Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.99.7 (sialyltransferase)
 1,534 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Gangliosides are sialo-glycosphingolipids that play important roles in the interaction of cells with their environment and are thus involved in the regulation of many cellular events. Sialic acid residues are important for the conformation of a glycomolecule, their structural stability and their functions. Although decreased brain ganglioside sialic acid has been previously reported as a result of chronic ethanol treatment in rats, no reports are available on the sialylation of specific gangliosides and/or the mechanism leading to depletion of their sialic acid residues. Therefore, in this investigation, we have examined the effects of chronic ethanol treatment on (1) incorporation of [4,5-3H]N-acetylmannosamine (ManNAc) into specific rat brain gangliosides, GD3, GD1a, GT1a, and GT1b; and (2) enzymatic activities of brain sialyltransferase and sialidase at specific subcellular levels. The experiments were done in male Wistar rats pair-fed with either ethanol or control liquid diets for a period of 8 weeks. The rats were intracerebroventricularly injected with labeled ManNAc (30 microCi/rat) and killed after 90 min. Radioactivity was determined in respective ganglioside bands separated on a thin layer chromatography system. Specific activities of sialyltransferase and sialidase were assessed using GM3 and GD3 as substrates, respectively. The results showed significant decreases of 57.7% (p < 0.001) and 68.9% (p < 0.001), respectively, in the labeled ManNAc incorporation into GD3 and GD1a fractions in rats of the ethanol group, compared with rats of the control group. No significant changes were noted in the incorporation of labeled ManNAc into GT1a or GT1b ganglioside fractions between the ethanol and control groups. Concomitantly, compared with control rats, a decrease of 18.9% (p < 0.05), 20.6% (p < 0.05), and 15.8% (p < 0.001) was found in the sialyltransferase activity, respectively, at the whole brain, and brain Golgi and synaptosomal levels. However, dramatic increases of 32.4% (p < 0.05), 105% (p < 0.001), and 150% (p < 0.001) in sialidase activity were found, respectively, at the whole brain and brain cytosol and synaptosomal fractions of rat treated chronically with ethanol. Thus, we conclude that the deleterious actions of ethanol on the sialylation of rat brain gangliosides is specific, and the reduced sialic acid label found in GD3 and GD1a in this study is mainly due to increased activity of brain sialidase. Furthermore, the study reaffirms our tenet that, regardless of whether it is the liver or the brain, glycosylation cascade is one of the main target of the deleterious attacks of ethanol.
Alcohol Clin Exp Res 1998 Sep
PMID:Long-term ethanol consumption selectively impairs ganglioside pathway in rat brain. 975 36

Sialic acids from the liver and serum of guinea-pig are composed of N-acetylneuraminic acid (Neu5Ac; 85% and 61%, respectively), N-acetyl-4-O-acetylneuraminic acid (Neu4,5Ac2; 10% and 32%, respectively) and N-glycolylneuraminic acid (Neu5Gc; 5% and 7%, respectively), besides traces of N-glycolyl-4-O-acetylneuraminic acid in serum. The analysis was carried out using thin-layer chromatography, high-performance liquid chromatography, electron impact ionization mass spectrometry, and different enzymes (sialidase, sialate esterase, and sialate-pyruvate lyase after hydrolysis and purification of the sialic acids by ion-exchange chromatography). We showed that this O-acetylation of sialic acids is due to the activity of an acetyl-coenzyme A:sialate-4-O-acetyltransferase (EC 2.3.1.44), which occurs together with sialyltransferase activity in Golgi-enriched membrane fractions of guinea-pig liver. The enzyme operates optimally at 30 degrees C in 70 mM potassium phosphate buffer at pH 6.7 and in the presence of 90 mM KCI with an apparent KM for AcCoA of 0.6 1microM and a Vmax of 20 pmol/mg protein x min. The enzyme is inhibited by coenzyme A in a mixed-competitive manner (Ki = 4.2 microM), as well as by parachloromercuribenzoate, MnCl2, saponin and Triton X-100.
Glycoconj J 1998 Sep
PMID:Enzymatic 4-O-acetylation of N-acetylneuraminic acid in guinea-pig liver. 1005 93

