Synthesis of a novel galactosylated lipid and its application to the hepatocyte-selective targeting of liposomal doxorubicin

This paper described the synthesis of a novel galactosylated lipid with mono-galactoside moiety, (5-Cholesten-3beta-yl) 4-oxo-4-[2-(lactobionyl amido) ethylamido] butanoate (CHS-ED-LA), and the targetability of doxorubicin (DOX), a model drug, in liposomes containing 10% mol/mol CHS-ED-LA (galactosylated liposomes, GalL) to the liver was studied. The weighted-average overall drug targeting efficiency (Te(*)) was used to evaluate the liver targetability of GalL DOX. The results showed that GalL DOX gave a relatively high (Te(*))(liver) value of 64.6%, while DOX in conventional liposome (CL DOX) only gave a (Te(*))(liver) value of 21.8%. In the liver, the GalL DOX was mainly taken up by parenchymal cells (88% of the total hepatic uptake). Moreover, preinjection of asialofetuin significantly inhibited the liver uptake of GalL DOX (from 70 to 12% of the total injected dose). It was suggested that liposomes containing such novel galactosylated lipid, CHS-ED-LA, had a great potential as drug delivery carriers for hepatocyte-selective targeting.

Bacterial and Plant Enterotoxin B Subunit–Autoantigen Fusion Proteins Suppress Diabetes Insulitis

Several bacterial and plant enterotoxin B subunit-islet autoantigen fusion proteins were compared for their ability to serve as islet autoantigen carriers and adjuvants for reduction of pancreatic islet inflammation associated with type 1 diabetes. The cholera toxin B subunit (CTB), the heat-labile toxin B subunit from enterotoxigenic Escherichia coli (LTB), the Shigella toxin B subunit (STB), and the plant toxin ricin B subunit (RTB) were genetically linked to the islet autoantigens proinsulin (INS) and glutamic acid decarboxylase (GAD). The adjuvant-autoantigen gene fusions were transferred to a bacterial expression vector and the corresponding fusion proteins synthesized in E. coli. The purified adjuvant-autoantigen proteins were fed to 5-wk-old nonobese diabetic (NOD) mice once a week for 4 wk. Histological examination of pancreatic islets isolated from inoculated mice showed significant levels of insulitis reduction in comparison with uninoculated mice. The ratio of serum anti-INS and anti-GAD IgG2c to IgG1 antibody isotype titers increased in all ligand-autoantigen inoculated animal groups, suggesting an increase in effector Th2 lymphocytes in B subunit-mediated insulitis suppression. The results of these experiments indicate that bacterial and plant enterotoxin B subunit ligand-autoantigens enhance insulitis reduction in NOD mice. This research prompts further exploration of a multiadjuvant/autoantigen co-delivery strategy that may facilitate type 1 diabetes prevention and suppression in animals and humans.

Bioplex technology: novel synthetic gene delivery pharmaceutical based on peptides anchored to nucleic acids

Non-viral gene delivery is an important approach in order to establish safe in vivo gene therapy in the clinic. Although viral vectors currently exhibit superior gene transfer efficacy, the safety aspect of viral gene delivery is a concern. In order to improve non-viral in vivo gene delivery we have designed a pharmaceutical platform called Bioplex (biological complex). The concept of Bioplex is to link functional entities via hybridising anchors, such as Peptide Nucleic Acids (PNA), directly to naked DNA. In order to promote delivery functional entities consisting of biologically active peptides or carbohydrates, are linked to the PNA anchor. The PNA acts as genetic glue and hybridises with DNA in a sequence specific manner. By using functional entities, which elicit receptor-mediated endocytosis, improved endosomal escape and enhance nuclear entry we wish to improve the transfer of genetic material into the cell. An important aspect is that the functional entities should also have tissue-targeting properties in vivo. Examples of functional entities investigated to date are the Simian virus 40 nuclear localisation signal to improve nuclear uptake and different carbohydrate ligands in order to achieve receptor specific uptake. The delivery system is also endowed with regulatory capability, since the release of functional entities can be controlled. The aim is to create a safe, pharmaceutically defined and stable delivery system for nucleic acids with enhanced transfection properties that can be used in the clinic.

