Carbohydrate sulfotransferases in lymphocyte homing

Hallmarks of the relationship between host and Trypanosoma cruzi sulfated glycoconjugates along the course of Chagas disease

American Trypanosomiasis or Chagas disease (ChD), a major problem that is still endemic in large areas of Latin America, is caused by Trypanosoma cruzi. This agent holds a major antigen, cruzipain (Cz). Its C-terminal domain (C-T) is retained in the glycoprotein mature form and bears several post-translational modifications. Glycoproteins containing sulfated N-linked oligosaccharides have been mostly implicated in numerous specific procedures of molecular recognition. The presence of sulfated oligosaccharides was demonstrated in Cz, also in a minor abundant antigen with serine-carboxypeptidase (SCP) activity, as well as in parasite sulfatides. Sulfate-bearing glycoproteins in Trypanosomatids are targets of specific immune responses. T. cruzi chronically infected subjects mount specific humoral immune responses to sulfated Cz. Unexpectedly, in the absence of infection, mice immunized with C-T, but not with sulfate-depleted C-T, showed ultrastructural heart anomalous pathological effects. Moreover, the synthetic anionic sugar conjugate GlcNAc₆SO₃-BSA showed to mimic the N-glycan-linked sulfated epitope (sulfotope) humoral responses that natural Cz elicits. Furthermore, it has been reported that sulfotopes participate via the binding of sialic acid Ig-like-specific lectins (Siglecs) to sulfosialylated glycoproteins in the immunomodulation by host-parasite interaction as well as in the parasite infection process. Strikingly, recent evidence involved Cz-sulfotope-specific antibodies in the immunopathogenesis and infection processes during the experimental ChD. Remarkably, sera from chronically T. cruzi-infected individuals with mild disease displayed higher levels of IgG₂ antibodies specific for sulfated glycoproteins and sulfatides than those with more severe forms of the disease, evidencing that T. cruzi sulfotopes are antigenic independently of the sulfated glycoconjugate type. Ongoing assays indicate that antibodies specific for sulfotopes might be considered biomarkers of human cardiac ChD progression, playing a role as predictors of stability from the early mild stages of chronic ChD.

Sulfur, sterol and trehalose metabolism in the deep-sea hydrocarbon seep tubeworm Lamellibrachia luymesi

BACKGROUND

Lamellibrachia luymesi dominates cold sulfide-hydrocarbon seeps and is known for its ability to consume bacteria for energy. The symbiotic relationship between tubeworms and bacteria with particular adaptations to chemosynthetic environments has received attention. However, metabolic studies have primarily focused on the mechanisms and pathways of the bacterial symbionts, while studies on the animal hosts are limited.

RESULTS

Here, we sequenced the transcriptome of L. luymesi and generated a transcriptomic database containing 79,464 transcript sequences. Based on GO and KEGG annotations, we identified transcripts related to sulfur metabolism, sterol biosynthesis, trehalose synthesis, and hydrolysis. Our in-depth analysis identified sulfation pathways in L. luymesi, and sulfate activation might be an important detoxification pathway for promoting sulfur cycling, reducing byproducts of sulfide metabolism, and converting sulfur compounds to sulfur-containing organics, which are essential for symbiotic survival. Moreover, sulfide can serve directly as a sulfur source for cysteine synthesis in L. luymesi. The existence of two pathways for cysteine synthesis might ensure its participation in the formation of proteins, heavy metal detoxification, and the sulfide-binding function of haemoglobin. Furthermore, our data suggested that cold-seep tubeworm is capable of de novo sterol biosynthesis, as well as incorporation and transformation of cycloartenol and lanosterol into unconventional sterols, and the critical enzyme involved in this process might have properties similar to those in the enzymes from plants or fungi. Finally, trehalose synthesis in L. luymesi occurs via the trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) pathways. The TPP gene has not been identified, whereas the TPS gene encodes a protein harbouring conserved TPS/OtsA and TPP/OtsB domains. The presence of multiple trehalases that catalyse trehalose hydrolysis could indicate the different roles of trehalase in cold-seep tubeworms.

CONCLUSIONS

We elucidated several molecular pathways of sulfate activation, cysteine and cholesterol synthesis, and trehalose metabolism. Contrary to the previous analysis, two pathways for cysteine synthesis and the cycloartenol-C-24-methyltransferase gene were identified in animals for the first time. The present study provides new insights into particular adaptations to chemosynthetic environments in L. luymesi and can serve as the basis for future molecular studies on host-symbiont interactions and biological evolution.

Laurent CD, Khoo KH, Mahal LK, Zandberg WF, Huang X, Klassen JS, Macauley MS. Carbohydrate Sulfation As a Mechanism for Fine-Tuning Siglec Ligands

The immunomodulatory family of Siglecs recognizes sialic acid-containing glycans as "self", which is exploited in cancer for immune evasion. The biochemical nature of Siglec ligands remains incompletely understood, with emerging evidence suggesting the importance of carbohydrate sulfation. Here, we investigate how specific sulfate modifications affect Siglec ligands by overexpressing eight carbohydrate sulfotransferases (CHSTs) in five cell lines. Overexpression of three CHSTs─CHST1, CHST2, or CHST4─significantly enhance the binding of numerous Siglecs. Unexpectedly, two other CHSTs (Gal3ST2 and Gal3ST3) diminish Siglec binding, suggesting a new mode to modulate Siglec ligands via sulfation. Results are cell type dependent, indicating that the context in which sulfated glycans are presented is important. Moreover, a pharmacological blockade of N- and O-glycan maturation reveals a cell-type-specific pattern of importance for either class of glycan. Production of a highly homogeneous Siglec-3 (CD33) fragment enabled a mass-spectrometry-based binding assay to determine ≥8-fold and ≥2-fold enhanced affinity for Neu5Acα2-3(6-O-sulfo)Galβ1-4GlcNAc and Neu5Acα2-3Galβ1-4(6-O-sulfo)GlcNAc, respectively, over Neu5Acα2-3Galβ1-4GlcNAc. CD33 shows significant additivity in affinity (≥28-fold) for the disulfated ligand, Neu5Acα2-3(6-O-sulfo)Galβ1-4(6-O-sulfo)GlcNAc. Moreover, joint overexpression of CHST1 with CHST2 in cells greatly enhanced the binding of CD33 and several other Siglecs. Finally, we reveal that CHST1 is upregulated in numerous cancers, correlating with poorer survival rates and sodium chlorate sensitivity for the binding of Siglecs to cancer cell lines. These results provide new insights into carbohydrate sulfation as a general mechanism for tuning Siglec ligands on cells, including in cancer.

