Alpha 2,3-sialyltransferase-IV is essential for L-selectin ligand function in inflammation

Protein glycosylation in cardiovascular health and disease

Protein glycosylation, which involves the attachment of carbohydrates to proteins, is one of the most abundant protein co-translational and post-translational modifications. Advances in technology have substantially increased our knowledge of the biosynthetic pathways involved in protein glycosylation, as well as how changes in glycosylation can affect cell function. In addition, our understanding of the role of protein glycosylation in disease processes is growing, particularly in the context of immune system function, infectious diseases, neurodegeneration and cancer. Several decades ago, cell surface glycoproteins were found to have an important role in regulating ion transport across the cardiac sarcolemma. However, with very few exceptions, our understanding of how changes in protein glycosylation influence cardiovascular (patho)physiology remains remarkably limited. Therefore, in this Review, we aim to provide an overview of N-linked and O-linked protein glycosylation, including intracellular O-linked N-acetylglucosamine protein modification. We discuss our current understanding of how all forms of protein glycosylation contribute to normal cardiovascular function and their roles in cardiovascular disease. Finally, we highlight potential gaps in our knowledge about the effects of protein glycosylation on the heart and vascular system, highlighting areas for future research.

The effects of glycosylation modifications on monocyte recruitment and foam cell formation in atherosclerosis

The monocyte recruitment and foam cell formation have been intensively investigated in atherosclerosis. Nevertheless, as the study progressed, it was obvious that crucial molecules participated in the monocyte recruitment and the membrane proteins in macrophages exhibited substantial glycosylation modifications. These modifications can exert a significant influence on protein functions and may even impact the overall progression of diseases. This article provides a review of the effects of glycosylation modifications on monocyte recruitment and foam cell formation. By elaborating on these effects, we aim to understand the underlying mechanisms of atherogenesis further and to provide new insights into the future treatment of atherosclerosis.

alpha2,3 sialic acid processing enzymes expression in gastric cancer tissues reveals that ST3Gal3 but not Neu3 are associated with Lauren's classification, angiolymphatic invasion and histological grade

Gastric cancer (GC) is one of the leading causes of cancer-related deaths worldwide. Despite progress in the last decades, there are still no reliable biomarkers for the diagnosis of and prognosis for GC. Aberrant sialylation is a widespread critical event in the development of GC. Neuraminidases (Neu) and sialyltransferases (STs) regulate the ablation and addition of sialic acid during glycoconjugates biosynthesis, and they are a considerable source of biomarkers in various cancers. This study retrospectively characterized Neu3 and ST3Gal3 expression by immunohistochemistry in 71 paraffin-embedded GC tissue specimens and analyzed the relationship between their expression and the clinicopathological parameters. Neu3 expression was markedly increased in GC tissues compared with non-tumoral tissues (p<0.0001). Intratumoral ST3Gal3 staining was significantly associated with intestinal subtype (p=0.0042) and was negatively associated with angiolymphatic invasion (p=0.0002) and higher histological grade G3 (p=0.0066). Multivariate analysis revealed that ST3Gal3 positivity is able to predict Lauren's classification. No associations were found between Neu3 staining and clinical parameters. The in silico analysis of mRNA expression in GC validation cohorts corroborates the significant ST3Gal3 association with higher histological grade observed in our study. These findings suggest that ST3Gal3 expression may be an indicator for aggressiveness of primary GC.

Neutrophils in acute inflammation: current concepts and translational implications

Modulation of neutrophil recruitment and function is crucial for targeting inflammatory cells to sites of infection to combat invading pathogens while, at the same time, limiting host tissue injury or autoimmunity. The underlying mechanisms regulating recruitment of neutrophils, 1 of the most abundant inflammatory cells, have gained increasing interest over the years. The previously described classical recruitment cascade of leukocytes has been extended to include capturing, rolling, adhesion, crawling, and transmigration, as well as a reverse-transmigration step that is crucial for balancing immune defense and control of remote organ endothelial leakage. Current developments in the field emphasize the importance of cellular interplay, tissue environmental cues, circadian rhythmicity, detection of neutrophil phenotypes, differential chemokine sensing, and contribution of distinct signaling components to receptor activation and integrin conformations. The use of therapeutics modulating neutrophil activation responses, as well as mutations causing dysfunctional neutrophil receptors and impaired signaling cascades, have been defined in translational animal models. Human correlates of such mutations result in increased susceptibility to infections or organ damage. This review focuses on current advances in the understanding of the regulation of neutrophil recruitment and functionality and translational implications of current discoveries in the field with a focus on acute inflammation and sepsis.

Lipoprotein sialylation in atherosclerosis: Lessons from mice

Sialylation is a dynamically regulated modification, which commonly occurs at the terminal of glycan chains in glycoproteins and glycolipids in eukaryotic cells. Sialylation plays a key role in a wide array of biological processes through the regulation of protein-protein interactions, intracellular localization, vesicular trafficking, and signal transduction. A majority of the proteins involved in lipoprotein metabolism and atherogenesis, such as apolipoproteins and lipoprotein receptors, are sialylated in their glycan structures. Earlier studies in humans and in preclinical models found a positive correlation between low sialylation of lipoproteins and atherosclerosis. More recent works using loss- and gain-of-function approaches in mice have revealed molecular and cellular mechanisms by which protein sialylation modulates causally the process of atherosclerosis. The purpose of this concise review is to summarize these findings in mouse models and to provide mechanistic insights into lipoprotein sialylation and atherosclerosis.

The sialyltransferase ST3Gal-IV guides murine T-cell progenitors to the thymus

T lymphocytes are important players in beneficial and detrimental immune responses. In contrast to other lymphocyte populations that develop in the bone marrow, T-cell precursors need to migrate to the thymus for further development. The interaction of P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1) is crucial for thymic entry of T-cell precursors during settings of T-cell lineage reconstitution. PSGL-1 has to be sialylated to function as a ligand for P-selectin, and the sialyltransferase ST3Gal-IV might play a critical role in this process. We therefore investigated the role of ST3Gal-IV for T-cell development using competitive mixed bone marrow chimeric mice. We found that ST3Gal-IV is dispensable for homing and engraftment of hematopoietic precursors in the bone marrow. However, ST3Gal-IV deficiency affects seeding of the thymus by early T-cell progenitors, leading to impaired restoration of the peripheral T-cell compartment. This defect could be restored by ectopic retroviral expression of ST3Gal-IV in hematopoietic stem cells derived from ST3Gal-IV-deficient donor mice. Our findings show that ST3Gal-IV plays a critical and nonredundant role for efficient T-cell lineage reconstitution after bone marrow transplantation.

Glycans and Glycan-Binding Proteins as Regulators and Potential Targets in Leukocyte Recruitment

Leukocyte recruitment is a highly controlled cascade of interactions between proteins expressed by the endothelium and circulating leukocytes. The involvement of glycans and glycan-binding proteins in the leukocyte recruitment cascade has been well-characterised. However, our understanding of these interactions and their regulation has expanded substantially in recent years to include novel lectins and regulatory pathways. In this review, we discuss the role of glycans and glycan-binding proteins, mediating the interactions between endothelium and leukocytes both directly and indirectly. We also highlight recent findings of key enzymes involved in glycosylation which affect leukocyte recruitment. Finally, we investigate the potential of glycans and glycan binding proteins as therapeutic targets to modulate leukocyte recruitment and transmigration in inflammation.