Elevation of ST6Gal I activity in malignant and transitional tissue in human colorectal cancer

OBJECTIVES

The aim of the present study was to investigate the activity of CMP-NeuAc:Galbeta(1,4)GlcNAc sialyltransferase (ST6Gal I) in colorectal cancer (CRC).

METHODS

ST6Gal I activity was determined in healthy, transitional and tumor tissues from the same patient using asialotransferrin and N-acetyllactosamine as acceptors.

RESULTS

ST6Gal I activities with asialotransferrin (n = 85) and N-acetyllactosamine (n = 40) as acceptors were statistically significantly enhanced in CRC tissue compared with healthy mucosa from the same patient (p = 0.001). Using transitional tissue (n = 27), enhancement versus healthy tissue was observed (p < 0.05). A positive correlation was found between ST6Gal I activity with N-acetyllactosamine and asialotransferrin in healthy (n = 32), tumorous (n = 32) and transitional tissue (n = 27), supporting the fact that the same enzyme was detected using both acceptors. Furthermore, we studied the relationship between some patients' clinicopathological features and ST6Gal I activity. Although the differences were not statistically significant, the levels of ST6Gal I activity in tumorous and transitional tissues varied with the histological grade of the tumor; however, we failed to find a correlation with the AJCC tumor classification.

CONCLUSIONS

This work reports enhanced ST6Gal I activity in tumor and transitional tissues from CRC patients. However, our overall results suggest that ST6Gal I activity is not indicative of the patient's outcome.

Galectins bind to the multivalent glycoprotein asialofetuin with enhanced affinities and a gradient of decreasing binding constants

Our previous isothermal titration microcalorimetry (ITC) studies of the binding of synthetic multivalent carbohydrates to the Man/Glc-specific lectins concanavalin A (ConA) and Dioclea grandiflora lectin (DGL) showed negative binding cooperativity that was due to the carbohydrate ligands and not the proteins [Dam, T. K., et al. (2002) Biochemistry 41, 1351-1358]. The negative cooperativity was associated with the decreasing functional valence of the carbohydrates upon progressive binding of their epitopes. The present study also shows negative cooperativity in the ITC binding data of asialofetuin (ASF), a glycoprotein that possesses nine LacNAc epitopes, to galectin-1, -2, -3, -4, -5, and -7, and truncated, monomer versions of galectin-3 and -5, which are members of a family of animal lectins. Although the observed K(a) values for binding of ASF to the galectins and two truncated forms are only 50-80-fold greater than that of LacNAc, analysis of the data in terms of the relationship between the observed macroscopic free energy of binding and the decreasing microscopic free energies of binding of the epitopes shows that the first LacNAc epitope of ASF binds with approximately 6000-fold higher affinity than the last epitope. Thus, the microscopic binding constants of the galectins for the first epitope(s) of ASF are in the nanomolar range, with a gradient of decreasing binding constants of the remaining epitopes. The results indicate that the above galectins bind with fractional, high affinities to multivalent glycoproteins such as ASF, independent of the quaternary structures of the galectins. These findings have important implications for the binding of galectins to multivalent carbohydrate receptors.

Characterization of benzodiazepine binding site on human α1-acid glycoprotein using flunitrazepam as a photolabeling agent

The binding of flunitrazepam (FNZP) by human alpha1-acid glycoprotein (hAGP) and the relationships between the extent of drug binding and desialylation and the genetic variants of hAGP were examined. The photolabeling specificity of [3H]FNZP was confirmed by findings in which other hAGP-binding ligands inhibited the formation of covalent bonds between [3H]FNZP and hAGP. The photolabeling of asialo-hAGP suggested that sialic acid does not involve in the binding of [3H]FNZP. No difference in the labeling could be found between the F1*S variants and A variant. Similarly, FNZP did not show a difference in binding affinity to the two genetic variants of hAGP. Sequence analysis of the photolabeled peptide indicated a sequence corresponding to Tyr91-Arg105 of hAGP.