Probing sulfatide-tissue lectin recognition with functionalized glycodendrimersomes

The small 3-O-sulfated galactose head group of sulfatides, an abundant glycosphingolipid class, poses the (sphinx-like) riddle on involvement of glycan bridging by tissue lectins (sugar code). First, synthesis of head group derivatives for functionalization of amphiphilic dendrimers is performed. Aggregation of resulting (biomimetic) vesicles, alone or in combination with lactose, demonstrates bridging by a tissue lectin (galectin-4). Physiologically, this can stabilize glycolipid-rich microdomains (rafts) and associate sulfatide-rich regions with specific glycoproteins. Further testing documents importance of heterobivalency and linker length. Structurally, sulfatide recognition by galectin-8 is shown to involve sphingosine's OH group as substitute for the 3′-hydroxyl of glucose of lactose. These discoveries underscore functionality of this small determinant on biomembranes intracellularly and on the cell surface. Moreover, they provide a role model to examine counterreceptor capacity of more complex glycans of glycosphingolipids and to start their bottom-up glycotope surface programming.

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Nanoparticle programming detects sulfatide-(N)-glycan bridging by galectins-4 and -8

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Protein design (linker/domain type) is a switch for aggregation activity

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Sphingosine's OH group is involved in contact building with a galectin

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.

Nucleolin mediates the binding of cancer cells to L-selectin under conditions of lymphodynamic shear stress

Head and neck squamous cell carcinoma (HNSCC) cells bind to lymphocytes via L-selectin in a shear-dependent manner. This interaction takes place exclusively under low-shear stress conditions, such as those found within the lymph node parenchyma. This represents a novel functional role for L-selectin-selectin ligand interactions. Our previous work has characterized as-of-yet unidentified L-selectin ligands expressed by HNSCC cells that are specifically active under conditions of low shear stress consistent with lymph flow. Using an affinity purification approach, we now show that nucleolin expressed on the surface of HNSCC cells is an active ligand for L-selectin. Parallel plate chamber flow-based experiments and atomic force microscopy (AFM) experiments show that nucleolin is the main functional ligand under these low-force conditions. Furthermore, AFM shows a clear relationship between work of deadhesion and physiological loading rates. Our results reveal nucleolin as the first major ligand reported for L-selectin that operates under low-shear stress conditions.

Molecular and functional analysis of PmCHST1b in nacre formation of Pinctada fucata martensii

Keratan sulfate possesses considerable amounts of negatively charged sulfonic acid groups and participates in biomineralization. In the present study, we investigated characteristics and functions of a CHST1 gene identified from the pearl oyster Pinctada fucata martensii (PmCHST1b) which participated in the synthesis of keratan sulfate. PmCHST1b amino acid sequence carried a typical sulfotransferase-3 domain (sulfotransfer-3 domain) and belonged to membrane-associated sulfotransferases. Homologous analysis of CHST1 from different species showed the conserved motif (5' PSB motif and 3' PB motif) which interacted with 3'-phosphoadenosine-5'-phosphosulfate (PAPS). Structure analysis of sulfotransferase domain indicted that PmCHST1b showed the conserved catalytic structure character and the relationships presented in the phylogenetic tree conformed to that of traditional taxonomy. Expression pattern of PmCHST1b in different tissues and development stages showed that PmCHST1b widely expressed in all the detected tissues and development stages and showed the highest expression level in the central zone of mantle (MC). PmCHST1b expressed highly in the trochophore, D-stage larvae and spat which corresponded to prodissoconch and dissoconch shell formation, respectively. RNA interference (RNAi) successfully inhibited expression level of PmCHST1b in MC (P<0.05), and sulfate polymer content in the extrapallial fluid significantly reduced (P<0.05). Crystallization of shell nacre became irregular. Results above indicated that PmCHST1b may affect nacre formation by participating in synthesis of keratan sulfate in extrapallial fluid. This study provided fundamental materials for further research on the role of sulfotransferases and keratan sulfate in nacre formation.

GlcNAc6ST-1 regulates sulfation of N-glycans and myelination in the peripheral nervous system

Highly specialized glial cells wrap axons with a multilayered myelin membrane in vertebrates. Myelin serves essential roles in the functioning of the nervous system. Axonal degeneration is the major cause of permanent neurological disability in primary myelin diseases. Many glycoproteins have been identified in myelin, and a lack of one myelin glycoprotein results in abnormal myelin structures in many cases. However, the roles of glycans on myelin glycoproteins remain poorly understood. Here, we report that sulfated N-glycans are involved in peripheral nervous system (PNS) myelination. PNS myelin glycoproteins contain highly abundant sulfated N-glycans. Major sulfated N-glycans were identified in both porcine and mouse PNS myelin, demonstrating that the 6-O-sulfation of N-acetylglucosamine (GlcNAc-6-O-sulfation) is highly conserved in PNS myelin between these species. P0 protein, the most abundant glycoprotein in PNS myelin and mutations in which at the glycosylation site cause Charcot-Marie-Tooth neuropathy, has abundant GlcNAc-6-O-sulfated N-glycans. Mice deficient in N-acetylglucosamine-6-O-sulfotransferase-1 (GlcNAc6ST-1) failed to synthesize sulfated N-glycans and exhibited abnormal myelination and axonal degeneration in the PNS. Taken together, this study demonstrates that GlcNAc6ST-1 modulates PNS myelination and myelinated axonal survival through the GlcNAc-6-O-sulfation of N-glycans on glycoproteins. These findings may provide novel insights into the pathogenesis of peripheral neuropathy.

Cytosolic sulfotransferase 1A1 regulates HIV-1 minus-strand DNA elongation in primary human monocyte-derived macrophages

Background

The cellular sulfonation pathway modulates key steps of virus replication. This pathway comprises two main families of sulfonate-conjugating enzymes: Golgi sulfotransferases, which sulfonate proteins, glycoproteins, glycolipids and proteoglycans; and cytosolic sulfotransferases (SULTs), which sulfonate various small molecules including hormones, neurotransmitters, and xenobiotics. Sulfonation controls the functions of numerous cellular factors such as those involved in cell-cell interactions, cell signaling, and small molecule detoxification. We previously showed that the cellular sulfonation pathway regulates HIV-1 gene expression and reactivation from latency. Here we show that a specific cellular sulfotransferase can regulate HIV-1 replication in primary human monocyte-derived macrophages (MDMs) by yet another mechanism, namely reverse transcription.

Methods

MDMs were derived from monocytes isolated from donor peripheral blood mononuclear cells (PBMCs) obtained from the San Diego Blood Bank. After one week in vitro cell culture under macrophage-polarizing conditions, MDMs were transfected with sulfotranserase-specific or control siRNAs and infected with HIV-1 or SIV constructs expressing a luciferase reporter. Infection levels were subsequently monitored by luminescence. Western blotting was used to assay siRNA knockdown and viral protein levels, and qPCR was used to measure viral RNA and DNA products.

Results

We demonstrate that the cytosolic sulfotransferase SULT1A1 is highly expressed in primary human MDMs, and through siRNA knockdown experiments, we show that this enzyme promotes infection of MDMs by single cycle VSV-G pseudotyped human HIV-1 and simian immunodeficiency virus vectors and by replication-competent HIV-1. Quantitative PCR analysis revealed that SULT1A1 affects HIV-1 replication in MDMs by modulating the kinetics of minus-strand DNA elongation during reverse transcription.

