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Inhibition of N-linked oligosaccharide processing in tumor cells is associated with enhanced tissue inhibitor of metalloproteinases (TIMP) gene expression.

Previous studies on tumor-cell glycosylation mutants and drugs which inhibit oligosaccharide processing suggest that expression of sialylated and highly branched complex-type N-linked oligosaccharides is required for efficient tumor-cell metastasis. These observations prompted the present investigation, in order to determine whether loss of sialylated and highly branched complex-type oligosaccharide in cellular glycoproteins might affect the expression of genes, particularly of genes which can influence the malignant phenotypes. Swainsonine, an inhibitor of Golgi alpha-mannosidase II, has previously been shown to inhibit invasion in vitro and reduces solid tumor in vivo. Metastatic sub-lines of the SP1 murine mammary carcinoma cells cultured in the presence of swainsonine for 48 hr showed approximately 3-fold enhancement of TIMP mRNA levels, while urokinase (uPA) transcripts remained unchanged. To determine whether swainsonine's effect on TIMP mRNA levels was related to inhibition of oligosaccharide processing, we examined somatic glycosylation mutants with processing defects which attenuate metastatic potential. The Golgi UDP-Gal transport defect in murine MDAY-D2 lymphoma cells, Chinese hamster ovary cells (CHO) and human MeWo melanoma cells (i.e., D35W25, Lec8, 3S5 cell lines, respectively) was associated with increased TIMP mRNA levels. A revertant of Lec8 showed a return to the wild-type levels of TIMP mRNA, consistent with a causal relationship between the glycosylation mutation and TIMP gene expression. Similarly, CHO and MDAY-D2 mutants defective in GlcNAc-TV (i.e., Lec4 and KBL-1 respectively), which also reduces metastatic potential, showed increases in TIMP transcript levels. Nuclear run-on assays showed that transcription of the TIMP gene was increased in cells where N-linked oligosaccharide processing was inhibited either by swainsonine or by a glycosylation mutation. The results suggest that cell-specific patterns of glycoprotein glycosylation in human, murine and hamster cell lines affects the transcription of select genes, including TIMP, which may influence the invasive phenotype.

Animals↗

Tissue-specific N-glycosylation, site-specific oligosaccharide patterns and lentil lectin recognition of rat Thy-1.

To examine the extent to which protein structure and tissue-type influence glycosylation, we have determined the oligosaccharide structures at each of the three glycosylation sites (Asn-23, 74 and 98) of the cell surface glycoprotein Thy-1 isolated from rat brain and thymus. The results show that there is tissue-specificity of glycosylation and that superimposed on this is a significant degree of site-specificity. On the basis of the site distribution of oligosaccharides, we find that no Thy-1 molecules are in common between the two tissues despite the amino acid sequences being identical. We suggest, therefore, that by controlling N-glycosylation a tissue creates an unique set of glycoforms (same polypeptide but with oligosaccharides that differ either in sequence or disposition). The structures at each of the three sites were also determined for the thymocyte Thy-1 that binds to lentil lectin (Thy-1 L+) and for that which does not (Thy-1 L-). Segregation of intact thymus Thy-1 into two distinct sets of glycoforms by lentil lectin was found to be due to the structures at site 74. Analysis of oligosaccharide structures at the 'passenger' sites (23 and 98) suggests that either Thy-1 L+ and Thy-1 L- molecules are made in different cell-types or that the biosynthesis of oligosaccharides at one site is influenced by the glycosylation at other sites.

Animals↗

Complex asparagine-linked oligosaccharides are required for morphogenic events during post-implantation development.

Complex asparagine (N)-linked oligosaccharides appear late in phylogeny and are highly regulated in vertebrates. Variations in these structures are found on the majority of cell-surface and secreted proteins. Complex N-linked oligosaccharide biosynthesis is initiated in the Golgi apparatus by the action of Mgat-1-encoded UDP-N-acetylglucosamine:alpha-3-D- mannoside beta-1,2-N-acetylglucosaminyltransferase I (GlcNAc-TI). To determine if these structures govern ontogenic processes in mammals, mouse embryos were generated that lacked a functional Mgat-1 gene. Inactivation of both Mgat-1 alleles produced deficiencies in GlcNAc-TI activity and complex N-linked oligosaccharides. Embryonic lethality occurred by day 10.5, thus establishing that complex N-linked oligosaccharides are required during post-implantation development. Remarkably, embryonic development proceeded into day 9 with the differentiation of multiple cell types. Complex N-linked oligosaccharides are important for morphogenic processes as neural tube formation, vascularization and the determination of left-right body plan asymmetry were impaired in the absence of a functional Mgat-1 gene.

