Selectins and other mammalian sialic acid-binding lectins

Clinical utility of RNA sequencing to resolve unusual GNE myopathy with a novel promoter deletion

INTRODUCTION

UDP N-acetylglucosamine2-epimerase/N-acetylmannosamine-kinase (GNE) gene mutations can cause mostly autosomal-recessive myopathy with juvenile-onset known as hereditary inclusion-body myopathy (HIBM).

METHODS

We describe a family of a patient showing an unusual HIBM with both vacuolar myopathy and myositis without quadriceps-sparing, hindering diagnosis. We show how genetic testing with functional assays, clinical transcriptome sequencing (RNA-seq) in particular, helped facilitate both the diagnosis and a better understanding of the genotype-phenotype relationship.

RESULTS

We identified a novel 7.08 kb pathogenic deletion upstream of GNE using array comparative genomic hybridization (aCGH) and a common Val727Met variant. Using RNA-seq, we found only monoallelic (Val727Met-allele) expression, leading to ~50% GNE reduction in muscle. Importantly, α-dystroglycan is hypoglycosylated in the patient muscle, suggesting HIBM could be a "dystroglycanopathy."

CONCLUSIONS

Our study shows the importance of considering aCGH for GNE-myopathies, and the potential of RNA-seq for faster, definitive molecular diagnosis of unusual myopathies. Muscle Nerve, 2019.

Exploration of the Sialic Acid World

Sialic acids are cytoprotectors, mainly localized on the surface of cell membranes with multiple and outstanding cell biological functions. The history of their structural analysis, occurrence, and functions is fascinating and described in this review. Reports from different researchers on apparently similar substances from a variety of biological materials led to the identification of a 9-carbon monosaccharide, which in 1957 was designated "sialic acid." The most frequently occurring member of the sialic acid family is N-acetylneuraminic acid, followed by N-glycolylneuraminic acid and O-acetylated derivatives, and up to now over about 80 neuraminic acid derivatives have been described. They appeared first in the animal kingdom, ranging from echinoderms up to higher animals, in many microorganisms, and are also expressed in insects, but are absent in higher plants. Sialic acids are masks and ligands and play as such dual roles in biology. Their involvement in immunology and tumor biology, as well as in hereditary diseases, cannot be underestimated. N-Glycolylneuraminic acid is very special, as this sugar cannot be expressed by humans, but is a xenoantigen with pathogenetic potential. Sialidases (neuraminidases), which liberate sialic acids from cellular compounds, had been known from very early on from studies with influenza viruses. Sialyltransferases, which are responsible for the sialylation of glycans and elongation of polysialic acids, are studied because of their significance in development and, for instance, in cancer. As more information about the functions in health and disease is acquired, the use of sialic acids in the treatment of diseases is also envisaged.

The Interaction of the Gut Microbiota with the Mucus Barrier in Health and Disease in Human

Glycoproteins are major players in the mucus protective barrier in the gastrointestinal and other mucosal surfaces. In particular the mucus glycoproteins, or mucins, are responsible for the protective gel barrier. They are characterized by their high carbohydrate content, present in their variable number, tandem repeat domains. Throughout evolution the mucins have been maintained as integral components of the mucosal barrier, emphasizing their essential biological status. The glycosylation of the mucins is achieved through a series of biosynthetic pathways processes, which generate the wide range of glycans found in these molecules. Thus mucins are decorated with molecules having information in the form of a glycocode. The enteric microbiota interacts with the mucosal mucus barrier in a variety of ways in order to fulfill its many normal processes. How bacteria read the glycocode and link to normal and pathological processes is outlined in the review.

Evaluation of the potential defensive strategy against Influenza A in cell line models

Background: Influenza virus can cause both seasonal infections and unpredictable pandemics. Rapidly evolving avian H5N1 and  H7N9 viruses have a potential pandemic threat for humans. Since avian Influenza can be transmitted by domestic birds, serving as a key link between wild birds and humans, an effective measure to control the influenza transmission would be eradication of the infection in poultry. It is known that the virus penetrates into the cell through binding with the terminal oligosaccharides - sialic acids (SA) - on the cell surfaces. Removal of SA might be a potential antiviral strategy. An approach to developing chicken lines that are resistant to influenza viruses could be the creation of genetically modified birds. Thus it is necessary to select a gene that provides defense to influenza. Here we have expressed in cells a range of exogenous sialidases and estimated their activity and specificity towards SA residues. Methods: Several bacterial, viral and human sialidases were tested. We adopted bacterial sialidases from Salmonella and Actinomyces for expression on the cell surface by fusing catalytic domains with transmembrane domains. We also selected Influenza A/PuertoRico/8/34/H1N1 neuraminidase and human membrane sialidase ( hNeu3) genes. Lectin binding assay was used for estimation of a α (2,3)-sialylation level by fluorescent microscopy and FACS.   Results: We compared sialidases from bacteria, Influenza virus and human. Sialidases from Salmonella and Influenza A neuraminidase effectively cleaved α (2-3)-SA receptors. Viral neuraminidase demonstrated a higher activity. Sialidases from Actinomyces and hNeu3 did not show any activity against α (2-3) SA under physiological conditions. Conclusion: Our results demonstrated that sialidases with different specificity and activity can be selected as genes providing antiviral defence. Combining chosen sialidases with different activity together with tissue-specific promoters would provide an optimal level of desialylation. Tissue specific expression of the sialidases could protect domestic birds from infection.

Evaluation of defense strategy against Influenza A in cell line models

Background: Influenza virus can cause both seasonal infections and unpredictable pandemics. Rapidly evolving avian H5N1 virus is getting increasingly infective for humans. Since avian Influenza can be transmitted by domestic birds, serving as a key link between wild aquatic birds and humans, an effective measure to control the influenza transmission would be eradication of the infection in poultry. It is known that the virus penetrates into the cell through binding with the terminal oligosaccharides - sialic acids (SA) - on the cell surfaces. Removal of SA might be a potential antiviral strategy. An approach to developing chicken lines that are resistant to influenza viruses could be the creation of genetically modified birds. Thus it is necessary to select a gene that provides defense to influenza. Here we have expressed in cells a range of exogenous sialidases and estimated their activity and specificity towards SA residues. Methods: Several bacterial, viral and human sialidases were tested. We adopted bacterial sialidases from Salmonella and Actinomyces for expression on the cell surface by fusing catalytic domains with transmembrane domains. We also selected Influenza A/PuertoRico/8/34/H1N1 neuraminidase and human membrane sialidase ( hNeu3) genes. Lectin binding assay was used for estimation of a α (2,3)-sialylation level by fluorescent microscopy and FACS.   Results: We compared sialidases from bacteria, Influenza virus and human. Sialidases from Salmonella and Influenza A neuraminidase effectively cleaved α (2-3)-SA receptors. Viral neuraminidase demonstrated a higher activity. Sialidases from Actinomyces and hNeu3 did not show any activity against α (2-3) SA under physiological conditions. Conclusion: Our results demonstrated that sialidases with different specificity and activity can be selected as genes providing antiviral defence. Combining chosen sialidases with different activity together with tissue-specific promoters would provide an optimal level of desialilation to prevent infection. Tissue specific expression of the sialidases could protect domestic birds from infection.

