, reduces side effects such as neutropenia, intestinal mucositis and infections, and extends overall survival. This review highlights the critical contribution of E-selectin and its specific antagonist, uproleselan, in the regulation of cancer growth, dissemination, and drug resistance in the context of the bone marrow microenvironment.

Structural and functional diversity of neutrophil glycosylation in innate immunity and related disorders

The granulated neutrophils are abundant innate immune cells that utilize bioactive glycoproteins packed in cytosolic granules to fight pathogenic infections, but the neutrophil glycobiology remains poorly understood. Facilitated by technological advances in glycoimmunology, systems glycobiology and glycoanalytics, a considerable body of literature reporting on novel aspects of neutrophil glycosylation has accumulated. Herein, we summarize the building knowledge of the structural and functional diversity displayed by N- and O-linked glycoproteins spatiotemporally expressed and sequentially brought-into-action across the diverse neutrophil life stages during bone marrow maturation, movements to, from and within the blood circulation and microbicidal processes at the inflammatory sites in peripheral tissues. It transpires that neutrophils abundantly decorate their granule glycoproteins including neutrophil elastase, myeloperoxidase and cathepsin G with peculiar glyco-signatures not commonly reported in other areas of human glycobiology such as hyper-truncated chitobiose core- and paucimannosidic-type N-glycans and monoantennary complex-type N-glycans. Sialyl Lewis^x, Lewis^x, poly-N-acetyllactosamine extensions and core 1-/2-type O-glycans are also common neutrophil glyco-signatures. Granule-specific glycosylation is another fascinating yet not fully understood feature of neutrophils. Recent literature suggests that unconventional biosynthetic pathways and functions underpin these prominent neutrophil-associated glyco-phenotypes. The impact of glycosylation on key neutrophil effector functions including extravasation, degranulation, phagocytosis and formation of neutrophil extracellular traps during normal physiological conditions and in innate immune-related diseases is discussed. We also highlight new technologies that are expected to further advance neutrophil glycobiology and briefly discuss the untapped diagnostic and therapeutic potential of neutrophil glycosylation that could open avenues to combat the increasingly prevalent innate immune disorders.

Acute Myeloid Leukemia Chemo-Resistance Is Mediated by E-selectin Receptor CD162 in Bone Marrow Niches

The interactions of leukemia cells with the bone marrow (BM) microenvironment is critical for disease progression and resistance to treatment. We have recently found that the vascular adhesion molecule E-(endothelial)-selectin is a key niche component that directly mediates acute myeloid leukemia (AML) chemo-resistance, revealing E-selectin as a promising therapeutic target. To understand how E-selectin promotes AML survival, we investigated the potential receptors on AML cells involved in E-selectin-mediated chemo-resistance. Using CRISPR-Cas9 gene editing to selectively suppress canonical E-selectin receptors CD44 or P-selectin glycoprotein ligand-1 (PSGL-1/CD162) from human AML cell line KG1a, we show that CD162, but not CD44, is necessary for E-selectin-mediated chemo-resistance in vitro. Using preclinical models of murine AML, we then demonstrate that absence of CD162 on AML cell surface leads to a significant delay in the onset of leukemia and a significant increase in sensitivity to chemotherapy in vivo associated with a more rapid in vivo proliferation compared to wild-type AML and a lower BM retention. Together, these data reveal for the first time that CD162 is a key AML cell surface receptor involved in AML progression, BM retention and chemo-resistance. These findings highlight specific blockade of AML cell surface CD162 as a potential novel niche-based strategy to improve the efficacy of AML therapy.

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

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

Resident Memory B Cells

In mammals, adaptive immunity is mediated by a broadly diverse repertoire of naive B and T lymphocytes that recirculate between secondary lymphoid organs. Initial antigen exposure promotes lymphocyte clonal expansion and differentiation, including the formation of memory cells. Antigen-specific memory cells are maintained at higher frequencies than their naive counterparts and have different functional and homing abilities. Importantly, a subset of memory cells, known as tissue-resident memory cells, is maintained without recirculating in nonlymphoid tissues, often at barrier surfaces, where they can be reactivated by antigen and rapidly perform effector functions that help protect the tissue in which they reside. Although antigen-experienced B cells are abundant at many barrier surfaces, their characterization as tissue-resident memory B (BRM) cells is not well developed. In this study, we describe the characteristics of memory B cells in various locations and discuss their possible contributions to immunity and homeostasis as bona fide BRM cells.