Animals↗

Prenatal diagnosis of infantile GM 2 gangliosidosis type II (Sandhoff disease) by detection of N-acetylglucosaminyl-oligosaccharides in amniotic fluid with high-performance liquid chromatography.

Prenatal diagnosis of Sandhoff disease (infantile onset) at 16 weeks gestation has been made by detection and analysis of N-acetylglucosaminyl-oligosaccharides in amniotic fluid using high performance liquid chromatography. The elution profile for the branched chain oligosaccharides was identical with that obtained with neonatal and infantile Sandhoff urine. The concentration of the oligosaccharides in the fluid was 1/100th that of urine but when calculated relative to creatinine the levels were similar. No oligosaccharides were detected in normal control amniotic fluids (10 patients) at a similar gestational age. Based on the levels of the amniotic fluid oligosaccharides and the sensitivity limits of the assay, prenatal diagnosis of patients with the juvenile onset form of the disease may also be possible with this technique.

Acetylglucosamine↗

Development of a mass fingerprinting tool for automated interpretation of oligosaccharide fragmentation data.

The bioinformatic tool GlycosidIQ was developed for computerized interpretation of oligosaccharide mass spectrometric fragmentation based on matching experimental data with theoretically fragmented oligosaccharides generated from the database GlycoSuiteDB. This use of the software for glycofragment mass fingerprinting obviates a large part of the manual, labor intensive, and technically challenging interpretation of oligosaccharide fragmentation. Using 130 negative ion electrospray ionization-tandem mass spectrometry fragment spectra from identified oligosaccharide structures, it was shown that the GlycosidIQ scoring algorithms were able to correctly identify oligosaccharides in the great majority of cases (correct structure top ranked in 78% of the cases and an additional 17% were ranked second highest in the sample set).

Algorithms↗

Fragmentation characteristics of permethylated oligosaccharides using a matrix-assisted laser desorption/ionization two-stage time-of-flight (TOF/TOF) tandem mass spectrometer.

Matrix-assisted laser desorption/ionization two-stage time-of-flight (MALDI-TOF/TOF) tandem mass spectrometry (MS/MS) was applied to characterize permethylated oligosaccharides. Under these ionization conditions such derivatives yield intense signals corresponding to sodium-cationized molecular species. A systematic study was conducted on a series of neutral and sialylated permethylated oligosaccharides to allow rationalization of the fragmentation processes. The major fragments observed in the MALDI-TOF/TOF-MS/MS spectra result from cleavage of glycosidic bonds, preferentially at N-acetylhexosamine and sialic acid residues. The fragments originating from both the reducing and the non-reducing ends of the glycan yield information on sequence and branching. Cross-ring cleavages, which are very informative of the linkages of the monosaccharide residues constituting these oligosaccharides, and 'internal' cleavage ions which are derived from elimination of substituents from around the pyranose ring, were also observed. This extensive fragmentation was shown to be useful for the structural characterization of oligosaccharides. MALDI-TOF/TOF-MS/MS of permethylated oligosaccharides appears to be a powerful tool for carbohydrate structural analysis.

Methylation↗

Characterization of oligosaccharide moieties of glycopeptides by microwave-assisted partial acid hydrolysis and mass spectrometry.

