Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

The sialylation and desialylation in the rat epididiymis is the transference or remotion of sialic acid, to or from an adequate acceptor (glyco or sialogycoprotein). The sialylation of the glycoprotein or glycolipids is determinated by sialyltransferase activity; the homogenates from caput region showed 14 times more sialyltransferase activity than homogenates from cauda epididymis. The desialylation of the sialoglycoproteins is quantified by neuraminidase activity, and it can be observed that the homogenate from the caput zone shows 3 times more activity than homogenates from cauda epididymis. When relatione the activities of sialytransferase/neuraminidase of the caput zone and the cauda zone, the obtained values were 0.19 +/- 0.03 and 0.04 +/- 0.005, respectively. The relation between the activities of neuraminidase/sialiltransferase of the caput and the cauda zone showed the following valves: 5 +/- 0.6 and 25 +/- 3.3, respectively. The results have shown that sialylation is more active in the caput than in the cauda. Besides, while valvating the desialylation we observe that it is more effective in the cauda epididymis.
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PMID:[Role of sialyltransferase and neuraminidase in the epididymis of rats]. 248 56

The cation-independent mannose 6-phosphate receptor (MPRCI) functions in the packaging of both newly made and extracellular lysosomal enzymes into lysosomes. The subcellular location of MPRCI reflects these two functions; receptor is found in the Golgi complex, in endosomes, and on the cell surface. To learn about the intracellular pathway followed by surface receptor and to study the relationship between the receptor pools, we examined the entry of the surface MPRCI into Golgi compartments that contain sialyltransferase. Sialic acid was removed from surface-labeled K562 cultured human erythroleukemia cells by neuraminidase treatment. When the cells were returned to culture at 37 degrees C, surface MPRCI was resialylated by the cells with a half-time of 1-2 h. Resialylation was inhibited by reduced temperature, a treatment that allows surface molecules to reach endosomes but blocks further transport. These results indicate that surface MPRCI is transported to the sialyltransferase compartment in the Golgi complex. After culture at 37 degrees C, a small fraction (10-20%) of the resialylated receptor was found on the cell surface. Because a similar fraction of the total receptor pool is found on the cell surface, it is likely that cell surface MPRCI mixes with the cellular pool after resialylation. These data also support the idea that extracellular and newly made lysosomal enzymes are transported to lysosomes through a common compartment.
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PMID:Transport of surface mannose 6-phosphate receptor to the Golgi complex in cultured human cells. 254 Feb

The effect of retinoid induced suppression of in vitro invasive ability of A549 human lung carcinoma cells on sialyltransferase activity and sialic acid content was investigated. Inhibition by retinol acetate of cell invasive potential was accompanied by a significant decrease in the enzyme activity of intact cells as well as total and cell surface neuraminidase-releasable sialic acid contents. Moreover, reversibility of the invasion-suppressed A549 cell phenotype resulted in a return of invasion potential, sialyltransferase activity and surface sialic acid content to invasive cell levels. These findings suggest that membrane-bound sialic acid plays a role in invasiveness of A549 cells.
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PMID:Reversibility of retinoid effect on sialyltransferase activity, sialic acid content and invasive ability of human lung carcinoma cells. 262 20

The lentivirus caprine arthritis-encephalitis virus (CAEV) is a pathogen of goats. It is transmitted in milk and causes a persistent infection in goats, which often fail to produce neutralizing antibodies to the virus. Native CAEV particles are remarkably resistant to digestion with proteinase K and are neutralized extremely slowly by immune sera. Our studies showed that the virus particles are heavily sialylated. Studies with highly specific sialyltransferase enzymes identified penultimate carbohydrate linkages typical of O- and N-linked oligosaccharides on the virus and suggested that the virus may be more heavily sialylated on O-linked than on N-linked oligosaccharides. Removal of sialic acids from the virus by neuraminidase treatment did not reduce infectivity of the particles. However, desialylation rendered the virus more susceptible to proteolysis by proteinase K. Desialylation also enhanced the kinetics of neutralization of the virus by goat antibodies. These results suggest that the carbohydrates on the viral surface are important both in protecting viral proteins from digestion by proteases and in protecting the virus from rapid neutralization by antibodies.
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PMID:Sialic acids on the surface of caprine arthritis-encephalitis virus define the biological properties of the virus. 283 2