Integration of biomimicry and nanotechnology for significantly improved detection of circulating tumor cells (CTCs)

Circulating tumor cells (CTCs) have received a great deal of scientific and clinical attention as a biomarker for diagnosis and prognosis of many types of cancer. Given their potential significance in clinics, a variety of detection methods, utilizing the recent advances in nanotechnology and microfluidics, have been introduced in an effort of achieving clinically significant detection of CTCs. However, effective detection and isolation of CTCs still remain a tremendous challenge due to their extreme rarity and phenotypic heterogeneity. Among many approaches that are currently under development, this review paper focuses on a unique, promising approach that takes advantages of naturally occurring processes achievable through application of nanotechnology to realize significant improvement in sensitivity and specificity of CTC capture. We provide an overview of successful outcome of this biomimetic CTC capture system in detection of tumor cells from in vitro, in vivo, and clinical pilot studies. We also emphasize the clinical impact of CTCs as biomarkers in cancer diagnosis and predictive prognosis, which provides a cost-effective, minimally invasive method that potentially replaces or supplements existing methods such as imaging technologies and solid tissue biopsy. In addition, their potential prognostic values as treatment guidelines and that ultimately help to realize personalized therapy are discussed.

Oxidative stress and reactive oxygen species in endothelial dysfunction associated with cardiovascular and metabolic diseases

Reactive oxygen species (ROS) are reactive intermediates of molecular oxygen that act as important second messengers within the cells; however, an imbalance between generation of reactive ROS and antioxidant defense systems represents the primary cause of endothelial dysfunction, leading to vascular damage in both metabolic and atherosclerotic diseases. Endothelial activation is the first alteration observed, and is characterized by an abnormal pro-inflammatory and pro-thrombotic phenotype of the endothelial cells lining the lumen of blood vessels. This ultimately leads to reduced nitric oxide (NO) bioavailability, impairment of the vascular tone and other endothelial phenotypic changes collectively termed endothelial dysfunction(s). This review will focus on the main mechanisms involved in the onset of endothelial dysfunction, with particular focus on inflammation and aberrant ROS production and on their relationship with classical and non-classical cardiovascular risk factors, such as hypertension, metabolic disorders, and aging. Furthermore, new mediators of vascular damage, such as microRNAs, will be discussed. Understanding mechanisms underlying the development of endothelial dysfunction is an important base of knowledge to prevent vascular damage in metabolic and cardiovascular diseases.

The p38 pathway, a major pleiotropic cascade that transduces stress and metastatic signals in endothelial cells

By gating the traffic of molecules and cells across the vessel wall, endothelial cells play a central role in regulating cardiovascular functions and systemic homeostasis and in modulating pathophysiological processes such as inflammation and immunity. Accordingly, the loss of endothelial cell integrity is associated with pathological disorders that include atherosclerosis and cancer. The p38 mitogen-activated protein kinase (MAPK) cascades are major signaling pathways that regulate several functions of endothelial cells in response to exogenous and endogenous stimuli including growth factors, stress and cytokines. The p38 MAPK family contains four isoforms p38α, p38β, p38γ and p38δ that are encoded by four different genes. They are all widely expressed although to different levels in almost all human tissues. p38α/MAPK14, that is ubiquitously expressed is the prototype member of the family and is referred here as p38. It regulates the production of inflammatory mediators, and controls cell proliferation, differentiation, migration and survival. Its activation in endothelial cells leads to actin remodeling, angiogenesis, DNA damage response and thereby has major impact on cardiovascular homeostasis, and on cancer progression. In this manuscript, we review the biology of p38 in regulating endothelial functions especially in response to oxidative stress and during the metastatic process.

E-selectin ligand-1 (ESL-1) is a novel adiponectin binding protein on cell adhesion

BACKGROUND

Adiponectin (APN) is an adipocyte-derived bioactive molecule with anti-diabetic and anti-atherogenic properties. Although anti-diabetic effects are mostly mediated by the adiponectin receptors AdipoR1 and AdipoR2, the anti-atherogenic mechanisms have not been fully elucidated.

METHODS AND RESULTS

In this study, we identified E-selectin ligand (ESL)-1 as a novel APN-binding protein by mass spectrometry analysis of HepG2 cell-derived immunoprecipitant with an anti-APN antibody. Cell adhesion assays using fluorescence-labelled monocyte cell line THP-1 cells and human umbilical vein endothelial cells (HUVECs) revealed that APN-pre-treated THP-1 cells had reduced binding ability to HUVECs. This APN-mediated suppressive effect on monocyte binding to endothelial cells was partially abrogated by targeting ESL-1 with shRNA in THP-1 cells. In addition, serial mutagenesis analysis disclosed that five extracellular amino acids close to the N-terminus of ESL-1 were essential for binding with APN.