Human-derived natural antibodies: biomarkers and potential therapeutics

The immune system generates antibodies and antigen-specific T-cells as basic elements of the immune networks that differentiate self from non-self in a finely tuned manner. The antigen-specific nature of immune responses ensures that normal immune activation contains non-self when tolerating self. Here we review the B-1 subset of lymphocytes which produce self-reactive antibodies. By analyzing the IgM class of natural antibodies that recognize antigens from the nervous system, we emphasize that natural antibodies are biomarkers of how the immune system monitors the host. The immune response activated against self can be detrimental when triggered in an autoimmune genetic background. In contrast, tuning immune activity with natural antibodies is a potential therapeutic strategy.

Siglec-8 in induced sputum of COPD patients

Chronic obstructive pulmonary disease (COPD) is related to infiltration and activation of inflammatory cells in airways and pulmonary tissue. In COPD, neutrophils are prominent, while eosinophilic influx is typical to asthma. Inflammatory cells express sialic acid-binding immunoglobulin like lectins called Siglecs, a family of innate immune receptors that are transmembrane I-type lectins binding sialic acid. One member of the Siglec family, Siglec-8, is expressed mostly in eosinophils and may be an important therapeutic target in asthma or COPD. The aim of our project was to quantify Siglec-8 expression in induced sputum cells of COPD patients treated with long-acting beta2-agonists (LABA) or combined with long-acting antimuscarinic agents (LAMA) - tiotropium bromide. Thirty stable COPD patients (21 males and 9 females, mean age 67 years) receiving 12 μg BID formoterol therapy were assessed before and after 3 months' add-on therapy consisting of 18 μg QID tiotropium. In all patients, spirometry, lung volumes, and DLCO were performed before and after therapy. The patients were subjected to sputum induction before and after therapy. Sputum cells were isolated and processed to obtain cell membranes. Siglec-8 protein expression was assessed using Western blot. In patients receiving tiotropium and formoterol, improved FEV1 and lung volumes were observed compared with formoterol-only treated patients. The mean Siglec-8 level was significantly higher in eosinophilic subgroup of COPD patients compared with non-eosinophilic patients before therapy 40,000 vs. 15,000 Adj. Vol. INT/mm(2). Our data show that Siglec-8 may be involved in COPD pathogenesis and may influence COPD phenotyping.

Anti-inflammatory effect of glucose-mannose binding lectins isolated from Brazilian beans

Selectins are essential for leukocyte recruitment in inflammation. Because of a lectin domain present in the selectin structure, we investigated the anti-inflammtory activity of six mannose–glucose binding lectins from brazilian beans: Dioclea guianensis-DguiL; D. grandiflora-DgL; Cratylia floribunda-CfL; D. violacea-D.vL; D. virgata-DvirL and Canavalia brasiliensis-ConBr. The lectins were injected intravenously (i.v.) into rats (0.1 and 1.0 mg/kg; 30 min before irritants) and its activities compared to E. coli endotoxin (LPS,30 μg/kg i.v.). Three lectins (DvL, CfL and DguiL), although less intense than LPS, inhibited the neutrophil migration induced by carrageenan (Cg, 300 μg) in a dose-dependent manner (0.1 and 1.0 mg/kg). DvL activity was reversed by 0.1 M α-D-methyl-mannoside (α-CH3), but not by 0.1 M α-D-galactose. The fMLP (44 ng)-induced neutrophil migration was also reduced by these lectins. Endotoxin contamination of lectin samples could be excluded since α-CH3 treatment reversed the DvL effect, but did not modify LPS inhibitory activity. Carrageenan (300 μg)-induced paw oedema was also reduced by LPS or lectin treatments. Conversely, none of the tested lectins inhibited dextran (Dex, 300 μg)-induced paw oedema, a classical leukocyte independent model, or zymosan (Zy, 1.0 mg)-induced peritonitis and paw oedema. LPS showed no effect upon Dex-induced paw oedema and barely reduced (25%) the oedematogenic effects of zymosan. As proposed for LPS, the lectin inhibitory activity was better observed on neutrophil-mediated inflammatory reactions. We speculate that the plant lectin antiinflammatory activity is probably due to a competitive blockage of a common leukocyte and/or endothelial selectin carbohydrate ligand.

Transmembrane mucins as novel therapeutic targets

Membrane-tethered mucin glycoproteins are abundantly expressed at the apical surfaces of simple epithelia, where they play important roles in lubricating and protecting tissues from pathogens and enzymatic attack. Notable examples of these mucins are MUC1, MUC4 and MUC16 (also known as cancer antigen 125). In adenocarcinomas, apical mucin restriction is lost and overall expression is often highly increased. High-level mucin expression protects tumors from killing by the host immune system, as well as by chemotherapeutic agents, and affords protection from apoptosis. Mucin expression can increase as the result of gene duplication and/or in response to hormones, cytokines and growth factors prevalent in the tumor milieu. Rises in the normally low levels of mucin fragments in serum have been used as markers of disease, such as tumor burden, for many years. Currently, several approaches are being examined that target mucins for immunization or nanomedicine using mucin-specific antibodies.

Direct validation of NGcGM3 ganglioside as a new target for cancer immunotherapy

OBJECTIVE

The target concept means not only an aberrant expression of a particular molecule in tumour tissues but also evidence of a clear therapeutic advantage, as a consequence of immune-intervention, in an antigen-positive relevant tumour model. Since we reported the presence of NGcGM3 ganglioside in human breast tumours years ago and though Phase I clinical trials of a ganglioside containing vaccine have been conducted, a definitive direct validation of this peculiar molecule as target for cancer immunotherapy has remained unperformed.

METHODS

Two animal models were used: leghorn chickens and C57BL/6 mice. The murine 3LL-D122 cell line, the derived subcutaneous tumours and metastatic lung lesions were processed for gangliosides identification. Active immunotherapy experiments in the 3LL-D122 spontaneous lung metastasis model were performed with NGcGM3/VSSP vaccine prepared by conjugation of NGcGM3 with the outer membrane proteins of Neisseria meningitides.

RESULTS

The 3LL-D122 Lewis lung carcinoma results were consistent with an increased expression of NGcGM3 from primary tumours to metastatic lesions, as observed in human breast cancer samples. Both vaccines, prepared with synthetic or natural-source-derived ganglioside, showed similar anti-tumour and immunogenicity profiles. Finally, a clear involvement of NK1.1(+) cells and CD8(+) T cells in the anti-metastatic effect elicited by the vaccine was manifested.

CONCLUSIONS

While 'proof of concept' Phase II and III clinical trials with the NGcGM3/VSSP vaccine in cancer patients are currently ongoing these results reasonably sustain the validation of this peculiar ganglioside as a novel target for cancer immunotherapy.