Leukocyte Trafficking and Hemostasis in the Mouse Fetus in vivo: A Practical Guide

In vivo observations of blood cells and organ compartments within the fetal mammalian organism are difficult to obtain. This practical guide describes a mouse model for in vivo observation of the fetal yolk-sac and corporal microvasculature throughout murine gestation, including imaging of various organ compartments, microvascular injection procedures, different methods for staining of blood plasma, vessel wall and circulating cell subsets. Following anesthesia of pregnant mice, the maternal abdominal cavity is opened, the uterus horn exteriorized, and the fetus prepared for imaging while still connected to the placenta. Microinjection methods allow delivery of substances directly into the fetal circulation, while substances crossing the placenta can be easily administered via the maternal circulation. Small volume blood sample collection allows for further in vitro workup of obtained results. The model permits observation of leukocyte-endothelial interactions, hematopoietic niche localization, platelet function, endothelial permeability studies, and hemodynamic changes in the mouse fetus, using appropriate strains of fluorescent protein expressing reporter mice and various sophisticated intravital microscopy techniques. Our practical guide is of interest to basic physiologists, developmental biologists, cardiologists, and translational neonatologists and reaches out to scientists focusing on the origin and regulation of hematopoietic niches, thrombopoiesis and macrophage heterogeneity.

Role of metaplasia during gastric regeneration

Spasmolytic polypeptide/trefoil factor 2 (TFF2)-expressing metaplasia (SPEM) is a mucous-secreting reparative lineage that emerges at the ulcer margin in response to gastric injury. Under conditions of chronic inflammation with parietal cell loss, SPEM has been found to emerge and evolve into neoplasia. Cluster-of-differentiation gene 44 (CD44) is known to coordinate normal and metaplastic epithelial cell proliferation. In particular, CD44 variant isoform 9 (CD44v9) associates with the cystine-glutamate transporter xCT, stabilizes the protein, and provides defense against reactive oxygen species (ROS). xCT stabilization by CD44v9 leads to defense against ROS by cystine uptake, glutathione (GSH) synthesis, and maintenance of the redox balance within the intracellular environment. Furthermore, p38 signaling is a known downstream ROS target, leading to diminished cell proliferation and migration, two vital processes of gastric epithelial repair. CD44v9 emerges during repair of the gastric epithelium after injury, where it is coexpressed with other markers of SPEM. The regulatory mechanisms for the emergence of CD44v9 and the role of CD44v9 during the process of gastric epithelial regeneration are largely unknown. Inflammation and M2 macrophage infiltration have recently been demonstrated to play key roles in the induction of SPEM after injury. The following review proposes new insights into the functional role of metaplasia in the process of gastric regeneration in response to ulceration. Our insights are extrapolated from documented studies reporting oxyntic atrophy and SPEM development and our current unpublished findings using the acetic acid-induced gastric injury model.

Expression of Bace1 is positive with the progress of atherosclerosis and formation of foam cell

Previous studies have shown that the occurrence of atherosclerosis is closely related to changes of α2, 6-sialic acid transferase I (ST6Gal-I). Bace1 has been identified as a protease responsible for the cleavage and secretion of Golgi-resident ST6Gal-I. There have been only a few attempts to clarify the direct connection between Bace1 and atherosclerosis. The purpose of this study was to investigate the relationship between Bace1 gene and atherosclerosis. Expressions of Bace1 protein and mRNA in ApoE^-/- mice fed on high-fat diet were evaluated and the development of atherosclerosis was assessed in Bace1^-/- mice fed on high-fat diet. In vitro, the expression of Bace1 gene was detected in foam cell model and the formation of foam cells was examined after knocking down Bace1 by siRNA. We observed a significant increase in Bace1 expression in the aortic root in the model of atherosclerosis in ApoE^-/-mice. The expression of Bace1 protein and mRNA levels had a remarkable increase in high-fat group. After knocking out the Bace1 gene, serum lipid levels were significantly lower and intimal thickness was obvious thinner than those in wild-type mice with high-fat diet. Expression of Bace1 protein and mRNA levels were significantly elevated in foam cell. The formation of foam cells was blocked when Bace1 was knocked down by siRNA interferes. Our results suggested that elevated Bace1 gene had a positive role in the progression of atherosclerosis. Affecting the glycosyltransferase may be one of its mechanisms.

Human T cell glycosylation and implications on immune therapy for cancer

Glycosylation is an important post-translational modification, giving rise to a diverse and abundant repertoire of glycans on the cell surface, collectively known as the glycome. When focusing on immunity, glycans are indispensable in virtually all signaling and cell-cell interactions. More specifically, glycans have been shown to regulate key pathophysiological steps within T cell biology such as T cell development, thymocyte selection, T cell activity and signaling as well as T cell differentiation and proliferation. They are of major importance in determining the interaction of human T cells with tumor cells. In this review, we will describe the role of glycosylation of human T cells in more depth, elaborate on the importance of glycosylation in the interaction of human T cells with tumor cells and discuss the potential of cancer immunotherapies that are based on manipulating the glycome functions at the tumor immune interface.^1,2

Carcinoembryonic antigen carrying SLeX as a new biomarker of more aggressive gastric carcinomas

Malignant transformation of gastric cells is accompanied by the deregulated expression of glycosyltransferases leading to the biosynthesis of tumor-associated glycans such as the sialyl-Lewis X antigen (SLe^x). SLe^x presence on cell surface glycoconjugates increases the invasive capacity of gastric cancer cells and is associated with tumor metastasis. ST3Gal IV enzyme is involved in the synthesis of SLe^x antigen and overexpressed in gastric carcinomas. Herein, we identified the glycoproteins carrying SLe^x in gastric cancer cells overexpressing ST3Gal IV enzyme and evaluated their biomarker potential for gastric carcinoma.

Methods: SLe^x modified glycoproteins were identified applying western blot and mass spectrometry. Immunoprecipitation, proximity ligation assay (PLA), E-selectin binding assay and CRISPR/cas9 knockout experiments were performed to characterize the presence of SLe^x on the identified glycoprotein. Protein N-glycans of the SLe^x protein carrier were in deep analyzed by porous-graphitized-carbon liquid-chromatography and tandem mass spectrometry glycomics. In silico expression analysis of α2-3 sialyltransferase ST3Gal IV and SLe^x protein carrier was performed and the conjoint expression of the SLe^x modified glycoproteins evaluated by immunohistochemistry and PLA in a series of gastric carcinomas.

Results: Carcinoembryonic antigen (CEA; CEACAM5) was identified and validated by different methodologies as a major carrier of SLe^x. N-glycomics of CEA revealed that complex N-glycans are capped with α2-3 linked sialic acid (Neu5Acα2-3Galβ1-4GlcNAc). Data set analysis of ST3Gal IV and CEA showed that ST3Gal IV expression was associated with patient´s poor survival, whereas CEA did not show any prognostic value. The co-expression of both CEA and SLe^X was observed in 86,3% of gastric carcinoma cases and 74,5% of the total cases displayed the conjoint CEA+SLe^xin situ PLA expression. This expression was associated with clinicopathological features of the tumors, including infiltrative pattern of tumor growth, presence of venous invasion and patient's poor survival. CEA immunoprecipitation from gastric carcinoma tissues also confirmed the presence of SLe^x.

Conclusion: CEA is the major glycoprotein carrying SLe^x in gastric carcinoma and the conjoint detection of CEA-SLe^x is associated with aggressive tumor features highlighting its PLA detection as a biomarker of gastric cancer patient prognosis for theranostic applications.

Lysophosphatidic acid decreased macrophage foam cell migration correlated with downregulation of fucosyltransferase 8 via HNF1α

BACKGROUND AND AIMS

Aberrant fucosylation, such as α-1,6 fucosylation catalyzed by fucosyltransferase 8 (Fut8), is associated with reduced cell migration and is responsible for cholesterol-enriched foam cell accumulation in the intima in the early stage of atherosclerosis. The current study evaluated the impact of glycosyltransferases on foam cell migration induced by lysophosphatidic acid (LPA) and its potential mechanism.