Conclusions

These studies have identified SULT1A1 as a cellular regulator of HIV-1 reverse transcription in primary human MDMs. The normal substrates of this enzyme are small phenolic-like molecules, raising the possibility that one or more of these substrates may be involved. Targeting SULT1A1 and/or its substrate(s) may offer a novel host-directed strategy to improve HIV-1 therapeutics.

Electronic supplementary material

The online version of this article (doi:10.1186/s12985-016-0491-9) contains supplementary material, which is available to authorized users.

Prognostic impact of chondroitin-4-sulfotransferase CHST11 in ovarian cancer

Ovarian cancer (OvCa) accounts for the highest tumor-related mortality among gynecological malignancies, but the underlying mechanisms are poorly understood. Glycosaminoglycans are abundantly present in ovarian tumors, and there is rising evidence that chondroitin sulfate (CS) as well as diverse carbohydrate sulfotransferases (CHSTs), the enzymes involved in the sulfation process of these structures, plays an important role in metastatic spread of tumor cells. mRNA expression levels of CHST3/7/11/12/13/15 were compared between malignant (86 OvCas) and non-malignant tumors (6 borderline tumors and 3 cystadenomas). CHST11 and CHST15 were further chosen for Western blot analysis in a cohort of 216 OvCas. Protein expression levels were correlated with clinicopathologic prognostic parameters and survival data. A significantly higher mRNA expression of CHST11, CHST12, and CHST15 was measured in ovarian cancer samples in comparison to non-malignant ones, and the same trend was observed for CHST13. For CHST3 and CHST7, no significant differences were found between the two groups. At protein level, high CHST11 expression was independently associated with unfavorable progression-free survival (PFS; p = 0.027). A similar trend was observed for CHST15, showing a nearly significant correlation between high expression levels and shorter recurrence-free survival in patients without macroscopic residual tumor after surgery (p = 0.053). We conclude that CHSTs involved in the synthesis of CS-A and CS-E might influence ovarian cancer progression, and we suggest CHST11 as independent unfavorable prognostic factor in this entity.

Role of the endothelial surface layer in neutrophil recruitment

Neutrophil recruitment in most tissues is limited to postcapillary venules, where E- and P-selectins are inducibly expressed by venular endothelial cells. These molecules support neutrophil rolling via binding of PSGL-1 and other ligands on neutrophils. Selectins extend ≤ 38 nm above the endothelial plasma membrane, and PSGL-1 extends to 50 nm above the neutrophil plasma membrane. However, endothelial cells are covered with an ESL composed of glycosaminoglycans that is ≥ 500 nm thick and has measurable resistance against compression. The neutrophil surface is also covered with a surface layer. These surface layers would be expected to completely shield adhesion molecules; thus, neutrophils should not be able to roll and adhere. However, in the cremaster muscle and in many other models investigated using intravital microscopy, neutrophils clearly roll, and their rolling is easily and quickly induced. This conundrum was thought to be resolved by the observation that the induction of selectins is accompanied by ESL shedding; however, ESL shedding only partially reduces the ESL thickness (to 200 nm) and thus is insufficient to expose adhesion molecules. In addition to its antiadhesive functions, the ESL also presents neutrophil arrest-inducing chemokines. ESL heparan sulfate can also bind L-selectin expressed by the neutrophils, which contributes to rolling and arrest. We conclude that ESL has both proadhesive and antiadhesive functions. However, most previous studies considered either only the proadhesive or only the antiadhesive effects of the ESL. An integrated model for the role of the ESL in neutrophil rolling, arrest, and transmigration is needed.

Intracellular killing of bacteria: is Dictyostelium a model macrophage or an alien?

Predation of bacteria by phagocytic cells was first developed during evolution by environmental amoebae. Many of the core mechanisms used by amoebae to sense, ingest and kill bacteria have also been conserved in specialized phagocytic cells in mammalian organisms. Here we focus on recent results revealing how Dictyostelium discoideum senses and kills non-pathogenic bacteria. In this model, genetic analysis of intracellular killing of bacteria has revealed a surprisingly complex array of specialized mechanisms. These results raise new questions on these processes, and challenge current models based largely on studies in mammalian phagocytes. In addition, recent studies suggest one additional level on complexity by revealing how Dictyostelium recognizes specifically various bacterial species and strains, and adapts its metabolism to process them. It remains to be seen to what extent mechanisms uncovered in Dictyostelium are also used in mammalian phagocytic cells.

Modulation of glycan recognition by clustered saccharide patches

All cells in nature are covered with a dense and complex array of glycan chains. Specific recognition and binding of glycans is a critical aspect of cellular interactions, both within and between species. Glycan-protein interactions tend to be of low affinity but high specificity, typically utilizing multivalency to generate the affinity required for biologically relevant binding. This review focuses on a higher level of glycan organization, the formation of clustered saccharide patches (CSPs), which can constitute unique ligands for highly specific interactions. Due to technical challenges, this aspect of glycan recognition remains poorly understood. We present a wealth of evidence for CSPs-mediated interactions, and discuss recent advances in experimental tools that are beginning to provide new insights into the composition and organization of CSPs. The examples presented here are likely the tip of the iceberg, and much further work is needed to elucidate fully this higher level of glycan organization.

Poly-LacNAc as an age-specific ligand for rotavirus P[11] in neonates and infants

Rotavirus (RV) P[11] is an unique genotype that infects neonates. The mechanism of such age-specific host restriction remains unknown. In this study, we explored host mucosal glycans as a potential age-specific factor for attachment of P[11] RVs. Using in vitro binding assays, we demonstrated that VP8* of a P[11] RV (N155) could bind saliva of infants (60.3%, N = 151) but not of adults (0%, N = 48), with a significantly negative correlation between binding of VP8* and ages of infants (P<0.01). Recognition to the infant saliva did not correlate with the ABO, secretor and Lewis histo-blood group antigens (HBGAs) but with the binding of the lectin Lycopersicon esculentum (LEA) that is known to recognize the oligomers of N-acetyllactosamine (LacNAc), a precursor of human HBGAs. Direct evidence of LacNAc involvement in P[11] binding was obtained from specific binding of VP8* with homopolymers of LacNAc in variable lengths through a glycan array analysis of 611 glycans. These results were confirmed by strong binding of VP8* to the Lec2 cell line that expresses LacNAc oligomers but not to the Lec8 cell line lacking the LacNAc. In addition, N155 VP8* and authentic P[11] RVs (human 116E and bovine B223) hemagglutinated human red blood cells that are known to express poly-LacNAc. The potential role of poly-LacNAc in host attachment and infection of RVs has been obtained by abrogation of 116E replication by the PAA-conjugated poly-LacNAc, human milk, and LEA positive infant saliva. Overall, our results suggested that the poly-LacNAc could serve as an age-specific receptor for P[11] RVs and well explained the epidemiology that P[11] RVs mainly infect neonates and young children.