The erythrocyte receptors for S-fimbriated Escherichia coli, which causes sepsis and meningitis in newborn infants, were investigated. Neuraminidase and trypsin treatments of erythrocytes abolished the hemagglutination ability of the bacteria. To identify the receptor glycoproteins, we separated erythrocyte membrane proteins by gel electrophoresis, blotted them to nitrocellulose, and incubated them with 125I-labeled bacteria. The only bacterium-binding bands identified corresponded to glycophorin A dimer and monomer, and the binding was abolished by neuraminidase treatment of the blot. Radiolabeled bacteria also bound to purified glycophorin A adsorbed to polyvinyl chloride microwells, and the binding was inhibited by other sialoglycoproteins and isolated sialyloligosaccharides containing the NeuAc alpha 2-3Gal sequence. Oligosaccharides which contain the NeuAc alpha 2-3Gal beta 1-3GalNAc and NeuAc alpha 2-3Gal beta 1-3(NeuAc alpha 2-6)GalNAc sequence and which are identical to the O-linked saccharides of glycophorin A were twofold more effective inhibitors of binding than were other oligosaccharides containing the NeuAc alpha 2-3Gal sequence. The replacement of sialic acid in asialoerythrocytes with a purified Gal beta 1-3GalNAc alpha 2-3 sialyltransferase, which forms the O-linked NeuAc alpha 2-3Gal beta 1-3GalNAc sequence in asialoglycophorins, restored bacterial hemagglutination. These results indicated that the major erythrocyte receptor for S-fimbriated E. coli is the NeuAc alpha 2-3Gal beta 1-3GalNAc sequence of the O-linked oligosaccharide chains of glycophorin A.
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PMID:Identification of the O-linked sialyloligosaccharides of glycophorin A as the erythrocyte receptors for S-fimbriated Escherichia coli. 287 51

The intracellular movement of cell surface transferrin receptor (TfR) after internalization was studied in K562 cultured human erythroleukemia cells. The sialic acid residues of the TfR glycoprotein were used to monitor transport to the Golgi complex, the site of sialyltransferases. Surface-labeled cells were treated with neuraminidase, and readdition of sialic acid residues, monitored by isoelectric focusing of immunoprecipitated TfR, was used to assess the movement of receptor to sialyltransferase-containing compartments. Asialo-TfR was resialylated by the cells with a half-time of 2-3 h. Resialylation occurred in an intracellular organelle, since it was inhibited by treatments that allow internalization of surface components but block transfer out of the endosomal compartment. Moreover, roughly half of the resialylated molecules were cleaved when cells were retreated with neuraminidase after culturing, indicating that this fraction of the molecules had returned to the cell surface. These results suggest that TfR is transported from the cell surface to the Golgi complex, the intracellular site of sialyltransferases, and then returns to the cell surface. This pathway, which has not been previously described for a cell surface receptor, may be different from the route followed by TfR in iron uptake, since reported rates of transferrin uptake and release are significantly more rapid than the resialylation of asialo-TfR.
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PMID:Intracellular movement of cell surface receptors after endocytosis: resialylation of asialo-transferrin receptor in human erythroleukemia cells. 298 85

We have investigated the ganglioside levels, composition and metabolism in two lines of doxorubicin-resistant cells and in the corresponding wild strains, the C6 rat glioblastoma and the HTC rat hepatoma. The only ganglioside present was GM3, and its level was increased 2-fold in C6 resistant cells and decreased nearly 2-fold in HTC resistant cells. A decrease of cytidine 5'-monophospho-N-acetylneuraminic acid:galactosylglucosylceramide sialyltransferase activity was observed in both resistant lines as compared to sensitive ones, and could not, therefore, explain the increase in the GM3 level observed in the C6 resistant line. Alterations of acid neuraminidase activity were also observed; a 5-fold decrease was noticed in the C6 resistant line and could account for the increase in the GM3 level observed in these cells; in contrast, a 2-fold increase of acid neuraminidase activity was noticed in the HTC resistant cells: together, with reduced synthesis, it could explain the decrease in the GM3 level observed in these cells. No alterations of exogenous ganglioside transport was exhibited by the C6 resistant cells.
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PMID:Alteration of ganglioside composition and metabolism in doxorubicin-resistant rat tumoral cells. 319 50