METHODS

The mobility of foam cells was evaluated via transwell and scratch assays. The expression of Fut8 and α-1,6 fucosylation of proteins were assessed by RT-PCR, Western blotting, etc. Overexpression of Fut8 was used to explore the direct relationship between Fut8 and foam cell migration. Dual luciferase reporter assay was performed to determine whether the regulation of Fut8 by LPA occurred at the transcriptional level. Binding of hepatocyte nuclear factor 1-alpha (HNF1α) to the Fut8 promoter was assessed by electrophoretic mobility shift assay and chromatin immunoprecipitation assay.

RESULTS

We found that the migration capacity of foam cells induced by LPA was significantly decreased. Fut8 and α-1,6 fucosylation showed the most obvious decline after treatment with 200 μM LPA for 24 h. Overexpression of Fut8 was able to restore the foam cell migration capacity. Another important finding was that the LPA₁ and LPA₃ (LPA_1,3) receptors were involved in the regulation of Fut8. It is interesting to note that LPA led to a decrease in Fut8 gene transcription activity, and HNF1α transcription factor played a positive role in downregulation of Fut8 promoter activity.

CONCLUSIONS

Our results strongly indicated that the LPA-LPA_{1, 3} receptor-HNF1α pathway is involved in the downregulation of Fut8, leading to diminished foam cell migration.

Dystrophin deficiency promotes leukocyte recruitment in mdx mice

BACKGROUND

A growing body of evidence defines inflammation as a hallmark feature of disease pathogenesis of Duchenne muscular dystrophy. To tailor potential immune modulatory interventions, a better understanding of immune dysregulation in Duchenne muscular dystrophy is needed. We now asked whether dystrophin deficiency affects the cascade of leukocyte recruitment.

METHODS

We performed intravital microscopy on the cremaster muscle of wild-type and dystrophin-deficient mdx mice. Recruitment was triggered by preparation alone (traumatic inflammation) or in combination with scrotal TNFα injections. Neutrophilic infiltration of the cremaster muscle was assessed on tissue sections. Integrin expression on circulating neutrophils and serum levels of pro-inflammatory cytokines were measured by flow cytometry.

RESULTS

Mdx mice show increased rolling and adhesion at baseline (traumatic inflammation) and a more profound response upon TNFα injection compared with wild-type animals. In both models, neutrophilic infiltration of the cremaster muscle is increased. Upregulation of the integrins LFA-1 and Mac-1 on circulating leukocytes and pro-inflammatory cytokines IL-6 and CCL2 in the serum points toward systemically altered immune regulation in mdx mice.

CONCLUSION

We are the first to show exaggerated activation of the leukocyte recruitment cascade in a dystrophin-deficient organism in vivo.

A Peptide Analogue of Selectin Ligands Attenuated Atherosclerosis by Inhibiting Monocyte Activation

Background

Circulating monocytes play a critical role in the pathogenesis of atherosclerosis. Monocyte homing to sites of atherosclerosis is primarily initiated by selectin. Thus, blockade of the interaction of selectins and their ligands holds a significant role in monocyte homing which might be a potential approach to treat atherosclerosis. Here, we investigated the efficacy of a novel peptide analogue of selectin ligands IELLQAR in atherosclerosis.

Methods and Results

In this study, we firstly measured the effect of the IELLQAR selectin-binding peptide on the inhibition of binding of selectins to monocytes by flow cytometry, which exhibited a dose-dependent inhibitory effect on the binding of the P-, E-, and L-selectins to monocytes, especially the inhibition of P-selectin binding to human peripheral blood monocytes (PBMCs) (half maximal inhibitory concentration (IC₅₀~5 μM)) and THP-1 cells (IC₅₀~10 μM). Furthermore, IELLQAR inhibited P-selectin-induced activation of CD11b on the surface of monocytes and decreased adhesion of monocytes to the endothelium. ApoE^-/- mice with or without IELLQAR (1 or 3 mg/kg) fed a Western-type diet (WTD) or which had disturbed blood flow-induced shear stress underwent partial left carotid artery ligation (PLCA) to induce atherosclerosis. In the WTD- and PLCA-induced atherosclerosis models, atherosclerotic plaque formation and monocyte/macrophage infiltration of the arterial wall both decreased in ApoE^-/- mice treated with the IELLQAR peptide. Our results also revealed that IELLQAR inhibited the differentiation of monocytes into macrophages through P-selectin-dependent activation of the nuclear factor- (NF-) κB and mammalian target of rapamycin (mTOR) pathways.

Conclusion

Collectively, our results demonstrated that IELLQAR, a peptide analogue of selectin ligands, inhibited selectin binding to monocytes, which led to subsequent attenuation of atherosclerosis via inhibition of monocyte activation. Hence, use of the IELLQAR peptide provides a new approach and represents a promising candidate for the treatment of atherosclerosis in the early stage of disease.

C/EBPδ drives interactions between human MAIT cells and endothelial cells that are important for extravasation

Many mediators and regulators of extravasation by bona fide human memory-phenotype T cells remain undefined. Mucosal-associated invariant T (MAIT) cells are innate-like, antibacterial cells that we found excelled at crossing inflamed endothelium. They displayed abundant selectin ligands, with high expression of FUT7 and ST3GAL4, and expressed CCR6, CCR5, and CCR2, which played non-redundant roles in trafficking on activated endothelial cells. MAIT cells selectively expressed CCAAT/enhancer-binding protein delta (C/EBPδ). Knockdown of C/EBPδ diminished expression of FUT7, ST3GAL4 and CCR6, decreasing MAIT cell rolling and arrest, and consequently the cells' ability to cross an endothelial monolayer in vitro and extravasate in mice. Nonetheless, knockdown of C/EBPδ did not affect CCR2, which was important for the step of transendothelial migration. Thus, MAIT cells demonstrate a program for extravasastion that includes, in part, C/EBPδ and C/EBPδ-regulated genes, and that could be used to enhance, or targeted to inhibit T cell recruitment into inflamed tissue.

Expression of Lewis-a glycans on polymorphonuclear leukocytes augments function by increasing transmigration

PMN-expressed fucosylated glycans from the Lewis glycan family, including Lewis-x (Le^x) and sialyl Lewis-x (sLe^x), have previously been implicated in the regulation of important PMN functions, including selectin-mediated trafficking across vascular endothelium. Although glycans, such as Le^x and sLe^x, which are based on the type 2 sequence (Galβ1-4GlcNAc-R), are abundant on PMNs, the presence of type 1 Galβ1-3GlcNAc-R glycans required for PMN expression of the closely related stereoisomer of Le^x, termed Lewis-A (Le^a), has not, to our knowledge, been reported. Here, we show that Le^a is abundantly expressed by human PMNs and functionally regulates PMN migration. Using mAbs whose precise epitopes were determined using glycan array technology, Le^a function was probed using Le^a-selective mAbs and lectins, revealing increased PMN transmigration across model intestinal epithelia, which was independent of epithelial-expressed Le^a Analyses of glycan synthetic machinery in PMNs revealed expression of β1-3 galactosyltransferase and α1-4 fucosyltransferase, which are required for Le^a synthesis. Specificity of functional effects observed after ligation of Le^a was confirmed by failure of anti-Le^a mAbs to enhance migration using PMNs from individuals deficient in α1-4 fucosylation. These results demonstrate that Le^a is expressed on human PMNs, and its specific engagement enhances PMN migration responses. We propose that PMN Le^a represents a new target for modulating inflammation and regulating intestinal, innate immunity.

