Biosynthesis of fucose containing lacto-series glycolipids in human colonic adenocarcinoma Colo 205 cells

Alpha1,3-fucosyltransferase 9 (FUT9; Fuc-TIX) preferentially fucosylates the distal GlcNAc residue of polylactosamine chain while the other four alpha1,3FUT members preferentially fucosylate the inner GlcNAc residue

We analyzed the substrate specificity of six human alpha1,3-fucosyltransferases (alpha1,3FUTs) for the 2-aminobenzamide (2AB)-labelled polylactosamine acceptor, Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAcbeta1- 3Galbeta1-4GlcNAc-2AB (3LN-2AB). FUT9 preferentially fucosylated the distal GlcNAc residue of the polylactosamine chain while the other four alpha1,3FUT members, FUT3, FUT4, FUT5 and FUT6, preferentially fucosylated the inner GlcNAc residue. This indicated that FUT9 exhibits more efficient activity for the synthesis of Lewis x carbohydrate epitope (Le(x); CD15; stage-specific embryonal antigen-1 (SSEA-1)). In contrast, the other four members synthesize more effectively the internal Le(x) epitope. FUT7 could not transfer a fucose to an acceptor which is non-sialylated.

Cloning of a novel member of the UDP-galactose:beta-N-acetylglucosamine beta1,4-galactosyltransferase family, beta4Gal-T4, involved in glycosphingolipid biosynthesis

A novel putative member of the human UDP-galactose:beta-N-acetylglucosamine beta1,4-galactosyltransferase family, designated beta4Gal-T4, was identified by BLAST analysis of expressed sequence tags. The sequence of beta4Gal-T4 encoded a type II membrane protein with significant sequence similarity to other beta1,4-galactosyltransferases. Expression of the full coding sequence and a secreted form of beta4Gal-T4 in insect cells showed that the gene product had beta1,4-galactosyltransferase activity. Analysis of the substrate specificity of the secreted form revealed that the enzyme catalyzed glycosylation of glycolipids with terminal beta-GlcNAc; however, in contrast to beta4Gal-T1, -T2, and -T3, this enzyme did not transfer galactose to asialo-agalacto-fetuin, asialo-agalacto-transferrin, or ovalbumin. The catalytic activity of beta4Gal-T4 with monosaccharide acceptor substrates, N-acetylglucosamine as well as glucose, was markedly activated in the presence of alpha-lactalbumin. The genomic organization of the coding region of beta4Gal-T4 was contained in six exons. All intron/exon boundaries were similarly positioned in beta4Gal-T1, -T2, and -T3. beta4Gal-T4 represents a new member of the beta4-galactosyltransferase family. Its kinetic parameters suggest unique functions in the synthesis of neolactoseries glycosphingolipids.

A family of human beta4-galactosyltransferases. Cloning and expression of two novel UDP-galactose:beta-n-acetylglucosamine beta1, 4-galactosyltransferases, beta4Gal-T2 and beta4Gal-T3

BLAST analysis of expressed sequence tags (ESTs) using the coding sequence of the human UDP-galactose:beta-N-acetylglucosamine beta1, 4-galactosyltransferase, designated beta4Gal-T1, revealed a large number of ESTs with identical as well as similar sequences. ESTs with sequences similar to that of beta4Gal-T1 could be grouped into at least two non-identical sequence sets. Analysis of the predicted amino acid sequence of the novel ESTs with beta4Gal-T1 revealed conservation of short sequence motifs as well as cysteine residues previously shown to be important for the function of beta4Gal-T1. The likelihood that the identified ESTs represented novel galactosyltransferase genes was tested by cloning and sequencing of the full coding region of two distinct genes, followed by expression. Expression of soluble secreted constructs in the baculovirus system showed that these genes represented genuine UDP-galactose:beta-N-acetylglucosamine beta1, 4-galactosyltransferases, thus designated beta4Gal-T2 and beta4Gal-T3. Genomic cloning of the genes revealed that they have identical genomic organizations compared with beta4Gal-T1. The two novel genes were located on 1p32-33 and 1q23. The results demonstrate the existence of a family of homologous galactosyltransferases with related functions. The existence of multiple beta4-galactosyltransferases with the same or overlapping functions may be relevant for interpretation of biological functions previously assigned to beta4Gal-T1.