Sialic acid reduces acute endotoxemia-induced liver dysfunction in the rat

Endotoxemia caused by LPS is a life-threatening and inflammatory condition contributing to multiple organ failure. Viruses or bacteria require sialic acid (SA) for target-cell binding. We suggest that exogenous SA through masking or mediating the binding of LPS to the target cells may attenuate LPS-induced liver dysfunction and cecal ligation and puncture-induced shock. We found that SA can directly scavenge O2-, H2O2, and NO activity by a chemiluminescence analyzer and bind to LPS with high affinity using surface plasmon resonance. Intravenous SA significantly increased plasma SA concentration within 4 h. We then assessed the potential effect of SA on LPS-induced acute endotoxemia in the rat. Intravenous LPS (10-50 mg/kg) dose-dependently increased plasma endotoxin and reactive oxygen species in the blood, bile, and liver and increased plasma alanine aminotransferase and aspartate aminotransferase levels as well as TNF-alpha, monocyte chemoattractant protein 1, tissue inhibitor of metalloproteinase 1, IL-1beta, and IL-6 levels in the rats. Thirty minutes after LPS stimulation, SA decreased LPS-enhanced endotoxin level, oxidative stress, alanine aminotransferase and aspartate aminotransferase levels, and cytokine concentration and ameliorated histopathologic alteration in the liver. We found that SA increased LPS-depressed Mn-superoxide dismutase, CuZn-superoxide dismutase, and heat shock protein 70 and decreased LPS-enhanced iNOS and proapoptotic Bax protein expression in the liver by Western blot. Sialic acid was given after treatment to rats subjected to cecal ligation and puncture, and the hypotensive effect was blunted for 6 h. In conclusion, SA treatment can counteract LPS-enhanced acute endotoxemia and oxidative injury via a direct scavenging reactive oxygen species activity and neutralization potential.

Chip-mass spectrometry for glycomic studies

The introduction of micro- and nanochip front end technologies for electrospray mass spectrometry addressed a major challenge in carbohydrate analysis: high sensitivity structural determination and heterogeneity assessment in high dynamic range mixtures of biological origin. Chip-enhanced electrospray ionization was demonstrated to provide reproducible performance irrespective of the type of carbohydrate, while the amenability of chip systems for coupling with different mass spectrometers greatly advance the chip/MS technique as a versatile key tool in glycomic studies. A more accurate representation of the glycan repertoire to include novel biologically-relevant information was achieved in different biological sources, asserting this technique as a valuable tool in glycan biomarker discovery and monitoring. Additionally, the integration of various analytical functions onto chip devices and direct hyphenation to MS proved its potential for glycan analysis during the recent years, whereby a new analytical tool is on the verge of maturation: lab-on-chip MS glycomics. The achievements until early beginning of 2007 on the implementation of chip- and functional integrated chip/MS in systems glycobiology studies are reviewed here.

Sialidase fusion protein as a novel broad-spectrum inhibitor of influenza virus infection

Influenza is a highly infectious disease characterized by recurrent annual epidemics and unpredictable major worldwide pandemics. Rapid spread of the highly pathogenic avian H5N1 strain and escalating human infections by the virus have set off the alarm for a global pandemic. To provide an urgently needed alternative treatment modality for influenza, we have generated a recombinant fusion protein composed of a sialidase catalytic domain derived from Actinomyces viscosus fused with a cell surface-anchoring sequence. The sialidase fusion protein is to be applied topically as an inhalant to remove the influenza viral receptors, sialic acids, from the airway epithelium. We demonstrate that a sialidase fusion construct, DAS181, effectively cleaves sialic acid receptors used by both human and avian influenza viruses. The treatment provides long-lasting effect and is nontoxic to the cells. DAS181 demonstrated potent antiviral and cell protective efficacies against a panel of laboratory strains and clinical isolates of IFV A and IFV B, with virus replication inhibition 50% effective concentrations in the range of 0.04 to 0.9 nM. Mouse and ferret studies confirmed significant in vivo efficacy of the sialidase fusion in both prophylactic and treatment modes.

Mechanisms of cell death induction by L-amino acid oxidase, a major component of ophidian venom

L-amino acid oxidase (LAAO) from the Malayan pit viper induces both necrosis and apoptosis in Jurkat cells. Cell death by necrosis is attributed to H2O2 produced by oxidation of alpha-amino acids. In the presence of catalase that effectively scavenges H2O2, a switch to apoptosis is observed. The major factors contributing to apoptosis are proposed to be: (i) generation of toxic intermediates from fetal calf serum (ii) binding and internalization of LAAO. The latter process appears to be mediated by the glycan moiety of the enzyme as desialylation reduces cytotoxicity. D-amino acid oxidase (DAAO), which catalyzes the same reaction as LAAO but lacks glycosylation, triggers necrosis as a consequence of H2O2 production but not apoptosis in the presence of catalase. Thus induction of cell death by LAAO appears to involve both the generation of H2O2 and the molecular interaction of the glycan moiety of the enzyme with structures at the cell surface.

Increased expression of the selectin ligand sialyl–Lewisx by biochemical engineering of sialic acids

Sialylation of glycoproteins and glycolipids plays an important role during development, regeneration and pathogenesis of several diseases. The precursor of all physiological sialic acids is N-acetyl-d-mannosamine. Using N-propanoyl mannosamine, a novel precursor of sialic acid, we showed earlier that sialic acids with a prolonged N-acyl side chain (e.g., N-propanoyl neuraminic acid) are incorporated into cell surface glycoconjugates. In this study, we report the structural and functional consequences of the incorporation of the nonphysiological sialic acid, N-propanoyl neuraminic acid, into glycoconjugates of HL60-I cells. These cells do not express UDP-GlcAc-2-epimerase, the key enzyme of the biosynthesis of N-acetyl-d-mannosamine. Therefore, they do not express sialyl-Lewis(x) structures and consequently do not bind to selectins. Application of N-acetyl-d-mannosamine leads to the expression of sialyl-Lewis(x) structures and to binding to selectins. Surprisingly, incorporation of N-propanoyl neuraminic acid into glycoconjugates of these cells leads to a dramatic increase of sialyl-Lewis(x) structures and to increased adhesion to selectins.

Primary structure and characteristics of a lectin from skin mucus of the Japanese eel Anguilla japonica

Two types of lactose-binding lectins, AJL-1 and AJL-2, were purified from the skin mucus extract of the Japanese eel Anguilla japonica by lactose affinity chromatography and subsequent gel filtration. The molecular masses of AJL-1 and AJL-2 were 16,091 and 31,743 Da, respectively. Intact AJL-1 was comprised of two identical 16-kDa subunits having blocked N termini and no disulfide bonds. AJL-2 was a homodimer with disulfide bonds. Based on the N-terminal amino acid sequence of the AJL-2 monomer, the nucleotide sequence of cDNA encoding this lectin was determined by 3'- and 5'-rapid amplification of cDNA ends. The deduced amino acid sequence showed approximately 30% homology with C-type lectins, which bind to carbohydrates in a Ca(2+)-dependent manner. In addition, AJL-2 exhibited highly conserved consensus amino acid residues of the C-type carbohydrate recognition domain, although this lectin showed Ca(2+)-independent activity. Gene expression of AJL-2 was detected only in the skin by Northern blot analysis, and this lectin localization was demonstrated in the club cells by immunohistochemistry. These results indicate that AJL-2 is secreted on the body surface and function as a component of skin mucus. AJL-2 agglutinated Escherichia coli and suppressed its growth, suggesting that this lectin is involved in host defense.