Phenotypic changes induced by expression of beta-galactoside alpha2,6 sialyltransferase I in the human colon cancer cell line SW948

Beta-galactoside alpha2,6 sialyltransferase (ST6Gal.I), the enzyme which adds sialic acid in alpha2,6-linkage on lactosaminic termini of glycoproteins, is frequently overexpressed in cancer, but its relationship with malignancy remains unclear. In this study, we have investigated the phenotypic changes induced by the expression of alpha2,6-sialylated lactosaminic chains in the human colon cancer cell line SW948 which was originally devoid of ST6Gal.I. Clones derived from transfection with the ST6Gal.I cDNA were compared with untransfected cells and mock transfectants. The ST6Gal.I-expressing clones show (1) increased adherence to fibronectin and collagen IV but not to hyaluronic acid. Treatment with Clostridium perfrigens neuraminidase reduces the binding to fibronectin and collagen IV of ST6Gal.I-expressing cells but not that of ST6Gal.I-negative cells; (2) accumulation and more focal distribution of beta1 integrins on the cell surface; (3) different distribution of actin fibers; (4) flatter morphology and reduced tendency to multilayer growth; (5) improved ability to heal a scratch wound; (6) reduced ability to grow at the subcutaneous site of injection in nude mice. Our data suggest that the presence of alpha2,6-linked sialic acid on membrane glycoconjugates increases the binding to extracellular matrix components, resulting in a membrane stabilization of beta1 integrins, further strengthening the binding. This mechanism can provide a basis for the flatter morphology and the reduced tendency to multilayer growth, resulting in a more ordered tissue organization. These data indicate that in the cell line SW948, the effect of ST6Gal.I expression is consistent with the attenuation of the neoplastic phenotype.

Purification, characterization, cDNA cloning, and expression of asialofetuin-binding C-type lectin from eggs of shishamo smelt (Osmerus [Spirinchus] lanceolatus)

A novel C-type lectin (OLABL) was isolated from the eggs of shishamo smelt [Osmerus (Spirinchus) lanceolatus] by affinity chromatography on asialofetuin-Sepharose. OLABL had a molecular mass of 29 kDa on SDS-PAGE under nonreducing conditions and two subunits with masses of 15 kDa (OLABL-H) and 14 kDa (OLABL-L) under reducing conditions. Thus, OLABL is a heterodimeric protein. cDNA sequence analysis revealed that the H- and L-subunits of OLABL were composed of 137 and 136 amino acid residues, respectively, and showed almost identical (95%) sequences, with slight differences in the N-terminal and C-terminal regions. Since each subunit contained only the characteristic motif of C-type lectin-like domain (CTLD), EPN-E-WND, OLABL is a member of group VII of the CTLD-containing protein family. Although OLABL had an EPN sequence that is known as a mannose-specific motif found in the collectin family, OLABL agglutinated rabbit erythrocytes without the addition of Ca(2+) ion, and this activity was inhibited by l-rhamnose and d-galactose derivatives, but not by d-mannose and d-glucose. These results indicate that OLABL has similar characteristics to AJL-2, a calcium-independent lactose specific lectin isolated from Japanese eel skin mucus. Recombinant OLABLs (rHisOLABLs), His-tagged homodimers of the H- and L-subunits, were refolded from inclusion bodies expressed by Escherichia coli. rHisOLABL-L was recovered as a soluble form, but rHisOLABL-H was hardly dissolved in a renaturing buffer. The specific activities of rHisOLABL-L, rHisOLABL-H, and native OLABL were 500, 36, and 20, respectively. These findings suggest that the combination of subunits may affect the solubility and activity of these dimeric form lectins.

Role of E-cadherin Molecules in Spheroid Formation of Hepatocytes Adhered on Galactose-Carrying Polymer as an Artificial Asialoglycoprotein Model

The role of E-cadherin in the spheroid formation of hepatocytes adhered on the poly(N-p-vinylbenzyl-D-lactonamide) (PVLA) as a model ligand for asialoglycoprotein receptors (ASGP-R) of hepatocytes was studied. Expression of E-cadherin was increased in round hepatocytes adhered on a high-coating density of PVLA (100 microg/ml), and also in flat ones adhered on a low-coating density of PVLA (1 microg/ml) in the presence of epidermal growth factor (EGF). Hepatocyte spheroids formed on the high-coating density of PVLA in the presence of EGF after 48 h were inhibited by an anti-E-cadherin monoclonal antibody (ECCD-1). From immunofluorescence and confocal laser microscopy, E-cadherin was localized in the intercellular boundaries and concentrated at the inside surface of aggregated cells. As a result, E-cadherin could play an important role in hepatocyte assembly.