Galactose 6-O-sulfotransferases are not required for the generation of Siglec-F ligands in leukocytes or lung tissue

Eosinophil accumulation is a characteristic feature of the immune response to parasitic worms and allergens. The cell surface carbohydrate-binding receptor Siglec-F is highly expressed on eosinophils and negatively regulates their accumulation during inflammation. Although endogenous ligands for Siglec-F have yet to be biochemically defined, binding studies using glycan arrays have implicated galactose 6-O-sulfate (Gal6S) as a partial recognition determinant for this receptor. Only two sulfotransferases are known to generate Gal6S, namely keratan sulfate galactose 6-O-sulfotransferase (KSGal6ST) and chondroitin 6-O-sulfotransferase 1 (C6ST-1). Here we use mice deficient in both KSGal6ST and C6ST-1 to determine whether these sulfotransferases are required for the generation of endogenous Siglec-F ligands. First, we characterize ligand expression on leukocyte populations and find that ligands are predominantly expressed on cell types also expressing Siglec-F, namely eosinophils, neutrophils, and alveolar macrophages. We also detect Siglec-F ligand activity in bronchoalveolar lavage fluid fractions containing polymeric secreted mucins, including MUC5B. Consistent with these observations, ligands in the lung increase dramatically during infection with the parasitic nematode, Nippostrongylus brasiliensis, which is known to induce eosinophil accumulation and mucus production. Surprisingly, Gal6S is undetectable in sialylated glycans from eosinophils and BAL fluid analyzed by mass spectrometry. Furthermore, none of the ligands we describe are diminished in mice lacking KSGal6ST and C6ST-1, indicating that neither of the known galactose 6-O-sulfotransferases is required for ligand synthesis. These results establish that ligands for Siglec-F are present on several cell types that are relevant during allergic lung inflammation and argue against the widely held view that Gal6S is critical for glycan recognition by this receptor.

Whole-exome sequencing in a single proband reveals a mutation in the CHST8 gene in autosomal recessive peeling skin syndrome

Generalized peeling skin syndrome (PSS) is an autosomal recessive genodermatosis characterized by lifelong, continuous shedding of the upper epidermis. Using whole-genome homozygozity mapping and whole-exome sequencing, we identified a novel homozygous missense mutation (c.229C>T, R77W) within the CHST8 gene, in a large consanguineous family with non-inflammatory PSS type A. CHST8 encodes a Golgi transmembrane N-acetylgalactosamine-4-O-sulfotransferase (GalNAc4-ST1), which we show by immunofluorescence staining to be expressed throughout normal epidermis. A colorimetric assay for total sulfated glycosaminoglycan (GAG) quantification, comparing human keratinocytes (CCD1106 KERTr) expressing wild type and mutant recombinant GalNAc4-ST1, revealed decreased levels of total sulfated GAGs in cells expressing mutant GalNAc4-ST1, suggesting loss of function. Western blotting revealed lower expression levels of mutant recombinant GalNAc4-ST1 compared to wild type, suggesting that accelerated degradation may result in loss of function, leading to PSS type A. This is the first report describing a mutation as the cause of PSS type A.

The sialome--far more than the sum of its parts

The glycome is defined as the glycan repertoire of cells, tissues, and organisms, as found under specified conditions. The vastly diverse glycome is generated by a nontemplate driven biosynthesis, which is indirectly encoded in the genome, and very dynamic. Due to this overwhelming diversity, glycomic analysis must be approached at different hierarchical levels of complexity. In this review five such levels of complexity and the experimental approaches used for analysis at each level are discussed for a subclass of the glycome: the sialome. The sialome, in analogy to the canopy of a forest, covers the cell membrane with diverse array of complex sialylated structures. Sialome complexity includes modification of sialic acid core structure (the leaves and flowers), the linkage to the underlying sugar (the stems), the identity, and arrangement of the underlying glycans (the branches), the structural attributes of the underlying glycans (the trees), and finally, the spatial organization of the sialoglycans in relation to components of the intact cell surface (the forest). Understanding the full complexity of the sialome thus requires combined analyses at multiple levels, that is, the sialome is far more than the sum of its parts.

Roles of GlcNAc-6-O-sulfotransferases in lymphoid and nonlymphoid tissues

Recent studies using sulfotransferase-deficient mice have revealed various physiological functions of sulfated glycans. Studies using gene-targeted mice deficient in both N-acetylglucosamine-6-O-sulfotransferase (GlcNAc6ST)-1 and GlcNAc6ST-2 showed that these sulfotransferases play critical roles in lymphocyte homing. Recent studies indicated that GlcNAc6ST-2 is expressed not only in lymph node high endothelial venules but also in the colonic epithelial cells in mice, and that this sulfotransferase plays a critical role in GlcNAc-6-O-sulfation of the colonic-mucins, as revealed by liquid chromatography coupled to electrospray ionization tandem mass spectrometry of the colonic-mucin O-glycans from wild-type (WT) and GlcNAc6ST-2-deficient mice. After induction of colitis by dextran sulfate sodium, significantly more leukocyte infiltration was observed in the colon of GlcNAc6ST-2-deficient mice than in that of WT mice. These studies demonstrate that GlcNAc-6-O-sulfotransferases play important roles not only in lymphoid tissues but also in nonlymphoid tissues. This chapter describes experimental procedures for assessing the functions of GlcNAc-6-O-sulfotransferases using gene-targeted mice.

Effects of N-glycosylation on the activity and localization of GlcNAc-6-sulfotransferase 1

N-Acetylglucosamine-6-sulfotransferase-1 (GlcNAc6ST-1) is a Golgi-resident glycoprotein that is responsible for sulfation of the l-selectin ligand on endothelial cells. Here, we report the sites at which GlcNAc6ST-1 is modified with N-linked glycans and the effects that each glycan has on enzyme activity, specificity, and localization. We determined that glycans are added at three of four potential N-linked glycosylation sites: N196, N410, and N428. The N428 glycan is required for the production of sulfated cell surface glycans: cells expressing a mutant enzyme lacking this glycan were unable to sulfate the sialyl Lewis X tetrasaccharide or a putative extended core 1 O-linked glycan. The N196 and N410 glycans differentially affect sulfation of two different substrates: cells that express an enzyme lacking the N410 glycan are able to sulfate the sialyl Lewis X substrate, but produce reduced levels of a sulfated peripheral lymph node addressin epitope and cells that express an enzyme lacking the N196 glycan are able to produce a sulfated peripheral lymph node addressin epitope, but are impaired in their ability to sulfate sialyl Lewis X. The glycans' effects on enzyme activity may be mediated, in part, by changes in enzyme localization. While most mutants that lacked glycans localized normally within the Golgi, the N428A mutant and a mutant lacking all glycans were also found to localize ectopically. Altered trafficking of mutants may be associated with the mechanisms by which misglycosylated enzyme is degraded.

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.