Targeting of cell receptors and gene transfer efficiency: a balancing act

Vectors conjugated with ligands recognized by cell surface receptors are of interest for cystic fibrosis gene therapy since these vectors would allow cell-specific targeting. However, an efficient and specific uptake may be abrogated by a subsequent intracellular trafficking leading to an inefficient gene transfer. This has been shown for polylysine substituted with mannose residues. While mannose-specific membrane lectins are predominantly expressed at the surface of airway cells and mannosylated complexes are the most efficiently incorporated glycosylated complexes in these cells, mannosylated complexes lead to a low gene transfer efficiency because of an inefficient exit from endosomal compartments, a high accumulation in lysosomes and an inefficient nuclear import. In contrast, the entry of low amounts of lactosylated complexes is balanced by more efficient intracellular trafficking, leading to an efficient gene transfer. This emphasizes that for a successful gene transfer, it is necessary to find the balance between efficient and specific uptake, and intracellular trafficking that overcomes the various cellular barriers and enables the plasmid to reach the nucleus.

Cloning and expression of a membrane-bound CMP-N-acetylneuraminic acid hydroxylase from the starfish Asterias rubens

The sialic acid N-glycolylneuraminic acid (Neu5Gc) is synthesized by the action of CMP-Neu5Ac hydroxylase. The enzyme from various mammals has been purified, characterized and sequenced by cDNA cloning. Although functional sequence motifs can be postulated from comparisons with several enzymes, no global homologies to any other proteins have been found. The unusual characteristics of this hydroxylase raise questions about its evolution. As echinoderms are phylogenetically the oldest organisms possessing Neu5Gc, they represent a starting point for investigations on the origin of this enzyme. Despite many similarities with its mammalian counterpart, CMP-Neu5Ac hydroxylase from the starfish A. rubens exhibits fundamental differences, most notably its association with a membrane and a requirement for high ionic strength. In order to shed light on the structural basis for these differences, the primary structure of CMP-Neu5Ac hydroxylase from A. rubens has been determined by PCR and cDNA-cloning techniques, using initial sequence information from the mouse enzyme. The complete assembled cDNA contained an ORF coding for a protein of 653 amino acids with a molecular mass of 75 kDa. The deduced amino-acid sequence exhibited a high degree of homology with the mammalian enzyme, although the C-terminus was some 60 residues longer. This extension consists of a terminal hydrophobic region, which may mediate membrane-binding, and a preceding hydrophilic sequence which probably serves as a hinge or linker. The identity of the ORF was confirmed by expression of active CMP-Neu5Ac hydroxylase in E. coli at low temperatures.

Gene therapy of cystic fibrosis: the glycofection approach

Many cells express surface membrane lectins that selectively bind and carry glycoconjugates into intracellular endosomes; in addition, various intracellular membrane and soluble lectins act as shuttles between different compartments. On this basis, we developed glycosylated polycations, now called glycofectins (glycosylated polylysine and polyethyleneimine). Recently, we set up a simple way to transform oligosaccharides into glycosynthons suitable to substitute proteins or polymers. Glycofectins bind plasmid DNA leading to compact glycoplexes. Glycoplexes prepared with glycofectins were found to be much more active than naked plasmid to transfer genes to various types of cells including human airway epithelial and serous cells. The gene transfer efficiency was found to depend on the nature of the sugars borne by glycofectins. It appeared that the sugar-dependent efficiency was not only related to the uptake but also to the intracellular traffic of glycoplexes.

Human airway mucin glycosylation: a combinatory of carbohydrate determinants which vary in cystic fibrosis

Human airway mucins represent a very broad family of polydisperse high molecular mass glycoproteins, which are part of the airway innate immunity. Apomucins, which correspond to their peptide part, are encoded by at least 6 different mucin genes (MUC1, MUC2, MUC4, MUC5B, MUC5AC and MUC7). The expression of some of these genes (at least MUC2 and MUC5AC) is induced by bacterial products, tobacco smoke and different cytokines. Human airway mucins are highly glycosylated (70-80% per weight). They contain from one single to several hundred carbohydrate chains. The carbohydrate chains that cover the apomucins are extremely diverse, adding to the complexity of these molecules. Structural information is available for more than 150 different O-glycan chains corresponding to the shortest chains (less than 12 sugars). The biosynthesis of these carbohydrate chains is a stepwise process involving many glycosyl- or sulfo-transferases. The only structural element shared by all mucin O-glycan chains is a GalNAc residue linked to a serine or threonine residue of the apomucin. There is growing evidence that the apomucin sequences influence the first glycosylation reactions. The elongation of the chains leads to various linear or branched extensions. Their non-reducing end, which corresponds to the termination of the chains, may bear different carbohydrate structures, such as histo-blood groups A or B determinants, H and sulfated H determinants, Lewis a, Lewis b, Lewis x or Lewis y epitopes, as well as sialyl- or sulfo- (sometimes sialyl- and sulfo-) Lewis a or Lewis x determinants. The synthesis of these different terminal determinants involves three different pathways with a whole set of glycosyl- and sulfo-transferases. Due to their wide structural diversity forming a combinatory of carbohydrate determinants as well as their location at the surface of the airways, mucins are involved in multiple interactions with microorganisms and are very important in the protection of the underlying airway mucosa. Airway mucins are oversulfated in cystic fibrosis and this feature has been considered as being linked to a primary defect of the disease. However, a similar pattern is observed in mucins from patients suffering from chronic bronchitis when they are severely infected. Airway mucins from severely infected patients suffering either from cystic fibrosis or from chronic bronchitis are also highly sialylated, and highly express sialylated and sulfated Lewis x determinants, a feature which may reflect severe mucosal inflammation or infection. These determinants are potential sites of attachment for Pseudomonas aeruginosa, the pathogen responsible for most of the morbidity and mortality in cystic fibrosis, and the expression of the sulfo- and glycosyl-transferases involved in their biosynthesis is increased by TNFalpha. In summary, airway inflammation may simultaneously induce the expression of mucin genes (MUC2 and MUC5AC) and the expression of several glycosyl- and sulfo-transferases, therefore modifying the combinatory glycosylation of these molecules.

Pharmacology of selectin inhibitors in ischemia/reperfusion states

Recently, the selectin family of glycoprotein adhesion molecules (P-selectin, E-selectin, and L-selectin) has been implicated in the pathogenesis of a number of inflammatory disease states. The selectins modulate the early adhesive interactions between circulating neutrophils and the endothelium. Both P-selectin and E-selectin can be expressed on the surface of endothelial cells following stimulation by a number of inflammatory mediators. In contrast, L-selectin is constitutively expressed on the surface of neutrophils at very high levels. In addition, neutrophils also express ligands for the endothelial selectins, including the carbohydrate sialyl Lewis(x) and the high-affinity ligand P-selectin glycoprotein ligand 1, which facilitate neutrophil-endothelial interactions. Selectins have been extensively investigated in ischemia/reperfusion injury states. The study of selectin involvement in ischemia/reperfusion injury has been facilitated by the development of highly specific selectin antagonists, including monoclonal antibodies, carbohydrates, small molecule inhibitors, and soluble forms of P-selectin glycoprotein ligand 1. This article reviews the results of current studies of selectin antagonists in experimental models of ischemia/reperfusion injury.

