Reiko Sato

Isolation and characterization of antibodies against three consecutive Tn-antigen clusters from a phage library displaying human single-chain variable fragments

The Tn-antigen, GalNAcalpha-Ser/Thr, is a tumour-associated carbohydrate antigen that may provide a sensitive and specific marker for pre-clinical detection of carcinoma and a target for cancer therapies. We recently reported that MLS128 monoclonal antibody treatment significantly inhibited colon and breast cancer cell growth. On the basis of our observations, the present study aimed to produce human anti-Tn-antigen antibodies with specificity similar to that of MLS128 monoclonal antibody, which recognizes a structure of three consecutive Tn-antigens (Tn3). Six phage clones displaying human single-chain variable fragments (scFvs) were isolated from a newly constructed phage library by panning and screening with a synthetic Tn3-peptide. Deduced amino-acid sequences of six anti-Tn3 scFvs exhibited a high degree of homology. Of those, anti-Tn3 4E10 and 4G2 scFv proteins were successfully purified from phage-infected Escherichia coli to near homogeneity. Surface plasmon resonance analyses revealed a K(D) of purified scFv proteins for Tn3 on an order of 10(-7) M, which is high for carbohydrate-specific monovalent antibodies. Further analyses suggested that both scFv proteins also bind to Tn2 and cultured colon and breast cancer cells. These results demonstrated the potential for use of these scFvs in developing antibody therapeutics targeting colon and breast cancer.

Synthesis of Monomethyl Derivatives of P-Nitrophenyl α-D-Gluco, Galacto, and Mannopyranosides and their Hydrolytic Properties Against α-Glycosidases

ABSTRACT All possible monomethyl derivatives of p-nitrophenyl α-D-gluco, galacto, and mannopyranosides were synthesized. Hydrolytic activities of α-glucosidase (rice), α-galactosidases (green coffee bean, Mortierella vinacea, and Aspergillus niger), and α-mannosidases (almond and jack bean) against them were elucidated. The 6-O-methyl galactopyranoside and mannopyranoside were hydrolyzed by the M. vinacea α-galactosidase and the almond and jack bean α-mannosidases, respectively, while these enzymes did not act on the 2-, 3-, and 4-O-methyl derivatives. On the other hand, rice α-glucosidase and green coffee bean and A. niger α-galactosidases had no hydrolyzing activities at all against the respective four monomethylated substrates.

Surface plasmon resonance and NMR analyses of anti Tn-antigen MLS128 monoclonal antibody binding to two or three consecutive Tn-antigen clusters

Tn-antigens are tumour-associated carbohydrate antigens that are involved in metastatic processes and are associated with a poor prognosis. MLS128 monoclonal antibody recognizes the structures of two or three consecutive Tn-antigens (Tn2 or Tn3). Since MLS128 treatment inhibits colon and breast cancer cell growth [Morita, N., Yajima, Y., Asanuma, H., Nakada, H., and Fujita-Yamaguchi, Y. (2009) Inhibition of cancer cell growth by anti-Tn monoclonal antibody MLS128. Biosci. Trends 3, 32-37.], understanding the interaction between MLS128 and Tn-clusters may allow us to the development of novel cancer therapeutics. Although MLS128 was previously reported to have specificity for Tn3 rather than Tn2, similar levels of Tn2/Tn3 binding were unexpectedly observed at 37°C. Thus, thermodynamic analyses were performed via surface plasmon resonance (SPR) using synthetic Tn2- and Tn3-peptides at 10, 15, 20, 25 and 30°C. SPR results revealed that MLS128s association constants for both antigens were highly temperature dependent. Below 25°C MLS128s association constant for Tn3-peptide was clearly higher than that for Tn2-peptide. At 30°C, however, the association constant for Tn2-peptide was higher than that for Tn3-peptide. This reversal of affinity is due to the sharp increase in K(d) for Tn3. These results were confirmed by NMR, which directly measured MLS128-Tn binding in solution. This study suggested that thermodynamic control plays a critical role in the interaction between MLS128/Tn2 and MLS128/Tn3.

