Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.99.6 (sialyltransferase)
 1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Gangliosides are sialylated glycosphingolipids whose biosynthesis is catalyzed by a series of endoplasmic reticulum (ER)- and Golgi-resident glycosyltransferases. Protein expression, processing, and subcellular localization of the key regulatory enzymes for ganglioside biosynthesis, sialyltransferase II (ST-II) and N-acetylgalactosaminyltransferase I (GalNAcT), were analyzed upon transient expression of the two enzymes in the neuroblastoma cell lines NG108-15 and F-11. The enzymes were endowed with a C-terminal epitope tag peptide (FLAG) for immunostaining and immunoaffinity purification using a FLAG-specific antibody. Mature ST-II-FLAG and GalNAcT-FLAG were expressed as N-glycoproteins with noncomplex oligosaccharides. ST-II-FLAG was distributed to the Golgi apparatus, whereas GalNAcT-FLAG was found in the ER and Golgi. Inhibition of early N-glycoprotein processing with castanospermine resulted in a distribution of ST-II-FLAG to the ER, whereas that of GalNAcT-FLAG remained unaltered. In contrast to GalNAcT, the activity of ST-II and the amount of immunostained enzyme were reduced concomitantly by 75% upon incubation with castanospermine. This was due to a fourfold increased turnover of ST-II-FLAG, which was not found with GalNAcT-FLAG. The ER retention and increased turnover of ST-II-FLAG were most likely due to its inability to bind to calnexin upon inhibition of early N-glycoprotein processing. Calnexin binding was not observed for GalNAcT-FLAG, indicating a differential effect of N-glycosylation on the turnover and subcellular localization of the two glycosyltransferases.
 ...
PMID:Effect of N-glycosylation on turnover and subcellular distribution of N-acetylgalactosaminyltransferase I and sialyltransferase II in neuroblastoma cells. 1082 Jan 96

Three key regulatory enzymes in ganglioside biosynthesis, sialyltransferase I (ST1), sialyltransferase II (ST2), and N-acetylgalactosaminyltransferase I (GalNAcT), have been expressed as fusion proteins with green, yellow, or red fluorescent protein (GFP, YFP, or RFP) in F-11A cells. F-11A cells are a substrain of murine neuroblastoma F-11 cells that contain only low endogenous ST2 and GalNAcT activity. The subcellular localization of the fusion proteins has been determined by fluorescence microscopy, and the ganglioside composition of these cells was analyzed by high-performance thin-layer chromatography (HPTLC). ST2-GFP (85 kDa) shows a distinct Golgi localization, whereas ST1-YFP (85 kDa) and GalNAcT-RFP (115 kDa) are broadly distributed in ER and Golgi. Untransfected F-11A cells contain mainly GM3, whereas stable transfection with ST2 or GalNAcT results in the predominant expression of b-series complex gangliosides (BCGs). This result indicates that the expression of ST2 enhances the activity of endogenous GalNAcT and vice versa. The specificity of this reaction has been verified by in vitro activity assays with detergent-solubilized enzymes, suggesting the formation of an enzyme complex between ST2 and GalNAcT but not with ST1. Complex formation has also been verified by co-immunoprecipitation of ST2-GFP upon transient transfection with GalNAcT-HA-RFP and by GFP-to-RFP FRET signals that are confined to the Golgi. FRET analysis also suggests that ST2-GFP binds tightly to pyrene-labeled GM3 but not to ST1. We hypothesize that an ST2-GM3 complex is associated with GalNAcT, resulting in the enhanced conversion of GM3 to GD3 and BCGs in the Golgi. Taken together, our results support the concept that ganglioside biosynthesis is tightly regulated by the formation of glycosyltransferase complexes in the ER and/or Golgi.
 ...
PMID:Regulation of ganglioside biosynthesis by enzyme complex formation of glycosyltransferases. 1223 91

Gangliosides are sialic acid-containing glycosphingolipids abundant in the central nervous tissues. The quantity and expression pattern of gangliosides in brain change drastically during early development and are mainly regulated through stage-specific expression of glycosyltransferase (ganglioside synthase) genes. It is still unclear, however, how the transcriptional activation of glycosyltransferase genes is regulated during development. In this study, we investigated the epigenetic regulation of two key glycosyltransferases, N-acetylgalactosaminyltransferase I (GA2/GM2/GD2/GT2-synthase) and sialyltransferase II (GD3-synthase), in embryonic, postnatal, and adult mouse brains. Combined bisulfite restriction analysis assay showed that DNA methylation in the 5' regions of these glycosyltransferase genes was not associated with their expression patterns. On the other hand, chromatin immunoprecipitation assay of both glycosyltransferase genes showed that their histone H3 acetylation was highly correlated to their mRNA expression levels during development. In fact, we confirmed that the expression patterns of gangliosides and glycosyltransferases in neuroepithelial cells were changed after treatment with a histone deacetylase inhibitor, sodium butyrate. Our studies provide the first evidence that efficient histone acetylation of the glycosyltransferase genes in mouse brain contributes to the developmental alteration of ganglioside expression.
 ...
PMID:Histone acetylation-mediated glycosyltransferase gene regulation in mouse brain during development. 2121 66

The quantity and expression pattern of gangliosides in mammalian brain change drastically during development and are mainly regulated through stage-specific expression of ganglioside synthase genes. Despite extensive investigations in the past, it remains largely unclear how the transcriptional activation of the genes encoding glycosyltransferases is regulated. Here, we show that in the neuronogenic cultures of mouse embryonic brain-derived neuroepithelial cells, histone modifications including acetylated histone H3 and histone H4, but not histone H3 trimethylation at lysine 27 of two genes encoding two key regulatory GTs, namely, N-acetylgalactosaminyltransferase I and sialyltransferase II, were extensively and gradually enhanced, respectively. As a consequence, the level of each GT mRNA was increased correspondingly. Hyperacetylation of histones on the GalNAcT promoter resulted in recruitment of the trans-activation factors Sp2 and AP-1 when cellular histone deacetylases 1 and 2 were knocked down with RNA interference or inhibited by treatment with valproic acid. Moreover, epigenetic activation of GalNAcT was also detected, as accompanied by a pronounced induction of neural differentiation in primary neuroepithelium culture responding to an exogenous supplement of ganglioside GM1, a downstream product of the gene's encoding enzyme. Our findings thus provide direct evidence of novel pathways for ganglioside expression via the epigenetic up-regulation of ganglioside synthase genes during neural development.
...
PMID:Epigenetic activation of mouse ganglioside synthase genes: implications for neurogenesis. 2410 78