Endotoxin-induced lung inflammation is independent of the complement membrane attack complex

Several products of the activated complement system are known to modulate endothelial cell function in vitro. It has been shown that the membrane attack complex (MAC) (C5b-C9) can enhance tumor necrosis factor alpha (TNF-alpha)-induced expression of P- and E-selectin and intercellular adhesion molecule type 1 in cell cultures of human umbilical vein endothelial cells. In the present study the potential role of this synegism for lung injury during endotoxin-mediated septic shock in vivo was examined using a model of C6-deficient PVG (C-) (RT1(C)) rats and the congenic PVG (C+) (RT1(C)) strain. Following administration of a high (5 mg/kg) or low (0.5 mg/kg) dose of lipopolysaccharide (LPS) (Escherichia coli O55:B5), we determined the expression of cytokines, chemokines, and adhesion molecules as well as the recruitment of leukocytes in the lung. Challenge with intraperitoneal i.p. injections of LPS resulted in a strong induction of TNF-alpha, interleukin-1alpha/beta, cytokine-induced neutrophil chemoattractant, interferon-inducible protein 10, macrophage inflammatory proteins 1alpha and 2, macrophage chemotactic protein 1, and P-selectin. However, there were no significant differences between PVG (C-) and PVG (C+) rats. Immunoperoxidase staining showed a similar increase of lung infiltration by CD11b/c(+) leukocytes in both rat strains. We therefore conclude that the described synergism between TNF-alpha and the MAC of the complement system on the induction of endothelial adhesion molecules is dispensable for inflammatory processes during endotoxin-mediated septic shock in vivo.

Cepaea hortensis agglutinin-I, specific for O-glycosidically linked sialic acids, selectively labels endothelial cells of distinct vascular beds

The lectin Cepaea hortensis agglutinin-I (CHA-I) binds to O-glycosidically linked sialic acids with previously characterized specificity. Employing histochemistry, we demonstrate that CHA-I is a useful probe for detecting sialic acids in formalin-fixed human tissues in a specific manner. It stains the endothelium of arteries and veins in all tissues examined, and labels the capillaries in distinct vascular beds including the brain, colon, thyroid, pituitary, and adrenal. By contrast, the endothelial sinusoids in the liver, spleen, and bone marrow remained unstained. The staining pattern of CHA-I overlaps with the distribution of the sialomucin and L-selectin ligand podocalyxin, which includes positivity of podocytes and interstitial but not glomerular capillaries. CHA-I-positive epithelial structures were found in the lung, liver and kidney. Colon carcinoma cells were labelled with CHA-I but not haemangiosarcomas. In summary, CHA-I is a useful tool for detecting O-glycosidically linked sialic acids in formalin-fixed tissues, and a potentially powerful tool for the isolation and characterization of unknown sialomucins in normal and eventually in diseased tissues.

Sialoforms of dipeptidylpeptidase IV from rat kidney and liver

Dipeptidylpeptidase IV (DPP IV, CD26), a serine-type exo- and endopeptidase found in the cell surface membrane of many tissues, was employed as a model membrane glycoprotein to study the expression of sialoforms on cell surface glycoproteins. Native, enzymatically active DPP IV was purified from plasma membranes of kidney and liver by lectin affinity chromatography in conjunction with crown ether anion exchange chromatography. The enzyme was gradient-eluted in continuous fractions, all showing a single polypeptide band of about 100 kDa when separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing, denaturing conditions. Analysis of the purified DPP IV by isoelectric focusing (IEF) showed that it consists of several polypeptides of different isoelectric points (IP) ranging from 5.5 to 7.0. In vitro- desialylation of the enzyme and subsequent isoelectric focusing revealed that the differences in isoelectric points were due to differences in the degree of sialylation. Differences in the degree of sialylation between the fractions were also demonstrated by SDS-PAGE under nonreducing and nondenaturing conditions. Increased sialylation of the enzyme as demonstrated by isoelectric focusing resulted in increased migration velocity in nonreducing and nondenaturing SDS-polyacrylamide gels. In vitro -desialylation of the enzyme and its resialylation confirmed that sialylation was responsible for this extraordinary migration behavior. The native enzyme was predominantly sialylated via alpha 2, 6-linkage, as shown by lectin affinity blotting employing Sambucus nigra agglutinin (SNA) and Maackia amurensis agglutinin (MAA). These findings demonstrate that a distinct membrane glycoprotein may exist in various sialoforms, distinguished from each other by a different number of sialic acid residues. Moreover, these sialoforms can be individually purified by crown ether anion exchange chromatography.

Purified group X secretory phospholipase A(2) induced prominent release of arachidonic acid from human myeloid leukemia cells

Group X secretory phospholipase A(2) (sPLA(2)-X) possesses several structural features characteristic of both group IB and IIA sPLA(2)s (sPLA(2)-IB and -IIA) and is postulated to be involved in inflammatory responses owing to its restricted expression in the spleen and thymus. Here, we report the purification of human recombinant COOH-terminal His-tagged sPLA(2)-X, the preparation of its antibody, and the purification of native sPLA(2)-X. The affinity-purified sPLA(2)-X protein migrated as various molecular species of 13-18 kDa on SDS-polyacrylamide gels, and N-glycosidase F treatment caused shifts to the 13- and 14-kDa bands. NH(2)-terminal amino acid sequencing analysis revealed that the 13-kDa form is a putative mature sPLA(2)-X and the 14-kDa protein possesses a propeptide of 11 amino acid residues attached at the NH(2) termini of the mature protein. Separation with reverse-phase high performance liquid chromatography revealed that N-linked carbohydrates are not required for the enzymatic activity and pro-sPLA(2)-X has a relatively weak potency compared with the mature protein. The mature sPLA(2)-X induced the release of arachidonic acid from phosphatidylcholine more efficiently than other human sPLA(2) groups (IB, IIA, IID, and V) and elicited a prompt and marked release of arachidonic acid from human monocytic THP-1 cells compared with sPLA(2)-IB and -IIA with concomitant production of prostaglandin E(2). A prominent release of arachidonic acid was also observed in sPLA(2)-X-treated human U937 and HL60 cells. Immunohistochemical analysis of human lung preparations revealed its expression in alveolar epithelial cells. These results indicate that human sPLA(2)-X is a unique N-glycosylated sPLA(2) that releases arachidonic acid from human myeloid leukemia cells more efficiently than sPLA(2)-IB and -IIA.