Enabling techniques and strategic workflow for sulfoglycomics based on mass spectrometry mapping and sequencing of permethylated sulfated glycans

Sulfate modifications on terminal epitopes of N- and O-glycans have increasingly been implicated as critical determinants mediating a diverse range of biological recognition functions. To address these low abundance but important sulfated glycans, and the sulfoglycome in general, further development of enrichment strategies and enabling mass spectrometry (MS)-based mapping techniques are needed. In this report, we demonstrate that the sulfated glycans, with and without additional sialylation, can be successfully permethylated by the sodium hydroxide slurry method and be distinguished from phosphorylated glycans by virtue of this derivatization. In conjunction with simple microscale postderivatization fractionation steps, permethyl derivatives fully retaining the negatively charged sulfate moiety and separated from the nonsulfated ones, can be efficiently detected and sequenced de novo by advanced MS/MS in the positive-ion mode. In particular, we show that the highly sequence and linkage informative high energy collision induced dissociation (CID) MS/MS afforded by MALDI-TOF/TOF can be extended to sulfoglycomic applications. The sulfated parent ion selected for CID MS/MS was found to mostly retain the sulfate moiety and therefore allow efficient fragmentation via the usual array of glycosidic, cross ring, and concerted double cleavages. Collectively, the optimized strategy enables a high sensitivity detection and critical mapping of the sulfoglycome such as the one derived from lymph node tissues or cell lines in both negative and positive-ion modes. Novel sulfated epitopes were identified from a crude mouse lymph node preparation, which fully attested to the practical utility of the methodology developed.

Imaging the glycome

Molecular imaging enables visualization of specific molecules in vivo and without substantial perturbation to the target molecule's environment. Glycans are appealing targets for molecular imaging but are inaccessible with conventional approaches. Classic methods for monitoring glycans rely on molecular recognition with probe-bearing lectins or antibodies, but these techniques are not well suited to in vivo imaging. In an emerging strategy, glycans are imaged by metabolic labeling with chemical reporters and subsequent ligation to fluorescent probes. This technique has enabled visualization of glycans in living cells and in live organisms such as zebrafish. Molecular imaging with chemical reporters offers a new avenue for probing changes in the glycome that accompany development and disease.

Solid-phase synthesis of alpha-glucosamine sulfoforms with fragmentation analysis by tandem mass spectrometry

Sulfated epitopes of alpha-glucosamine (GlcN sulfoforms) were prepared by solid-phase synthesis as models of internal glucosamines within heparan sulfate. An orthogonally protected 2'-hydroxyethyl GlcN derivative was immobilized on a trityl resin support and subjected to regioselective deprotection and sulfonation conditions, which were optimized with the aid of on-resin infrared or Raman analysis. The sulfoforms were cleaved from the resin under mild Lewis acid conditions without affecting the O- or N-sulfate groups and purified by reversed-phase high-performance liquid chromatography (HPLC). The alpha-GlcN sulfoforms and their 4- O-benzyl ethers were examined by electrospray ionization tandem mass spectrometry (ESI-MS/MS), with product ion spectra produced by collision-induced dissociation (CID). ESI-MS/MS revealed significant differences in parent ion stabilities and fragmentation rates as a function of sulfate position. Ion fragmentation by CID resulted in characteristic mass losses with strong correlation to the positions of both free hydroxyl groups and sulfate ions. Most of these fragmentation patterns are consonant with elimination pathways, and suggest possible strategies for elucidating the structures of glucosamine-derived sulfoforms with identical m/ z ratios. In particular, fragmentation analysis can easily distinguish GlcN sulfoforms bearing the relatively rare 3- O-sulfate from isomers with the more common 6- O-sulfate.

Transgenic LacZ under control of Hec-6st regulatory sequences recapitulates endogenous gene expression on high endothelial venules

Hec-6st is a highly specific high endothelial venule (HEV) gene that is crucial for regulating lymphocyte homing to lymph nodes (LN). The enzyme is also expressed in HEV-like vessels in tertiary lymphoid organs that form in chronic inflammation in autoimmunity, graft rejection, and microbial infection. Understanding the molecular nature of Hec-6st regulation is crucial for elucidating its function in development and disease. However, studies of HEV are limited because of the difficulties in isolating and maintaining the unique characteristics of these vessels in vitro. The novel pClasper yeast homologous recombination technique was used to isolate from a BAC clone a 60-kb DNA fragment that included the Hec-6st (Chst4) gene with flanking sequences. Transgenic mice were generated with the beta-galactosidase (LacZ) reporter gene inserted in-frame in the exon II of Hec-6st within the isolated BAC DNA fragment. LacZ was expressed specifically on HEV in LN, as indicated by its colocalization with peripheral node vascular addressin. LacZ was increased in nasal-associated lymphoid tissue during development and was reduced in LN and nasal-associated lymphoid tissue by LTbetaR-Ig (lymphotoxin-beta receptor human Ig fusion protein) treatment in a manner identical to the endogenous gene. The transgene was expressed at high levels in lymphoid accumulations with characteristics of tertiary lymphoid organs in the salivary glands of aged mice. Thus, the Hec-6s-LacZ construct faithfully reproduces Hec-6st tissue-specific expression and can be used in further studies to drive expression of reporter or effector genes, which could visualize or inhibit HEV in autoimmunity.

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

L-selectin belongs to the C-type lectin family of glycoproteins and is constitutively expressed on most leukocytes. L-selectin mediates leukocyte rolling in inflamed microvessels and high endothelial venules (HEV) via binding to specific carbohydrate structures on selectin ligands. Previous studies using sialidase treatment suggested a role of sialic acid residues in L-selectin-dependent rolling. To investigate the role of the alpha2,3-sialyltransferase (ST3Gal)-IV on L-selectin ligand activity in vivo, we studied leukocyte rolling in inflamed venules of the cremaster muscle and in Peyer's patch HEV of ST3Gal-IV-deficient mice and littermate control mice. In cremaster muscle venules with or without TNF-alpha treatment, L-selectin-dependent rolling was almost completely abolished in ST3Gal-IV(-/-) mice. In both models, L-selectin interacts with P-selectin glycoprotein ligand-1 (PSGL-1) presented by adherent leukocytes and leukocyte fragments, but not with endothelial L-selectin ligands. In contrast, L-selectin-dependent rolling in Peyer's patch HEV, which is mediated by unknown endothelial L-selectin ligands, was not impaired in the absence of ST3Gal-IV. Our in vivo data show that PSGL-1, the molecule responsible for L-selectin-mediated leukocyte interactions in inflammation, is dependent on ST3Gal-IV, while alpha2,3-sialylation by ST3Gal-IV is not necessary for L-selectin ligand activity on high endothelial cells of Peyer's patch HEV.