Microwave-assisted partial acid hydrolysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry were used to study oligosaccharide structures of glycopeptides. Tryptic N-glycosylated peptides of horseradish peroxidase, with MH+ ions at m/z 2533, 2612, 3355, 3673, and 5647, were used as test cases. Within a microwave exposure with trifluoroacetic acid of 2 min, partial cleavages of the oligosaccharides of these tryptic N-glycosylated peptides were observed. The data showed that the most labile group within the oligosaccharides is the fucose (Fuc) residue, and that a majority of the end cleavage products are peptides with one N-acetylglucosamine (GlcNAc) residue linked to asparagine (Asn). In addition, the glycopeptides with m/z 3355 and 3673 carry an oligosaccharide (Xyl)Man3(Fuc)GlcNAc2, the glycopeptide at m/z 5647 carries two oligosaccharides (Xyl)Man3(Fuc)GlcNAc2, and the glycopeptides at m/z 2612 and 2533 carry (Xyl)Man3GlcNAc2 and (Fuc)GlcNAc, respectively. However, the glycosylation site of the m/z 2612 peptide at Asn286 is partially occupied. This simple and rapid method is particularly useful in identifying glycopeptides and obtaining monosaccharide compositions of glycopeptides.

Acids↗

Systematic identification of N-acetylheparosan oligosaccharides by tandem mass spectrometric fragmentation.

Recently, a useful procedure for the preparation of both even- and odd-numbered series of N-acetylheparosan (NAH) oligosaccharides was established. The present report describes findings when these NAH oligosaccharides were subjected to comparative mass spectrometry (MS)/MS fragmentation analysis by matrix-assisted laser desorption/ionization (MALDI)-LIFT-time-of-flight (TOF)/TOF-MS/MS, and electrospray ionization (ESI) collision-induced dissociation (CID) MS/MS. The resultant fragment ions were systematically assigned to elucidate fragmentation characteristics. In the MALDI-LIFT-MS/MS experiments, all the NAH oligosaccharides underwent unique glycosidic cleavages that included B-Y ion cleavages (nomenclature system of Domon and Costello, Glycoconjugate J. 1988; 5: 397) at the C-1 side, and C-Z ion cleavages at the C-4 side, with respect to glucuronic acid (GlcA). In addition, (0,2)A and/or (0,2)X cross-ring cleavages were observed for relatively small oligosaccharides. The former observation clearly reflects the occurrence of a GlcA-N-acetylglucosamine (GlcNAc) alternating structure of NAH, while the latter feature implies the occurrence of the -beta-1-4-glucuronide linkage. Extensive glycosidic cleavages were also observed in the ESI-CID-MS/MS fragmentation, though cleavage specificity was less evident than in the case of MALDI-LIFT-TOF/TOF-MS/MS. The information obtained in this study should be valuable for understanding both biosynthetic and degradation processes of NAH and its derivatives including heparin and heparan sulfate, as well as artificially modified NAH oligosaccharides.

Gas Chromatography-Mass Spectrometry↗

Matrix-assisted laser desorption/ionization in-source decay combined with tandem time-of-flight mass spectrometry of permethylated oligosaccharides: targeted characterization of specific parts of the glycan structure.

Matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF/TOF-MS) has been introduced in recent years as a valuable tool for the structural characterization of permethylated oligosaccharides. In this report, we describe the combination of MALDI in-source decay (ISD) with the subsequent TOF/TOF-MS analyses of specific fragments, allowing the detailed characterization of the selected part of the oligosaccharide molecule. Part of the second-generation fragment ions were different from those observed in conventional MALDI-TOF/TOF-MS experiments. Other fragments, which had already been observed in conventional MALDI-TOF/TOF-MS and again showed up in second-generation fragment analysis, could be assigned to specific parts of the molecule. Our approach disclosed different structural features of the oligosaccharides: due to permethylation, the glycosidic linkage fragments allowed the distinction between terminal, monosubstituted and disubstituted monosaccharides and indicated the oligosaccharide sequence. Moreover, substitution positions were deduced based on characteristic cross-ring fragmentation by high-energy collision-induced fragmentation. In conclusion, combination of MALDI-ISD with TOF/TOF-MS allows the detailed characterization of specific moieties of permethylated oligosaccharides and is, therefore, a powerful technique for structural glycomics.

Animals↗

Thyroglobulin glycosylation: location and nature of the N-linked oligosaccharide units in bovine thyroglobulin.