CONCLUSION

Our results highlight the fact that interaction between APN and ESL-1 could provide a fundamental mechanism underlying the anti-atherogenic properties of APN.

E-selectin ligand-1 controls circulating prostate cancer cell rolling/adhesion and metastasis

Circulating prostate cancer (PCa) cells preferentially roll and adhere on bone marrow vascular endothelial cells, where abundant E-selectin and stromal cell-derived factor 1 (SDF-1) are expressed, subsequently initiating a cascade of activation events that eventually lead to the development of metastases. To elucidate the roles of circulating PCa cells' rolling and adhesion behaviors in cancer metastases, we applied a dynamic cylindrical flow-based microchannel device that is coated with E-selectin and SDF-1, mimicking capillary endothelium. Using this device we captured a small fraction of rolling PCa cells. These rolling cells display higher static adhesion ability, more aggressive cancer phenotypes and stem-like properties. Importantly, mice received rolling PCa cells, but not floating PCa cells, developed cancer metastases. Genes coding for E-selectin ligands and genes associated with cancer stem cells and metastasis were elevated in rolling PCa cells. Knock down of E-selectin ligand 1(ESL-1), significantly impaired PCa cells' rolling capacity and reduced cancer aggressiveness. Moreover, ESL-1 activates RAS and MAP kinase signal cascade, consequently inducing the downstream targets. In summary, circulating PCa cells' rolling capacity contributes to PCa metastasis, and that is in part controlled by ESL-1.

Recent advances toward the development of inhibitors to attenuate tumor metastasis via the interruption of lectin-ligand interactions

Aberrant glycosylation is a well-recognized phenomenon that occurs on the surface of tumor cells, and the overexpression of a number of ligands (such as TF, sialyl Tn, and sialyl Lewis X) has been correlated to a worse prognosis for the patient. These unique carbohydrate structures play an integral role in cell-cell communication and have also been associated with more metastatic cancer phenotypes, which can result from binding to lectins present on cell surfaces. The most well studied metastasis-associated lectins are the galectins and selectins, which have been correlated to adhesion, neoangiogenesis, and immune-cell evasion processes. In order to slow the rate of metastatic lesion formation, a number of approaches have been successfully developed which involve interfering with the tumor lectin-substrate binding event. Through the generation of inhibitors, or by attenuating lectin and/or carbohydrate expression, promising results have been observed both in vitro and in vivo. This article briefly summarizes the involvement of lectins in the metastatic process and also describes different approaches used to prevent these undesirable carbohydrate-lectin binding events, which should ultimately lead to improvement in current cancer therapies.

Implications of the E-selectin S128R mutation for drug discovery

The C-type lectin E-selectin mediates the rolling of circulating leukocytes on vascular endothelial cells during the inflammatory process. In numerous studies, the S128R mutation of the E-selectin was associated with cardiovascular and autoimmune diseases. There is evidence that the S128R E-selectin mutation leads to a loss in ligand specificity, thus increasing leukocyte recruitment. Apart from the natural tetrasaccharide ligand sialyl Lewis(x) (sLe(x)), it has previously been proposed that non-fucosylated carbohydrates also bind to S128R E-selectin. To evaluate the therapeutic potential of the antagonism of the E-selectin mutant, ligand specificity was reinvestigated on a molecular basis. We determined the ligand specificity of wild-type and S128R E-selectin in a target-based competitive assay, a glycan array screen and cell-based binding assays under static and flow conditions. Regarding ligand-specificity, the binding properties of S128R E-selectin were identical to those of wt E-selectin, i.e., no mutant-specific binding of 3'-sialyl-N-acetyllactosamine, heparin, fetuin and K562 cells was observed. Additionally, the binding affinities of glycomimetic E-selectin antagonists were identical for wt and S128R E-selectin. Overall, the previous reports on carbohydrate ligand promiscuity of S128R E-selectin could not be confirmed.

Reactive oxygen species in inflammation and tissue injury

Abstract Reactive oxygen species (ROS) are key signaling molecules that play an important role in the progression of inflammatory disorders. An enhanced ROS generation by polymorphonuclear neutrophils (PMNs) at the site of inflammation causes endothelial dysfunction and tissue injury. The vascular endothelium plays an important role in passage of macromolecules and inflammatory cells from the blood to tissue. Under the inflammatory conditions, oxidative stress produced by PMNs leads to the opening of inter-endothelial junctions and promotes the migration of inflammatory cells across the endothelial barrier. The migrated inflammatory cells not only help in the clearance of pathogens and foreign particles but also lead to tissue injury. The current review compiles the past and current research in the area of inflammation with particular emphasis on oxidative stress-mediated signaling mechanisms that are involved in inflammation and tissue injury.