Expression of beta-1,4-galactosyltransferase-I in rat during inflammation

beta-1,4-Galactosyltransferase-I (beta-1,4-GalT-I) which is one of the best-studied glycosyltransferases, plays a key role in the synthesis of selectin ligands such as sialy Lewis (sLe( x )) and sulfated sLe( x ). Previous studies showed that inflammatory responses of beta-1,4-GalT-I-deficient mice were impaired because of the defect in selectin-ligand biosynthesis. However, the expression of beta-1,4-GalT-I during inflammation and its biological function remains to be elucidated. Real-time PCR showed that intraperitoneal administration of LPS strongly induced beta-1,4-GalT-I mRNA expression in the lung, heart, liver, spleen, kidney, lymph node, hippocampus, and testis, as well as in the cerebral cortex. In the rat lung, liver and testis, LPS stimulation of beta-1,4-GalT-I mRNA expression is time-dependent and biphasic. Lectin-fluorescent staining with RCA-I showed that LPS induced expression of galactose-containing glycans in rat lung and liver to the higher lever. Morphology analysis observed that galactose-containing glycans and beta-1,4-GalT-I mRNA was mostly expressed in neutrophils, macrophages and endothelial cells. These findings indicated that beta-1,4-GalT-I may play an important role in the inflammation reaction.

Sulfated L-selectin ligands as a therapeutic target in chronic inflammation

The homing of lymphocytes to peripheral lymph nodes is initiated by an adhesive interaction between L-selectin on lymphocytes and peripheral node addressin (PNAd), a set of sialomucins displayed on high endothelial venules (HEVs) of lymph nodes. The monoclonal antibody MECA-79 reacts with the PNAd sialomucins by recognizing an N-acetylglucosamine (GlcNAc)-6-sulfated oligosaccharide, which overlaps with sialyl 6-sulfo Lewis X, the L-selectin recognition determinant. Two HEV-expressed sulfotransferases, GlcNAc6ST-1 and GlcNAc6ST-2, are essential for the expression of the MECA-79 epitope and L-selectin ligand activity on lymph-node HEVs. PNAd, as defined by MECA-79 staining, is also expressed on activated blood vessels at several sites of chronic inflammation. Recent evidence indicates that the same two sulfotransferases underlie the formation of functional PNAd at these sites. Experiments in a sheep model of asthma demonstrate that a chronic inflammatory disease can be ameliorated by targeting PNAd.

Matrix morphogenesis in cornea is mediated by the modification of keratan sulfate by GlcNAc 6-O-sulfotransferase

Matrix assembly and homeostasis in collagen-rich tissues are mediated by interactions with proteoglycans (PGs) substituted with sulfated glycosaminoglycans (GAGs). The major GAG in cornea is keratan sulfate (KS), which is N-linked to one of three PG core proteins. To ascertain the importance of the carbohydrate chain sulfation step in KS functionality, we generated a strain of mice with a targeted gene deletion in Chst5, which encodes an N-acetylglucosamine-6-O-sulfotransferase that is integral to the sulfation of KS chains. Corneas of homozygous mutants were significantly thinner than those of WT or heterozygous mice. They lacked high-sulfated KS, but contained the core protein of the major corneal KSPG, lumican. Histochemically stained KSPGs coassociated with fibrillar collagen in WT corneas, but were not identified in the Chst5-null tissue. Conversely, abnormally large chondroitin sulfate/dermatan sulfate PG complexes were abundant throughout the Chst5-deficient cornea, indicating an alteration of controlled PG production in the mutant cornea. The corneal stroma of the Chst5-null mouse exhibited widespread structural alterations in collagen fibrillar architecture, including decreased interfibrillar spacing and a more spatially disorganized collagen array. The enzymatic sulfation of KS GAG chains is thus identified as a key requirement for PG biosynthesis and collagen matrix organization.

Carbohydrate microarrays reveal sulphation as a modulator of siglec binding

Siglecs are receptors on cells of the immune, haemopoietic, and nervous systems that recognize sialyl-glycans with differing preferences for sialic acid linkage and oligosaccharide backbone sequence. We investigate here siglec binding using microarrays of Lewis(x) (Le(x))- and 3'-sialyl-Le(x)-related probes with different sulphation patterns. These include sulphation at position 3 of the terminal galactose of Le(x), position 6 of the galactose of Le(x) and sialyl-Le(x), position 6 of N-acetylglucosamine of Le(x) and sialyl-Le(x), or both positions of sialyl-Le(x). Recombinant soluble forms of five siglecs have been investigated: human Siglec-7, -8, -9, and murine Siglec-F and CD22 (Siglec-2). Each siglec has a different binding pattern. Unlike two C-type lectins of leukocytes, L-selectin and Langerin, which also bind to sulphated analogues of sialyl-Le(x), the siglecs do not give detectable binding signals with sulphated analogues that are lacking sialic acid. The sulphate groups modulate, however, positively or negatively the siglec binding intensities to the sialyl-Le(x) sequence.

A sulfated metabolite produced by stf3 negatively regulates the virulence of Mycobacterium tuberculosis

Sulfated molecules have been shown to modulate isotypic interactions between cells of metazoans and heterotypic interactions between bacterial pathogens or symbionts and their eukaryotic host cells. Mycobacterium tuberculosis, the causative agent of tuberculosis, produces sulfated molecules that have eluded functional characterization for decades. We demonstrate here that a previously uncharacterized sulfated molecule, termed S881, is localized to the outer envelope of M. tuberculosis and negatively regulates the virulence of the organism in two mouse infection models. Furthermore, we show that the biosynthesis of S881 relies on the universal sulfate donor 3'-phosphoadenosine-5'-phosphosulfate and a previously uncharacterized sulfotransferase, stf3. These findings extend the known functions of sulfated molecules as general modulators of cell-cell interactions to include those between a bacterium and a human host.

Molecular basis for G protein control of the prokaryotic ATP sulfurylase

Sulfate assimilation is a critical component of both primary and secondary metabolism. An essential step in this pathway is the activation of sulfate through adenylation by the enzyme ATP sulfurylase (ATPS), forming adenosine 5'-phosphosulfate (APS). Proteobacterial ATPS overcomes this energetically unfavorable reaction by associating with a regulatory G protein, coupling the energy of GTP hydrolysis to APS formation. To discover the molecular basis of this unusual role for a G protein, we biochemically characterized and solved the X-ray crystal structure of a complex between Pseudomonas syringae ATPS (CysD) and its associated regulatory G protein (CysN). The structure of CysN*D shows the two proteins in tight association; however, the nucleotides bound to each subunit are spatially segregated. We provide evidence that conserved switch motifs in the G domain of CysN allosterically mediate interactions between the nucleotide binding sites. This structure suggests a molecular mechanism by which conserved G domain architecture is used to energetically link GTP turnover to the production of an essential metabolite.