Fucosylation of complex glycosphingolipids by recombinant fucosyltransferase-VII

Fucosyltransferase VII (FucT-VII) is one of five known alpha 1-->3fucosyltransferases capable of transferring fucose to the C-3 position of N-acetylglucosamine residues found in lactosamine based glycans. Previous studies have indicated that FucT-VII has a very restricted specificity, capable of fucosylating only terminally alpha 2-->3sialylated carbohydrate substrates, resulting in the synthesis of the sialyl Lewis x (sLe(x)) epitope. Although FucT-VII is expressed in cells of myeloid origin, the monosialylganglioside fraction of HL60 cells contains only internally and/or multiply fucosylated polylactosamine structures; no monofucosylated sLe(x) derivatives are detected. We now report that the structure of the final product formed by the action of FucT-VII on sialynorhexaosylceramide (a glycosphingolipid substrate having multiple fucosylation sites) is extended monofucosyl sLe(x) and fucosylation is restricted to the terminal GlcNAc-V. This indicates that the biosynthesis of all fucosylated monosialylated gangliosides found in HL60 cells (including the E-selectin binding fractions) involves at least one additional alpha 1-->3fucosyltransferase.

Characterization and purification of fucosyltransferases from the cytosol of rat colon

The occurrence and baseline characteristics of fucosyltransferases (alpha-1,2, alpha-1,3 and alpha-1,4) in the cytosol (soluble) and pellet (membrane-bound) of rat colon have been studied since the fucosylation process is known to alter in colon pathology. All enzymes studied in the colon pellet had higher activity when compared to the cytosol. The colon pellet alpha-1,3 fucosyltransferase preferred desialylated alpha 1-acid glycoprotein as acceptor substrate. Both soluble and membrane-bound enzymes, alpha-1,2 and alpha-1,3 fucosyltransferases, required Mn2+, Mg2+ and Ca2+ for maximum activity but were inactivated by Cu2+ ions. Both soluble alpha-1,2 and alpha-1,3 fucosyltransferases showed optimal activity at pH 6.0, whereas the optimum for their membrane-bound activities were at pH 5.8 and 6.2, respectively. Furthermore, a soluble alpha-1,3 fucosyltransferase from rat colon was purified and during purification the co-presence of alpha-1,3/4 fucosyltransferase was detected. The acceptor of preference for the purified soluble alpha-1,3 fucosyltransferase was desialylated glycoprotein while low molecular weight substrates were poor acceptors. Both the purified fucosyltransferases were inhibited by N-ethylmaleimide. The M(r) values determined by SDS-PAGE electrophoresis of alpha-1,3/4 fucosyltransferase and of alpha-1,3 fucosyltransferase were 68,780 and 40,680 respectively. In conclusion, based on their properties, the purified soluble colon alpha-1,3 fucosyltransferase appeared to be of plasma-type (or FT-I) while the soluble alpha-1,3/4 fucosyltransferase corresponded to Lewis-type or FT-III.

Galactosylgloboside expression in seminoma. Inverse correlation with metastatic potential

BACKGROUND

Altered glycosylation is a common phenotype expressed in essentially all types of human cancer and has been found to be correlated closely with the invasive and metastatic properties of a given tumor. Because there was no prognostic information concerning aberrant glycosylation of seminoma, the authors studied this topic.

METHODS

Glycosphingolipid (GSL) composition of orchiectomy samples of seminoma were analyzed systematically. GSL patterns from seminoma samples of the following three groups were compared after a 44-month postoperative period: Stage I disease with no evidence of metastasis during the 44-month postoperative period, Stage I with metastatic relapse during this period, and Stage II with retroperitoneal lymph node metastasis. Unknown GSLs detected were analyzed chemically by 1H-nuclear magnetic resonance spectroscopy and mass spectrometry.

RESULTS

All nonmetastatic seminomas (n = 12) contained a GSL band that was identified as galactosylgloboside (Gb5; Gal beta 1-->3GalNAc beta 1-->3Gal alpha 1-->4 Gal beta 1-->4Glc beta 1-->1Cer). All metastatic seminomas (n = 5) lacked this GSL, although the sample sizes were admittedly small.