Coordinated and unique functions of the E-selectin ligand ESL-1 during inflammatory and hematopoietic recruitment in mice

Beyond its well-established roles in mediating leukocyte rolling, E-selectin is emerging as a multifunctional receptor capable of inducing integrin activation in neutrophils, and of regulating various biological processes in hematopoietic precursors. Although these effects suggest important homeostatic contributions of this selectin in the immune and hematologic systems, the ligands responsible for transducing these effects in different leukocyte lineages are not well defined. We have characterized mice deficient in E-selectin ligand-1 (ESL-1), or in both P-selectin glycoprotein-1 (PSGL-1) and ESL-1, to explore and compare the contributions of these glycoproteins in immune and hematopoietic cell trafficking. In the steady state, ESL-1 deficiency resulted in a moderate myeloid expansion that became more prominent when both glycoproteins were eliminated. During inflammation, PSGL-1 dominated E-selectin binding, rolling, integrin activation, and extravasation of mature neutrophils, but only the combined deficiency in PSGL-1 and ESL-1 completely abrogated leukocyte recruitment. Surprisingly, we find that the levels of ESL-1 were strongly elevated in hematopoietic progenitor cells. These elevations correlated with a prominent function of ESL-1 for E-selectin binding and for migration of hematopoietic progenitor cells into the bone marrow. Our results uncover dominant roles for ESL-1 in the immature compartment, and a functional shift toward PSGL-1 dependence in mature neutrophils.

Overlapping roles for endothelial selectins in murine hematopoietic stem/progenitor cell homing to bone marrow

Selectins are carbohydrate-binding adhesion molecules that are critically involved in leukocyte recognition of endothelium. The endothelial selectins have been implicated in homing of hematopoietic stem and progenitor cells (HSPCs) to the bone marrow (BM) during bone marrow transplant (BMT), but the precise roles of individual selectins in this process have never been defined. BMT of lethally irradiated mice lacking both endothelial selectins (E/P KO) with limiting numbers of wild type BM cells rescued significantly fewer E/P KO than WT recipients, but higher numbers of transplanted WT cells rescued E/P KOs in a dose-dependent fashion. Short-term homing assays confirmed a substantial defect in HSPC homing to BM in E/P KO mice. In contrast, BMT of E-selectin null or P-selectin null mice at limiting cell number uniformly rescued greater than 95% of the transplanted animals. Consistent with these functional results, flow cytometric analysis revealed both E-selectin ligands and P-selectin ligands on distinct subsets of HSPC. These results demonstrate overlapping functions for the endothelial selectins in HSPC homing to BM in the setting of BMT, and define a novel aspect of HSPC heterogeneity linked to selectin ligand expression.

Targeting Underglycosylated MUC1 for the Selective Capture of Highly Metastatic Breast Cancer Cells Under Flow

The underglycosylated form of the MUC1 glycoprotein, uMUC1, has been identified as a ligand for both E-selectin and ICAM-1 and can play multiple potential roles during rolling and firm adhesion events in the metastatic cascade. Using flow cytometry and confocal microscopy, the T47D and ZR-75-1 cell lines were verified to highly express uMUC1, however it was found that only ZR-75-1 cells expressed the E-selectin binding moiety sialyl Lewis x (sLe^x). Furthermore, perfusing T47D cells through E-selectin coated microtubes resulted in fast rolling velocities and low numbers of interacting cells and blocking uMUC1 with the SM3 antibody had no effect. ZR-75-1 cells, on the other hand, were highly dependent on the E-selectin:uMUC1 interaction as exemplified by significant increases in cell rolling velocities and decreases in the number of interacting cells when blocking with SM3 or when uMUC1 expression was knocked down via siRNA transfection. Whereas uMUC1 interactions with E-selectin supported cell rolling, P-selectin: uMUC1 interactions exclusively facilitated cell tethering, while L-selectin surfaces supported no cell adhesive interactions. These experimental observations are consistent with molecular dynamics simulations of uMUC1 bound to E-, P-, and L-selectin where the degree of residue contact correlated with the differential adhesion of uMUC1 to each selectin. Finally, an E-selectin and SM3 combined surface coating captured approximately 30% of the total number of interacting cancer cells comparable to the number of adhered cells when utilizing E-selectin and ICAM-1 combined surfaces. The E-selectin/SM3 surface strategy offers a viable method to selectively capture cancer cells from whole blood samples.

