Shuichi Tsuji

Handbook of glycosyltransferases and related genes

The CHST14 gene, localized at 15q14, is a single exon gene with an open reading frame of 1131 base pairs, encoding a 43 kDa protein dermatan-4-Osulfotransferase-1 (D4ST1) that catalyzes the 4-O-sulfation of N-acetyl-D-galactosamine residues in dermatan sulfate (DS). Both nearly exhaustively desulfated DS and partially desulfated DS serve as excellent substrates for the enzyme. Chst14/D4st1-deficient mice showed growth retardation as well asmultiple system abnormalities including neurology such as decreased neurogenesis and diminished T. Kosho (*) School of Medicine, Department of Medical Genetics, Shinshu University, Matsumoto, Japan e-mail: ktomoki@shinshu-u.ac.jp S. Mizumoto • K. Sugahara Laboratory of Proteoglycan Signaling and Therapeutics, Hokkaido University Graduate School of Life Science, Kita-ku, Sapporo, Japan e-mail: mizumoto@sci.hokudai.ac.jp; k-sugar@sci.hokudai.ac.jp N. Taniguchi et al. (eds.), Handbook of Glycosyltransferases and Related Genes, DOI 10.1007/978-4-431-54240-7_156, # Springer Japan 2014 1135 proliferation of neural stem cells. Recently, recessive loss-of-function mutations in the CHST14 gene were found to cause a specific form of Ehlers-Danlos syndrome (EDS) designated as D4ST1-deficient EDS (DD-EDS). The disorder is characterized by progressive multisystem fragility-related manifestations (skin hyperextensibilty and fragility, progressive spinal and foot deformities, large subcutaneous hematoma) and various malformations (facial features, congenital eye/heart/gastrointestinal defects, congenital multiple contractures). Glycosaminoglycan (GAG) chains from the affected skin fibroblasts were composed of a negligible amount of DS and excess chondroitin sulfate (CS), which was suggested to result from an impaired lock by 4-O-sulfation due to D4ST1 deficiency followed by back epimerization from L-iduronic acid to D-glucuronic acid. GAG chains of decorin from the affected skin fibroblasts were composed exclusively of CS and no DS, the opposite features observed in normal controls. Thus, skin fragility in the disorder was supposed to be caused by impaired assembly of collagen fibrils mediated by decorin bearing a CS chain that replaced a DS chain. The disorder stresses the importance of the role of CHST14/ D4ST1 and DS in human development and maintenance of extracellular matrices.

Synthetic Sialyl Compounds as Well as Natural Gangliosides Induce Neuritogenesis in a Mouse Neuroblastoma Cell Line (Neuro2a)

Amphipathic compounds containing N‐acetylneuraminic acid (sialic acid) [for example, D‐N‐acetylneuraminyl‐(α2‐1)‐2S, 3R,4E‐2‐N‐tetracosanoyl sphingenine, sialyl alkyl glycerol ethers, and sialyl cholesterols] induced neuritogenesis in a neuroblastoma cell line (Neuro2a). The sialic acid in the hydrophilic moiety of the compounds is specifically required for neuritogenesis. The requirement for molecular specificity of the hydrophobic moiety, however, is rather low. Regarding the hydrophobic moiety, no preference for cholesterol, alkyl glycerol ether, or ceramide residues was observed as to their neuritogenic activity. Sialyl compounds with α‐ketosidic sialyl linkages were more active than the corresponding β‐anomers. These sialyl compounds induced the growth of only one neurite, but a long one, from the cell body. This type of neuritogenesis is completely different from that induced by compounds capable of elevating the concentration of intracellular cyclic AMP, which induced the appearance of many neurites from a single cell body. Besides this morphological change, the active sialyl compounds also caused a change in the carbohydrate composition of the cell surface. Sialyl compound treatment drastically increased the concentration of peanut agglutinin binding sites.