α(1,3)-Fucosyltransferase VII and α(2,3)-Sialyltransferase IV Are Up-Regulated in Activated CD4 T Cells and Maintained After Their Differentiation into Th1 and Migration into Inflammatory Sites

Activated Th1 CD4 T cells bind to P-selectin and migrate into inflamed tissue, whereas Th2 cells do not. We show that α(1,3)-fucosyltransferase VII (FucT-VII) and α(2,3)-sialyltransferase IV (ST3GalIV), which are crucial for the biosynthesis of functional P-selectin ligands, are absent in naive CD4 T cells, but are rapidly up-regulated upon activation. Th1 or Th2 differentiation in the presence of polarizing cytokines leads to down-regulation of FucT-VII mRNA selectively in Th2 but not in Th1 cells. Influencing the differentiation by varying the priming dose of antigenic peptide results in similar FucT-VII down-regulation only in Ag-specific Th2 cells. ST3GalIV levels remain elevated. FucT-VII and ST3GalIV mRNAs are also up-regulated by Th1 cells primed in vivo and recruited into the lymph nodes draining delayed-type hypersensitivity sites. We identify FucT-VII gene expression as a principal difference between Th1 and Th2 cells, and underscore the importance of FucT-VII and ST3GalIV expression for the biosynthesis of functional selectin ligands.

Structure and conformation of complex carbohydrates of glycoproteins, glycolipids, and bacterial polysaccharides

For nuclear magnetic resonance determinations of the conformation of oligosaccharides in solution, simple molecular mechanics calculations and nuclear Overhauser enhancement measurements are adequate for small oligosaccharides that adopt single, relatively rigid conformations. Polysaccharides and larger or more flexible oligosaccharides generally require additional types of data, such as scalar and dipolar coupling constants, which are most conveniently measured in 13C-enriched samples. Nuclear magnetic resonance relaxation data provide information on the dynamics of oligosaccharides, which involves several different types of internal motion. Oligosaccharides complexed with lectins and antibodies have been successfully studied both by X-ray crystallography and by nuclear magnetic resonance spectroscopy. The complexes have been shown to be stabilized by a combination of polar hydrogen bonding interactions and van der Waals attractions. Although theoretical calculations of the conformation and stability of free oligosaccharides and of complexes with proteins can be carried out by molecular mechanics methods, the role of solvent water for these highly polar molecules continues to present computational problems.

Loxosceles spider venom induces the production of alpha and beta chemokines: implications for the pathogenesis of dermonecrotic arachnidism

Bites from the brown recluse spider and other Loxosceles arachnids result in dermonecrotic skin lesions. Neutrophils (PMN) are essential to the development of Loxosceles-induced skin lesions, but paradoxically, in vitro PMN activation is inhibited by direct exposure to Loxosceles venom. Neutrophil activation occurs in response to a myriad of soluble mediators that include members of both the alpha and beta chemokine families. Because arachnid envenomation results in the exposure of several different cell types to venom, we investigated venom-induced expression of alpha and beta chemokines in both endothelial cells (human umbilical vein; HUVEC) and epithelial cells (A549 pneumocytes). Chemokine-specific capture enzyme immunoassays (EIA) were used to measure Loxosceles deserta venom-induced alpha chemokines: interleukin-8 (IL-8), growth-related oncogene-alpha (GRO-alpha), and beta chemokines: monocyte chemoattractant protein-1(MCP-1), and regulated on activation, normal T cell expressed and secreted (RANTES) in cell-free conditioned media from HUVEC and A549 cell monolayers. Exposure of HUVECs (8 h) to Laxosceles venom resulted in the production of IL-8 (5.2+/-1.30 ng/ml), MCP-1 (1.44+/-0.11 ng/ml) and GRO-alpha (1.97+/-0.15 ng/ml) in a dose and time-dependent manner. Exposure of A549 cell monolayers to venom resulted in IL-8 (7.74+/-0.30 ng/ml), and MCP-1 (2.61+/-0.31 ng/ml), but neither GRO-alpha nor RANTES accumulated during an 8-hour incubation period. Chemokines accumulated in a venom dose and time-dependent manner. Neither cell type secreted RANTES in response to Loxosceles venom. These data indicate that Loxosceles spider venom is a potent inducer of alpha and beta chemokines in both endothelial and epithelial cell types. Based on the established roles of IL-8, MCP-1, and GRO-alpha, in inflammation, these observations have relevance to the pathophysiology of Loxosceles-induced dermonecrosis.

Developmental patterns of GalBeta1,3(4)GlcNAc alpha2,3-sialyltransferase (ST3Gal III) expression in the mouse: in situ hybridization using DIG-labeled RNA probes

Sialic acids are key determinants for biological processes, such as cell-cell interaction and differentiation. Sialyltransferases contribute to the diversity in carbohydrate structure through their attachment of sialic acid in various terminal positions on glycolipid and glycoprotein (N-linked and O-linked) carbohydrate groups. Galbeta 1,3(4)GlcNAc alpha2,3-sialyltransferase (ST3Gal III) is involved in the biosynthesis of sLe(x)and sLe(a) known as selectin ligands and tumor-associated carbohydrate structures. The appearance and differential distribution of ST3Gal III mRNA during mice embryogenesis [embryonic (E) days; E9, E11, E13, E15] were investigated by in situ hybridization with digoxigenin-labeled RNA probes coupled with alkaline phosphatase detection. On E9, all tissues were positive for ST3Gal III mRNA expression, whereas ST3Gal III mRNA on E11 was not detected throughout all tissues. On E13, ST3Gal III mRNA was expressed in different manner in various tissues. In this stage, ST3Gal III mRNA was positive only in the liver, pancreas and bladder. On E15, specific signal for ST3Gal III was detected in the liver, lung and forebrain. These results indicate that ST3GAI III is differently expressed at developmental stages of mice embryo, and this may be importantly related with regulation of organogenesis in mice.

Molecular cloning of a novel alpha2,3-sialyltransferase (ST3Gal VI) that sialylates type II lactosamine structures on glycoproteins and glycolipids

A novel member of the human CMP-NeuAc:beta-galactoside alpha2, 3-sialyltransferase (ST) subfamily, designated ST3Gal VI, was identified based on BLAST analysis of expressed sequence tags, and a cDNA clone was isolated from a human melanoma line library. The sequence of ST3Gal VI encoded a type II membrane protein with 2 amino acids of cytoplasmic domain, 32 amino acids of transmembrane region, and a large catalytic domain with 297 amino acids; and showed homology to previously cloned ST3Gal III, ST3Gal IV, and ST3Gal V at 34, 38, and 33%, respectively. Extracts from L cells transfected with ST3Gal VI cDNA in a expression vector and a fusion protein with protein A showed an enzyme activity of alpha2, 3-sialyltransferase toward Galbeta1,4GlcNAc structure on glycoproteins and glycolipids. In contrast to ST3Gal III and ST3Gal IV, this enzyme exhibited restricted substrate specificity, i.e. it utilized Galbeta1,4GlcNAc on glycoproteins, and neolactotetraosylceramide and neolactohexaosylceramide, but not lactotetraosylceramide, lactosylceramide, or asialo-GM1. Consequently, these data indicated that this enzyme is involved in the synthesis of sialyl-paragloboside, a precursor of sialyl-Lewis X determinant.