E-selectin ligand 1 regulates bone remodeling by limiting bioactive TGF-β in the bone microenvironment

TGF-β is abundantly produced in the skeletal system and plays a crucial role in skeletal homeostasis. E-selectin ligand-1 (ESL-1), a Golgi apparatus-localized protein, acts as a negative regulator of TGF-β bioavailability by attenuating maturation of pro-TGF-β during cartilage homeostasis. However, whether regulation of intracellular TGF-β maturation by ESL-1 is also crucial during bone homeostasis has not been well defined. Here, we show that Esl-1(-/-) mice exhibit a severe osteopenia with elevated bone resorption and decreased bone mineralization. In primary culture, Esl-1(-/-) osteoclast progenitors show no difference in osteoclastogenesis. However, Esl-1(-/-) osteoblasts show delayed differentiation and mineralization and stimulate osteoclastogenesis more potently in the osteoblast-osteoclast coculture, suggesting that ESL-1 primarily acts in osteoblasts to regulate bone homeostasis. In addition, Esl-1(-/-) calvaria exhibit an elevated mature TGF-β/pro-TGF-β ratio, with increased expression of TGF-β downstream targets (plasminogen activator inhibitor-1, parathyroid hormone-related peptide, connective tissue growth factor, and matrix metallopeptidase 13, etc.) and a key regulator of osteoclastogenesis (receptor activator of nuclear factor κB ligand). Moreover, in vivo treatment with 1D11, a pan-TGF-β antibody, significantly improved the low bone mass of Esl-1(-/-) mice, suggesting that elevated TGF-β signaling is the major cause of osteopenia in Esl-1(-/-) mice. In summary, our study identifies ESL-1 as an important regulator of bone remodeling and demonstrates that the modulation of TGF-β maturation is pivotal in the maintenance of a homeostatic bone microenvironment and for proper osteoblast-osteoclast coupling.

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.

Differential inhibition of polymorphonuclear leukocyte recruitment in vivo by dextran sulphate and fucoidan

The selectin-mediated rolling of leukocytes along the endothelial cells is a prerequisite step followed by firm adhesion and extravasation into the inflamed tissue. This initial contact can be suppressed by sulphated polysaccharides. We have studied the effect of sulphated polysaccharides on the ultimate polymorphonuclear leukocyte (PMN) recruitment and plasma leakage in rabbit skin in response to intradermal injection of various inflammatory mediators. PMN infiltration evoked by various PMN chemoattractants (FMLP, C5a desArg, LTB₄ and IL-8) was significantly inhibited after intravenous injection of dextran sulphate (25 mg/kg), heparin (2 × 90 mg/kg) or fucoidan (1 mg/kg). PMN-dependent plasma leakage was equally well reduced by the different sulphated polymers. Vascular permeability induced by histamine or thrombin acting via a PMN-independent mechanism was not reduced. Fucoidan was the only polysaccharide able to suppress IL-1-induced PMN infiltration for 60–70%. Local administration of dextran sulphate had no effect on PMN-dependent plasma leakage. Differential inhibition of PMN recruitment was determined after injection of dextran sulphate or fucoidan depending on the type of insult. Therefore, these results suggest that different adhesion pathways are utilized during PMN recruitment in vivo in response to chemoattractants and IL-1.

HECA-452 is a non-function blocking antibody for isolated sialyl Lewis x adhesion to endothelial expressed E-selectin under flow conditions

E-selectin, expressed on inflamed endothelium, and sialyl Lewis x (sLe(x)), present on the surface of leukocytes, play a key role in leukocyte-endothelial interactions during leukocyte recruitment to sites of inflammation. HECA-452 is a monoclonal antibody (mAb) that recognizes sLe(x) and is routinely used by investigators from diverse fields who seek to unravel the mechanisms of leukocyte adhesion. The data regarding the ability of HECA-452 to inhibit carbohydrate-mediated leukocyte adhesion to E-selectin remains conflicted, in part due to the presence of a variety of potential E-selectin reactive moieties on leukocytes. Recognizing this, we utilized a complementary approach to gain insight into HECA-452 adhesion assays. Specifically, we used sLe(x) microspheres to investigate the hypothesis that HECA-452 is a non-function blocking mAb for isolated sLe(x) mediated adhesion to endothelial expressed E-selectin. Flow cytometric analysis revealed that HECA-452 recognizes and binds to the sLe(x) microspheres. Perfusion of the sLe(x) microspheres over human umbilical vein endothelial cells (HUVEC) at 1.5 dyn/cm² revealed that the microspheres attach to 4h interleukin (IL)-1β activated HUVEC specifically via E-selectin. Pretreatment of the sLe(x) microspheres with HECA-452 did not influence sLe(x) microsphere initial tethering and accumulation on IL-1β activated HUVEC. Neuraminidase and fucosidase treatments of sLe(x) microspheres revealed that sialic acid and fucose are required for E-selectin binding, whereas HECA-452 recognition of sLe(x) does not depend on the fucose moiety to the extent required for E-selectin recognition. This latter finding suggests there are potential subtle differences between the sLe(x) antigens for E-selectin and HECA-452. Combined, the data indicate that HECA-452 is a non-inhibitor of sLe(x)-mediated adhesion to endothelial expressed E-selectin.