CONCLUSION

Only the presence or absence of galactosylgloboside (Gb5), but of no other GSL or gangliosides, clearly correlated with metastatic potential in patients with seminoma. This observation is useful in the estimation of prognosis of patients with seminoma, especially those with Stage I disease.

Repression of the Lewis fucosyl transferase by retinoic acid increases apical sialosyl Lewis(a) secretion in colorectal carcinoma cultures

The rate of polarised secretion of sialosyl Lewis(a)(19-9) molecular species (SiaLeams) by SW1116 colorectal carcinoma cells is stimulated at least ninefold by the presence of 3 microM retinoic acid (RA). In order to investigate the intracellular origins of this augmentation, carcinoma cell membranes, membrane subfractions, and media were studied to determine alterations in sialosyl Lewis(a) levels, oligosaccharide composition, and core structures accompanying the capacity to increase export of this epitope. We observed a nine- to twentyfold increase in sialosyl Lewis(a) epitope levels in a light membrane subfraction from RA-treated cells. Antigenic molecules of < 200,000 M(r) on acrylamide gradient gels were concentrated in two doublets in the apparent M(r) range 106,000-152,000 on Western blots. Carbohydrate analyses of oligosaccharides from SiaLeams of membrane subfractions and apical media indicated much higher fucose/mannose, fucose/sialic, fucose/sialosyl Lewis(a), fucose/total CHO, and (3H) fucose incorporation in control samples than RA samples. Western blots of samples from membrane subfractions and media indicated that, in contrast to the effect of RA on the sialosyl Lewis(a) epitope, RA treatment did not augment cysteine-rich, PDTRP, blood group H-2, blood group A, and EGF receptor-like region epitopes in the media. In addition, Northern blots using the Lewis fucosyl transferase (FTIII) cDNA showed a dramatic diminution of mRNA encoding FTIII but apparently unaltered levels of sialyl transferase (ST4) mRNA. Since subterminal fucosylation of lactosyl termini blocks terminal sialylation, we conclude that one mechanism of sialosyl Lewis(a) induction in this culture system is the lower expression of the Lewis fucosyl transferase mRNA. Therefore less subterminal fucosylation of GlcNAc permits the prior sialylation of terminal Gal beta 1-3 moieties at oligosaccharide termini destined for export from the Golgi.

Acceptor specificity of different length constructs of human recombinant alpha 1,3/4-fucosyltransferases. Replacement of the stem region and the transmembrane domain of fucosyltransferase V by protein A results in an enzyme with GDP-fucose hydrolyzing activity

The acceptor specificity of recombinant full-length, membrane-bound fucosyltransferases, expressed in COS-7 cells, and soluble, protein-A chimeric forms of alpha 1,3-fucosyltransferase (Fuc-T) III, Fuc-TIV, and Fuc-TV was analyzed toward a broad panel of oligosaccharide, glycolipid, and glycoprotein substrates. Our results on the full-length enzymes confirm and extend previous studies. However, chimeric Fuc-Ts showed increased activity toward glycoproteins, whereas chimeric Fuc-TIII and Fuc-TV had a decreased activity with glycosphingolipids, compared to the full-length enzymes. Unexpectedly, chimeric Fuc-TV exhibited a GDP-fucose hydrolyzing activity. In substrates with multiple acceptor sites, the preferred site of fucosylation was identified. Fuc-TIII and Fuc-TV catalyzed fucose transfer exclusively to OH-3 of glucose in lacto-N-neotetraose and lacto-N-tetraose, respectively, as was demonstrated by 1H NMR spectroscopy. Thin layer chromatography immunostaining revealed that FucT-IV preferred the distal GlcNAc residue in nLc6Cer, whereas Fuc-TV preferred the proximal Gl-cNAc residue. Incubation of Fuc-TIV or Fuc-TV with VI3NeuAcnLc6Cer resulted in products with the sialyl-LewisX epitope as well as the VIM-2 structure. To identify polar groups on acceptors that function in enzyme binding, deoxygenated substrate analogs were tested as acceptors. All three Fuc-Ts had an absolute requirement for a hydroxyl at C-6 of galactose in addition to the accepting hydroxyl at C-3 or C-4 of GlcNAc.