TNF up-regulates ST3GAL4 and sialyl-Lewisx expression in lung epithelial cells through an intronic ATF2-responsive element

We have previously shown that tumor necrosis factor (TNF) induced the up-regulation of the sialyltransferase gene ST3GAL4 (α2,3-sialyltransferase gene) BX transcript through mitogen- and stress-activated kinase 1/2 (MSK1/2), extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) signaling pathways. This up-regulation resulted in sialyl-Lewis^x (sLe^x) overexpression on high-molecular-weight glycoproteins in inflamed airway epithelium and increased the adhesion of Pseudomonas aeruginosa PAO1 and PAK strains to lung epithelial cells. In the present study, we describe a TNF-responsive element in an intronic region of the ST3GAL4 gene, whose TNF-dependent activity is repressed by ERK/p38 and MSK1/2 inhibitors. This TNF-responsive element contains potential binding sites for ETS1 and ATF2 transcription factors related to TNF signaling. We also show that ATF2 is involved in TNF responsiveness, as well as in TNF-induced ST3GAL4 BX transcript and sLe^x overexpression in A549 lung epithelial cells. Moreover, we show that TNF induces the binding of ATF2 to the TNF-responsive element. Altogether, these data suggest that ATF2 could be a potential target to prevent inflammation-induced P. aeruginosa binding in the lung of patients suffering from lung diseases such as chronic bronchitis or cystic fibrosis.

Aberrant sialylation causes dilated cardiomyopathy and stress-induced heart failure

Dilated cardiomyopathy (DCM), the third most common cause of heart failure, is often associated with arrhythmias and sudden cardiac death if not controlled. The majority of DCM is of unknown etiology. Protein sialylation is altered in human DCM, with responsible mechanisms not yet described. Here we sought to investigate the impact of clinically relevant changes in sialylation on cardiac function using a novel model for altered glycoprotein sialylation that leads to DCM and to chronic stress-induced heart failure (HF), deletion of the sialyltransferase, ST3Gal4. We previously reported that 12- to 20-week-old ST3Gal4 (-/-) mice showed aberrant cardiac voltage-gated ion channel sialylation and gating that contribute to a pro-arrhythmogenic phenotype. Here, echocardiography supported by histology revealed modest dilated and thinner-walled left ventricles without increased fibrosis in ST3Gal4 (-/-) mice starting at 1 year of age. Cardiac calcineurin expression in younger (16-20 weeks old) ST3Gal4 (-/-) hearts was significantly reduced compared to WT. Transverse aortic constriction (TAC) was used as a chronic stressor on the younger mice to determine whether the ability to compensate against a pathologic insult is compromised in the ST3Gal4 (-/-) heart, as suggested by previous reports describing the functional implications of reduced cardiac calcineurin levels. TAC'd ST3Gal4 (-/-) mice presented with significantly reduced systolic function and ventricular dilation that deteriorated into congestive HF within 6 weeks post-surgery, while constricted WT hearts remained well-adapted throughout (ejection fraction, ST3Gal4 (-/-) = 34 ± 5.2 %; WT = 53.8 ± 7.4 %; p < 0.05). Thus, a novel, sialo-dependent model for DCM/HF is described in which clinically relevant reduced sialylation results in increased arrhythmogenicity and reduced cardiac calcineurin levels that precede cardiomyopathy and TAC-induced HF, suggesting a causal link among aberrant sialylation, chronic arrhythmia, reduced calcineurin levels, DCM in the absence of a pathologic stimulus, and stress-induced HF.

Sphingosine-1-phosphate receptor 3 promotes leukocyte rolling by mobilizing endothelial P-selectin

Sphingosine-1-phosphate (S1P) participates in inflammation; however, its role in leukocyte rolling is still unclear. Here we use intravital microscopy in inflamed mouse cremaster muscle venules and human endothelial cells to show that S1P contributes to P-selectin-dependent leukocyte rolling through endothelial S1P receptor 3 (S1P₃) and Gα_q, PLCβ and Ca²⁺. Intra-arterial S1P administration increases leukocyte rolling, while S1P₃ deficiency or inhibition dramatically reduces it. Mast cells involved in triggering rolling also release S1P that mobilizes P-selectin through S1P₃. Histamine and epinephrine require S1P₃ for full-scale effect accomplishing it by stimulating sphingosine kinase 1 (Sphk1). In a counter-regulatory manner, S1P₁ inhibits cAMP-stimulated Sphk1 and blocks rolling as observed in endothelial-specific S1P₁^−/− mice. In agreement with a dominant pro-rolling effect of S1P₃, FTY720 inhibits rolling in control and S1P₁^−/− but not in S1P₃^−/− mice. Our findings identify S1P as a direct and indirect contributor to leukocyte rolling and characterize the receptors mediating its action.

The lipid sphingosine-1-phosphate (S1P) is known to mediate leukocyte recruitment in inflammation. Here, Nussbaum et al. show that S1P, via its receptor S1P3, also regulates leukocyte rolling on endothelium by promoting the presentation of the adhesion molecule P-selectin on the endothelial surface.

The cancer glycome: carbohydrates as mediators of metastasis

Glycosylation is a frequent post-translational modification which results in the addition of carbohydrate determinants, "glycans", to cell surface proteins and lipids. These glycan structures form the "glycome" and play an integral role in cell-cell and cell-matrix interactions through modulation of adhesion and cell trafficking. Glycosylation is increasingly recognized as a modulator of the malignant phenotype of cancer cells, where the interaction between cells and the tumor micro-environment is altered to facilitate processes such as drug resistance and metastasis. Changes in glycosylation of cell surface adhesion molecules such as selectin ligands, integrins and mucins have been implicated in the pathogenesis of several solid and hematological malignancies, often with prognostic implications. In this review we focus on the functional significance of alterations in cancer cell glycosylation, in terms of cell adhesion, trafficking and the metastatic cascade and provide insights into the prognostic and therapeutic implications of recent findings in this fast-evolving niche.

ST3Gal-4 is the primary sialyltransferase regulating the synthesis of E-, P-, and L-selectin ligands on human myeloid leukocytes

The precise glycosyltransferase enzymes that mediate selectin-ligand biosynthesis in human leukocytes are unknown. This knowledge is important because selectin-mediated cell tethering and rolling is a critical component of both normal immune response and various vascular disorders. We evaluated the role of 3 α(2,3)sialyltransferases, ST3Gal-3, -4, and -6, which act on the type II N-Acetyllactosamine structure (Galβ1,4GlcNAc) to create sialyl Lewis-X (sLe(X)) and related sialofucosylated glycans on human leukocytes of myeloid lineage. These genes were either silenced using lentiviral short hairpin RNA (shRNA) or functionally ablated using the clustered regularly interspaced short palindromic repeat/Cas9 technology. The results show that ST3Gal-4, but not ST3Gal-3 or -6, is the major sialyltransferase regulating the biosynthesis of E-, P-, and L-selectin ligands in humans. Reduction in ST3Gal-4 activity lowered cell-surface HECA-452 epitope expression by 75% to 95%. Glycomics profiling of knockouts demonstrate an almost complete loss of the sLe(X) epitope on both leukocyte N- and O-glycans. In cell-adhesion studies, ST3Gal-4 knockdown/knockout cells displayed 90% to 100% reduction in tethering and rolling density on all selectins. ST3Gal-4 silencing in neutrophils derived from human CD34(+) hematopoietic stem cells also resulted in 80% to 90% reduction in cell adhesion to all selectins. Overall, a single sialyltransferase regulates selectin-ligand biosynthesis in human leukocytes, unlike mice where multiple enzymes contribute to this function.