The neural cell adhesion molecules L1 and CHL1 are cleaved by BACE1 protease in vivo

The β-site amyloid precursor protein-cleaving enzyme BACE1 is a prime drug target for Alzheimer disease. However, the function and the physiological substrates of BACE1 remain largely unknown. In this work, we took a quantitative proteomic approach to analyze the secretome of primary neurons after acute BACE1 inhibition, and we identified several novel substrate candidates for BACE1. Many of these molecules are involved in neuronal network formation in the developing nervous system. We selected the adhesion molecules L1 and CHL1, which are crucial for axonal guidance and maintenance of neural circuits, for further validation as BACE1 substrates. Using both genetic BACE1 knock-out and acute pharmacological BACE1 inhibition in mice and cell cultures, we show that L1 and CHL1 are cleaved by BACE1 under physiological conditions. The BACE1 cleavage sites at the membrane-proximal regions of L1 (between Tyr(1086) and Glu(1087)) and CHL1 (between Gln(1061) and Asp(1062)) were determined by mass spectrometry. This work provides molecular insights into the function and the pathways in which BACE1 is involved, and it will help to predict or interpret possible side effects of BACE1 inhibitor drugs in current clinical trials.

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.

Cisterna-specific localization of glycosylation-related proteins to the Golgi apparatus

The Golgi apparatus is an intracellular organelle playing central roles in post-translational modification and in the secretion of membrane and secretory proteins. These proteins are synthesized in the endoplasmic reticulum (ER) and transported to the cis-, medial-and trans-cisternae of the Golgi. While trafficking through the Golgi, proteins are sequentially modified with glycan moieties by different glycosyltransferases. Therefore, it is important to analyze the glycosylation function of the Golgi at the level of cisternae. Markers widely used for cis-, medial- and trans-cisternae/trans Golgi network (TGN) in Drosophila are GM130, 120 kDa and Syntaxin16 (Syx16); however the anti-120 kDa antibody is no longer available. In the present study, Drosophila Golgi complex-localized glycoprotein-1 (dGLG1) was identified as an antigen recognized by the anti-120 kDa antibody. A monoclonal anti-dGLG1 antibody suitable for immunohistochemistry was raised in rat. Using these markers, the localization of glycosyltransferases and nucleotide-sugar transporters (NSTs) was studied at the cisternal level. Results showed that glycosyltransferases and NSTs involved in the same sugar modification are localized to the same cisternae. Furthermore, valuable functional information was obtained on the localization of novel NSTs with as yet incompletely characterized biochemical properties.

Glycomechanics of the metastatic cascade: tumor cell-endothelial cell interactions in the circulation

Hydrodynamic shear force plays an important role in the leukocyte adhesion cascade that involves the tethering and rolling of cells along the endothelial layer, their firm adhesion or arrest, and their extravasation or escape from the circulatory system by inducing passive deformation, or cell flattening, and microvilli stretching, as well as regulating the expression, distribution, and conformation of adhesion molecules on leukocytes and the endothelial layer. Similarly, the dissemination of circulating tumor cells (CTCs) from the primary tumor sites is believed to involve tethering, rolling, and firm adhesion steps before their eventual extravasation which leads to secondary tumor sites (metastasis). Of particular importance to both the leukocyte adhesion cascade and the extravasation of CTCs, glycoproteins are involved in all three steps (capture, rolling, and firm adhesion) and consist of a variety of important selectin ligands. This review article provides an overview of glycoprotein glycosylation associated with the abnormal glycan expression on cancer cell surfaces, where well-established and novel selectin ligands that are cancer related are discussed. An overview of computational approaches on the effects of fluid mechanical force on glycoprotein mediated cancer cell rolling and adhesion is presented with a highlight of recent flow-based and selectin-mediated cell capturing/enriching devices. Finally, as an important branch of the glycoprotein family, mucins, specifically MUC1, are discussed in the context of their aberrant expression on cancer cells and their role as cancer cell adhesion molecules. Since metastasis relies heavily on glycoprotein interactions in the bloodstream where the fluid shear stress highly regulates cell adhesion forces, it is important to study and understand the glycomechanics of all relevant glycoproteins (well-established and novel) as they relate to the metastatic cascade.