Biosynthesis of sialyl-oligomeric-Lewisx and VIM-2 epitopes: site specificity of human milk fucosyltransferase

In a previous study we have established the order of fucosylation of a trimer of Gal beta 1-->4GlcNAc (LacNAc) linked to a synthetic hydrophobic aglycon, (LacNAc)3-[(trifluoroacetamido)phenyl]ethyl, by a partially purified alpha 3-fucosyltransferase preparation from normal human milk [De Vries, Th., Norberg, T., Lönn, H., & van den Eijnden, D. H. (1993) Eur. J. Biochem. 216, 769-777]. Using the same fucosyltransferase preparation, we have now studied the fucosylation of the oligosaccharide NeuAc alpha 2-->3(LacNAc)3-Me. This compound was generated from the asialo analogue by use of an alpha 3-sialyltransferase preparation from human placenta. The location of the fucose residues in the monofucosylated and difucosylated intermediate products was determined by analyzing digests obtained after endo-beta-galactosidase treatment using HPLC on amino-bonded silica. In addition, the fucosylated NeuAc alpha 2-->3(LacNAc)3-Me structures were characterized by high-pH anion-exchange chromatography with pulsed amperometric detection and were identified by 400-MHz 1H-NMR spectroscopy. Intermediate products included oligosaccharides that contained the VIM-2, sialyl-LewisX, and sialyl-dimeric-LewisX epitopes. The final product was identified as the sialyl-trimeric-LewisX oligosaccharide. Kinetic analysis of the fucosylation reaction indicated that there is a significant difference in the rate of transfer of the first, second, and third fucose residues onto the acceptor molecule. Transfer of the first fucose occurred to either of the three GlcNAc residues in NeuAc alpha 2-->3(LacNAc)3-Me with only a modest preference for the proximal and medial residues. A similar slight preference for these GlcNAc residues was found for the attachment of the second fucose residue.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemoenzymic synthesis of sialylated and fucosylated oligosaccharides having an N-acetyllactosaminyl core

Several sialylated and fucosylated oligosaccharides, based upon the N-acetyllactosaminyl core structure, have been synthesized from a single trisaccharide glycoside, beta-D-GlcNAc-(1-->3)-beta-D-Gal-(1-->4)-beta-D-GlcNAc-OCH2(CH2)++ +7CO2CH3, by the sequential use of several glycosyltransferases and one sialidase. In these chemoenzymic syntheses, selective internal monofucosylation of a dimeric N-acetyl-lactosaminyl tetrasaccharide is achieved via two routes. It is demonstrated that the pentasaccharide beta-D-Gal-(1-->4)-beta-D-GlcNAc-(1-->3)-beta-D-Gal-(1-->4)-[alpha- L-Fuc-(1-->3)]-beta-D-GlcNAc-OCH2(CH2)7-CO2CH3 is an acceptor for the rat liver beta-D-Gal-(1-->3/4)-D-Glc-NAc alpha 2,3- and beta-D-Gal-(1-->4)-D-GlcNAc alpha 2,6-sialyltransferases. Among the structures obtained is the terminal hexasaccharide of the CD-65/VIM-2 epitope.

The use of human milk fucosyltransferase in the synthesis of tumor-associated trimeric X determinants

We have studied the fucosylation of a chemically synthesized trimer of N-acetyllactosamine [(LacNAc)3-EtPhNHCOCF3] with a fucosyltransferase preparation from normal human milk, which utilizes both type-1 and type-2 structures, whether sialylated or not. When fucose residues were added enzymically to the (LacNAc)3-EtPhNHCOCF3 hexasaccharide, mono-, di-, or trifucosylated oligosaccharide species were formed, containing the Lewisx determinant (Gal beta 1-->4[Fuc alpha 1-->3]Glc-NAc beta 1-->3). With excess GDP-fucose and prolonged reaction times, the trifucosylated product was formed in almost quantitative yield. Kinetic analysis of the fucosylation reaction indicated that there is a significant difference in the rate of transfer of the first, second and third fucose residues onto the acceptor molecule. The location of the fucose residues in the monofucosylated and difucosylated intermediate products was assessed by analyzing the digests obtained after endo-beta-galactosidase treatment by HPLC and reverse-phase chromatography. In addition, the fucosylated (LacNAc)3-EtPhNHCOCF3 structures were characterized by HPLC and were identified by 400-MHz 1H-NMR spectroscopy. There is a highly preferred order in which the fucosyl residues are attached to (LacN-Ac)3-EtPhNHCOCF3. In the major pathway, the first two fucose residues are transferred with equal preference to the medial (GN3) and proximal (GN1) GlcNAc residues, whereas the third fucose is attached to the distal (GN5) GlcNAc residue. These results are of relevance in understanding the role of alpha-3-fucosyltransferase in the biosynthesis of Lewisx-related cell-surface carbohydrate structures, that function as ligands for selectin-type cell-adhesion molecules and may play a role in the invasion and metastasis of several carcinoma.