Characterization of Mouse ST8Sia II (STX) as a Neural Cell Adhesion Molecule-specific Polysialic Acid Synthase REQUIREMENT OF CORE α1,6-LINKED FUCOSE AND A POLYPEPTIDE CHAIN FOR POLYSIALYLATION

We previously showed that mouse ST8Sia II (STX) exhibits polysialic acid (PSA) synthase activity in vivo as well as in vitro (Kojima, N., Yoshida, Y., and Tsuji, S. (1995) FEBS Lett. 373, 119-122, 1995). In this paper, we reported that the neural cell adhesion molecule (NCAM) was specifically polysialylated by a single enzyme, ST8Sia II. PSA-expressing Neuro2a cells (N2a-STX) were established by stable transfection of the mouse ST8Sia II gene. Only the 140- and 180-kDa isoforms of NCAM in N2a-STX cells were specifically polysialylated in vivo, although other membrane proteins of N2a-STX were polysialylated in vitro. A recombinant soluble mouse ST8Sia II synthesized PSA on a recombinant soluble NCAM fused with the Fc region of human IgG1 (NCAM-Fc) as well as fetuin. However, NCAM-Fc served as a 1500-fold better acceptor for ST8Sia II than fetuin. Treatment of NCAM-Fc with Charonia lampas α-fucosidase, which is able to cleave α1,6-linked fucose, clearly reduced the polysialylation of NCAM-Fc by ST8Sia II. PSA was not synthesized on the N-glycanase-treated NCAM-Fc polypeptide or the free N-glycans of NCAM-Fc. When fetuin and its glycopeptide and N-glycans of fetuin were used as substrates for ST8Sia II, PSA was found to be synthesized on native fetuin and its glycopeptide but not on free N-glycans. These results strongly suggested that core α1,6-fucose on N-glycans as well as the antennary structures of N-glycans and the polypeptide regions are required for the polysialylation by ST8Sia II. Furthermore, oligo and single α2,8-sialylated glycoproteins were no longer polysialylated by mouse ST8Sia II. Therefore, the single enzyme, ST8Sia II, directly transferred all α2,8-sialic acid residues on the α2,3-linked sialic acids of N-glycans of specific NCAM isoforms to yield PSA-NCAM. Polysialylation did not require any initiator α2,8-sialyltransferase but did depend on the carbohydrate and protein structures of NCAM.

Enzymatic activity of a developmentally regulated member of the sialyltransferase family (STX): evidence for α2,8‐sialyltransferase activity toward N‐linked oligosaccharides

We have detected sialyltransferase activity of recombinant mouse STX, which was cloned from rat brain as a new member of the sialyltransferase family, but sialyltransferase activity of which had not been detected previously [Livingston and Paulson, J. Biol. Chem. (1993) 268, 11504–11507]. The activity of mouse STX was specific toward sialylated glycoproteins. N‐Glycanase treatment and linkage‐specific sialidase treatment of glycoproteins revealed that STX transfers sialic acids through α2,8‐linkages to only N‐linked oligosaccharides of glycoproteins. However, polymerase activity for polysialic acid synthesis was not detected for this sialyltransferase. Since this α2,8‐sialyltransferase gene is highly restricted in fetal and newborn brain, it may be involved in the polysialylation of glycoproteins, especially of N‐CAM.

A developmentally regulated member of the sialyltransferase family (ST8Sia II, STX) is a polysialic acid synthase

We found polysialic acid synthase activity of ST8Sia II (STX) in vitro and in vivo. Previously, we showed that mouse ST8Sia II exhibits α2,3‐sialylated N‐glycan α2,8‐sialyltransferase activity, but the polysialic acid synthase activity of ST8Sia II was not detected at that time [Kojima, N. et al. (1995) FEBS Lett. 360, 1–4]. When fetuin was [14C]sialylated with ST8Sia II and then its N‐linked oligosaccharides were analyzed, a part of the N‐linked oligosaccharides was eluted in the void volume from a Sephadex G‐50 column, and was eluted from the DEAE‐Toyopearl column at almost the same salt concentration as that where colomic acid was eluted. In addition, a series of 14C‐labeled oligo‐sialic acids were obtained from the oligosaccharides on partial mild acid hydrolysis. These results indicated that a part of N‐linked oligosaccharides of fetuin were polysialylated with ST8Sia II. Transfection of ST8Sia II gene into several cell lines including NIH3T3 led to the expression of polysialic acids on the cell surface. Thus, ST8Sia II can directly synthesize polysialic acid chains on α2,3‐sialylated N‐linked oligosaccharides of glycoproteins without any initiator sialyltransferase.

