Glycosylation of Nα-lauryl-O-(β-D-xylopyranosyl)-L-serinamide as a saccharide primer in cells

In vitro synthesis of mucin-type O-glycans using saccharide primers comprising GalNAc-Ser and GalNAc-Thr residues

Mucin-type O-glycosylation of serine or threonine residue in proteins is known to be one of the major post-translational modifications. In this study, two novel alkyl glycosides, N^α-lauryl-O-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-l-serineamide (GalNAc-Ser-C12) and N^α-lauryl-O-(2-acetamido-2-deoxy-α-d-galactopyranosyl)-l-threonineamide (GalNAc-Thr-C12) were synthesized as saccharide primers to prime mucin-type O-glycan biosynthesis in cells. Upon incubating human gastric cancer MKN45 cells with the saccharide primers, 22 glycosylated products were obtained, and their structures were analyzed using liquid chromatography-mass spectrometry and enzyme digestion. The amounts of glycosylated products were dependent on the amino acid residues in the saccharide primers. For example, in vitro synthesis of T antigen (Galβ1-3GalNAc), fucosyl-T (Fucα1-2Galβ1-3GalNAc), and sialyl-T (NeuAcα2-3Galβ1-3GalNAc) preferred a serine residue, whereas sialyl-Tn (NeuAcα2-6GalNAc) preferred a threonine residue. Furthermore, the glycosylated products derived from GalNAc-Ser/Thr-C12 and Gal-GalNAc-Ser/Thr-C12 using cell-free synthesis showed the same amino acid selectivity as those in the cell experiments. These results indicate that glycosyltransferases involved in the biosynthesis of mucin-type O-glycans distinguish amino acid residues conjugated to GalNAc. The saccharide primers developed in this study might be useful for comparing mucin-type oligosaccharides in cells and constructing oligosaccharide libraries to study cell function.

Comparative Quantification Method for Glycosylated Products Elongated on β-Xylosides Using a Stable Isotope-Labeled Saccharide Primer

The structures and amounts of glycosaminoglycan (GAG) produced by cells have attracted much interest because GAG biosynthesis activity can change in cellular processes such as disease and differentiation. β-Xylosides, also called saccharide primers, have been used as artificial acceptors not only to generate GAG oligosaccharides in cells and tissues but also to investigate their biosynthetic pathways. Various analytical methods have been applied to confirm the structure and amounts of GAG oligosaccharides elongated using saccharide primers, yet sample preparation processes such as solid-phase extraction in analysis can cause experimental error and disrupt accurate comparative quantification of glycosylated products. In this study, we developed a new quantification method using a deuterium-labeled saccharide primer. The "heavy" and "light" primers were chemically synthesized, and priming abilities were confirmed by liquid chromatography-tandem mass spectrometry. Relative peak areas of light/heavy products showed good linearity and were well correlated with the theoretical amounts of glycosylated products. Then, as a validation study, we carried out a biosynthesis inhibition assay using known GAG biosynthesis inhibitors. According to the relative quantification using saccharide primers, differences in the mode-of-action among the four GAG biosynthesis inhibitors were dependent on the GAG biosynthetic pathway. Our results indicate that the method will likely forge a new path for comparative glycosaminoglycomics using cultured cells and tissues.

Saccharide Primers Comprising Xylosyl-Serine Primed Phosphorylated Oligosaccharides Act as Intermediates in Glycosaminoglycan Biosynthesis

β-Xylosides have been used as an artificial initiator of glycosaminoglycan (GAG) biosynthesis to investigate its mechanism and to obtain these oligosaccharides. In GAG biosynthesis, phosphorylation on the xylose residue is a crucial step. However, little attention has been paid to phosphorylated oligosaccharides obtained from β-xylosides. In a previous study, we demonstrated that a novel β-xyloside, N-lauryl-O-β-xyloyranosyl-serinamide (Xyl-Ser-C12), had excellent GAG-type oligosaccharide priming ability, whereas phosphorylated oligosaccharides were not found in the primed oligosaccharides. This study examines the potential of Xyl-Ser-C12 and three of its derivatives for use as a probe to investigate the GAG biosynthesis mechanism. Glycosylated products were obtained by incubation of the β-xylosides in normal human dermal fibroblast cells and compared by liquid chromatography-electrospray ionization-mass spectrometry. By the optimized method to detect phosphorylated products, Xyl-Ser-C12 was demonstrated to prime not only GAG-type oligosaccharides but also a variety of xylose-phosphorylated products. Among the synthesized β-xylosides, those consisting of xylosyl-serine primed large amounts of phosphorylated and GAG-type oligosaccharides, whereas the others primed sialyloligosaccharides mainly. The majority of the phosphorylated products were considered to be GAG intermediates, which are less observed in nature. To our best knowledge, this is the first report showing that the amino acid residues around the Xyl attachment position strongly affect the phosphorylation efficiency and GAG chain-priming ability of β-xylosides. This study leads to the possibility of the use of β-xyloside as a probe to observe the Xyl phosphorylation process during GAG biosynthesis and investigate comparative glycosaminoglycomics between different cells.

Glycolipid dynamics in generation and differentiation of induced pluripotent stem cells

Glycosphingolipids (GSLs) are glycoconjugates that function as mediators of cell adhesion and modulators of signal transduction. Some well-defined markers of undifferentiated human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) are glycoconjugates, such as SSEA-3, SSEA-4, TRA-1-60 and TRA-1-81. However, Comprehensive GSL profiles of hiPSCs have not yet been elucidated. The global images of GSLs from the parental cells, hiPSCs, and differentiated cells revealed that there are parental cell-independent specific glycolipids, including Globo H (fucosyl-Gb5Cer) and H type1 antigen (fucosyl-Lc4Cer) that are novel markers for undifferentiated hiPSCs. Interestingly, undifferentiated hiPSCs expressed H type 1 antigen, specific for blood type O, regardless of the cells’ genotypes. Thus, in this study, we defined the dynamics of GSL remodeling during reprogramming from parental cell sets to iPSC sets and thence to iPSC-neural cells.

Involvement of Ext1 and heparanase in migration of mouse FBJ osteosarcoma cells

To know the involvement of glycosaminoglycans (GAGs) in the metastasis of mouse FBJ osteosarcoma cells, N(α)-lauroyl-O-(β-D-xylopyranosyl)-L-serinamide (Xyl-Ser-C12), which initiates elongation of GAG chains using the glycan biosynthesis system in cells, was administered to FBJ cells with different metastatic capacities. Production of glycosylated products derived from Xyl-Ser-C12, especially heparan sulfate (HS) GAG-type oligosaccharides such as GalNAc-GlcA-GlcNAc-GlcA-Gal-Gal-Xyl-Ser-C12, was indicated in poorly metastatic FBJ-S1 cells more than in highly metastatic FBJ-LL cells by LC-MS. The results of RT-PCR revealed that HS synthases, Ext1 and Ext2, were expressed in FBJ-S1 cells more than in FBJ-LL cells. Furthermore, siRNA against Ext1 suppressed the expression of HS and enhanced the motility of FBJ-S1 cells. In addition, the expression of heparanase (HPSE) was enhanced in Ext-1-knockdown FBJ-S1 cells, and responsible for the increase in cell motility caused by the down-regulation of Ext1 expression. Our data provide the first evidence that Ext1 regulates the expression of HPSE and also indicated that levels of Ext1 and HPSE influenced the motility of FBJ cells.