The cDNA sequence of bovine thyroglobulin (bTg) predicts 14 putative N-linked glycosylation sites. We have characterized the glycopeptides contained in a tryptic digest of bovine thyroglobulin in order to establish actual glycosylation sites. The distribution of oligosaccharide types within the known sites of N-linked glycosylation has also been examined. Each glycopeptide was subjected to neutral and amino sugar analysis, as well as sialic acid analysis. Thirteen of the 14 putative N-linked glycosylation sites in bTg were confirmed as glycopeptides in the mature protein. Nine of these confirmed glycosylation sites appear to bear complex or hybrid type oligosaccharide units and four contain oligosaccharide structures in which only mannose and glucosamine were seen. Complex or hybrid type glycosylation was confirmed at asparagine residues 91, 464, 476, 834, 928, 1121, 1757, 1851, and 2232, while oligosaccharides containing only mannose and glucosamine were found at asparagine residues 1346, 1995, 2104, and 2277. Analysis of the amino acid sequence in the region of each putative glycosylation site predicts a high probability of a beta turn at 10 of the 13 sites. While glycosylation was distributed through most of the length of the thyroglobulin sequence, no oligosaccharides containing only mannose and glucosamine were found in the N-terminal half of the molecule. Several of the glycosylated peptides showed microheterogeneity and occurred in two or more discrete peaks on HPLC. A single putative site at asparagine residue 179 was not recovered in the purified glycopeptide population.

Amino Acid Sequence↗

Antibodies to three chondroitin sulfate-containing proteoglycans in squid skin recognize hexa- or longer chondroitin oligosaccharides as major antigenic determinants.

The reactivities of antibodies to three squid skin proteoglycans with (a) chondroitin-derived oligosaccharides and chondroitin sulfate-derived disaccharides, (b) the proteoglycans and their constituents, and (c) chondroitin, chondroitin sulfate, and hyaluronic acid were studied with enzyme-linked immunosorbant assay inhibition tests. Immunization of rabbits with two chondroitin proteoglycans (ChPG I and ChPG II) and an oversulfated chondroitin sulfate proteoglycan (CSSPG) gave rise to highly reactive antisera which were mainly reactive with the glycosaminoglycans, the oligosaccharides, and the core proteins obtained after digestion of proteoglycans with chondroitinase AC. Inhibition of binding of antibodies to ChPG I, ChPG II, and CSSPG with chondroitin-derived oligosaccharides revealed that the minimal antigenically active structure was the hexasaccharide of chondroitin and that the respective octasaccharide was more active. Sulfated delta-disaccharides were not reactive with antibodies to ChPG I and II, whereas some reactivities (30% maximum inhibition) were obtained with antibodies to CSSPG. Chondroitin chains (80 kDa) of ChPG I and II were responsible for most of the reactivity with proteoglycans (78-95% maximum inhibition). Chemically desulfated chondroitin sulfate (12 kDa) showed considerable cross-reactivity with all antisera tested (62-68% maximum inhibition), whereas the nonsulfated molecule of hyaluronic acid and a hyaluronic acid fraction of 16 kDa were not reactive. The reactivities of antibodies with the proteoglycans' oligosaccharides and core proteins obtained by chondroitinase AC digestion were mainly due to the presence of nonsulfated chondroitin sulfate structures. This study clearly shows that the major antigenic determinants recognized by antibodies to squid skin proteoglycans, each containing chondroitin sulfates with different sulfation patterns, involve hexa- or larger chondroitin oligosaccharides.

Animals↗

Transfer of two oligosaccharides to protein in a Chinese hamster ovary cell B211 which utilizes polyprenol for its N-linked glycosylation intermediates.