Molecular Cloning and Expression of a Fifth Type of α2,8-Sialyltransferase (ST8Sia V) ITS SUBSTRATE SPECIFICITY IS SIMILAR TO THAT OF SAT-V/III, WHICH SYNTHESIZE GD1c, GT1a, GQ1b AND GT3

The cDNAs encoding a new α2,8-sialyltransferase (ST8Sia V) were cloned from a mouse brain cDNA library by means of a polymerase chain reaction-based method using the nucleotide sequence information on mouse ST8Sia I (GD3 synthase) and mouse ST8Sia III (Siaα2,3Galβ1,4GlcNAcα2,8-sialyltransferase), both of which exhibit activity toward glycolipids. The predicted amino acid sequence of ST8Sia V shows 36.1% and 15.0% identity to those of mouse ST8Sia I and III, respectively. The recombinant protein A-fused ST8Sia V expressed in COS-7 cells exhibited an α2,8-sialyltransferase activity toward GM1b, GD1a, GT1b, and GD3, and synthesized GD1c, GT1a, GQ1b, and GT3, respectively. The apparent Km values for GM1b, GD1a, GT1b and GD3 were 1.1, 0.082, 0.070, and 0.28 mM, respectively. However, ST8Sia V did not exhibit activity toward GM3. Thus, the substrate specificity of ST8Sia V is different from those of ST8Sia I and III, both of which exhibit activity toward GM3. Transfection of the ST8Sia V gene into COS-7 cells, which express GD1a as a major glycolipid, led to the expression of determinants for monoclonal antibody 4F10, which recognizes GT1a and GQ1b, suggesting that ST8Sia V exhibits activity toward gangliosides GD1a and/or GT1b in vivo. The expression of the ST8Sia V gene was tissue- and developmental stage-specific, and was clearly different from those of other α2,8-sialyltransferase genes. The ST8Sia V gene was strongly expressed in the brain and weakly in other tissues such as the liver. In addition, its expression was greater in the adult than fetal brain. These results strongly indicate that ST8Sia V is a candidate for SAT-V, the α2,8-sialyltransferase involved in GD1c, GT1a, GQ1b, and GT3 synthesis.

Isolation of 10 Differentially Expressed cDNAs in Differentiated Neuro2a Cells Induced Through Controlled Expression of the GD3 Synthase Gene

Abstract: Recently, we showed that transfection of GD3 synthase cDNA into Neuro2a cells, a mouse neuroblastoma cell line, causes cell differentiation with neurite sprouting. In a search for the genes involved in this ganglioside‐induced Neuro2a differentiation, we used a tetracycline‐regulated GD3 synthase cDNA expression system combined with differential display PCRs to identify mRNAs that were differentially expressed at four representative time points during the process. We report here the identification of 10 mRNAs that are expressed highly at the Neuro2a differentiated stage. These cDNAs were named GDAP1–GDAP10 for (ganglioside‐induced differentiation‐associated protein) cDNAs. It is interesting that in retinoic acid‐induced neural differentiated mouse embryonic carcinoma P19 cells, GDAP mRNA expression levels were also up‐regulated (except that of GDAP3), ranging from three to > 10 times compared with nondifferentiated P19 cells. All the GDAP genes (except that of GDAP3) were developmentally regulated. The GDAP1, 2, 6, 8, and 10 mRNAs were expressed highly in the adult mouse brain, whereas all the other GDAP mRNAs were expressed in most tissues. Our results suggested that these GDAP genes might be involved in the signal transduction pathway that is triggered through the expression of a single sialyltransferase gene to induce neurite‐like differentiation of Neuro2a cells.