As described previously (I. Kijima-Suda et al., Cancer Res., 46: 858-862, 1986), a sialyltransferase inhibitor, 5-fluoro-2',3'-isopropylidene-5'-O-(4-N-acetyl-2,4-dideoxy-3,6,7,8-tetra -O- acetyl-1-methoxycarbonyl-D-glycero-alpha-D-galactooctapyranosyl)ur idine (KI-8110), inhibits pulmonary metastasis of murine colon adenocarcinoma 26 sublines of high (NL-17) and low (NL-44) metastatic potential. To investigate the mechanism of this inhibition, the effect of KI-8110 on the metastatic cascade, especially on the interaction between tumor cells and platelets which may play a crucial role in tumor cell metastasis, was examined. NL-17 cells induced irreversible platelet aggregation in heparinized human platelet-rich plasma in vitro. This activity was reduced by pretreatment of the tumor cells with KI-8110. Inhibition of aggregation was also induced by the treatment of tumor cells with neuraminidase or Limax flavus agglutinin, a lectin specific for sialic acid. Sialic acid, fucose, sialyllactose, and bovine submaxillary mucin inhibited this tumor cell-induced platelet aggregation, while galactose, mannose, lactose, alpha 1-acid glycoprotein, fetuin, and asialo-bovine submaxillary mucin did not. KI-8110 also inhibited platelet-derived growth factor-dependent growth of NL-17 cells, but showed no effect on insulin or epidermal growth factor-dependent growth of the tumor cells. Platelet-derived growth factor-induced phosphorylation of membrane protein was reduced by treatment of NL-17 cells with KI-8110. The same result was obtained in the neuraminidase-treated membrane fraction of NL-17 cells. These results suggest that KI-8110 inhibits experimental tumor cell metastasis by inhibiting the interaction between tumor cells and host platelets in at least two pathways, and this may be due to a reduction of sialic acid contents of the membrane surface of tumor cells.
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PMID:Possible mechanism of inhibition of experimental pulmonary metastasis of mouse colon adenocarcinoma 26 sublines by a sialic acid: nucleoside conjugate. 328 33

Previous studies have demonstrated the ability of retinoic acid (RA) to inhibit the growth of two spontaneous murine melanoma cell lines (B16-F1 and S91-C2) and to augment both sialyltransferase activity and the sialylation of an Mr 160,000 cell-surface glycoprotein. The present study examined the effects of RA on an ultraviolet irradiation-induced murine melanoma cell line K-1735P. Like the two spontaneous melanomas, the uv-induced melanoma exhibited susceptibility to the growth-inhibitory action of RA. Both the anchorage-dependent and the anchorage-independent growths of the K-1735P cells were suppressed by RA, with IC50 values of 5 X 10(-9) and 3 X 10(-12) M, respectively. Sialyltransferase activity in both S91-C2 and K-1735P cells treated with 10(-6) or 10(-5) M RA increased two- and three-fold, respectively, as compared with untreated cells. In contrast, cell-surface sialo- and galactoglycoproteins, revealed by labeling with periodate and tritiated borohydrate or with neuraminidase, galactose oxidase, and tritiated borohydrate, respectively, varied between the S91-C2 and the K-1735P cells, and each cell line's modulation by RA was also distinct. These findings suggest that although RA can increase the activity of sialyltransferase in different melanoma cells, this increased activity may, in turn, result in an increased sialylation of distinct cell-surface glycoproteins.
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PMID:Enhancement of sialyltransferase in two melanoma cell lines that are growth-inhibited by retinoic acid results in increased sialylation of different cell-surface glycoproteins. 339 Dec 45

Adipocytes treated with neuraminidase show markedly reduced responsiveness to insulin without any alteration in insulin binding. In addition, several studies have separately demonstrated both insulin resistance and decreases in membrane sialic acid content and associated biosynthetic enzymes in diabetes mellitus. In the present study, we investigated the role that sialic acid residues may play in insulin action and in the hepatic insulin resistance associated with nonketotic diabetes. Primary cultures of hepatocytes from normal rats treated with neuraminidase demonstrated a dose-dependent decrease in insulin-stimulated lipogenesis. At a concentration of neuraminidase that decreases insulin action by 50%, 23% of total cellular sialic acid content was released. Neuraminidase-releasable sialic acid was significantly decreased in hepatocytes from diabetic rats and this was associated with significant insulin resistance. Treatment of hepatocytes from diabetic rats with cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NANA) enhanced insulin responsiveness 39%. The enhanced insulin responsiveness induced by CMP-NANA was blocked by cytidine 5'-monophosphate (CMP) suggesting that the CMP-NANA effect was catalyzed by a cell surface sialyltransferase. CMP reduced neuraminidase-releasable [14C]sialic acid incorporation into hepatocytes by 43%. The data demonstrate a role for cell surface sialic acid residues in hepatic insulin action and support a role for decreased cell surface sialic acid residues in the insulin resistance of diabetes mellitus.
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PMID:Role of sialic acid in insulin action and the insulin resistance of diabetes mellitus. 340 69


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