Cell membrane glycoconjugates undergo characteristic changes as a consequence of neoplastic transformation. The cancer-associated carbohydrate structures play key roles in cancer progression by altering the cell-cell and cell-environment interactions. In this review, we will discuss some of the most relevant cancer-associated carbohydrate structures, including the β1,6-branching of N-linked chains, the sialyl Lewis antigens, the α2,6-sialylated lactosamine, the Thomsen-Friedenreich-related antigens and gangliosides. We will describe the mechanisms leading to the expression of these structures and their interactions with sugar binding molecules, such as selectins and galectins. Finally, we will discuss how the glycosylation machinery of the cell is controlled by signal transduction pathways, epigenetic mechanisms and responds to hypoxia.

We attempted to determine whether ␤1,3-galactosyltransferase ␤3Gal-T5 is involved in the biosynthesis of a specific subset of type 1 chain carbohydrates and expressed in a cancer-associated manner. We transfected Chinese hamster ovary (CHO) cells expressing Fuc-TIII with ␤3Gal-T cDNAs and studied the relevant glycoconjugates formed. ␤3Gal-T5 directs synthesis of Lewis type 1 antigens in CHO cells more efficiently than ␤3Gal-T1, whereas ␤3Gal-T2, -T3, and -T4 are almost unable to direct synthesis. In the clone expressing Fuc-TIII and ␤3Gal-T5 (CHO-FT-T5), sialyl-Lewis a synthesis is strongly inhibited by swainsonine but not by benzyl-␣-GalNAc, and sialyl-Lewis x is absent, although it is detected in the clones expressing Fuc-TIII and ␤3Gal-T1 (CHO-FT-T1) or Fuc-TIII and ␤3Gal-T2 (CHO-FT-T2). Endo-␤-galactosidase treatment of Nglycans prepared from clone CHO-FT-T5 releases (؎NeuAc␣233)Gal␤133[Fuc␣134]GlcNAc␤133Gal but not GlcNAc␤133Gal or type 2 chain oligosaccharides, which are found in CHO-FT-T1 cells. This result indicates that ␤3Gal-T5 expression prevents poly-Nacetyllactosamine and sialyl-Lewis x synthesis on Nglycans. Kinetic studies confirm that ␤3Gal-T5 prefers acceptors having the GlcNAc␤133Gal end, including lactotriosylceramide. Competitive reverse transcriptase mediated-polymerase chain reaction shows that the ␤3Gal-T5 transcript is expressed in normal colon mucosa but not or poorly in adenocarcinomas. Moreover, recombinant carcinoembryonic antigen purified from a CHO clone expressing Fuc-TIII and ␤3Gal-T5 reacts with anti-sialyl-Lewis a and carries type 1 chains on oligosaccharides released by endo-␤-galactosidase. We conclude that ␤3Gal-T5 down-regulation plays a relevant role in determining the cancer-associated glycosylation pattern of N-glycans.Type 1 chain oligosaccharides found in N-and O-glycans, as well as in glycolipids, contain the distinctive Gal␤133GlcNAc disaccharide as their core structure. It is synthesized by ␤1,3-galactosyltransferases (

The tetrasaccharide structures Siaα2,3Galβ1,3(Fucα1,4)GlcNAc and Siaα2,3Galβ1,4(Fucα1,3)GlcNAc constitute the epitopes of the carbohydrate antigens sialyl-Lewis a (sLea) and sialyl-Lewis x (sLex), respectively, and are the minimal requirement for selectin binding to their counter-receptors. Interaction of sLex expressed on the cell surface of leucocytes with E-selectin on endothelial cells allows their arrest and promotes their extravasation. Similarly, the rolling of cancer cells ectopically expressing the selectin ligands on endothelial cells is potentially a crucial step favoring the metastatic process. In this review, we focus on the biosynthetic steps giving rise to selectin ligand expression in cell lines and native tissues of gastrointestinal origin, trying to understand whether and how they are deregulated in cancer. We also discuss the use of such molecules in the diagnosis of gastrointestinal cancers, particularly in light of recent data questioning the ability of colon cancers to express sLea and the possible use of circulating sLex in the early detection of pancreatic cancer. Finally, we reviewed the data dealing with the mechanisms that link selectin ligand expression in gastrointestinal cells to cancer malignancy. This promising research field seems to require additional data on native patient tissues to reach more definitive conclusions.

Sialyltransferases have a wide impact on the biology of cancer and can be the target of innovative therapies. Our unified view provides a conceptual framework to understand the impact of altered glycosylation in cancer.