Effect of heparin addition on expansion of cord blood hematopoietic progenitor cells in three-dimensional coculture with stromal cells in nonwoven fabrics.

Primary human cord blood mononuclear cells (CB MNCs) were inoculated into layers of primary human bone marrow stromal cells prepared in a nonwoven fabric porous carrier [three dimensional (3-D)] or on a dish [two dimensional (2-D)] using a cytokine-free medium and were cultured for 7 days with or without the addition of heparin. The number of progenitor cells increased threefold during the 3-D coculture, whereas it decreased in the 2-D culture. Heparin addition to the 3-D coculture further increased the number of progenitors twofold, whereas the addition of desulfated heparin had no effect. The heparin effect was also observed in a 3-D culture of CB MNCs without stromal cells when conditioned medium was employed. The coating of the carrier with N-(O-β-(6-O-sulfogalactopyranosyl)-6-oxyhexyl)-3,5-bis (dodecyloxy)-benzamide instead of heparin addition also increased the number of progenitor cells in the 3-D culture of CB MNCs without stromal cells when the conditioned medium was employed. The 3-D coculture constructed with nonwoven fabrics and stromal cells was clearly superior to the 2-D culture because of the expansion of CB hematopoietic progenitor cells without cytokine addition. Heparin addition to the 3-D coculture further increased the number of progenitor cells, which may result from a synergistic effect of soluble cytokines produced by stromal cells with the sulfur group of heparin.

Novel carbohydrate-binding activity of pancreatic trypsins to N-linked glycans of glycoproteins

How glycosylation affects the reactivity of proteins to trypsin is not well understood. Bovine and porcine pancreatic trypsins were discovered to bind to α-Man, Neu5Acα2,6Galβ1,4Glc, and α-galactose sequences by binding studies with biotinylated sugar-polymers. Quantitative kinetic studies supported that phenylmethylsulfonyl fluoride (PMSF)-treated trypsin binds to glycolipid analogues possessing α-Man or α-NeuAc but not to those possessing β-galactose or β-GlcNAc residue. Enzyme-linked immunosorbent assay (ELISA) showed that trypsin binds to six kinds of biotinylated glycoproteins possessing high mannose-type and complex-type N-glycans but not to bovine submaxillary mucin, which possesses only O-glycans. Further, the binding of trypsin to glycoproteins was differentially changed by treatments with sequential exoglycosidases, endoglycosidase H, or N-glycosidase F. Quantitative kinetic studies indicated that PMSF-treated trypsin binds with bovine thyroglobulin with the affinity constant of 1010 m–1, which was the highest among the glycoproteins examined, and that α-galactosidase treatment decreased it to 105 m–1. PMSF-treated trypsin bound to other glycoproteins, including ovomucoid, a trypsin inhibitor, with the affinity constants of 108-105 mol–1 and were markedly changed by glycosidase treatments in manners consistent with the sugar-binding specificities suggested by ELISA. Thus, the binding site for glycans was shown to be distinct from the catalytic site, allowing trypsin to function as an uncompetitive activator in the hydrolysis of a synthetic peptide substrate. Correspondingly the carbohydrate-binding activities of trypsin were unaffected by treatment with PMSF or soybean trypsin inhibitor. The results indicate the presence of an allosteric regulatory site on trypsin that sugar-specifically interacts with glycoproteins in addition to the proteolytic catalytic site.

Synthesis of 3,4,5‐Tris(alkyloxy)benzyl Glycosides as Glycolipid Analogues

Abstract A series of 3,4,5‐tris(alkyloxy)benzyl glycosides of D‐glucose, D‐galactose, D‐mannose, N‐acetyl‐D‐glucosamine and N‐acetyl‐D‐galactosamine were prepared by the trichloroacetimidate procedure. After immobilization on a hydrophobic surface, the affinity of the carbohydrate to a lectin was evaluated using a surface plasmon resonance biosensor. The selective interaction achieved with the lectin showed that the glycosides had potential for use as glycolipid analogues. The 3,4,5‐tris(dodecyloxy)benzyl glycosides were soluble in ethanol, and potentially would be useful for cell culture experiments.