Clinical aspects of glycoprotein biosynthesis

Glycoproteins are widely distributed among species in soluble and membrane-bound forms, associated with many different functions. The heterogenous sugar moieties of glycoproteins are assembled in the endoplasmic reticulum and in the Golgi and are implicated in many roles that require further elucidation. Glycoprotein-bound oligosaccharides show significant changes in their structures and relative occurrences during growth, development, and differentiation. Diverse alterations of these carbohydrate chains occur in diseases such as cancer, metastasis, leukemia, inflammatory, and other diseases. Structural alterations may correlate with activities of glycosyltransferases that assemble glycans, but often the biochemical origin of these changes remains unclear. This suggests a multitude of biosynthetic control mechanisms that are functional in vivo but have not yet been unraveled by in vitro studies. The multitude of carbohydrate alterations observed in disease states may not be the primary cause but may reflect the growth and biochemical activity of the affected cell. However, knowledge of the control mechanisms in the biosynthesis of glycoprotein glycans may be helpful in understanding, diagnosing, and treating disease.

Human epidermal keratinocyte expression of sialyl-Lewis X

Cell-surface oligosaccharides can function as ligands for intercellular adhesion receptors, matrix proteins, and growth factors. We report that human neonatal and adult epidermal keratinocytes (KC) express sialyl Lewis X [s-Le(x); SA alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3R], a ligand for endothelial and platelet selectins. Freshly isolated or cultured KC bind FH6 monoclonal antibody (MoAb), which is specific for s-Le(x)-containing oligosaccharides. The relevant epitope is bona fide s-Le(x), because sialidase treatment of KC suspensions abrogates FH6 binding while generating de novo KC reactivity with anti-Le(x). KC stained in ice-cold suspension display a knobby membrane distribution of s-Le(x) detectable by immunofluorescence microscopy. As others have reported, FH6 appeared not to bind KC in perpendicular skin sections. However, basal KC in intact epidermal sheets exhibited obvious "honeycomb" reactivity with FH6 when stained and viewed en face, suggesting that s-Le(x) in intact epidermis may occur in bands that parallel the major tissue axis. FH6 specifically immunoprecipitated proteins of Mr 34 kd, 44 kd, and 56 kd from [35S]-labeled KC, and anti-Le(x) precipitated similar proteins from sialidase-treated KC. The enzymatic basis for KC s-Le(x) expression was studied by analyzing acceptor specificities and other properties of KC fucosyltransferases. Results indicate that KC express both Lewis- and myeloid-type alpha 1-3fucosyltransferases. KC s-Le(x) could be an important element of the epithelial milieu, because both epithelial cells and immune cells that home to epithelia express s-Le(x) and related structures, and because KC s-Le(x) is well positioned for selectin-mediated platelet binding after trans-cutaneous wounding. The apparent distributions of s-Le(x) in epidermis and on isolated KC are compatible with a functional role for s-Le(x) in these intercellular interactions.

Occurrence and specificities of α3-fucosyltransferases

The Le(x) (CD15) carbohydrate antigen and sialylated and oligomeric derivatives thereof have been implicated in cell adhesion processes. Expression of these antigens is developmentally regulated and (re)occurrence of several members of this group has been reported in malignant transformation of cells. Studies on the enzymology and genetics of alpha 3-fucosyltransferases, glycosyltransferases that play a key role in the biosynthesis of these antigens, would yield insight in the regulation of expression of these carbohydrate structures. In this paper the existing literature on these enzymes is reviewed and placed in the context of cell adhesion and malignancy.