Glycosyltransferases, glycosylation and atherosclerosis

Cardiovascular diseases arising from atherosclerosis are currently the leading cause of mortality worldwide. Leukocyte recruitment is a key step for the successful initiation of atherosclerosis and occurs predominantly in the inflamed endothelium. Leukocyte recruitment is mediated by a group of adhesive molecules and chemokine receptors, which are often glycosylated protein. Recent studies demonstrated that post-translational glycosylation by glycosyltransferases is necessary for adhesive molecules and chemokine receptors activities. Several glycosyltransferases, such as α2,3-sialyltransferases IV, α1,3-fucosyltransferases IV and VII, core 2 β1,6-N-acetylglucosaminyltransferase-I, are considered to participate in the synthesis of glycosylation for adhesive molecules and chemokine receptors, and the initiation of atherosclerotic lesions. In this review, we will discuss new data concerning the roles of different glycosyltransferases in atherogenesis. The knowledge of glycosyltransferases in atherogenesis offers the opportunity to develop novel therapeutic strategies.

Deficiency of the sialyltransferase St3Gal4 reduces Ccl5-mediated myeloid cell recruitment and arrest: short communication

RATIONALE

Sialylation by α2,3-sialyltransferases has been shown to be a crucial glycosylation step in the generation of functional selectin ligands. Recent evidence suggests that sialylation also affects the binding of chemokines to their corresponding receptor.

OBJECTIVE

Because the chemokine receptors for Ccl5 and Ccl2 are important in atherogenic recruitment of neutrophils and monocytes, we here investigated the role of α2,3-sialyltransferase IV (ST3Gal-IV) in Ccl5- and Ccl2-mediated myeloid cell arrest and further studied its relevance in a mouse model of atherosclerosis.

METHODS AND RESULTS

St3Gal4-deficient myeloid cells showed a reduced binding of Ccl5 and an impaired Ccl5-triggered integrin activation. Correspondingly, Ccl5-induced arrest on tumor necrosis factor-α-stimulated endothelium was almost completely abrogated, as observed in flow chamber adhesion assays and during ex vivo perfusion or intravital microscopy of carotid arteries. Moreover, Ccl5-triggered neutrophil and monocyte extravasation into the peritoneal cavity was severely reduced in St3Gal4(-/-) mice. In contrast, St3Gal4 deficiency did not significantly affect Ccl2 binding and only marginally decreased Ccl2-induced flow arrest of myeloid cells. In agreement with the crucial role of leukocyte accumulation in atherogenesis, and the importance of Ccl5 chemokine receptors mediating myeloid cell recruitment to atherosclerotic vessels, St3Gal4 deficiency drastically reduced the size, stage, and inflammatory cell content of atherosclerotic lesions in Apoe(-/-) mice on high-fat diet.

CONCLUSIONS

In summary, these findings identify ST3Gal-IV as a promising target to reduce inflammatory leukocyte recruitment and arrest.

p85-RhoGDI2, a novel complex, is required for PSGL-1-induced β1 integrin-mediated lymphocyte adhesion to VCAM-1

P-selectin glycoprotein ligand-1 and β1 integrin play essential roles in T cell trafficking during inflammation. E-selectin and vascular cell adhesion molecule-1 are their ligands expressed on inflammation-activated endothelium. During the tethering and rolling of lymphocytes on endothelium, P-selectin glycoprotein ligand-1 binds E-selectin and induces signals. Subsequently, β1 integrin is activated and mediates stable adhesion. However, the intracellular signal pathways from PSGL-1 to β1 integrin have not yet been fully understood. Here, we find that p85, a regulatory subunit of phosphoinositide 3-kinase, forms a novel complex with Rho-GDP dissociation inhibitor-2, a lymphocyte-specific RhoGTPases dissociation inhibitor. Phosporylations of the p85-bound Rho-GDP dissociation inhibitor-2 on 130 and 153 tyrosine residues by c-Abl and Src were required for the complex to be recruited to P-selectin glycoprotein ligand-1 and thereby regulate β1 integrin-mediated T cell adhesion to vascular cell adhesion molecule-1. Both shRNAs to Rho-GDP dissociation inhibitor-2 and p85 and over-expression of Rho-GDP dissociation inhibitor-2 Y130F and Y153F significantly reduced the above-mentioned adhesion. Although Rho-GDP dissociation inhibitor-2 in the p85-Rho-GDP dissociation inhibitor-2 complex was also phosphorylated on 24 tyrosine residue by Syk, the phosphorylation is not required for the adhesion. Taken together, we find that specific phosphorylations on 130 and 153 tyrosine residues of p85-bound Rho-GDP dissociation inhibitor-2 are pivotal for P-selectin glycoprotein ligand-1-induced β1 integrin-mediated lymphocyte adhesion to vascular cell adhesion molecule-1. This will shed new light on the mechanisms that connect leukocyte initial rolling with subsequent adhesion.

Expression of ST3GAL4 leads to SLe(x) expression and induces c-Met activation and an invasive phenotype in gastric carcinoma cells

Sialyl-Lewis X (SLe(x)) is a sialylated glycan antigen expressed on the cell surface during malignant cell transformation and is associated with cancer progression and poor prognosis. The increased expression of sialylated glycans is associated with alterations in the expression of sialyltransferases (STs). In this study we determined the capacity of ST3GAL3 and ST3GAL4 sialyltransferases to synthesize the SLe(x) antigen in MKN45 gastric carcinoma cells and evaluated the effect of SLe(x) overexpression in cancer cell behavior both in vitro and in vivo using the chicken chorioallantoic membrane (CAM) model. The activation of tyrosine kinase receptors and their downstream molecular targets was also addressed. Our results showed that the expression of ST3GAL4 in MKN45 gastric cancer cells leads to the synthesis of SLe(x) antigens and to an increased invasive phenotype both in vitro and in the in vivo CAM model. Analysis of phosphorylation of tyrosine kinase receptors showed a specific increase in c-Met activation. The characterization of downstream molecular targets of c-Met activation, involved in the invasive phenotype, revealed increased phosphorylation of FAK and Src proteins and activation of Cdc42, Rac1 and RhoA GTPases. Inhibition of c-Met and Src activation abolished the observed increased cell invasive phenotype. In conclusion, the expression of ST3GAL4 leads to SLe(x) antigen expression in gastric cancer cells which in turn induces an increased invasive phenotype through the activation of c-Met, in association with Src, FAK and Cdc42, Rac1 and RhoA GTPases activation.

Expression of the sialyltransferase, ST3Gal4, impacts cardiac voltage-gated sodium channel activity, refractory period and ventricular conduction

The sequential glycosylation process typically ends with sialic acid residues added through trans-Golgi sialyltransferase activity. Individuals afflicted with congenital disorders of glycosylation often have reduced glycoprotein sialylation and present with multi-system symptoms including hypotonia, seizures, arrhythmia and cardiomyopathy. Cardiac voltage-gated Na(+) channel (Nav) activity can be influenced by sialic acids likely contributing to an external surface potential causing channels to gate at less depolarized voltages. Here, a possible pathophysiological role for reduced sialylation is investigated by questioning the impact of gene deletion of the uniformly expressed beta-galactoside alpha-2,3-sialyltransferase 4 (ST3Gal4) on cardiac Nav activity, cellular refractory period and ventricular conduction. Whole-cell patch-clamp experiments showed that ventricular Nav from ST3Gal4 deficient mice (ST3Gal4(-/-)) gated at more depolarized potentials, inactivated more slowly and recovered from fast inactivation more rapidly than WT controls. Current-clamp recordings indicated a 20% increase in time to action potential peak and a 30ms decrease in ST3Gal4(-/-) myocyte refractory period, concurrent with increased Nav recovery rate. Nav expression, distribution and maximal Na(+) current levels were unaffected by ST3Gal4 expression, indicating that reduced sialylation does not impact Nav surface expression and distribution. However, enzymatic desialylation suggested that ST3Gal4(-/-) ventricular Nav are less sialylated. Consistent with the shortened myocyte refractory period, epicardial conduction experiments using optical mapping techniques demonstrated a 27% reduction in minimum ventricular refractory period and increased susceptibility to arrhythmias in ST3Gal4(-/-) ventricles. Thus, deletion of a single sialyltransferase significantly impacts ventricular myocyte electrical signaling. These studies offer insight into diseases of glycosylation that are often associated with pathological changes in excitability and highlight the importance of glycosylation in cardiac physiology.

