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

It is generally recognized that no one cell culture system can be universally applied to all cell types commonly used for biopharmaceutical manufacture. The analogous concept that no single cell type may be useful for the expression of all biopharmaceutical products may also gain credence in the biotechnology community. It may be that like specialized bioreactors, there will come to exist a variety of cell types that will be used for the production of different types of biopharmaceutical products. In addition, it may not be enough in the future just to demonstrate the stability of expression of the amino acid backbone of the protein only; the carbohydrate portion of the molecule may become the subject of real scrutiny. Questions such as how the carbohydrate side chain affects the performance of the molecule in vivo are being asked of more DNA constructs. The next question becomes, how can we control the expression of carbohydrate moieties on the molecule? Such questions are in the future of the biotech manufacturing field. Aside from those examples mentioned above dealing with the insertion of receptors, other more subtle attempts at modifying cellular metabolism are taking place. It was reported at a recent meeting that the sialyltransferase gene was inserted into a CHO line which did not normally express this enzyme (116). The transfected line was capable of expressing the transferase and, more importantly, the enzyme functioned correctly in sialylating glycoproteins. Other very complex relationships exist between the substratum and the cell that could have very direct consequences on culture maintenance. For example, researchers recently published results indicating that collagenase synthesis and secretion is stimulated in rabbit fibroblasts by autocrine factors. They determined that these autocrine proteins had sequence homology to serum amyloid-A and beta-2-microglobulin. It may be that using serum supplements in the medium in those systems that couple fibroblast and collagen substratum may not be prudent, especially for long-term culture. The traditional selection of a cell type for expressing heterologous proteins has generally been limited to the more "common" cell types such as CHO cells, C127 cells, and myeloma cells. In many cases these cell types were selected because there was a great deal of preexisting literature on the cell type (i.e., "cookbook" methods of transfection for the cell) or the cell was simply being carried in the lab at the time the effort was made to express a biopharmaceutical product.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Large-scale animal cell culture: a biological perspective. 136 73

Monolayers of hepatocytes attached on collagen-coated dishes were cultured for 20-24 h and were found suitable to study the activity and secretion of CMP-N-acetylneuraminate:asialo-alpha 1-acid glycoprotein sialyltransferase. A progressive increase of sialyltransferase activity in the culture medium was observed during incubation of the hepatocytes. After 24 h 34-48% of the total sialyltransferase activity of the hepatocyte incubation system was present in the medium. The enzyme activity present in the medium was soluble in nature and could not be stimulated by Triton X-100. The secretion of the enzyme was stimulated about twofold by dexamethasone. The activity of sialyltransferase in the hepatocytes was also increased by dexamethasone. The Km of either hepatocyte or medium sialyltransferase for CMP-sialic acid was only slightly changed by dexamethasone, whereas the Vmax was increased about twofold. The secretion of sialyltransferase could be inhibited partially by the anti-microtubular agent colchicine. The dexamethasone-induced increase of the sialyltransferase activity in cells and media could be eliminated by inclusion of alpha-amanitin in the culture media at 0 h. The inhibiting effect of alpha-amanitin was only partially expressed when the drug was added 4 h after the addition of dexamethasone to the media. The results suggest that isolated rat hepatocytes actively secrete sialyltransferase and that the increase in the sialyltransferase activity in cells and media owing to the synthetic glucocorticosteroid dexamethasone results from increased synthesis of the enzyme molecule. It is supposed that in the intact rat the increased levels of the enzyme activity in serum observed in inflammation may originate from an induction of the synthesis of sialyltransferase in the hepatocytes of rat liver by the increased levels of circulating corticosteroids.
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PMID:Activity and secretion of sialyltransferase in primary monolayer cultures of rat hepatocytes cultured with and without dexamethasone. 371 1

Platelet sialyltransferase activity was determined in four patients with primary platelet release disorder. Basal enzyme activity was significantly reduced in all. Moreover, enzyme activity in response to stimulation by collagen or sodium arachidonate was also reduced. Platelet total and surface sialic-acid content was normal. The results indicate that defective membrane sialytransferase may be involved in the pathogenesis of primary platelet release disorder.
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PMID:Reduced platelet sialyltransferase activity in patients with primary release disorder. 610 96

Proteolytic and sialyltransferase activities were determined in extracts of 65 human primary breast tumors, 6 lymph node metastases, 6 fibroadenomas and 27 normal tissues. Using proteins and synthetic selective substrates, we observed the presence of collagen-peptidases, plasminogen activator, cathepsin-B and cathepsin-D-like enzymes, and sialyltransferase. No active or trypsin-activatable type-IV collagenase activity was detected. Although individual variations between tumors were large, proteinase and sialyltransferase contents were significantly elevated in malignant breast tissues. Enzyme activities were found to be related to the epithelial volume of the tumor. No significant correlation was found between the proteinase or sialyltransferase activities and the degree of differentiation of the tumor cells, or the degree to which tumors had metastasized to regional lymph nodes. Since large variations of enzyme levels apparently reflect the heterogeneity of epithelial cell densities in tumor samples, proteolytic or sialyltransferase activities cannot therefore be used as a measure of quantitative evaluation of invasive properties in breast cancer.
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PMID:Proteinases and sialyltransferase in human breast tumors. 632 71