Stable expression of a cDNA encoding a human beta 1 --> 3galactosyltransferase responsible for lacto-series type 1 core chain synthesis in non-expressing cells: variation in the nature of cell surface antigens expressed

Transient expression of a human colonic adenocarcinoma Colo 205 cell derived cDNA in cell lines which ordinarily express only neolacto-series glycolipids has resulted in the expression of a beta 1 --> 3galactosyltransferase gene responsible for synthesis of glycolipids based upon the lacto-series type 1 core chain. Calcium phosphate transfected cells were panned on anti-IgM coated plates after initial treatment with a combination of monoclonal antibodies specific for type 1 chain terminal structures (TE-3) and a very broadly specific antibody reactive with multiple type 1 chain derivatives (TE-2). Adherent cells after panning were capable of efficiently transferring Gal in beta 1 --> 3-linkage to the acceptor glycolipid Lc3. Using these reagents, clones of stably transfected human colonic adenocarcinoma HCT-15 cells were produced and isolated. Parental HCT-15 cells do not express type 1 chain based antigens. The nature of the type 1 chain based antigens produced in each of these clones was analyzed by solid phase antibody binding assays. Three types of behavior were observed. Formation of type 1 terminal structures that were either exclusively sialylated or fucosylated, or a mixture of sialylated and fucosylated determinants occurred. In contrast, no difference in type 2 antigen expression between any clone and the parental cells was observed. These data suggest that coordination of subsequent reactions capable of modifying type 1 chain structures is not the same in all clones. The relationship of these results to aspects of cellular regulation of carbohydrate biosynthesis is discussed.

Extended type-1 chain glycosphingolipid antigens. Isolation and characterization of trifucosyl-Leb antigen (III4V4VI2Fuc3Lc6)

A Lewis-b-active glycosphingolipid containing a repetitive type-1 chain carbohydrate core was isolated from human colonic adenocarcinoma cell line Colo205. This glycosphingolipid was purified by HPLC and preparative high-performance thin-layer chromatography and its structure elucidated by positive-ion fast-atom-bombardment mass spectrometry with collision-induced disassociation, 1H-NMR spectroscopy and methylation analysis. The glycosphingolipid was found to be a trifucosylated derivative of this novel carbohydrate core, having the following structure: [formula; see text].

CD62 and endothelial cell-leukocyte adhesion molecule 1 (ELAM-1) recognize the same carbohydrate ligand, sialyl-Lewis x

The leukocyte receptor CD62, which is expressed on activated platelets and endothelial cells, is shown to mediate cell adhesion by binding a sialylated carbohydrate structure, sialyl-Lewis x, found on neutrophils, monocytes, and tumor cells. This structure has previously been identified as the ligand for another member of the LEC-CAM family of cell adhesion molecules, endothelial cell-leukocyte adhesion molecule 1, which also binds neutrophils and monocytes. The results demonstrate that although the two LEC-CAMs differ in their biological activities by their distribution and mode of expression, they are capable of mediating cell adhesion by recognition of the same carbohydrate ligand.

Characterization of two monoclonal antibodies specific for lacto-series type 1 chain Gal beta 1----3GlcNAc-terminal structures

Murine monoclonal antibodies, TE-1 and TE-3, generated by immunization with a biosynthetic reaction product containing a terminal Gal beta 1----3GlcNAc structure have been produced and found to react specifically with underivatized type 1 chain lacto-series carbohydrate structures. Detailed analysis of these antibodies, both IgM, indicates two differing classes of epitope specificity. Antibody TE-1 was found to bind preferentially to longer chain carbohydrate structures containing a terminal Gal beta 1----3GlcNAc disaccharide, indicating that optimal antibody binding involved more than recognition of this disaccharide. In contrast, antibody TE-3 was found to bind strongly carbohydrate structures containing terminal Gal beta 1----3GlcNAc structures irrespective of chain length. Modification of core chain structures by addition of fucose and/or sialic acid residues completely abolished antibody binding with either antibody. TLC immunostaining of neutral glycolipids isolated from a variety of human colonic adenocarcinoma cell lines indicated intensely stained bands, particularly with antibody TE-3, which correlated with the level of expression of type 1 chain based glycolipid derivatives. These antibodies are applied to the detailed study of the regulation of synthesis of lacto-series type 1 chain based carbohydrate structures.