Endothelial heterogeneity and adhesion molecules N-glycosylation: implications in leukocyte trafficking in inflammation

Inflammation is a major contributing element to a host of diseases with the interaction between leukocytes and the endothelium being key in this process. Much is understood about the nature of the adhesion molecule proteins expressed on any given leukocyte and endothelial cell that modulates adhesive interactions. Although it is appreciated that these proteins are heavily glycosylated, relatively little is known about the roles of these posttranslational modifications and whether they are regulated, and if so how during inflammation. Herein, we suggest that a paucity in this understanding is one major reason for the lack of successful therapies to date for modulating leukocyte-endothelial interactions in human inflammatory disease and discuss developing paradigms of (i) how endothelial adhesion molecule glycosylation (with a focus on N-glycosylation) maybe a critical element in understanding endothelial heterogeneity between different vascular beds and species, (ii) how adhesion molecule N-glycosylation may be under distinct, and as yet, unknown modes of regulation during inflammatory stress to affect the inflammatory response in a vascular bed- and disease-specific manner (analogous to a "zip code" for inflammation) and finally (iii) to underscore the concept that a fuller appreciation of the role of adhesion molecule glycoforms is needed to provide foundations for disease and tissue-specific targeting of inflammation.

Extracellular RNA promotes leukocyte recruitment in the vascular system by mobilising proinflammatory cytokines

Extracellular RNA (eRNA), released from cells under conditions of injury or vascular disease, acts as potent prothrombotic factor and promotes vascular hyperpermeability related to oedema formation in vivo. In this study, we aimed to investigate the mechanism by which eRNA triggers inflammatory processes, particularly associated with different steps of leukocyte recruitment. Using intravital microscopy of murine cremaster muscle venules, eRNA (but not DNA) significantly induced leukocyte adhesion and transmigration in vivo, which was comparable in its effects to the function of tumour-necrosis-factor-α (TNF-α). In vitro, eRNA promoted adhesion and transmigration of monocytic cells on and across endothelial cell monolayers. eRNA-induced monocyte adhesion in vitro was mediated by activation of the vascular endothelial growth factor (VEGF)/VEGF-receptor-2 system and was abolished by neutralising antibodies against intercellular adhesion molecule-1 or the β2-integrin Mac-1. Additionally, eRNA induced the release of TNF-α from monocytic cells in a time- and concentration-dependent manner, which involved activation of TNF-α-converting enzyme (TACE) as well as the nuclear factor κB signalling machinery. In vivo, inhibiton of TACE significantly reduced eRNA-induced leukocyte adhesion. Our findings present evidence that eRNA in connection with tissue/vascular damage provokes a potent inflammatory response by inducing leukocyte recruitment and by mobilising proinflammatory cytokines from monocytes.

Coordinated roles of ST3Gal-VI and ST3Gal-IV sialyltransferases in the synthesis of selectin ligands

Binding of selectins to their glycan ligands is a prerequisite for successful leukocyte trafficking. During synthesis and transport through the secretory pathway, selectin ligands are constructed with the participation of one or more sialyltransferases of the ST3Gal subfamily. Previous studies established that ST3Gal-IV only partially contributes to selectin ligand formation, indicating that other ST3Gal-sialyltransferases are involved. By generating and analyzing St3gal6-null mice and St3gal4/St3gal6 double-deficient mice, in the present study, we found that binding of E- and P-selectin to neutrophils and L-selectin binding to lymph node high endothelial venules is reduced in the absence of ST3Gal-VI and to a greater extent in double-deficient mice. In an ex vivo flow chamber assay, P- and E-selectin-dependent leukocyte rolling was mildly reduced in St3gal6-null mice and more severely in double-deficient mice. In inflamed cremaster muscle venules of St3gal6-null mice, we found impaired P-selectin-dependent, but not E-selectin-dependent leukocyte rolling, whereas in double-deficient mice, E-selectin-dependent rolling was almost completely absent. Furthermore, neutrophil recruitment into the inflamed peritoneal cavity and lymphocyte homing to secondary lymphoid organs were impaired in St3gal6-null mice and more severely in double-deficient mice. The results of the present study demonstrate the coordinated participation of both ST3Gal-VI and ST3Gal-IV in the synthesis of functional selectin ligands.

TNF regulates sialyl-Lewisx and 6-sulfo-sialyl-Lewisx expression in human lung through up-regulation of ST3GAL4 transcript isoform BX

Bronchial mucins from severely infected patients suffering from lung diseases such as chronic bronchitis or cystic fibrosis exhibit increased amounts of sialyl-Lewis(x) (NeuAcα2-3Galβ1-4[Fucα1-3]GlcNAc-R, sLe(x)) glycan structures. In cystic fibrosis, sLe(x) and its sulfated form 6-sulfo-sialyl-Lewis(x) (NeuAcα2-3Galβ1-4[Fucα1-3](HO(3)S-6)GlcNAc-R, 6-sulfo-sLe(x)) serve as receptors for Pseudomonas aeruginosa and are involved in the chronicity of airway infection. However, little is known about the molecular mechanisms regulating the changes in glycosylation and sulfation of mucins in airways. Herein, we show that the pro-inflammatory cytokine TNF increases the expression of α2,3-sialyltransferase gene ST3GAL4, both in human bronchial mucosa and in A549 lung carcinoma cells. The role of sialyltransferase ST3Gal IV in sLe(x) biosynthesis was confirmed by siRNA silencing of ST3GAL4 gene. BX is the major transcript isoform expressed in healthy bronchial mucosa and in A549 cells, and is up-regulated by TNF in both models. Bioinformatics analysis and luciferase assays have confirmed that the 2 kb genomic sequence surrounding BX exon contains a promoter region regulated by TNF-related transcription factors. These results support further work aiming at the development of anti-inflammatory strategy to reduce chronic airway infection in diseases such as cystic fibrosis.

The role of milk sialyllactose in intestinal bacterial colonization

Milk oligosaccharides influence the composition of intestinal microbiota and thereby mucosal inflammation. Some of the major milk oligosaccharides are α2,3-sialyllactose (3SL) and α2,6-sialyllactose, which are mainly produced by the sialyltransferases ST3GAL4 and ST6GAL1, respectively. Recently, we showed that mice fed milk deficient in 3SL were more resistant to dextran sulfate sodium-induced colitis. By contrast, the exposure to milk containing or deficient in 3SL had no impact on the development of mucosal leukocyte populations. Milk 3SL mainly affected the colonization of the intestine by clostridial cluster IV bacteria.