An optimized protocol for nano-LC-MALDI-TOF-MS coupling for the analysis of proteolytic digests of glycoproteins

Matrix-assissted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analyses of complete proteolytic digests are often hampered by contaminations and the complexity of the sample. This results in suppression effects and the formation of adducts which are difficult to assign, thus leading to low scores in database searches. In particular, signals of post-translationally modified peptides such as glycopeptides are often of low intensity or completely suppressed. Online liquid chromatography electrospray ionization mass spectrometry (ESI-MS) can, in part, overcome this problem, but the analytes are completely consumed during the run. Coupling of nano-flow HPLC (nano-LC), microfractionation and MALDI-TOF-MS combines separation and high-sensitivity UV detection with the possibility of collecting fractionated peptides and preserving the sample for detailed mass spectrometric analyses. Here we report on an optimized protocol for nano-LC-MALDI-TOF-MS analyses of glycoproteins. This protocol improves spectral quality, resulting in better protein identification scores in database searches. Furthermore, post-translationally modified peptides could be detected with higher sensitivity by changing the experimental conditions, allowing assignment, localization and characterization of the respective carbohydrate substituents.

Comprehensive Identification of Post-translational Modifications of Rat Bone Osteopontin by Mass Spectrometry†

Osteopontin (OPN) is a highly modified protein that is found in many tissues and has been associated with a variety of physiological and pathological processes. Bone OPN is a potent inhibitor of hydroxyapatite crystal formation and stimulates bone resorption by osteoclasts; these activities, as well as others, are dependent upon phosphorylation of the protein. We have used mass spectrometry (MS) to perform a comprehensive analysis of the post-translational modification of OPN purified from rat bone. Matrix-assisted laser desorption time-of-flight (MALDI-TOF) MS showed masses of 37.6 and 36.8 kDa before and after enzymatic dephosphorylation, respectively, corresponding to a content of approximately 10.4 phosphate groups. Using proteolytic digestion and tandem MS, we localized 29 sites of phosphorylation: S10, S11, S46, S47, T50, S60, S62, S65, S146, T154, S160, S164, S167, S193, S196, S203, S220, S223, S232, S241, S245, S257, S262, S267, S278, S290, S295, S296, and S297. In addition, Y150 was shown to be sulfated and T107, T110, T116, and T121 are O-glycosylated. No glycan was detected at the potential N-glycosylation site. Other modifications, including deamidation, oxidation, and carbamylation, are also present. A 36-amino acid sequence from residues 67-102 could not be analyzed in detail, even after sialidase treatment, presumably because of the presence of a large number of acidic residues. In comparison to the previously characterized cow milk isoform, rat bone OPN is sulfated and has an additional site of glycosylation, many different sites of phosphorylation, and a lower overall phosphate content.

IgA1 is the premier serum glycoprotein recognized by human galectin-1 since T antigen (Galbeta1-->3GalNAc-) is far superior to non-repeating N-acetyl lactosamine as ligand

Human heart galectin-1 (HHL) was separated by high pressure liquid chromatography from endogenous glycoproteins co-purified with it during affinity chromatography. These glycoproteins offered excellent ligands for HHL binding and were rich in T antigen (Galbeta1-->3 GalNAc-) of O-linked oligosaccharides. In enzyme linked lectin assay and hemagglutination inhibition assay, human IgA1, bovine fetuin and other O-glycosylated T antigen-bearing glycoproteins bound to the lectin efficiently in contrast to single N-acetyl lactosamine (LacNAc)-bearing N-linked oligosaccharides released from them and to IgG which is not O-glycosylated. HHL binding to IgA1 and fetuin was unaffected by removal of their N-linked oligosaccharides by alpha-mannosidase. When immobilized, O-glycosylated serum proteins but not IgG could capture HHL from its solutions. Desialylated or polymeric IgA1 was better inhibitor than monomeric IgA1. The findings suggest a possible role for galectin-1 in anchoring of microbial and cancer cells known to be rich in T antigen, in high serum IgA1 turn over and in tissue sequestering of IgA1 immune complexes especially after their microbial desialylation in IgA nephropathy and other immune complex-mediated disorders.