Sialylation of the Sialic Acid Binding Lectin Sialoadhesin Regulates Its Ability to Mediate Cell Adhesion

The macrophage-specific cell surface receptor sialoadhesin, which is a member of the newly recognized family of sialic acid binding lectins called siglecs, binds glycoprotein and glycolipid ligands containing a2-3–linked sialic acid on the surface of several leukocyte subsets. Recently, the sialic acid binding activity of the siglec CD22 has been demonstrated to be regulated by sialylation of the CD22 receptor molecule. In the present work, we show that desialylation of in vivo macrophage sialylconjugates enhances sialoadhesin-mediated lectin activity. Herein, we show that receptor sialylation of soluble sialoadhesin inhibits its binding to Jurkat cell ligands, and that charge-dependent repulsion alone cannot explain this inhibition. Furthermore, we show that the inhibitory effect of sialic acid is partially dependent on the presence of an intact exocyclic side chain. These results, in conjunction with previous findings, suggest that sialylation of siglecs by specific glycosyltransferases may be a common mechanism by which siglec-mediated adhesion is regulated.

Sialylation of the Sialic Acid Binding Lectin Sialoadhesin Regulates Its Ability to Mediate Cell Adhesion

The macrophage-specific cell surface receptor sialoadhesin, which is a member of the newly recognized family of sialic acid binding lectins called siglecs, binds glycoprotein and glycolipid ligands containing a2-3–linked sialic acid on the surface of several leukocyte subsets. Recently, the sialic acid binding activity of the siglec CD22 has been demonstrated to be regulated by sialylation of the CD22 receptor molecule. In the present work, we show that desialylation of in vivo macrophage sialylconjugates enhances sialoadhesin-mediated lectin activity. Herein, we show that receptor sialylation of soluble sialoadhesin inhibits its binding to Jurkat cell ligands, and that charge-dependent repulsion alone cannot explain this inhibition. Furthermore, we show that the inhibitory effect of sialic acid is partially dependent on the presence of an intact exocyclic side chain. These results, in conjunction with previous findings, suggest that sialylation of siglecs by specific glycosyltransferases may be a common mechanism by which siglec-mediated adhesion is regulated.

Cloning and expression of cDNA for a human Sia alpha 2,3Gal beta 1, 4GlcNA:alpha 2,8-sialyltransferase (hST8Sia III)

The cDNA encoding human Sia-alpha2,3-Gal-beta1,4-GlcNAc-R:alpha2, 8-sialyltransferase, hST8Sia III, was isolated by screening of a human brain cDNA library with polymerase chain reaction-amplified DNA probe generated from the sequence of mouse ST8Sia III (mST8Sia III) and by 5' rapid amplification of cDNA ends of mRNA isolated from human brain tissues. Comparative analysis of the predicted protein-coding region between our cloned hST8Sia III and mST8Sia III showed 92 and 96% identities in the nucleotide and the amino acid sequence, respectively. The soluble hST8Sia III protein expressed in COS-7 showed an extremely high catalytic activity of transferring sialic acid through alpha2,8-linkage to intact fetuin glycoprotein, whereas the transferring activity was completely undetectable toward either alpha2,6-sialylated glycoprotein or desialylated glycoprotein acceptors. Northern analysis of hST8Sia III showed that the transcript corresponding to 11 kb was expressed in both human fetal and adult brain, while the expression of the 5.5-kb transcript was restricted to fetal liver, indicating that the expression of hST8Sia III is developmentally and tissue-specifically regulated.

Neutrophil adhesion to human endothelial cells is induced by the membrane attack complex: the roles of P-selectin and platelet activating factor

A variety of inflammatory diseases are accompanied by activation of the complement system. We examined the role of the membrane attack complex (MAC) in mediating neutrophil adhesion to endothelial cells. To assemble the MAC in endothelial cell monolayers, a C5b-like molecule was created through the treatment of purified C5 with the oxidizing agent chloramine-T, followed by addition of the remaining components (C6-C9) that constitute the MAC. Use of this method abrogated potentially confounding effects mediated by other complement components (e.g., C5a). MAC assembly resulted in a rapid (30 min), concentration-dependent increase in neutrophil adherence. A monoclonal antibody directed against P-selectin inhibited MAC-mediated neutrophil adhesion. A whole cell EIA confirmed P-selectin expression after formation of the MAC. Incubation of neutrophils with the platelet-activating factor receptor antagonist, CF 3988, also significantly decreased adhesion, indicating that PAF plays a role in MAC-mediated adhesion. These results suggest that the MAC can promote neutrophil adhesion through P-selectin and PAF-mediated mechanisms.

Prognostic markers in rectal carcinoma

Guidelines from two major organizations have recently supported the use of only the serological marker carcinoembryonic antigen (CEA) for the prognostication and monitoring of patients with colorectal carcinoma. However, in view of the exciting advances made recently in elucidating the molecular and cellular biology of adenocarcinoma of the rectum, the molecules that transform the well-ordered normal rectal epithelium into an invasive adenocarcinoma may yield information about the ultimate behavior of that cancer. Consequently, assessing the expression of molecules within a primary cancer may predict the probability of regional and distant metastasis, response to therapy, and outcome. This review analyzes the current state of intratumoral expression of several molecular markers for the management of rectal cancer and evaluates their potential for defining which patients may undergo rectal sphincter preservation and need adjuvant therapy.

Bull sperm binding to oviductal epithelium is mediated by a Ca2+-dependent lectin on sperm that recognizes Lewis-a trisaccharide

Sperm binding to oviductal epithelium produces a reservoir in vivo that may serve to maintain sperm fertility and provide sperm for fertilization when ovulation occurs. Previously, it was determined that bull sperm binding could be blocked by fucoidan and its component fucose; furthermore, treatment of epithelium with fucosidase prevented binding. The present study was conducted to further characterize binding. Because fucose would probably be present on the epithelium as part of oligosaccharide moieties of glycoproteins and/or glycolipids, competitive binding inhibition activity was tested for fucose in five linkages commonly found in oligosaccharides. Binding inhibition was assayed by determining the concentration of motile, frozen/thawed sperm bound to fresh epithelial explants in the presence of test inhibitors. Initially, 5 monosaccharides were tested at 30 mM (fucose, mannose, sialic acid, glucose, N-acetyl glucosamine, and galactose), and only fucose significantly reduced sperm binding compared to vehicle control (p = 0.03). Of the oligosaccharides tested (lacto-N-fucopentaose I, 3-fucosyllactose, Lewis-X, Lewis-a, and GlcNAcbeta1-4[Fucalpha1-6]GlcNAc-O-Me), only Lewis-a significantly reduced binding, and it did so in a dose-dependent fashion (p = 0.009 at 12.5 mM). Ca2+ dependency of binding was examined. Sperm were incubated with explants in Tyrode's albumin lactate pyruvate (TALP) containing 2 mM CaCl2 or lacking CaCl2 and containing 2 mM EGTA. Sperm-binding density was reduced significantly in EGTA (p < 0.03) but could be restored by readdition of CaCl2. Also, live sperm were labeled with the oligosaccharide ligand Lewis-a conjugated to fluorescein isothiocyanate-tagged polyacrylamide. Sperm exhibited labeling on the head only in the presence of Ca2+. Labeling could be blocked by fucose or Lewis-a-polyacrylamide. It was concluded that bull sperm bind to an oligosaccharide ligand on the oviductal epithelium that resembles Lewis-a and that binding is Ca2+-dependent.