The role of alpha-4 integrin in the aetiology of multiple sclerosis: current knowledge and therapeutic implications

Multiple sclerosis (MS) has been recognised as a disease since the mid-19th century. The delineation of its CNS pathology, revealing the presence of inflammatory demyelination and relative sparing of axons, was originally interpreted as evidence of infection. Despite many studies, a primary infectious aetiology of MS has not been found. However, the occurrence of acute demyelinating disease following a variety of infections and vaccinations, leading to MS in about a third of cases, provides evidence for the existence of an auto-allergic pathogenesis for the disease. Improved understanding of the role of the blood-brain barrier in protecting the CNS, and the mechanisms by which cells gain entry into the brain and spinal cord has advanced the understanding of MS. Evidence of the central role of the adhesion molecule alpha4beta1-integrin (very late activation antigen-4 [VLA-4]) for lymphocytes in endothelial transmigration into the CNS specifically, has provided a major insight into the pathogenesis of human demyelinating disease and its experimental model, experimental autoimmune encephalomyelitis (EAE). This finding has led to a new window of therapeutic opportunity in MS. Monoclonal antibodies to VLA-4 abrogate the development of EAE in sensitised animals and may actually reverse its clinical and pathological findings in manifest disease. Natalizumab, one such monoclonal antibody, which is administered intravenously, has been found to be a promising agent in the treatment of MS. Although single doses produced no improvement in the speed or quality of recovery from acute exacerbations of MS in a phase II trial, long-term administration (in phase II and phase III trials) have produced significant benefits with results showing both a marked reduction in the risk of new magnetic resonance imaging lesions and a significant reduction in the risk of exacerbations within 2 months of the initiation of therapy. Phase III double-blinded controlled trials have provided additional evidence of safety and a favourable impact on exacerbation rates over the 1 year of administration. Unfortunately, the success of natalizumab has been curtailed by three cases of progressive multifocal leukoencephalopathy, which have prompted the manufacturer to voluntary withdraw the drug from the market. An independent review board is currently investigating the safety of the drug to determine whether it should return to the market. The demonstration that selective modulation (blocking) of the adhesion molecule VLA-4 by natalizumab in MS, resembling that observed in experimental disease, represents a major advance in rational therapy.

Expression of N-acetylglucosamine 6-O-sulfotransferases (GlcNAc6STs)-1 and -4 in human monocytes: GlcNAc6ST-1 is implicated in the generation of the 6-sulfo N-acetyllactosamine/Lewis x epitope on CD44 and is induced by TNF-alpha

Sulfation at the 6-O position of N-acetylglucosamine (GlcNAc) in the context of sialyl 6-sulfo Lewis x occurs constitutively on specific glycoproteins present on high-walled endothelial venules (HEV) and is important for L-selectin dependent homing of lymphocytes. Here, the proinflammatory cytokine, TNF-alpha, induced the expression of 6-sulfo N-acetyllactosamine (LacNAc)/Lewis x on human peripheral blood monocytes (PBM). This epitope was detected by monoclonal antibody (mAb) AG107 after neuraminidase treatment suggesting a sialylated epitope, which was present on the cell adhesion molecule, CD44. Treatment of human PBM with TNF-alpha up-regulated the expression of N-acetylglucosamine 6-O-sulfotransferase-1 (GlcNAc6ST-1) and GlcNAc6ST-4, as determined by reverse transcriptase polymerase chain reaction (RT-PCR). However, only GlcNAc6ST-1 was induced by TNF-alpha in the human SR91 cell line, which also up-regulated the AG107 epitope. In ECV304 cells, the expression of GlcNAc6ST-4 alone was insufficient to generate the AG107 epitope. However, the transfection of GlcNAc6ST-1 resulted in significant sulfate incorporation into CD44 and generated the 6-sulfo LacNAc/Lewis x epitope on CD44, which was present largely on N-linked glycans. This demonstrates the induction of GlcNAc6STs in human monocytes in response to TNF-alpha and implicates GlcNAc6ST-1 in the generation of the 6-sulfo LacNAc/Lewis x epitope on CD44.

L-Selectin ligands in lymphoid tissues and models of inflammation

Both lymphocyte recirculation through the lymphoid tissues and leukocyte recruitment to sites of inflammation are essential components of immune surveillance, and are necessary for sustained protection against pathogens. This process is mediated by the leukocyte-endothelial adhesion cascade of which the interaction of leukocyte L-Selectin with its endothelial ligand initiates the first critical tethering and rolling step. As well as discussing the constitutive L-Selectin ligands in lymphoid tissues, this review examines the literature regarding their induction in inflammation, and draws attention to recent findings regarding soluble L-Selectin ligands that suggest an emerging multifunctional role in leukocyte recirculation and inflammation.

Enhanced detection of sulfated glycosylation sites in glycoproteins

We demonstrate a method that enhances the mass spectral signal of mono- and disulfated glycopeptides, present in glycoproteins that contain many other nonsulfated glycoforms. This method utilizes the tripeptide Lys-Lys-Lys as an ion-pairing reagent to complex selectively to sulfated species, and enhance their ion signal. The method is applied to the analysis of glycopeptides released from the enzymatic digestion of ovine luteinizing hormone. In this analysis, a disulfated glycopeptide is identified that was previously not detectable by MS assays, and a monosulfated glycoform, present at less than 1% abundance, is identified without any separation or enrichment of these species prior to analysis. In addition to enhancing the ion signal of sulfated glycopeptides, the ion-pairing technique is useful in obtaining structural information about the sulfated species.

Molecular mechanism for cancer-associated induction of sialyl Lewis X and sialyl Lewis A expression-The Warburg effect revisited

Cell adhesion mediated by selectins and their carbohydrate ligands, sialyl Lewis X and sialyl Lewis A, figures heavily in cancer metastasis. Expression of these carbohydrate determinants is markedly enhanced in cancer cells, but the molecular mechanism that leads to cancer-associated expression of sialyl Lewis X/A has not been well understood. Results of recent studies indicated involvement of two principal mechanisms in the accelerated expression of sialyl Lewis X/A in cancers; 'incomplete synthesis' and ' neo synthesis.' As to 'incomplete synthesis,' we have recently found further modified forms of sialyl Lewis X and sialyl Lewis A in non-malignant colonic epithelium, which have additional 6-sulfation or 2 --> 6 sialylation. The impairment of GlcNAc 6-sulfation and 2 --> 6 sialylation upon malignant transformation leads to accumulation of sialyl Lewis X/A in colon cancer cells. Epigenetic changes such as DNA methylation and/or histone deacetylation are suggested to lie behind such incomplete synthesis. As to the mechanism called ' neo synthesis,' recent studies have indicated that cancer-associated alterations in the sugar transportation and intermediate carbohydrate metabolism play important roles. Cancer cells are known to exhibit a metabolic shift from oxidative to elevated anaerobic glycolysis (Warburg effect), which is correlated with the increased gene expression of sugar transporters and glycolytic enzymes induced by common cancer-specific genetic alterations. The increased sialyl Lewis X/A expression in cancer is a link in the chains of these events because our recent results indicated that these events accompany transcriptional induction of a set of genes closely related to its expression.