Redistributions of macrophages expressing the macrophage galactose-type C-type lectin (MGL) during antigen-induced chronic granulation tissue formation

Cell surface lectins are known to regulate trafficking of cells in the immune system, yet the role of macrophage galactose-type C-type lectin 1 and 2 (MGL1/2) is poorly understood. In this study, antigen-specific chronic inflammation was induced in a subcutaneous air pouch model in mice, and distribution of cells expressing MGL1/2 was investigated. Azobenzenearsonate-conjugated acetylated BSA, used as an antigen, was introduced into an air pouch of immunized mice, and tissue formation and distribution of MGL1/2-positive cells in the sub-dermal regions was examined. Thickness of the inflammatory tissue and number of MGL1/2-positive cells simultaneously reached the maximum at day 4 and returned to the control level at day 6 or 8. When additional antigenic challenges were given, a chronic granulation tissue, which had two distinct layers, was generated. In the chronic tissue, CD11b-positive/MGL1/2-negative cells were abundant in the area close to the antigenic stimulus, while the area far from the antigenic stimulus was dominated by MGL1/2-positive/CD11b-negative or -low cells. Flow cytometric analyses of isolated cells from the granulation tissue revealed that MGL1/2-positive cells expressed MHC class II at high levels, CD11b at low levels but no CD11c. MGL1/2-positive and -negative fractions were separated from cells in the granulation tissue and a higher level of IL-1alpha messenger RNA than negative populations was detected in the MGL1/2-positive fraction by the semi-quantitative reverse transcription-PCR method. IL-1alpha production by MGL1/2-positive cells was also immunohistochemically detected. Results suggest that MGL1/2-positive cells represent a distinct sub-population of macrophages, having unique functions in the generation and maintenance of granulation tissue induced by antigenic stimuli.

Characterization and cDNA cloning of monomeric lectins that correspond to the B-Chain of a type 2 ribosome-inactivating protein from the bark of Japanese elderberry (Sambucus sieboldiana)

Two monomeric lectins, SSA-b-3 and SSA-b-4, were purified from the bark tissue of Japanese elderberry, Sambucus sieboldiana. SDS-PAGE of the purified lectins showed the presence of single bands of 35 and 33 kDa for SSA-b-3 and SSA-b-4, respectively, irrespective of the presence of reducing agent. MS analysis as well as gel filtration of these lectins indicated that they exist mostly as monomeric lectins. Analysis of the N-terminal amino acid sequences of SSA-b-3 and SSA-b-4 yielded an identical sequence, indicating their close structural relationship. Four cDNA clones with extensive homology were obtained from the bark cDNA library and indicated to encode SSA-b-3 or SSA-b-4 from the comparison with the N-terminal sequences of these lectins. These clones were classified into two groups, three for SSA-b-3 and one for SSA-b-4, based on the predicted isoelectric points. The amino acid sequences of the encoded polypeptides were almost identical with the B-chain of a type 2 ribosome-inactivating protein from the same bark tissue, sieboldin-b, except for the absence of a small peptide containing a cystein residue, which is critical for the heteromeric dimerization with an A-subunit. Carbohydrate binding specificity and biological activity of these lectins are also reported.

Isolation and characterization of two N-acetyl-D-lactosamine specific lectins from tubers of Arisaema intermedium Blume and A. wallichianum Hook f

Two new lectins were purified from the tubers of Arisaema intermedium Blume and A. wallichianum Hook. f. (family: Araceae) by affinity chromatography on asialofetuin-linked amino activated silica beads. The bound lectins were eluted with 0.1 M glycine-HCl, pH 2.5. They gave a single band corresponding to subunit M(r) 13.4 kDa in SDS-PAGE, pH 8.3. On gel filtration chromatography, the lectins showed a M(r) of 51.2 kDa, suggesting a homotetrameric structure. Both the lectins gave a single peak on size exclusion HPLC and cation-exchange columns and a single band on PAGE, pH 4.5. However, like other monocot lectins, they gave multiple bands in isoelectric focusing and at PAGE 8.3. The lectins were inhibited by N-acetyl-D-lactosamine (LacNAc), a disaccharide and asialofetuin, a complex desialylated serum glycoprotein. They had no requirement for divalent metal ions i.e., Ca2+ and Mn2+ for their activity and were found to be mitogenic towards human lymphocytes. A. intermedium showed antiproliferative effect against various human cancer cell lines in vitro.