Cytidine monophosphate-N-acetylneuraminate hydroxylase in the starfish Asterias rubens and other echinoderms

The sialic acid N-glycolylneuraminic acid (Neu5Gc) is synthesised by an NADH-dependent hydroxylase which acts on CMP-N-acetylneuraminic acid (CMP-Neu5Ac). Although Neu5Gc is the predominant sialic acid in many echinoderms, little is known about the hydroxylase from organisms of this phylum. We show here that in contrast to the mammalian enzyme, the hydroxylase from various echinoderms is predominantly membrane-bound and exhibits optimal activity in the presence of 100 mM NaCl. A detailed characterisation of the hydroxylase from echinoderms was performed using fractionated gonads of the starfish Asterias rubens. Solubilisation using detergents led to an inactivation of the hydroxylase. However, the solubilised enzyme was reactivated by the addition of cytochrome b5 reductase together with the amphiphilic or soluble form of cytochrome b5. Although these latter proteins were only available from a mammalian source, the high affinity of the hydroxylase for cytochrome b5 suggests that, as with the mammalian enzyme, these electron carriers participate in the catalytic cycle of the hydroxylase from A. rubens in vivo. The relevance of these results to the interaction between cytochrome b5 and the hydroxylase is discussed.

Liver metastasis and adhesion to the sinusoidal endothelium by human colon cancer cells is related to mucin carbohydrate chain length

Mucin production by human colon cancer cells correlates with liver metastasis in animal models, but it is not known which steps in metastasis depend on specific alterations in mucin synthesis. Clonal variants of cell line LS174T selected for differences in mucin core carbohydrate expression have been further characterized biochemically, and tested for their ability to participate in metastasis-related events. LS-C mucin contains truncated carbohydrates enriched for sialyl Tn and these cells bind to basement membrane matrix to a greater extent than LS-B cells. This binding is partially inhibitable by antibody to sialyl Tn. LS-B produces more fully glycosylated mucin and preferentially binds to hepatic sinusoidal endothelial cells and E-selectin through sialylated peripheral mucin-associated carbohydrate structures. Adhesion of LS-B to endothelial cells is inhibited by neutralizing antibody to E-selectin, and inhibition of glycosylation or desialylation of LS-B mucin abrogates binding to E-selectin in vitro. LS-B cells spontaneously metastasized from cecum to liver and colonized the liver of athymic mice after splenic-portal injection to a significantly greater extent than LS-C, suggesting that expression of peripheral mucin carbohydrate structures is most important for metastasis of human colon cancer cells.

Differential gene expression of a human alpha2,3-sialyltransferase in leukaemic cell lines and leucocytes

The gene expression of the human Gal beta1,4(3)GlcNAc/Gal beta1,3GalNAc alpha-2,3-sialyltransferase was investigated in the leukaemic cell lines HL60, K-562, MOLT-4, THP-1 and in blood leucocytes. Five different transcripts were identified. In HL60 and THP-1 cells the expression levels of two of these changed during differentiation. Two potential AP1 binding sites were detected in the promoter regions of the gene. THP-1 cells contain proteins binding with higher affinities to these sequences in the sialyltransferase gene than to the AP1 consensus sequence, whereas nuclear extracts from HL60 cells have the opposite affinity.

Computational carbohydrate chemistry: what theoretical methods can tell us

Computational methods have had a long history of application to carbohydrate systems and their development in this regard is discussed. The conformational analysis of carbohydrates differs in several ways from that of other biomolecules. Many glycans appear to exhibit numerous conformations coexisting in solution at room temperature and a conformational analysis of a carbohydrate must address both spatial and temporal properties. When solution nuclear magnetic resonance data are used for comparison, the simulation must give rise to ensemble-averaged properties. In contrast, when comparing to experimental data obtained from crystal structures a simulation of a crystal lattice, rather than of an isolated molecule, is appropriate. Molecular dynamics simulations are well suited for such condensed phase modeling. Interactions between carbohydrates and other biological macromolecules are also amenable to computational approaches. Having obtained a three-dimensional structure of the receptor protein, it is possible to model with accuracy the conformation of the carbohydrate in the complex. An example of the application of free energy perturbation simulations to the prediction of carbohydrate-protein binding energies is presented.

Clinical and molecular prognostic factors in sphincter-preserving surgery for rectal cancer

As many as a third of patients with rectal cancers may be candidates for sphincter preservation surgery. The goal of the conservative management of adenocarcinoma of the distal rectum is to preserve rectal sphincter function without sacrificing local tumor control. To achieve this goal, a combined modality approach is necessary because multimodality therapy for more advanced disease has improved both local control and survival. Candidates for local excision are those with adenocarcinomas with a maximal diameter of less than 4 cm, mobile, and not poorly differentiated or mucinous and within 10 cm of the anal verge--usually within 6 cm. These criteria should be defined objectively by biopsy combined with state-of-the-art endorectal imaging. Newer molecular markers that are associated with prognosis and response to therapy may also be important for assessing prognosis, probability of local recurrence, and whether conservative treatment is appropriate. Patients with T0-3 N0 lesions meeting these standard clinicopathologic criteria have been treated successfully with wide local excision combined with chemotherapy and radiotherapy. Patients with larger or more advanced lesions may undergo low anterior resection with coloanal anastomosis. After resection, radiotherapy to at least 45 to 50 Gy is delivered to the pelvis and tumor bed often with concomitant chemotherapy. The overall rate of local failure in prospective single-institution trials in which local excision is performed with postoperative chemoradiotherapy has been 5% for T1 lesions, 7% for T2 lesions and 24% for T3 lesions. Although single-institution studies have supported the concept of conservative therapy, the safety and efficacy of this approach must still be confirmed in a multicenter, prospective trial, such as that underway in several of the cooperative oncology groups, before it may be considered a standard of practice.

Prevention of ischemia-reperfusion lung injury by sulfated Lewis(a) pentasaccharide. The Paris-Sud University Lung Transplantation Group

Inhibition of polymorphonuclear neutrophil (PMN) adhesion to the pulmonary endothelium attenuates ischemia-reperfusion (I/R) lung injury. We hypothesized that 3'-sulfated Lewis(a) (SuLa), a potent ligand for the selectin adhesion molecules, may have a beneficial effect on I/R lung injury, as measured by the filtration coefficient (K(fc)), and reduce pulmonary sequestration of PMN as assessed by the lung myeloperoxidase (MPO) activity. Blood-perfused rat lungs were subjected to 30 min of perfusion, 60 min of warm ischemia, and 90 min of reperfusion after treatment with either SuLa (200 microg) or saline. Effects of SuLa on PMN adhesion to cultured human umbilical vein endothelial cells (HUVEC) stimulated with tumor necrosis factor-alpha and calcium ionophore were also investigated. Compared with preischemia conditions, I/R induced a significant increase in K(fc), which was attenuated with SuLa (80 +/- 8 vs. 30 +/- 5%; P < 0.001). SuLa reduced lung MPO and PMN adhesion to stimulated HUVEC. These results indicate that SuLa reduces I/R-induced lung injury and PMN accumulation in lung. This protective effect might be related to inhibition of PMN adhesion to endothelial cells.