The expanding role of α2-3 sialylation for leukocyte trafficking in vivo

The ability of leukocytes to navigate through the different body compartments is an essential component for functioning immune defense and surveillance systems. In order to exit the blood circulation, leukocytes follow distinct recruitment steps, including capture of free-flowing leukocytes to, and rolling along, the vessel wall; firm leukocyte arrest on the endothelial lining; and postarrest modifications (spreading and crawling), which prepare the leukocyte for transmigration through the vascular wall. Post-translational glycosylation (including sialylation) has been known for many years to be functionally relevant for selectin ligands and, hence, selectin-mediated capture and rolling. Recently, sialylation by the α2-3 sialyltransferase ST3Gal-IV was identified to significantly influence chemokine-triggered firm leukocyte arrest, expanding the role of α2-3 sialylation from leukocyte rolling to subsequent chemokine-triggered leukocyte arrest. These findings make ST3Gal-IV an interesting drug target for modulating leukocyte trafficking in human disorders, including autoimmune diseases and cancer.

The GTPase-activating protein ARAP3 regulates chemotaxis and adhesion-dependent processes in neutrophils

Neutrophils form a vital part of the innate immune response, but at the same time their inappropriate activation contributes to autoimmune diseases. Many molecular components are involved in fine-tuning neutrophil function. We report here the first characterization of the role of ARAP3, a PI3K and Rap-regulated GTPase-activating protein for RhoA and Arf6 in murine neutrophils. We show that neutrophils lacking ARAP3 are preactivated in vitro and in vivo, exhibiting increased β2 integrin affinity and avidity. ARAP3-deficient neutrophils are hyperresponsive in several adhesion-dependent situations in vitro, including the formation of reactive oxygen species, adhesion, spreading, and granule release. ARAP3-deficient cells adhere more firmly under flow conditions in vitro and to the vessel wall in vivo. Finally, loss of ARAP3 interferes with integrin-dependent neutrophil chemotaxis. The results of the present study suggest an important function of ARAP3 downstream of Rap. By modulating β2 integrin activity, ARAP3 guards neutrophils in their quiescent state unless activated.

Myeloperoxidase attracts neutrophils by physical forces

Recruitment of polymorphonuclear neutrophils (PMNs) remains a paramount prerequisite in innate immune defense and a critical cofounder in inflammatory vascular disease. Neutrophil recruitment comprises a cascade of concerted events allowing for capture, adhesion and extravasation of the leukocyte. Whereas PMN rolling, binding, and diapedesis are well characterized, receptor-mediated processes, mechanisms attenuating the electrostatic repulsion between the negatively charged glycocalyx of leukocyte and endothelium remain poorly understood. We provide evidence for myeloperoxidase (MPO), an abundant PMN-derived heme protein, facilitating PMN recruitment by its positive surface charge. In vitro, MPO evoked highly directed PMN motility, which was solely dependent on electrostatic interactions with the leukocyte's surface. In vivo, PMN recruitment was shown to be MPO-dependent in a model of hepatic ischemia and reperfusion, upon intraportal delivery of MPO and in the cremaster muscle exposed to local inflammation or to intraarterial MPO application. Given MPO's affinity to both the endothelial and the leukocyte's surface, MPO evolves as a mediator of PMN recruitment because of its positive surface charge. This electrostatic MPO effect not only displays a so far unrecognized, catalysis-independent function of the enzyme, but also highlights a principal mechanism of PMN attraction driven by physical forces.

RAGE and ICAM-1 cooperate in mediating leukocyte recruitment during acute inflammation in vivo

The receptor for advanced glycation end products (RAGE) contributes to the inflammatory response in many acute and chronic diseases. In this context, RAGE has been identified as a ligand for the beta(2)-integrin Mac-1 under static in vitro conditions. Because intercellular adhesion molecule (ICAM)-1 also binds beta(2)-integrins, we studied RAGE(-/-), Icam1(-/-), and RAGE(-/-) Icam1(-/-) mice to define the relative contribution of each ligand for leukocyte adhesion in vivo. We show that trauma-induced leukocyte adhesion in cremaster muscle venules is strongly dependent on RAGE and ICAM-1 acting together in an overlapping fashion. Additional in vivo experiments in chimeric mice lacking endothelium-expressed RAGE and ICAM-1 located the adhesion defect to the endothelial compartment. Using microflow chambers coated with P-selectin, CXCL1, and soluble RAGE (sRAGE) demonstrated that sRAGE supports leukocyte adhesion under flow conditions in a Mac-1- but not LFA-1-dependent fashion. A static adhesion assay revealed that wild-type and RAGE(-/-) neutrophil adhesion and spreading were similar on immobilized sRAGE or fibrinogen. These observations indicate a crucial role of endothelium-expressed RAGE as Mac-1 ligand and uncover RAGE and ICAM-1 as a new set of functionally linked adhesion molecules, which closely cooperate in mediating leukocyte adhesion during the acute trauma-induced inflammatory response in vivo.

Human beta-galactoside alpha-2,3-sialyltransferase (ST3Gal III) attenuated Taxol-induced apoptosis in ovarian cancer cells by downregulating caspase-8 activity

Taxol triggers apoptosis in a variety of cancer cells, but it also upregulates cytoprotective proteins and/or pathways that compromise its therapeutic efficacy. In this report, we found that Taxol treatment resulted in caspase-8-dependent apoptosis in SKOV3 human ovarian cancer cells. Moreover, Taxol-induced apoptosis was associated with caspase-3 activation. Interestingly, Taxol treatment upregulated alpha-2,3-sialyltransferase (ST3Gal III) expression and forced expression of ST3Gal III attenuated Taxol-induced apoptosis. Furthermore, ST3Gal III overexpression inhibited Taxol-triggered caspase-8 activation, indicating that ST3Gal III upregulation produces cellular resistance to Taxol and hence reduces the efficacy of Taxol therapy.

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.

PSGL-1 function in immunity and steady state homeostasis

The substantial importance of P-selectin glycoprotein ligand 1 (PSGL-1) in leukocyte trafficking has continued to emerge beyond its initial identification as a selectin ligand. PSGL-1 seemed to be a relatively simple molecule with an extracellular mucin domain extended as a flexible rod, teleologically consistent with its primary role in tethering leukocytes to endothelial selectins. The rolling interaction between leukocyte and endothelium mediated by this selectin-PSGL-1 interaction requires branched O-glycan extensions on specific PSGL-1 amino acid residues. In some cells, such as neutrophils, the glycosyltransferases involved in formation of the O-glycans are constitutively expressed, while in other cells, such as T cells, they are expressed only after appropriate activation. Thus, PSGL-1 supports leukocyte recruitment in both innate and adaptive arms of the immune response. A complex array of amino acids within the selectins engage multiple sugar residues of the branched O-glycans on PSGL-1 and provide the molecular interactions responsible for the velcro-like catch bonds that support leukocyte rolling. Such binding of PSGL-1 can also induce signaling events that influence cell phenotype and function. Scrutiny of PSGL-1 has revealed a better understanding of how it performs as a selectin ligand and yielded unexpected insights that extend its scope from supporting leukocyte rolling in inflammatory settings to homeostasis including stem cell homing to the thymus and mature T-cell homing to secondary lymphoid organs. PSGL-1 has been found to bind homeostatic chemokines CCL19 and CCL21 and to support the chemotactic response to these chemokines. Surprisingly, the O-glycan modifications of PSGL-1 that support rolling mediated by selectins in inflammatory conditions interfere with PSGL-1 binding to homeostatic chemokines and thereby limit responsiveness to the chemotactic cues used in steady state T-cell traffic. The multi-level influence of PSGL-1 on cell traffic in both inflammatory and steady state settings is therefore substantially determined by the orchestrated addition of O-glycans. However, central as specific O-glycosylation is to PSGL-1 function, in vivo regulation of PSGL-1 glycosylation in T cells remains poorly understood. It is our purpose herein to review what is known, and not known, of PSGL-1 glycosylation and to update understanding of PSGL-1 functional scope.