HNA is an autosomal dominant recurrent focal neuropathy involving the brachial plexus. The etiology of HNA is unknown but the genetic defect most likely affects a non-neuronal tissue. We previously described linkage to chromosome 17q24-q25 in two HNA-families. Here we report the mutation analysis of two candidate genes: a cDNA encoding a putative sialyltransferase and the SFRS2 splicing factor including the c-myb ET-locus which is encoded on the opposite strand of the SFRS2 gene. The complete protein coding regions of both genes were studied by direct DNA sequencing. We did not find a disease associated mutation indicating that these genes are most likely not involved in the pathogenesis of HNA. However, we identified and characterized a rare AvaII polymorphism in the SFRS2 gene and detected a sequencing error, leading to an amino acid change (Val11Leu) in the published sequence of the putative sialyltransferase.
Ann Hum Genet 1998 Sep
PMID:Mutation analysis of a putative sialyltransferase gene, the SFRS2 splicing factor gene and the c-myb ET-locus in two families with hereditary neuralgic amyotrophy (HNA). 1008 36

We have previously shown that costimulation of endothelial cells with IL-1 + IL-4 markedly inhibits VCAM-1-dependent adhesion under flow conditions. We hypothesized that sialic acids on the costimulated cell surfaces may contribute to the inhibition. Northern blot analyses showed that Gal beta 1-4GlcNAc alpha 2, 6-sialyltransferase (ST6N) mRNA was up-regulated in cultured HUVEC by IL-1 or IL-4 alone, but that the expression was enhanced by costimulation, whereas the level of Gal beta 1-4GlcNAc/Gal beta 1-3GalNAc alpha2,3-sialyltransferase (ST3ON) mRNA was unchanged. Removing both alpha 2,6- and alpha 2,3-linked sialic acids from IL-1 + IL-4-costimulated HUVEC by sialidase significantly increased VCAM-1-dependent adhesion, whereas removing alpha 2,3-linked sialic acid alone had no effect; adenovirus-mediated overexpression of ST6N with costimulation almost abolished the adhesion, which was reversible by sialidase. The same treatments of IL-1-stimulated HUVEC had no effect. Lectin blotting showed that VCAM-1 is decorated with alpha 2,6- but not alpha 2,3-linked sialic acids. However, overexpression of alpha 2,6-sialyltransferase did not increase alpha 2,6-linked sialic acid on VCAM-1 but did increase alpha 2,6-linked sialic acids on other proteins that remain to be identified. These results suggest that alpha 2,6-linked sialic acids on a molecule(s) inducible by costimulation with IL-1 + IL-4 but not IL-1 alone down-regulates VCAM-1-dependent adhesion under flow conditions.
J Immunol 1999 Sep 01
PMID:Endothelial alpha 2,6-linked sialic acid inhibits VCAM-1-dependent adhesion under flow conditions. 1045 33

In this study, we report the first isolation and characterization of a bovine sialyltransferase gene. Bovine cDNAs prepared from different tissues contain an open-reading frame encoding a 405 amino acid sequence showing 83%, 75%, and 60% identity with human, murine, and chicken ST6Gal I (beta-galactoside alpha2,6-sialyltransferase) sequences, respectively. When transfected into COS-7 cells, a recombinant enzyme was obtained which catalyzed the in vitro alpha2, 6-sialylation of LacNAc (NeuAcalpha2-6Galbeta1-4GlcNAc) and LacdiNAc (NeuAcalpha2-6GalNAcbeta1-4GlcNAc) acceptor substrates. The K (m) values were 2.8 and 6.9 mM, respectively. Different relative efficiencies (Vmax/Km) for the two precursors (36 for LacNAc and 4.3 for LacdiNAc) were observed. Bovine ST6Gal I gene consists of four 5'-untranslated exons E(-2) to E(1), and five coding exons from E(2) to E(6). This later carries a 3'-untranslated region of 2. 7 kb. Gene sequence spans at least 80 kb of genomic DNA. Two processed pseudogenes have been identified. They are 94.3 and 95.6% similar to the bovine cDNA, respectively. Three families of mRNA isoforms were isolated. They differed by their 5'-untranslated regions and could be generated by three tissue-specific promoters. Family 1 is made up of exons E(-2) and E(1) to E(6), family 2 of exons E(-1) to E(6), and family 3 of exons E(1) to E(6). Tissular distribution of transcript families appears noticeably different than those described in human and rat.
Glycobiology 1999 Sep
PMID:Molecular cloning, expression and exon/intron organization of the bovine beta-galactoside alpha2,6-sialyltransferase gene. 1046 Aug 27