Facile synthesis of stable lipid analogues possessing a range of alkyl groups: application to artificial glycolipids

Efficient preparation of lipid analogues is described in which various long alkoxy chains and 2-hydroxyethyl group were covalently linked with benzoic acid derivatives. An alpha-mannopyranosyl group was stereoselectively introduced by the conventional imidate method into the terminal hydroxy group without any alternation of other moieties in a molecule. The resulting new glycoconjugates acted as models of natural glycolipids for protein-carbohydrate interactions.

Binding of Sperm to the Zona Pellucida Mediated by Sperm Carbohydrate-Binding Proteins is not Species-Specific in Vitro between Pigs and Cattle.

Carbohydrates are candidates for the basis of species-selective interaction of gametes during mammalian fertilization. In this study, we sought to clarify the roles of sugar residues in the species-selective, sperm–oocyte interaction in pigs and cattle. Acrosome-intact porcine and bovine sperm exhibited their strongest binding affinities for β-Gal and α-Man residues, respectively. Porcine-sperm specificity changed from β-Gal to α-Man after the acrosome reaction, while bovine-sperm specificity did not. Binding of acrosome-intact and acrosome-reacted sperm decreased after trypsinization, indicating that the carbohydrate-binding components are proteins. While immature oocytes bound homologous sperm preferentially to heterologous sperm, oocytes matured in vitro bound similar numbers of homologous and heterologous sperm. Lectin staining revealed the aggregation of α-Man residues on the outer surface of the porcine zona during maturation. In both species, zona-free, mature oocytes bound homologous sperm preferentially to heterologous sperm. The lectin-staining patterns of the zona pellucida and zona-free oocytes coincided with the carbohydrate-binding specificities of acrosome-intact and acrosome-reacted sperm, respectively, supporting the involvement of carbohydrates in gamete recognition in pigs and cattle. These results also indicate that sperm-zona pellucida and sperm–oolemma bindings are not strictly species-specific in pigs and cattle, and further suggest that sperm penetration into the zona and/or fusion with oolemma may be species-specific between pigs and cattle.

Effect of galactose residue in glycolipid coated onto a dish on ammonia consumption activity of primary rat hepatocytes

Coating a dish for suspension culture with 3,4,5-tris(dodecyloxy)benzyl alcohol (TDOB-OH), TDOB glucoside (TDOB-Glc), or TDOB galactoside (TDOB-Gal) did not change the morphology of hepatocytes and decreased cell adhesion density to 70%–84% of that without the coating. However, the specific ammonia consumption rate of the culture on a TDOB-Gal-coated dish was 1.81 times that without coating, whereas those of TDOB-OH-and TDOB-Glc-coated dishes were 1.18 and 0.31 times that without coating, respectively. TDOB-Gal coating on a dish for adhesion culture decreased cell adhesion density only by 10% and did not disturb cell spreading. The coating of TDOB-Gal at 1/10 to 1/4 density of that for a monolayer resulted in a higher specific rate of ammonia consumption than that at monolayer density, and the rate reached 1.97 times that without coating. The ammonia consumption activity of hepatocytes was considered to be increased specifically not by the glucose residues but by the galactose residue of the glycolipid, independently of cell spreading.

Effect of sugar residues in a glycolipid coated onto a dish on ammonia consumption and gluconeogenesis activity of primary rat hepatocytes

Coating of 3,4,5-tris(dodecyloxy)benzyl-beta-D-galactopyranoside (TDOB-Gal) on a dish for suspension culture increased the specific ammonia consumption rate of primary rat hepatocytes to 2.4 times that in the case of rat hepatocytes cultured in a dish without coating while there was no increase in the specific urea production rate. TDOB-beta-D-glucopyranoside (TDOB-Glc), -alpha-D-mannnoside, -beta-D-mannoside, 2-acetamido-2-deoxy-beta-D-glucopyranoside, and 2-acetamido-2-deoxy-beta-D-galactopyranoside had almost no influence on the above-mentioned specific rates. In the ammonia loading assay, cells on the dish with TDOB-Gal and -Glc coatings produced glucose, suggesting gluconeogenesis.