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.

E-selectin as a target for drug delivery and molecular imaging

E-selectin, also known as CD62E, is a cell adhesion molecule expressed on endothelial cells activated by cytokines. Like other selectins, it plays an important part in inflammation and in the adhesion of metastatic cancer cells to the endothelium. E-selectin recognizes and binds to sialylated carbohydrates present on the surface proteins of certain leukocytes. E-selectin has been chosen as a target for several therapeutic and medical imaging applications, based on its expression in the vicinity of inflammation, infection or cancer. These systems for drug delivery and molecular imaging include immunoconjugates, liposomes, nanoparticles, and microparticles prepared from a wide range of starting materials including lipids, synthetic polymers, polypeptides and organo-metallic structures. After a brief introduction presenting the selectin family and their implication in physiology and pathology, this review focuses on the formulation of these new delivery systems targeting E-selectin at a molecular level.

E-selectin is a viable route of infection for polymer-coated adenovirus retargeting in TNF-α-activated human umbilical vein endothelial cells

BACKGROUND

E-selectin is an attractive endothelial cell surface marker in inflammation and cancer.

PURPOSE

We sought to investigate retargeting of adenovirus via E-selectin as a viable pathway of infection in tumor necrosis factor-α (TNF-α)-activated human umbilical vein endothelial cells (HUVECs).

METHODS

E1, E3-deleted Ad5 expressing cytomegalovirus immediate-early (CMV IE) promoter-driven luciferase (Adluc) was coated with an amino-reactive multivalent hydrophilic polymer based on poly [N-(2-hydroxypropyl) methacrylamide] to generate pHPMA-adenovirus (pcAdluc). This was then retargeted by covalent attachment of a mouse antihuman E-selectin monoclonal antibody (MHES mAb), purified from the H18/7 hybridoma cell line (MHESpcAdluc).

RESULTS

MHESpcAdluc was efficiently taken up into HUVECs, generating a high level of transduction in TNF-α-treated E-selectin positive cells but not in untreated receptor-negative cells. Specific retargeting of MHESpcAdluc was demonstrated through reduced transduction of stimulated HUVEC when incubated in the presence of free E-selectin antibodies.

DISCUSSION AND CONCLUSION

Our results suggest that E-selectin could be a valuable target for gene transfer strategies internalizing polymer-coated modified adenovirus particles through a viable receptor-mediated endocytosis pathway, generating adequate levels of transgene expression per virus genome copy without compromising the specific activity of the parental virus.

Aberrant expression and function of death receptor-3 and death decoy receptor-3 in human cancer

Death receptor-3 (DR3) and death decoy receptor-3 (DcR3) are both members of the tumour necrosis factor receptor (TNFR) superfamily. The TNFR superfamily contains eight death domain-containing receptors, including TNFR1 (also called DR1), Fas (also called DR2), DR3, DR4, DR5, DR6, NGFR and EDAR. Upon the binding of these receptors with their corresponding ligands, the death domain recruits various proteins that mediate both the death and proliferation of cells. Receptor function is negatively regulated by decoy receptors (DcR1, DcR2, DcR3 and OPG). DR3/DcR3 are a pair of positive and negative players with which vascular endothelial growth inhibitor (VEGI) interacts. VEGI has been suggested to be a potential tumour suppressor. The inhibitory effects of VEGI on cancer are manifested in three main areas: a direct effect on cancer cells, an anti-angiogenic effect on endothelial cells, and the stimulation of dendritic cell maturation. A recent study indicated that DR3 may be a new receptor for E-selectin, which has been reported to be associated with cancer metastasis. DcR3 is a soluble receptor, highly expressed in various tumours, which lacks an apparent transmembrane segment, prevents cytokine response through ligand binding and neutralization, and is an inhibitor of apoptosis. DcR3 serves as a decoy receptor for FasL, LIGHT and VEGI. The cytokine LIGHT activates various anti-tumour functions and is expected to be a promising candidate for cancer therapy. Certain tumours may escape FasL-dependent immune-cytotoxic attack by expressing DcR3, which blocks FasL function. DR3/DcR3 play profound roles in regulating cell death and proliferation in cancer. The present review briefly discusses DR3/DcR3 and attempts to elucidate the role of these negative and positive players in cancer.

