Niro Inaba

Molecular Cloning and Characterization of a Novel UDP-GlcNAc:GalNAc-peptide β1,3-N-Acetylglucosaminyltransferase (β3Gn-T6), an Enzyme Synthesizing the Core 3 Structure of O-Glycans

The core 3 structure of theO-glycan, GlcNAcβ1–3GalNAcα1-serine/threonine, an important precursor in the biosynthesis of mucin-type glycoproteins, is synthesized by UDP-N-acetylglucosamine:GalNAc-peptide β1,3-N- acetylglucosaminyltransferase (β3Gn-T; core 3 synthase). The core 3 structure is restricted in its occurrence to mucins from specific tissues such as the stomach, small intestine, and colon. A partial sequence encoding a novel member of the human β3Gn-T family was found in one of the data bases. We cloned a complementary DNA of this gene and named it β3Gn-T6. The putative amino acid sequence of β3Gn-T6 retains the β3Gn-T motifs and is predicted to comprise a typical type II membrane protein. The soluble form of β3Gn-T6 expressed in insect cells showed β3Gn-T activity toward GalNAcα-p-nitrophenyl and GalNAcα1-serine/threonine. The β1,3-linkage between GlcNAc and GalNAc of the enzyme reaction product was confirmed by high performance liquid chromatography and NMR analyses. β3Gn-T6 effectively transferred a GlcNAc to the GalNAc residue on MUC1 mucin, resulting in the synthesis of a core 3 structure. Real time PCR analysis revealed that the β3Gn-T6 transcript was restricted in its distribution, mainly to the stomach, colon, and small intestine. We concluded that β3Gn-T6 is the most logical candidate for the core 3 synthase, which plays an important role in the synthesis of mucin-type O-glycans in digestive organs.

Differential Roles of TwoN-Acetylgalactosaminyltransferases, CSGalNAcT-1, and a Novel Enzyme, CSGalNAcT-2 INITIATION AND ELONGATION IN SYNTHESIS OF CHONDROITIN SULFATE

By a tblastn search with β1,4-galactosyltransferases as query sequences, we found an expressed sequence tag that showed similarity in β1,4-glycosyltransferase motifs. The full-length complementary DNA was obtained by a method of 5′-rapid amplification of complementary DNA ends. The predicted open reading frame encodes a typical type II membrane protein comprising 543 amino acids, the sequence of which was highly homologous to chondroitin sulfate N-acetylgalactosaminyltransferase (CSGalNAcT-1), and we designated this novel enzyme CSGalNAcT-2. CSGalNAcT-2 showed much strongerN-acetylgalactosaminyltransferase activity toward glucuronic acid of chondroitin poly- and oligosaccharides, and chondroitin sulfate poly- and oligosaccharides with a β1–4 linkage,i.e. elongation activity for chondroitin and chondroitin sulfate, but showed much weaker activity toward a tetrasaccharide of the glycosaminoglycan linkage structure (GlcA-Gal-Gal-Xyl-O-methoxyphenyl), i.e.initiation activity, than CSGalNAcT-1. Transfection of theCSGalNAcT-1 gene into Chinese hamster ovary cells yielded a change of glycosaminoglycan composition, i.e. the replacement of heparan sulfate on a syndecan-4/fibroblast growth factor-1 chimera protein by chondroitin sulfate, however, transfection of the CSGalNAcT-2 gene did not. The above results indicated that CSGalNAcT-1 is involved in the initiation of chondroitin sulfate synthesis, whereas CSGalNAcT-2 participates mainly in the elongation, not initiation. Quantitative real-time PCR analysis revealed that CSGalNAcT-2 transcripts were highly expressed in the small intestine, leukocytes, and spleen, however, both CSGalNAcTs were ubiquitously expressed in various tissues.

A novel β1,3-N-acetylglucosaminyltransferase (β3Gn-T8), which synthesizes poly-N-acetyllactosamine, is dramatically upregulated in colon cancer

A new member of the UDP‐N‐acetylglucosamine: β‐galactose β1,3‐N‐acetylglucosaminyltransferase (β3Gn‐T) family having the β3‐glycosyltransferase motifs was identified using an in silico method. This novel β3Gn‐T was cloned from a human colon cancer cell line and named β3Gn‐T8 based on its position in a phylogenetic tree and enzymatic activity. β3Gn‐T8 transfers GlcNAc to the non‐reducing terminus of the Galβ1–4GlcNAc of tetraantennary N‐glycan in vitro. HCT15 cells transfected with β3Gn‐T8 cDNA showed an increase in reactivity to both LEA and PHA‐L4 in a flow cytometric analysis. These results indicated that β3Gn‐T8 is involved in the biosynthesis of poly‐N‐acetyllactosamine chains on tetraantennary (β1,6‐branched) N‐glycan. In most of the colorectal cancer tissues examined, the level of β3Gn‐T8 transcript was significantly higher than in normal tissue. β3Gn‐T8 could be an enzyme involved in the synthesis of poly‐N‐acetyllactosamine on β1–6 branched N‐glycans in colon cancer.

Suppressive effects of F-1322 on the antigen-induced late asthmatic response and pulmonary eosinophilia in guinea pigs

We investigated the effects of F-1322 (N-[2-[4-(benzhydryloxy)piperidino]ethyl]-3-hydroxy-5-(3-pyridylmethoxy)-2-naphthamide), a new compound that inhibits both thromboxane A2 synthetase and 5-lipoxygenase and that functions as a histamine antagonist, on the Ascaris antigen-induced late asthmatic response and pulmonary eosinophilia in guinea pigs. Oral administration of F-1322 (10-100 mg/kg) inhibited the antigen-induced late asthmatic response in a dose-dependent manner. Histological analysis revealed that F-1322 prevented the accumulation of eosinophils in the airways and this was paralleled by a decrease in the number of eosinophils and lymphocytes recovered in bronchoalveolar lavage fluid. F-1322 (0.1-10 microM) inhibited eotaxin-induced chemotaxis and actin polymerization of eosinophils in vitro in a concentration-dependent manner, while oral administration of F-1322 dose-dependently suppressed the migration of eosinophils into the airways in vivo in response to infusion of interleukin 5 and eotaxin in combination. F-1322 may, thus, improve the late asthmatic response in this model, in part, by preventing the accumulation of eosinophils in the airways. The pharmacological profile of F-1322 indicates that this drug is likely to be useful in the treatment of allergic diseases such as asthma.