B211, a glycosylation mutant isolated from Chinese hamster ovary cells, synthesizes 10- to 15-fold less Glc3Man9GlcNAc2-P-P-lipid, the substrate used by the oligosaccharide transferase in the synthesis of asparagine-linked glycoproteins. B211 cells are also 10- to 15-fold deficient in the glucosylation of oligosaccharide-lipid. Despite these properties, protein glycosylation in B211 cells proceeds at a level similar to (50% of) parental cells. We asked whether the near wild-type level of glycosylation was due to the transfer of alternative oligosaccharide structures to protein in B211 cells. The aberrant size of [35S]methionine-labeled VSV G protein and the increased percentage of endoglycosidase H-resistant tryptic peptides as compared to parental cells supported this hypothesis. B211 cells were labeled with [2-3H]mannose either for 1 min or for 1 h in the presence of glycoprotein-processing inhibitors so that the oligosaccharides initially transferred to protein could be analyzed. In addition to Glc3Man9GlcNAc2, a second, endoglycosidase H-resistant oligosaccharide was transferred whose structure was determined by alpha-mannosidase digestion, gel filtration chromatography, and HPLC to be Glc0,1Man5GlcNAc2. Finally, since the synthesis of reduced amounts of Glc3Man9GlcNAc2-P-P-lipid was also a phenotype seen in another glycosylation mutant, Lec9, we analyzed the long-chain prenol in B211 cells. B211 cells synthesized and utilized polyprenol rather than dolichol for all N-linked glycosylation intermediates as determined by HPLC analysis of [3H]mevalonate-labeled lipids. Cell fusions analyzed by similar techniques indicated that B211, originally isolated as a concanavalin A-resistant cell line, is in the Lec9 complementation group.

Animals↗

Monosaccharide composition analysis of oligosaccharides and glycoproteins by high-performance liquid chromatography.

A simple and sensitive high-performance liquid chromatography (HPLC)-based method for complete monosaccharide composition analysis of oligosaccharides and glycoproteins is described. In this method, an oligosaccharide or glycoprotein is first hydrolyzed using an optimized method to give the constituent monosaccharides, which are subsequently labeled with 1-phenyl-3-methyl-5-pyrazolone (PMP) as previously described by Honda et al. (Anal, Biochem. 180, 351-357, (1989)). The labeled monosaccharides are separated by reverse-phase HPLC using a column developed especially for this purpose, monitored by uv absorbance at 245 nm, and quantitated by their integration values relative to standards. Sialic acids are acid-labile keto-sugars. They are, therefore, released with neuraminidases or by mild acid hydrolysis and then converted with neuraminic acid aldolase to their corresponding mannosamine derivatives, which are then PMP-labeled, separated, and quantitated as described above. Individual sialic acids including N-acetyl and N-glycolyl neuraminic acids are well resolved and quantitated by this method. This method has proven to be highly sensitive, requiring only 1 pmol for reliable detection. Quantitative analysis of neutral and amino sugars from both oligosaccharide and glycoprotein samples can be achieved using one acid hydrolysis and a set of equal molar monosaccharide standards. Similarly, quantitation of sialic acids works equally well with both free oligosaccharide and glycoprotein samples. Monosaccharide compositions of oligosaccharides and glycoproteins determined by this method were found to be highly accurate.

Antipyrine↗

Multimode high-performance liquid chromatography of fluorescently labeled oligosaccharides from glycoproteins.

A polymeric, secondary amine stationary phase was used to develop a method for the separation of 2-aminobenzamide (AB)-labeled neutral and anionic oligosaccharides from glycoproteins. Sequential hydrophilic interaction liquid and anion exchange chromatography were performed in the same chromatographic analysis (multimode HPLC) and unambiguous separation between neutral and anionic oligosaccharides was accomplished. Improved resolution was also achieved. The oligomannosidic-type structures from bovine ribonuclease B (Man4GlcNAc-AB-Man9GlcNAc-AB) were separated not only by size, but also by the branch location of terminal Manalpha(1 --> 2)-linked residues. Sialylated lactosamine-type oligosaccharides from human alpha1 acid glycoprotein were resolved according to charge, Fuc content, and the number of Galbeta(1 --> 4)Galbeta(1 --> 3) repeats. The minor fucosylated and polylactosamine species were well separated from the major sialylated tetra-antennary oligosaccharides. Volatile mobile phases were used to minimize sample handling for matrix assisted laser desorption mass spectrometric analysis of peak fractions. Novel polylactosamine structures (3-5 repeats) from alpha1-acid glycoprotein were deduced from the molecular weight analysis. Multimode HPLC should prove useful for preparing low pmol quantities of fluorescently labeled oligosaccharides with fewer steps and minimal sample handling for mass spectrometric analysis, important requisites for structural studies of sample-limited glycoproteins.