Direct measurements on CD24-mediated rolling of human breast cancer MCF-7 cells on E-selectin

Tumor cell rolling on the endothelium plays a key role in the initial steps of cancer metastasis, i.e., extravasation of circulating tumor cells (CTCs). Identification of the ligands that induce the rolling of cells is thus critical to understanding how cancers metastasize. We have previously demonstrated that MCF-7 cells, human breast cancer cells, exhibit the rolling response selectively on E-selectin-immobilized surfaces. However, the ligand that induces rolling of MCF-7 cells on E-selectin has not yet been identified, as these cells lack commonly known E-selectin ligands. Here we report, for the first time to our knowledge, a set of quantitative and direct evidence demonstrating that CD24 expressed on MCF-7 cell membranes is responsible for rolling of the cells on E-selectin. The binding kinetics between CD24 and E-selectin was directly measured using surface plasmon resonance (SPR), which revealed that CD24 has a binding affinity against E-selectin (K(D) = 3.4 ± 0.7 nM). The involvement of CD24 in MCF-7 cell rolling was confirmed by the rolling behavior that was completely blocked when cells were treated with anti-CD24. A simulated study by flowing microspheres coated with CD24 onto E-selectin-immobilized surfaces further revealed that the binding is Ca(2+)-dependent. Additionally, we have found that actin filaments are involved in the CD24-mediated cell rolling, as observed by the decreased rolling velocities of the MCF-7 cells upon treatment with cytochalasin D (an inhibitor of actin-filament dynamics) and the stationary binding of CD24-coated microspheres (the lack of actins) on the E-selectin-immobilized slides. Given that CD24 is known to be directly related to enhanced invasiveness of cancer cells, our results imply that CD24-based cell rolling on E-selectin mediates, at least partially, cancer cell extravasation, resulting in metastasis.

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.

E-selectin ligand-1 regulates growth plate homeostasis in mice by inhibiting the intracellular processing and secretion of mature TGF-beta

The majority of human skeletal dysplasias are caused by dysregulation of growth plate homeostasis. As TGF-beta signaling is a critical determinant of growth plate homeostasis, skeletal dysplasias are often associated with dysregulation of this pathway. The context-dependent action of TFG-beta signaling is tightly controlled by numerous mechanisms at the extracellular level and downstream of ligand-receptor interactions. However, TGF-beta is synthesized as an inactive precursor that is cleaved to become mature in the Golgi apparatus, and the regulation of this posttranslational intracellular processing and trafficking is much less defined. Here, we report that a cysteine-rich protein, E-selectin ligand-1 (ESL-1), acts as a negative regulator of TGF-beta production by binding TGF-beta precursors in the Golgi apparatus in a cell-autonomous fashion, inhibiting their maturation. Furthermore, ESL-1 inhibited the processing of proTGF-beta by a furin-like protease, leading to reduced secretion of mature TGF-beta by primary mouse chondrocytes and HEK293 cells. In vivo loss of Esl1 in mice led to increased TGF-beta/SMAD signaling in the growth plate that was associated with reduced chondrocyte proliferation and delayed terminal differentiation. Gain-of-function and rescue studies of the Xenopus ESL-1 ortholog in the context of early embryogenesis showed that this regulation of TGF-beta/Nodal signaling was evolutionarily conserved. This study identifies what we believe to be a novel intracellular mechanism for regulating TGF-beta during skeletal development and homeostasis.

Selectins promote tumor metastasis

Cancer metastasis is facilitated by cell-cell interactions between cancer cells and endothelial cells in distant tissues. In addition, cancer cell interactions with platelets and leukocytes contribute to cancer cell adhesion, extravasation, and the establishment of metastatic lesions. Selectins are carbohydrate-binding molecules that bind to sialylated, fucosylated glycan structures, and are found on endothelial cells, platelets and leukocytes. There are three members of the selectin family: P-selectin expressed on activated platelets and endothelial cells, L-selectin present on leukocytes and E-selectin expressed on activated endothelial cells. Besides the accepted roles of selectins in physiological processes, such as inflammation, immune response and hemostasis, there is accumulating evidence for the potential of selectins to contribute to a number of pathophysiological processes, including cancer metastasis. Cancer cell interactions with selectins are possible due to a frequent presence of carbohydrate determinants--selectin ligands on the cell surface of tumor cells from various type of cancer. The degree of selectin ligand expression by cancer cells is well correlated with metastasis and poor prognosis for cancer patients. Initial adhesion events of cancer cells facilitated by selectins result in activation of integrins, release of chemokines and are possibly associated with the formation of permissive metastatic microenvironment. While E-selectin has been evaluated as one of the initiating adhesion events during metastasis, it is becoming apparent that P-selectin and L-selectin-mediated interactions significantly contribute to this process as well. In this review we discuss the current evidence for selectins as potential facilitators of metastasis.