Feasibility on systemic delivery of asialoorosomucoid complex to hepatic origin cells mediated by asialoglycoprotein receptor

Receptor mediated gene delivery is a new gene transfer strategy. Asialoglycoprotein receptor (ASGP-R), the receptor of asialoorosomucoid (Asor), is specially expressed on the surface of hepatocyte. In this paper, the nuclide 131I was combined with Asor to form a kind of soluble nuclide-protein complex, which can be specifically endocytosed into hepatocyte by ASGP-R. After in travenous injection of the complex into experimental animals, the deposition of Asor in vivo and the targeting quality of hepatocyte was detected by ECT. This research testified the feasibility of targeting Asor complex delivery to hepatocyte mediated by ASGP-R in vivo, and provided foundation for the genetic diagnosis and gene therapy of hepatic cell-related diseases.

Different acceptor specificities of two glucuronyltransferases involved in the biosynthesis of HNK-1 carbohydrate

The biosynthesis of HNK-1 carbohydrate is mainly regulated by two glucuronyltransferases (GlcAT-P and GlcAT-S) and a sulfotransferase (HNK-1 ST). To determine how the two glucuronyltransferases are involved in the biosynthesis of the HNK-1 carbohydrate, we prepared soluble forms of GlcAT-P and GlcAT-S fused with the IgG-binding domain of protein A and then compared the enzymatic properties of the two enzymes. Both GlcAT-P and GlcAT-S transferred glucuronic acid (GlcA) not only to a glycoprotein acceptor, asialoorosomucoid (ASOR), but also to a glycolipid acceptor, paragloboside. The activity of GlcAT-P toward ASOR was enhanced fivefold in the presence of sphingomyelin, but there were no effects on that of GlcAT-S. The activities of the two enzymes toward paragloboside were only detected in the presence of phospholipids such as phosphatidylinositol. Kinetic analysis revealed that the K(m) value of GlcAT-P for ASOR was 10 times lower than that for paragloboside. Furthermore, acceptor specificity analysis involving various oligosaccarides revealed that GlcAT-P specifically recognized N-acetyllactosamine (Galbeta1-4GlcNAc) at the nonreducing terminals of acceptor substrates. In contrast, GlcAT-S recognized not only the terminal Galbeta1-4GlcNAc structure but also the Galbeta1-3GlcNAc structure and showed the highest activity toward triantennary N-linked oligosaccharides. GlcAT-P transferred GlcA to NCAM about twice as much as to ASOR, whereas GlcAT-S did not show any activity toward NCAM. These lines of evidence indicate that these two enzymes have significantly different acceptor specificities, suggesting that they may synthesize functionally and structurally different HNK-1 carbohydrates in the nervous system.

Targeted gene delivery into HepG2 cells using complexes containing DNA, cationized asialoorosomucoid and activated cationic liposomes

Unilamellar activated cationic liposomes containing 3beta[N-(N',N'-dimethylaminopropane)-carbamoyl] cholesterol, dioleoyl phosphatidylethanolamine (DOPE) and the N-hydroxysuccinimide ester of cholesteryl hemisuccinate (4:5:1, molar ratio) have been prepared and their DNA-binding capacity has been assessed in a gel retardation assay. Ternary complexes composed of activated cationic liposomes, carbodiimide-cationized asialoorosomucoid (Me+AOM) and pRSVL plasmid DNA were assembled for receptor-mediated DNA delivery into cells expressing the asialoglycoprotein receptor (ASGP-R). Binding of complexes in which Me+AOM was replaced by fluoresceinated Me+AOM (FMe+AOM) to the human hepatocellular cell line HepG2 at 4 degrees C was severely reduced by co-incubation with asialoorosomucoid (AOM). Moreover, assemblies containing liposomes, pRSVL DNA and Me+AOM (8:1:4, w/w/w) promoted high levels of luciferase activity in this cell line (1.3 x 10(7) relative light units/mg soluble cell protein). Assays conducted in the presence of a hundred-fold excess of the ligand AOM afforded considerably lower levels of transfection (2.5 x 10(5) relative light units/mg soluble cell protein). In contrast, the highest level of luciferase activity achieved with liposome, pRSVL DNA, AOM complexes was only a quarter of the best levels obtained with liposome, pRSVL DNA, Me+AOM assemblies. These findings strongly support the notion that complexes gain entry into hepatocyte-derived cells by ASGP-R mediation and that they are potentially useful gene carriers to liver hepatocytes.