Animals↗

Characterization of neutral oligosaccharide-alditols from Xenopus laevis egg jelly coats by matrix-assisted laser desorption Fourier transform mass spectrometry.

Neutral oligosaccharides were released by alkaline sodium borohydride reduction of the jelly coating from the South African clawed toad, Xenopus laevis. The oligosaccharides were isolated by HPLC and analyzed by matrix-assisted laser desorption ionization (MALDI)-Fourier transform mass spectrometry (FTMS). The mass spectrometry analysis allowed confirmation of 12 structures first proposed by Strecker et al. using nuclear magnetic resonance. In addition, seven new oligosaccharides with weak abundances were found and characterized by mass spectrometry. A method for discriminating metastable fragments from quasimolecular ions is described. It involves doping the sample with cesium chloride. Cesium-coordinated oligosaccharides do not fragment as readily as those coordinated to sodium. Tandem MS experiments are performed on an unknown oligosaccharide illustrating the potential of MALDI-collision-induced dissociation-FTMS.

Animals↗

Analysis of O-linked oligosaccharide alditols by high-pH anion-exchange chromatography with pulsed amperometric detection.

To apply high-pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) to the accurate and sensitive analysis of O-linked oligosaccharide alditol, removal of glycopeptides and peptides from oligosaccharide samples obtained by beta-elimination was first investigated. The results obtained by using fetuin as a model glycoprotein indicated that (glyco)peptides derivatized by fluorescamine are easily removed from the beta-eliminated oligosaccharide sample by means of a Sep-Pak C18 cartridge due to their increased hydrophobicity. This clean-up procedure was also effectively applied to the beta-eliminated oligosaccharide sample obtained from delipidated sheep erythrocyte ghosts. Furthermore, structural analysis of the oligosaccharide alditols by HPAEC-PAD was successfully performed in combination with partial and complete desialylation, composition analysis, periodate oxidation, and glycosidase digestion and revealed that sheep erythrocyte membrane glycoproteins contain Gal beta 1-->3Gal-NAc and Gal beta 1-->4GlcNAc beta 1-->3Gal beta 1-->3GalNac, to which one or two residues of Neu5Ac and Neu5Gc are attached in different combinations.

Animals↗

Structural analysis of O-linked oligosaccharide-alditols by electrospray-tandem mass spectrometry after mild periodate oxidation and derivatization with 2-aminopyridine.

O-linked oligosaccharide-alditols were analyzed by a combination of high-performance liquid chromatography (HPLC) and electrospray-tandem mass spectrometry (ESI-MS/MS). First, oligosaccharide-alditols were treated with sodium meta-periodate under conditions where core N-acetylgalactosaminitol is specifically degraded. The resulting fragments were labeled with 2-aminopyridine and purified on a reversed-phase column. Pyridylamino oligosaccharides yielded protonated molecular ions in positive-ion ES-MS and gave Y-series sequence ions, arising from glycosidic cleavages, by ESI-tandem mass spectrometry. Information on sugar sequence and branching of oligosaccharides linked at C6 and C3 to the N-acetylgalactosaminitol can be obtained. A systematic study of various oligosaccharide-alditols demonstrated that this approach constitutes a powerful tool for the structural characterization of O-glycans available only in limited quantities.

Aminopyridines↗

Analysis of the oligosaccharide chains of rhodopsin from normal rats and those with hereditary retinal dystrophy.

The nature of the oligosaccharides of rhodopsin from normal rats and from the Royal College of Surgeons (RCS) rats was examined by chemical, enzymatic and chromatographic procedures. This report is the first description of the structures of oligosaccharides of rat rhodopsin. The major oligosaccharide isomer of rat rhodopsin was shown to have the same structure as that from cow, human and frog. No neutral galactosylated species were detected. Although the site of the dystrophy in the RCS rat has been shown to be located at the retinal pigment epithelium, the possibility was examined that alterations in the glycosylation of rhodopsin might also be present. No differences were observed in either the amounts or structures of the rhodopsin oligosaccharide chains from young or adult control rats and RCS rats, although some differences were observed in the relative distribution of some oligosaccharide isomers between the RCS and controls. In addition, no differences in the amino acid content or SDS-PAGE patterns were detected.

Amino Acid Sequence↗