Mammalian glycosylation in immunity

Glycosylation produces a diverse and abundant repertoire of glycans, which are collectively known as the glycome. Glycans are one of the four fundamental macromolecular components of all cells, and are highly regulated in the immune system. Their diversity reflects their multiple biological functions that encompass ligands for proteinaceous receptors known as lectins. Since the discovery that selectins and their glycan ligands are important for the regulation of leukocyte trafficking, it has been shown that additional features of the vertebrate immune system are also controlled by endogenous cellular glycosylation. This Review focuses on the emerging immunological roles of the mammalian glycome.

Systems-level studies of glycosyltransferase gene expression and enzyme activity that are associated with the selectin binding function of human leukocytes

The application of systems biology methods in the emerging field of glycomics requires the collection and integration of glycosyltransferase data at the gene and enzyme level for the purpose of hypothesis generation. We systematically examined the relationship between gene expression, glycosyltransferase activity, glycan expression, and selectin-binding function in different systems, including human neutrophils, undifferentiated HL-60 (human promyelocytic cells), differentiated HL-60, and HL-60 synchronized in specific growth phases. Results demonstrate that 1) the sLe(X) (sialyl-Lewis-X) epitope is expressed in P-selectin glycoprotein ligand-1 (PSGL-1) from neutrophils at higher levels compared with HL-60. This variation may be due to differences in the relative activities of alpha1,3-fucosyltransferases and alpha2,3-sialyltransferases in these two cell types. 2) HL-60 cell differentiation along granulocyte lineage increased the activity of beta1,4GalT and beta1,3GlcNAcT by 1.6- to 3.2-fold. This may contribute to LacNAc chain extension as evidenced by the 1.7-fold increase in DSA-lectin (lectin recognizing LacNAc) binding to cells after differentiation. 3) The activity of enzymes contributing to sLe(X) formation in leukocytes likely varies as ST3[Galbeta1,4GlcNAc] < or = alpha1,3FT[sialyl-LacNAc] < beta1,3GlcNAcT. 4) O-glycan specific glycosyltransferase activity does not undergo periodic variation with cell cycle phases. Overall, gene expression and enzyme activity data combined with knowledge of biochemistry can predict the resulting glycan structures and yield viable experimentally testable hypothesis.

Nepmucin/CLM-9, an Ig domain-containing sialomucin in vascular endothelial cells, promotes lymphocyte transendothelial migration in vitro

Nepmucin/CLM-9 is an Ig domain-containing sialomucin expressed in vascular endothelial cells. Here we show that, like CD31, nepmucin was localized to interendothelial contacts and to vesicle-like structures along the cell border and underwent intracellular recycling. Functional analyses showed that nepmucin mediated homotypic and heterotypic cell adhesion via its Ig domain. Nepmucin-expressing endothelial cells showed enhanced lymphocyte transendothelial migration (TEM), which was abrogated by anti-nepmucin mAbs that block either homophilic or heterophilic binding. Notably, the mAbs that inhibited homophilic binding blocked TEM without affecting lymphocyte adhesion. These results suggest that endothelial nepmucin promotes lymphocyte TEM using multiple adhesion pathways.

VEGF expression by mesenchymal stem cells contributes to angiogenesis in pancreatic carcinoma

Little is known about the factors that enable the mobilisation of human mesenchymal stem cells (MSC) from the bone marrow into the blood stream and their recruitment to and retention in the tumour. We found specific migration of MSC towards growth factors present in pancreatic tumours, such as PDGF, EGF, VEGF and specific inhibitors Glivec, Erbitux and Avastin interfered with migration. Within a few hours, MSC migrated into spheroids consisting of pancreatic cancer cells, fibroblasts and endothelial cells as measured by time-lapse microscopy. Supernatant from subconfluent MSC increased sprouting of HUVEC due to VEGF production by MSC itself as demonstrated by RT-PCR and ELISA. Only few MSCs were differentiated into endothelial cells in vitro, whereas in vivo differentiation was not observed. Lentiviral GFP-marked MSCs, injected in nude mice xenografted with orthotopic pancreatic tumours, preferentially migrated into the tumours as observed by FACS analysis of green fluorescent cells. By immunofluorescence and intravital microscopic studies, we found the interaction of MSC with the endothelium of blood vessels. Mesenchymal stem cells supported tumour angiogenesis in vivo, that is CD31⁺ vessel density was increased after the transfer of MSC compared with siVEGF-MSC. Our data demonstrate the migration of MSC toward tumour vessels and suggest a supportive role in angiogenesis.

Leukocyte trafficking in a mouse model for leukocyte adhesion deficiency II/congenital disorder of glycosylation IIc

Leukocyte adhesion deficiency II (LAD II), also known as congenital disorder of glycosylation IIc (CDG-IIc), is a human disease in which a defective GDP-fucose transporter (SLC35C1) causes developmental defects and an immunodeficiency that is based on the lack of fucosylated selectin ligands. Since the study of in vivo leukocyte trafficking in patients with LAD II is experimentally limited, we analyzed this process in mice deficient for Slc35c1. We found that E-, L-, and P-selectin-dependent leukocyte rolling in cremaster muscle venules was virtually absent. This was accompanied by a strong but not complete decrease in firm leukocyte adhesion. Moreover, neutrophil migration to the inflamed peritoneum was strongly reduced by 89%. Previous reports showed surprisingly normal lymphocyte functions in LAD II, which indicated sufficient lymphocyte trafficking to secondary lymphoid organs. We now found that while lymphocyte homing to lymph nodes was reduced to 1% to 2% in Slc35c1(-/-) mice, trafficking to the spleen was completely normal. In accordance with this, we found a defect in the humoral response to a T cell-dependent antigen in lymph nodes but not in the spleen. Taken together, Slc35c1(-/-) mice show strongly defective leukocyte trafficking but normal lymphocyte homing to the spleen, which may explain normal lymphocyte functions in LAD II.

Sialyltransferase ST3Gal-IV controls CXCR2-mediated firm leukocyte arrest during inflammation

Recent in vitro studies have suggested a role for sialylation in chemokine receptor binding to its ligand (Bannert, N., S. Craig, M. Farzan, D. Sogah, N.V. Santo, H. Choe, and J. Sodroski. 2001. J. Exp. Med. 194:1661-1673). This prompted us to investigate chemokine-induced leukocyte adhesion in inflamed cremaster muscle venules of alpha2,3 sialyltransferase (ST3Gal-IV)-deficient mice. We found a marked reduction in leukocyte adhesion to inflamed microvessels upon injection of the CXCR2 ligands CXCL1 (keratinocyte-derived chemokine) or CXCL8 (interleukin 8). In addition, extravasation of ST3Gal-IV(-/-) neutrophils into thioglycollate-pretreated peritoneal cavities was significantly decreased. In vitro assays revealed that CXCL8 binding to isolated ST3Gal-IV(-/-) neutrophils was markedly impaired. Furthermore, CXCL1-mediated adhesion of ST3Gal-IV(-/-) leukocytes at physiological flow conditions, as well as transendothelial migration of ST3Gal-IV(-/-) leukocytes in response to CXCL1, was significantly reduced. In human neutrophils, enzymatic desialylation decreased binding of CXCR2 ligands to the neutrophil surface and diminished neutrophil degranulation in response to these chemokines. In addition, binding of alpha2,3-linked sialic acid-specific Maackia amurensis lectin II to purified CXCR2 from neuraminidase-treated CXCR2-transfected HEK293 cells was markedly impaired. Collectively, we provide substantial evidence that sialylation by ST3Gal-IV significantly contributes to CXCR2-mediated leukocyte adhesion during inflammation in vivo.