A single gene, SIAT1, encodes ST6Gal I, the sialyltransferase that mediates transfer of alpha2,6-linked sialic acids to Galbeta1, 4GlcNAc termini of N-linked glycoproteins. In vivo, multiple SIAT1 mRNA forms, differing only in the 5'-untranslated region, are expressed in a tissue-specific manner. This mRNA heterogeneity has been attributed, at least in part, to transcription from a number of physically distinct promoter regions. In mature B-lymphocytes, SIAT1 transcription initiates at P2, a regulatory region known to function only in B-lineage cells. Bacterial chloramphenicol acetyltransferase (CAT) under the control of the P2 region encompassing 415 bp 5'- and 125 bp 3' of the transcriptional initiation site is efficiently expressed in Louckes, a mature B-lymphoblastoid cell line. In contrast, CAT expression in Reh, a T-null/B-null precursor line, and in HepG2, a hepatoma line, are 14-fold and >25-fold less than in Louckes, respectively. The data is consistent with the presence of cis -acting regulatory elements residing both 5' and 3' of the P2 transcriptional initiation site. At least 370 bp of 5'-flanking sequence, coinciding with the inclusion of AP2 and NF-kappaB sites, is necessary for high level expression in Louckes. Exon sequences 3' of the transcription start site are also important for expression. A segment from(+)32 to(+)125 (position(+)1 is transcription start site) is capable of exerting promoter-like activity in Louckes, but not in Reh or HepG2. CAT expression by P2 is negligible in Reh cells. However, enhanced CAT activity is not accompanied by elevated mRNA levels. This observation is consistent with the relief of translational restraints imposed by the(+)32 to(+)125 region. Together, the data demonstrate that efficient and cell-specific transcription regulation in mature B lymphocytes is contained in a 495 bp P2 segment that is comprised of 370 bp of 5'-flanking region and 125 bp of transcribed region of Exon X.
Glycobiology 1999 Sep
PMID:Transcription of the beta-galactoside alpha2,6-sialyltransferase gene (SIAT1) in B-lymphocytes: cell type-specific expression correlates with presence of the divergent 5'-untranslated sequence. 1046 Aug 32

The tetrameric form of native serum-derived bovine acetylcholinesterase is retained in the circulation for much longer periods (mean residence time, MRT = 1390 min) than recombinant bovine acetylcholinesterase (rBoAChE) produced in the HEK-293 cell system (MRT = 57 min). Extensive matrix-assisted laser desorption ionization-time of flight analyses established that the basic structures of the N-glycans associated with the native and recombinant enzymes are similar (the major species (50-60%) are of the biantennary fucosylated type and 20-30% are of the triantennary type), yet the glycan termini of the native enzyme are mostly capped with sialic acid (82%) and alpha-galactose (12%), whereas glycans of the recombinant enzyme exhibit a high level of exposed beta-galactose residues (50%) and a lack of alpha-galactose. Glycan termini of both fetal bovine serum and rBoAChE were altered in vitro using exoglycosidases and sialyltransferase or in vivo by a HEK-293 cell line developed specifically to allow efficient sialic acid capping of beta-galactose-exposed termini. In addition, the dimeric and monomeric forms of rBoAChE were quantitatively converted to tetramers by complexation with a synthetic peptide representing the human ColQ-derived proline-rich attachment domain. Thus by controlling both the level and nature of N-glycan capping and subunit assembly, we generated and characterized 9 distinct bovine AChE glycoforms displaying a 400-fold difference in their circulatory lifetimes (MRT = 3.5-1390 min). This revealed some general rules and a hierarchy of post-translation factors determining the circulatory profile of glycoproteins. Accordingly, an rBoAChE was generated that displayed a circulatory profile indistinguishable from the native form.
J Biol Chem 2000 Sep 22
PMID:Hierarchy of post-translational modifications involved in the circulatory longevity of glycoproteins. Demonstration of concerted contributions of glycan sialylation and subunit assembly to the pharmacokinetic behavior of bovine acetylcholinesterase. 1086 10