Tumor-associated alterations of cell surface glycosylation play a crucial role in the adhesion and metastasis of carcinoma cells. The aim of this study was to examine the effect of alpha 2,6-sialylation on the adhesion properties of breast carcinoma cells. To this end mammary carcinoma cells, MDA-MB-435, were sense-transfected with sialyltransferase ST6Gal-I cDNA or antisense-transfected with a part of the ST6Gal-I sequence. Sense transfectants showed an enhanced ST6Gal-I mRNA expression and enzyme activity and an increased binding of the lectin Sambucus nigra agglutinin (SNA), specific for alpha 2,6-linked sialic acid. Transfection with ST6Gal-I in the antisense direction resulted in less enzyme activity and SNA reactivity. A sense-transfected clone carrying increased amounts of alpha 2,6-linked sialic acid adhered preferentially to collagen IV and showed reduced cell-cell adhesion and enhanced invasion capacity. In contrast, antisense transfection led to less collagen IV adhesion but enhanced homotypic cell-cell adhesion. In another approach, inhibition of ST6Gal-I enzyme activity by application of soluble antisense-oligodeoxynucleotides was studied. Antisense treatment resulted in reduced ST6 mRNA expression and cell surface 2,6-sialylation and significantly decreased collagen IV adhesion. Our results suggest that cell surface alpha 2,6-sialylation contributes to cell-cell and cell-extracellular matrix adhesion of tumor cells. Inhibition of sialytransferase ST6Gal-I by antisense-oligodeoxynucleotides might be a way to reduce the metastatic capacity of carcinoma cells.
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PMID:Cell surface alpha 2,6 sialylation affects adhesion of breast carcinoma cells. 1197 12

Beta-galactoside alpha2,6 sialyltransferase (ST6Gal.I), the enzyme which adds sialic acid in alpha2,6-linkage on lactosaminic termini of glycoproteins, is frequently overexpressed in cancer, but its relationship with malignancy remains unclear. In this study, we have investigated the phenotypic changes induced by the expression of alpha2,6-sialylated lactosaminic chains in the human colon cancer cell line SW948 which was originally devoid of ST6Gal.I. Clones derived from transfection with the ST6Gal.I cDNA were compared with untransfected cells and mock transfectants. The ST6Gal.I-expressing clones show (1) increased adherence to fibronectin and collagen IV but not to hyaluronic acid. Treatment with Clostridium perfrigens neuraminidase reduces the binding to fibronectin and collagen IV of ST6Gal.I-expressing cells but not that of ST6Gal.I-negative cells; (2) accumulation and more focal distribution of beta1 integrins on the cell surface; (3) different distribution of actin fibers; (4) flatter morphology and reduced tendency to multilayer growth; (5) improved ability to heal a scratch wound; (6) reduced ability to grow at the subcutaneous site of injection in nude mice. Our data suggest that the presence of alpha2,6-linked sialic acid on membrane glycoconjugates increases the binding to extracellular matrix components, resulting in a membrane stabilization of beta1 integrins, further strengthening the binding. This mechanism can provide a basis for the flatter morphology and the reduced tendency to multilayer growth, resulting in a more ordered tissue organization. These data indicate that in the cell line SW948, the effect of ST6Gal.I expression is consistent with the attenuation of the neoplastic phenotype.
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PMID:Phenotypic changes induced by expression of beta-galactoside alpha2,6 sialyltransferase I in the human colon cancer cell line SW948. 1619 7

During carcinogenesis aberrant N-glycosylation may lead to the development of subpopulations of tumor cells with altered adhesion properties and increased invasive potential. Biosynthesis of glycans and oligosaccharides is tissue-specific and developmentally regulated by number of glycosyltransferases of which fucosyl-, sialyl- and N-acetylglucosaminyltransferases often participate in synthesis of tumor type glycans. We analyzed the expression of selected glycosyltransferases (real-time PCR): fucosyltransferases FUT-1 and FUT-4, sialyltransferase SIAT4C and beta 1,6-N-acetylglucosaminyltransferase V (MGAT-5), in human melanoma cell lines: WM35 from primary tumor site and WM239, WM9, A375 from metastatic sites. In parallel their proliferation (crystal violet test) and adhesion to fibronectin and collagen IV (BD Biocoat assay) was assessed. Examined cell lines showed expression of all studied glycosyltransferases. The level of expression of fucosyltransferases was significantly higher in melanoma cell lines from metastatic site than from primary cell line: mRNA expression of FUT-1 was 100 times higher in A375 melanoma cell line from metastatic site (A375, solid tumor) than in WM35 primary cell line. The expression of FUT-4 in cell lines from metastatic sites: WM9 (lymph node) and WM239 (skin) was respectively 80 and 37 times higher than in WM 35 primary cell line. In all melanoma cell lines very low expression of MGAT-5 and high expression of SIAT4C was observed. Melanoma cells bound both to fibronectin and to collagen IV. LTA (Lotus tetragonolobus agglutinin), the lectin that specifically recognizes fucose residue of glycans and 20mM L-fucose by itself significantly reduced adhesion of all studied cell lines, both primary and metastatic, to fibronectin (20-50 %) and to collagen IV (20-50 %). In addition LTA reduced the proliferation (20-30 %) of metastatic cell lines (A375, WM9, WM239) and did not affect the growth of primary cell line (WM35). The results suggest that higher expression of fucosyltransferases (FUT-1, FUT-4) might be an important step in the formation of surface structures that facilitate metastasis of melanoma.
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PMID:Expression of fucosyltransferases contributes to melanoma invasive phenotype. 1789 65