Genomic Structure and Promoter Activity of the Mouse Polysialic Acid Synthase Gene (mST8Sia II) BRAIN-SPECIFIC EXPRESSION FROM A TATA-LESS GC-RICH SEQUENCE

The mouse ST8Sia II (mST8Sia II/STX) gene encodes a neural cell adhesion molecule-specific polysialic acid synthase whose expression is regulated during the developmental stages of mouse brain. To elucidate the molecular mechanism by which the expression is tissue-specifically and developmentally regulated, we isolated the complete genomic DNA and characterized the promoter of the gene for mST8Sia II. The gene encoding mST8Sia II was found to span about 80 kilobases and to be composed of six exons. Primer extension and S1 nuclease protection analyses revealed that the transcription started from 167 nucleotides upstream of the translational initiation site. Promoter analyses of the 5′-flanking region of the mST8Sia II gene using a luciferase gene reporter system revealed strong promoter activity in retinoic acid-induced differentiated P19 cells, which highly express the mST8Sia II gene. Deletion analyses demonstrated that the minimal promoter activity detected for the proximal region 325 base pairs upstream from the translational initiation codon (−158 to +167) could be modulated by various sequences within the 9.5-kilobase 5′-flanking region. The minimal promoter was embedded in a GC-rich domain (74%, GC content), in which two Sp1 binding motifs as well as a long purine-rich region were found, but it lacked TATA and CAAT boxes. The positive regulatory region located between −159 and −659 contained two additional Sp1 binding motifs and a long pyrimidine-rich region. We also found that the minimal promoter region of the mST8Sia II gene was sufficient for expression of a reporter gene in mST8Sia II gene-expressing neural differentiated P19 cells but not in nonexpressing ones. Thus the TATA-less GC-rich minimal promoter region of mST8Sia II probably controls the cell type-specific expression of the mST8Sia II gene.

Polysialic acid synthase (ST8Sia II/STX) mRNA expression in the developing mouse central nervous system.

Abstract: A comparative study was undertaken to correlate the immunohistochemical localization of polysialic acid (PSA) and the in situ localization of ST8Sia II mRNA. In situ hybridization of postnatal day 3 mouse brain showed high levels of ST8Sia II mRNA expression in the cerebral neocortex, striatum, hippocampus, subiculum, medial habenular nucleus, thalamus, pontine nuclei, and inferior colliculus; intermediate‐level expression in the olfactory bulb, hypothalamus, superior colliculus, and cerebellum; and low‐level expression in other regions. The distribution of ST8Sia II mRNA in the neocortex and cerebellum coincided with the immunohistochemical localization of PSA. During brain development, ST8Sia II mRNA started decreasing and had almost disappeared by postnatal day 14. Comparison between ST8Sia II and IV mRNA expression was also undertaken by northern blot analysis and competitive PCR analysis. During the late embryonic to early postnatal stages of the mouse CNS, the ST8Sia II mRNA showed abundant mRNA expression compared with the ST8Sia IV mRNA. Competitive PCR analysis of the adult mouse CNS showed weak expression of the two genes in the olfactory bulb, thalamus, hippocampus, and eyes. The regional and transient expression of ST8Sia II mRNA coincides with that of PSA, suggesting that ST8Sia II is closely involved in the biosynthesis and expression of PSA in the developing mouse CNS.

Calcium activated neutral protease from human skeletal muscle.

Koichi SUZUKI, Shoichi ISHIURA*, Shuichi TSUTI, Tetsuo KATAMOTO, Hideo SUGITA*p** and Kazutomo IMAHORI Department of Biochemistry, Faculty of Med&ine, University of Tokyo, Bunkyo-ku, Tokyo, Japan; *Division of Neu~muscu~r Research, Nat~~t Center for Nervous, rental, and Tuscan Disorders, Kodaira, Tokyo, Japan; and **De~r~~t of Ne~io~, Insti~te of Brain Research, Faculty of medicine, ~niversi~ of Tokyo, ~unky~~, Tokyo, Japan