Neural cell adhesion molecules (NCAMs) play critical roles during development of the nervous system. The aim of this study is to investigate the possible effect of ethanol exposure on the pattern of expression and sialylation of NCAM isoforms during postnatal rat brain development because alterations in NCAM content and distribution have been associated with defects in cell migration, synapse formation, and memory consolidation, and deficits in these processes have been observed after in utero alcohol exposure. The expression of NCAM isoforms in the developing cerebral cortex of pups from control and alcohol-fed mothers was assessed by western blotting, ribonuclease protection assay, and immunocytochemistry. The highly sialylated form of NCAM [polysialic acid (PSA)-NCAM] is mainly expressed during the neonatal period and then is down-regulated in parallel with the appearance of NCAM 180 and NCAM 140. Ethanol exposure increases PSA-NCAM levels during the neonatal period, delays the loss of PSA-NCAM, decreases the amount of NCAM 180 and NCAM 140 isoforms, and reduces sialyltransferase activity during postnatal brain development. Neuraminidase treatment of ethanol-exposed neonatal brains leads to more intense band degradation products, suggesting a higher content of NCAM polypeptides carrying PSA in these samples. However, NCAM mRNA levels are not changed by ethanol. Immunocytochemical analysis demonstrates that ethanol triggers an increase in PSA-NCAM immunolabeling in the cytoplasm of astroglial cells, accompanied by a decrease in immunogold particles over the plasma membrane. These findings indicate that ethanol exposure during brain development alters the pattern of NCAM expression and suggest that modification of NCAM could affect neuronal-glial interactions that might contribute to the brain defects observed after in utero alcohol exposure.
J Neurochem 2000 Sep
PMID:Alcohol exposure alters the expression pattern of neural cell adhesion molecules during brain development. 1093 76

Work addressing whether cystic fibrosis transmembrane conductance regulator (CFTR) plays a role in regulating organelle pH has remained inconclusive. We engineered a pH-sensitive excitation ratiometric green fluorescent protein (pHERP) and targeted it to the Golgi with sialyltransferase (ST). As determined by ratiometric imaging of cells expressing ST-pHERP, Golgi pH (pH(G)) of HeLa cells was 6.4, while pH(G) of mutant (DeltaF508) and wild-type CFTR-expressing (WT-CFTR) respiratory epithelia were 6.7-7.0. Comparison of genetically matched DeltaF508 and WT-CFTR cells showed that the absence of CFTR statistically increased Golgi acidity by 0.2 pH units, though this small difference was unlikely to be physiologically important. Golgi pH was maintained by a H(+) vacuolar (V)-ATPase countered by a H(+) leak, which was unaffected by CFTR. To estimate Golgi proton permeability (P(H(+))), we modeled transient changes in pH(G) induced by inhibiting the V-ATPase and by acidifying the cytosol. This analysis required knowing Golgi buffer capacity, which was pH dependent. Our in vivo estimate is that Golgi P(H(+)) = 7.5 x 10(-4) cm/s when pH(G) = 6.5, and surprisingly, P(H(+)) decreased as pH(G) decreased.
Am J Physiol Cell Physiol 2001 Sep
PMID:Proton leak and CFTR in regulation of Golgi pH in respiratory epithelial cells. 1150 68

Despite numerous reports suggesting that beta(1) integrin receptors undergo differential glycosylation, the potential role of N-linked carbohydrates in modulating integrin function has been largely ignored. In the present study, we find that beta(1) integrins are differentially glycosylated during phorbol ester (PMA)-stimulated differentiation of myeloid cells along the monocyte/macrophage lineage. PMA treatment of two myeloid cell lines, U937 and THP-1, induces a down-regulation in expression of the ST6Gal I sialyltransferase. Correspondingly, the beta(1) integrin subunit becomes hyposialylated, suggesting that the beta(1) integrin is a substrate for this enzyme. The expression of hyposialylated beta(1) integrin isoforms is temporally correlated with enhanced binding of myeloid cells to fibronectin, and, importantly, fibronectin binding is inhibited when the Golgi disrupter, brefeldin A, is used to block the expression of the hyposialylated form. Consistent with the observation that cells with hyposialylated integrins are more adhesive to fibronectin, we demonstrate that the enzymatic removal of sialic acid residues from purified alpha(5)beta(1) integrins stimulates fibronectin binding by these integrins. These data support the hypothesis that unsialylated beta(1) integrins are more adhesive to fibronectin, although desialylation of alpha(5) subunits could also contribute to increased fibronectin binding. Collectively our results suggest a novel mechanism for regulation of the beta(1) integrin family of cell adhesion receptors.
J Biol Chem 2002 Sep 06
PMID:Hyposialylation of integrins stimulates the activity of myeloid fibronectin receptors. 1209 85


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