Terminal Fuc␣1-3GlcNAc moieties are displayed by mammalian cell surface glycoconjugates in a tissue-specific manner. These oligosaccharides participate in selectin-dependent leukocyte adhesion and have been implicated in adhesive events during murine embryogenesis. Other functions for these molecules remain to be defined, as do the tissue-specific expression patterns of the corresponding ␣-(1-3)-fucosyltransferase (␣1-3FT) genes. This report characterizes a murine ␣1-3FT that shares 77% amino acid sequence identity with human ELAM ligand fucosyltransferase (ELFT, also termed Fuc-TIV). The corresponding gene maps to mouse chromosome 9 in a region of homology with the Fuc-TIV locus on human chromosome 11q. In vitro, the murine ␣1-3FT can efficiently fucosylate the trisaccharide Gal␣1-3Gal␤1-4GlcNAc (apparent K m of 0.71 mM) to form an unusual tetrasaccharide (Gal␣1-3Gal␤1-4[Fuc␣1-3]GlcNAc) described in periimplantation mouse tissues. The enzyme can also form the Lewis x determinant from Gal␤1-4GlcNAc (K m ‫؍‬ 2.05 mM), and the sialyl Lewis x determinant from NeuNAc␣2-3Gal␤1-4GlcNAc (K m ‫؍‬ 1.78 mM). However, it does not yield sialyl Lewis x determinants when expressed in a mammalian cell line that maintains sialyl Lewis x precursors. Transcripts from this gene accumulate to low levels in hematopoietic organs, but are unexpectedly abundant in epithelia that line the stomach, small intestine, colon, and epididymus. Epithelial cell-specific expression of this gene suggests function(s) in addition to, and distinct from, its proposed role in selectin ligand synthesis.Oligosaccharides represent major components of animal cell surfaces and are believed to function in cellular interactions during development and differentiation (1, 2), oncogenic transformation (3), and inflammation (4). Identification of specific oligosaccharide ligands for the selectin family of cell adhesion molecules directly links cell surface carbohydrates to cell-cell communication in the context of inflammatory response (5-7). The proposed ligands for E-selectin and P-selectin are fucosylated oligosaccharides (for review, see Refs. 4 and 8), whose biosynthesis is catalyzed by ␣-(1-3)-fucosyltransferases (␣1-3FTs).1 These enzymes are encoded by one or more distinct and tightly regulated ␣1-3FT genes.Much of the interest in discovering functional roles for oligosaccharides during development is derived from studies documenting precise temporal-spatial expression patterns for some oligosaccharides during human and murine embryogenesis (9 -12). The murine stage-specific embryonic antigen-1 (SSEA-1; (Gal␤1-4[Fuc␣1-3]GlcNAc; Lewis x)), for example, is expressed coincident with morula compaction at the 8 -16 cell stage of the preimplantation mouse embryo (13,14). Since SSEA-1 structural analogs appear to inhibit compaction, it has been suggested that this antigen may participate in this process (1, 2). While it has been proposed that the SSEA-1 determinant functions to promote homotypic adhesion (15), neither the physiological relevance of this interacti...

Three missense variants of ST3GAL3 are known to be responsible for a congenital disorder of glycosylation determining a neurodevelopmental disorder (intellectual disability/epileptic encephalopathy). Here we report a novel nonsense variant, p.Y220*, in two dichorionic infant twins presenting a picture of epileptic encephalopathy with impaired neuromotor development. Upon expression in HEK-293T cells, the variant appears totally devoid of enzymatic activity in vitro, apparently accumulated with respect to the wild-type or the missense variants, as detected by western blot, and in large part properly localized in the Golgi apparatus, as assessed by confocal microscopy. Both patients were found to efficiently express the CA19.9 antigen in the serum despite the total loss of ST3GAL3 activity, which thus appears replaceable from other ST3GALs in the synthesis of the sialyl-Lewis a epitope. Kinetic studies of ST3GAL3 revealed a strong preference for lactotetraosylceramide as acceptor and gangliotetraosylceramide was also efficiently utilized in vitro. Moreover, the p.A13D missense variant, the one maintaining residual sialyltransferase activity, was found to have much lower affinity for all suitable substrates than the wild-type enzyme with an overall catalytic efficiency almost negligible. Altogether the present data suggest that the apparent redundancy of ST3GALs deduced from knock-out mouse models only partially exists in humans. In fact, our patients lacking ST3GAL3 activity synthesize the CA19.9 epitope sialyl-Lewis a, but not all glycans necessary for fine brain functions, where the role of minor gangliosides deserves further attention.

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The pathways of metabolic processing of exogenously administered GM1 ganglioside in rat liver was investigated at the subcellular level. The GM1 used was 3H-labelled at the level of long-chain base ([Sph(sphingosine)-3H]GM1) or of terminal galactose ([Gal-3H]GM1). The following radioactive compounds, derived from exogenous GM1, were isolated and chemically characterized: gangliosides GM2, GM3, GD1a and GD1b (nomenclature of Svennerholm [(1964) J. Lipid Res. 5, 145-155] and IUPAC-IUB Recommendations [(1977) Lipids 12, 455-468]); lactosylceramide, glucosylceramide and ceramide; sphingomyelin. GM2, GM3, lactosylceramide, glucosylceramide and ceramide, relatively more abundant shortly after GM1 administration, were mainly present in the lysosomal fraction and reflected the occurrence of a degradation process. 3H2O was also produced in relevant amounts, indicating complete degradation of GM1, although no free long-chain bases could be detected. GD1a and GD1b, relatively more abundant later on after administration, were preponderant in the Golgi-apparatus fraction and originated from a biosynthetic process. More GD1a was produced starting from [Sph-3H]GM1 than from [Gal-3H]GM1, and radioactive GD1b was present only after [Sph-3H]GM1 injection. This indicates the use of two biosynthetic routes, one starting from a by-product of GM1 degradation, the other implicating direct sialylation of GM1. Both routes were used to produce GD1a, but only the first one for producing GD1b. Sphingomyelin was the major product of GM1 processing, especially at the longer times after injection, and arose from a by-product of GM1 degradation, most likely ceramide.