Synthetic glycoprotein mimics inhibit L-selectin-mediated rolling and promote L-selectin shedding

L-selectin is a leukocyte cell-surface protein that facilitates the rolling of leukocytes along the endothelium, a process that leads to leukocyte migration to a site of infection. Preventing L-selectin-mediated rolling minimizes leukocyte adhesion and extravasation; therefore, compounds that inhibit rolling may act as anti-inflammatory agents. To investigate the potential role of multivalent ligands as rolling inhibitors, compounds termed neoglycopolymers were synthesized that possess key structural features of physiological L-selectin ligands. Sulfated neoglycopolymers substituted with sialyl Lewis x derivatives (3',6-disulfo Lewis x or 6-sulfo sialyl Lewis x) or a sulfatide analog (3,6-disulfo galactose) inhibited L-selectin-mediated rolling of lymphoid cells. Functional analysis of the inhibitory ligands indicates that they also induce proteolytic release of L-selectin. Thus, their inhibitory potency may arise from their ability to induce shedding. Our data indicate that screening for compounds that promote L-selectin release can identify ligands that inhibit rolling.

Strategies for drug discovery by targeting sulfation pathways

Posttranslational modifications of proteins such as phosphorylation have been recognized as pivotal modulators of biological activity in healthy and diseased tissues. Sulfation is a key posttranslational modification the role of which in physiology and pathology is only now becoming appreciated. Whereas phosphorylation is central to intracellular signal transduction, sulfation modulates cell-cell and cell-matrix communication. Sulfation involves a class of enzymes known as sulfotransferases, which transfer sulfate from the ATP-like sulfate donor 3'phosphoadenosine-5'phosphosulate to glycoproteins, glycolipids or metabolites. This review focuses on Golgi-localized sulfotransferases, their molecular biology and biochemistry, and strategies towards discovery of sulfotransferase inhibitors that could have potential as therapeutics in inflammation, cancer and infectious diseases.

The stem region of the sulfotransferase GlcNAc6ST-1 is a determinant of substrate specificity

The GlcNAc-6-sulfotransferases are a family of Golgi-resident enzymes that modulate glycan function. Two members of this family, GlcNAc6ST-1 and -2, collaborate in the biosynthesis of ligands for the leukocyte adhesion molecule L-selectin. Although their biochemical properties are similar in vitro, the enzymes have distinct glycoprotein substrate preferences in vivo. The sulfotransferases share similar overall architecture with the exception of an extended stem region in GlcNAc6ST-1 that is absent in GlcNAc6ST-2. In this study we probed the importance of the stem region with respect to substrate preference, localization, and oligomerization. Analysis of truncation mutants demonstrated that perturbation of the stem region of GlcNAc6ST-1 affects the cellular substrate preference of the enzyme without altering its retention within the Golgi. A chimeric enzyme comprising the stem region of GlcNAc6ST-1 inserted between the catalytic and transmembrane domains of GlcNAc6ST-2 had the same substrate preference as native GlcNAc6ST-1. In cells, GlcNAc6ST-1 exists as a dimer; two cysteine residues within the stem and transmembrane domain were found to be critical for dimerization. However, disruption of the dimer by mutagenesis did not affect either localization or substrate preference. Collectively, these results indicate that the stem region of GlcNAc6ST-1 influences substrate specificity, independent of its role in dimerization or Golgi retention.

Ligands for L-selectin: homing, inflammation, and beyond

Understanding the molecular basis of lymphocyte homing to lymphoid organs was originally a problem of concern only to immunologists. With the discovery of L-selectin and its ligands, interested scientists have expanded to include glycobiologists, immunopathologists, cancer biologists, and developmental biologists. Going beyond its first discovered role in homing to lymph nodes, the L-selectin system is implicated in such diverse processes as inflammatory leukocyte trafficking in both acute and chronic settings, hematogenous metastasis of carcinoma cells, effector mechanisms for inflammatory demyelination of axons, and implantation of the early mammalian embryo. This review focuses on the ligands for L-selectin that are found on vascular endothelium, leukocytes, carcinoma cells, and at various extravascular sites. The discovery of selectins and their ligands has validated the long-predicted hypothesis that carbohydrate-directed cell adhesion is relevant in eukaryotic systems. Emphasis will be given to the carbohydrate and sulfation modifications of the ligands, which enable recognition by L-selectin. The rapid "homing" of labeled cells into the lymph nodes presumably had its basis in the special affinity of small lymphocytes for the endothelium of the postcapillary venules.

Identification, function and structure of the mycobacterial sulfotransferase that initiates sulfolipid-1 biosynthesis

Sulfolipid-1 (SL-1) is an abundant sulfated glycolipid and potential virulence factor found in Mycobacterium tuberculosis. SL-1 consists of a trehalose-2-sulfate (T2S) disaccharide elaborated with four lipids. We identified and characterized a conserved mycobacterial sulfotransferase, Stf0, which generates the T2S moiety of SL-1. Biochemical studies demonstrated that the enzyme requires unmodified trehalose as substrate and is sensitive to small structural perturbations of the disaccharide. Disruption of stf0 in Mycobacterium smegmatis and M. tuberculosis resulted in the loss of T2S and SL-1 formation, respectively. The structure of Stf0 at a resolution of 2.6 A reveals the molecular basis of trehalose recognition and a unique dimer configuration that encloses the substrate into a bipartite active site. These data provide strong evidence that Stf0 carries out the first committed step in the biosynthesis of SL-1 and establish a system for probing the role of SL-1 in M. tuberculosis infection.

Detection of a sulfotransferase (HEC-GlcNAc6ST) in high endothelial venules of lymph nodes and in high endothelial venule-like vessels within ectopic lymphoid aggregates: relationship to the MECA-79 epitope

The interaction of L-selectin on lymphocytes with sulfated ligands on high endothelial venules (HEVs) of lymph nodes results in lymphocyte rolling and is essential for lymphocyte homing. The MECA-79 monoclonal antibody reports HEV-expressed ligands for L-selectin by recognizing a critical sulfation-dependent determinant on these ligands. HEC-GlcNAc6ST, a HEV-localized sulfotransferase, is essential for the elaboration of functional ligands within lymph nodes, as well as the generation of the MECA-79 epitope. Here, we use an antibody against murine HEC-GlcNAc6ST to study its expression in relationship to the MECA-79 epitope. In lymph nodes, the enzyme is expressed in the Golgi apparatus of high endothelial cells, in close correspondence with luminal staining by MECA-79. In lymph node HEVs of HEC-GlcNAc6ST-null mice, luminal staining by MECA-79 is almost abolished, whereas abluminal staining persists although reduced in intensity. HEV-like vessels in several examples of inflammation-associated lymphoid neogenesis, including nonobese diabetic mice, also exhibit concomitant expression of the sulfotransferase and luminal MECA-79 reactivity. The correlation extends to ectopic lymphoid aggregates within the pancreas of RIP-BLC mice, in which CXCL13 is expressed in islets. Analysis of the progeny of RIP-BLC by HEC-GlcNAc6ST-null mice establishes that the enzyme is responsible for the MECA-79 defined luminal ligands.