Regulation of sialic acid O-acetylation in human colon mucosa

The expression of O-acetylated sialic acids in human colonic mucins is developmentally regulated, and a reduction of O-acetylation has been found to be associated with the early stages of colorectal cancer. Despite this, however, little is known about the enzymatic process of sialic acid O-acetylation in human colonic mucosa. Recently, we have reported on a human colon sialate-7(9)-O-acetyltransferase capable of incorporating acetyl groups into sialic acids at the nucleotide-sugar level [Shen et al., Biol. Chem. 383 (2002), 307-317]. In this report, we show that the CMP-N-acetyl-neuraminic acid (CMP-Neu5Ac) and acetyl-CoA (AcCoA) transporters are critical components for the O-acetylation of CMP-Neu5Ac in Golgi lumen, with specific inhibition of either transporter leading to a reduction in the formation of CMP-5-N-acetyl-9-O-acetyl-neuraminic acid (CMP-Neu5,9Ac2). Moreover, the finding that 5-N-acetyl-9-O-acetyl-neuraminic acid (Neu5,9Ac2 could be transferred from neo-synthesised CMP-Neu5,9Ac2 to endogenous glycoproteins in the same Golgi vesicles, together with the observation that asialofetuin and asialo-human colon mucin are much better acceptors for Neu5,9Ac2 than asialo-bovine submandibular gland mucin, suggests that a sialyltransferase exists that preferentially utilises CMP-Neu5,9Ac2 as the donor substrate, transferring Neu5,9Ac2 to terminal Galbeta1,3(4)R- residues.

Purification and characterization of two recombinant human glucuronyltransferases involved in the biosynthesis of HNK-1 carbohydrate in Escherichia coli

Two glucuronyltransferases (GlcAT-P and GlcAT-S) are involved in the biosynthesis of HNK-1 carbohydrate, which is spatially and temporally regulated in the nervous system. To clarify the enzymatic properties of the respective glucuronyltransferases, we established an expression system for producing large amounts of soluble forms of flag-tagged human GlcAT-P and GlcAT-S in Escherichia coli. Approximately 15 and 6 mg of enzymatically active flag-GlcAT-P and flag-GlcAT-S were purified from E. coli cells in 5 liters of culture medium, respectively. These recombinant enzymes transferred GlcA to a glycoprotein acceptor, asialo-orosomucoid (ASOR), as well as a glycolipid acceptor, paragloboside. The specific activity of the recombinant GlcAT-P (1100 nmol/min/mg) toward a glycoprotein acceptor, ASOR, was comparable to that of the enzyme (4300 nmol/min/mg) purified from rat brain. Phosphatidylinositol (PI) is specifically required for expression of the activity of the recombinant enzymes toward a glycolipid acceptor, paragloboside. The recombinant GlcAT-P was highly specific for the terminal type II structure, Galbeta1-4GlcNAc, while the recombinant GlcAT-S recognized not only the type II structure, Galbeta1-4GlcNAc, but also the type I structure, Galbeta1-3GlcNAc. These acceptor specificities were similar to those of the native enzymes.

Evidence of porcine and human endothelium activation by cancer-associated carbohydrates expressed on glycoproteins and tumour cells

It is well established that after metastatic cancer cells escape the primary tumour and enter the circulation, their interactions with microvascular endothelium of a target organ constitute an essential rate-limiting step in haematogenous cancer metastasis. However, the physiological and biochemical processes supporting neoplastic cell arrest and retention in the microcirculation are still poorly understood. In this study, we present experimental evidence that microvascular endothelium of metastasis-prone tissues undergoes activation in response to desialylated cancer-associated carbohydrate structures such as Thomsen-Friedenreich (TF) antigen (Galbeta1-3GalNAc) expressed on circulating glycoproteins and neoplastic cells. The metastasis-associated endothelium activation, manifested by marked increase in endothelial cell surface galectin-3 expression, causes gradual decrease in cancer cell velocities (from 72 x 10(2)+/- 33 x 10(2) microm s-1 to 7.6 x 10(2)+/- 1.9 x 10(2) microm s-1, mean +/-s.d.) accompanied by a corresponding increase in the percentage of rolling cells (from 3.3%+/- 1.2% to 24.3%+/- 3.6%, mean +/-s.d.), and results in human breast and prostate carcinoma cell arrest and retention in the microvasculature. This process, which could be of high importance in haematogenous cancer metastasis, was inhibited efficiently by an anti-TF antigen function-blocking antibody. Carbohydrate-mediated endothelial activation could be a process of physiological significance as it probably occurs in the interactions between a variety of circulating constituents and the vessel wall.

Purification and characterization of complex carbohydrate specific isolectins from wild legume seeds: Acacia constricta is (vinorama) highly homologous to Phaseolus vulgaris lectins

Vinorama isolectins (VL2-VL4) were purified from seeds of Acacia constricta (vinorama) using affinity chromatography on a fetuin-fractogel column followed by cationic-exchange chromatography. Each isolectin fraction presented a characteristic isoelectric point range from 5.5 to 8.4. Under native conditions, VL containing fractions migrated as tetramers of 133 kDa, while in SDS-PAGE, in presence of 2-mercaptoethanol, a single subunit band with M(r) of 34 kDa was observed. VL was found to be a glycoprotein with a 7.5% neutral sugar content. Antibodies to Phaseolus vulgaris lectins PHA and other wild legume lectins as Olneya tesota (palo fierro) PF2 and PF3, and Parkinsonia aculeate (palo verde) PV reacted with VL, but not with anti Glycine max agglutinin SBA or anti Lotus tetragonolobus agglutinin LTA. Furthermore, direct analysis of VL peptides showed sequences homologous to those reported in different lectins of the Phaseolus genus. VL2-VL4 did not have ABO serological or simple sugar specificity, but were inhibited by complex carbohydrates from fetuin and thyroglobulin. Asialofetuin carbohydrates strongly interacted with VL4 and VL3. Vinorama isolectins could be classified as "complex lectins".

Galectin-1 induces astrocyte differentiation, which leads to production of brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) is a neuroprotective polypeptide that is thought to be responsible for neuron proliferation, differentiation, and survival. An agent that enhances production of BDNF is expected to be useful for the treatment of neurodegenerative diseases. Here we report that galectin-1, a member of the family of beta-galactoside binding proteins, induces astrocyte differentiation and strongly inhibits astrocyte proliferation, and then the differentiated astrocytes greatly enhance their production of BDNF. Induction of astrocyte differentiation and BDNF production by an endogenous mammalian lectin may be a new mechanism for preventing neuronal loss after injury.

Receptor-mediated endocytosis by the asialoglycoprotein receptor: effect of ethanol administration on endosomal distribution of receptor and ligand

Using the asialoglycoprotein receptor (ASGP-R) and a representative ligand, asialoorosomucoid (ASOR), we have previously shown ethanol-induced impairment of endosomal acidification, receptor recycling and ligand binding, internalization, and degradation. In the current study, we further investigated ethanol-induced alterations in receptor/ligand trafficking by labeling endosomes in vivo with either Texas-Red-ASOR or 125I-ASOR, and then assessing the receptor/ligand content of endosomes. We assessed two fractions after both 5 and 25 min of labeling: 'early endosomes' (EEs; endosomes from the cell periphery) and 'late endosomes' (LEs; endosomes farther into the cell interior). At both time points, significantly more ligand was found in EE fractions isolated from chow- and pair-fed controls (3:1, EE to LE, respectively). However, endosomes isolated from ethanol-fed animals showed a shift over time toward a more equal ligand distribution between endosome fractions (P < or = 0.05). Analysis of the ASGP-R content revealed a distribution pattern between the endosome fractions similar to that observed for ligand distribution. Impairment of receptor-ligand dissociation was assessed in endosome fractions by determining bound/free ligand ratios. Analysis showed that most of the ligand present in both endosome fractions was free (56-99%), although more was bound to receptor in EE vs LE of both control and ethanol animals (P < or = 0.05). At 5 min, more ligand remained bound in endosomes from ethanol-fed animals compared with control endosomes (P < or = 0.05), and the same pattern was observed at the latter time point. These results suggest that delayed dissociation may cause the receptor ligand complexes to travel farther into the cell interior, which may impair proper trafficking of the ligand to lysosomes and alter the receptor recycling.