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:2.4.99.6 (sialyltransferase)
1,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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

Sialyltransferase (Gal beta 1,4GlcNAc alpha 2,6 sialyltransferase) was localized by immunoelectron microscopy in rat liver hepatocytes using affinity-purified antibodies. Immunoreactivity for sialyltransferase was found in the Golgi apparatus, where it was restricted to an interconnected system consisting of the trans-cisternae and the trans-tubular network. This region of the Golgi apparatus exhibited both TPPase and CMPase activity and was the intracellular site where sialic acid residues bound to glycoprotein were detected using the Limax flavus lectin. Sialyltransferase and sialic acid residues were not detected in medial and cis-cisternae of the Golgi apparatus. These findings suggest that in rat hepatocytes sialylation of N-linked glycoproteins occurs in the complex formed by the trans-cisternae and the trans-tubular network of Golgi apparatus.
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PMID:Demonstration of an extensive trans-tubular network continuous with the Golgi apparatus stack that may function in glycosylation. 300 Jun 3

The recycling of cellular glycoproteins to the site of Golgi mannosidase I, an enzyme of asparagine-linked oligosaccharide synthesis, was studied in K562 human erythroleukemia cells. Cells were metabolically labeled in the presence of deoxymannojirimycin, a reversible inhibitor of Golgi mannosidase I. This generates glycoproteins with immature oligosaccharides in their normal locations. Transport to the mannosidase I compartment was then assessed by testing for the conversion of oligosaccharides into mature forms during reculture without deoxymannojirimycin. Transferrin receptor (TfR) was acted on by mannosidase I during reculture, suggesting that it returned to the region of the Golgi complex where this enzyme resides. The slow rate of this transport (t1/2 greater than 6 h) implies that it is probably different than TfR movement during transferrin internalization (t1/2 = 10-20 min) and TfR transport to the sialyltransferase compartment in the Golgi complex (t1/2 = 2-3 h) (Snider, M. D., and O. C. Rogers, 1985, J. Cell Biol., 100:826-834). The total cell glycoprotein pool was also transported to the mannosidase I compartment with a half-time of 4 h. Because this transport is 5-10 times faster than the rate of de novo glycoprotein synthesis in these cells, it is likely that most of the glycoprotein traffic through the Golgi complex is composed of recycling molecules.
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PMID:Membrane traffic in animal cells: cellular glycoproteins return to the site of Golgi mannosidase I. 301 99

Liver slices from control and inflamed rats were incubated in McCoy's medium and incorporation of [3H]leucine into liver and medium proteins and into albumin and alpha 1-acid glycoprotein was monitored over 48 hr. The release of the new acute phase reactant, sialyltransferase was also monitored in this system. Earlier observations in which liver slices were incubated for 6 hr showed that increased leucine incorporation into liver and medium proteins and alpha 1-acid glycoprotein, coupled with decreased incorporation into albumin, correlated with the acute phase response of these proteins. Increased incorporation of leucine into these proteins was found following 48 hr incubation in McCoy's medium showing that slices were able to express the changes characteristic of the acute phase response over this longer time period of incubation. Sialyltransferase was released into medium in a linear fashion up to 15 hr and continued to increase for 30 hr in this system; there was a substantial increase in release of enzyme activity from slices from inflamed rats when compared to controls. Monokine-conditioned medium prepared from peritoneal exudate cells isolated from rats at various times after lipopolysaccharide administration was used to induce the acute phase response by intraperitoneal injection. Slices were prepared from these rats and sialyltransferase release from slices was monitored. Monokines prepared from peritoneal exudate cells isolated from rats at about 30 hr were most effective in stimulating sialyltransferase release from liver slices.
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PMID:Studies on the effect of inflammation on the acute phase response using rat liver slices. 310 62

The role of monocyte derived factors in the acute phase response to inflammation is discussed. The kinetics of response of alpha 1-acid glycoprotein, sialyltransferase and albumin to a rat monokine preparation is described. There was an increase in synthesis of alpha 1-acid glycoprotein and sialyltransferase and a decrease in albumin synthesis following administration. However, the kinetics of response of sialyltransferase to the monokine was much slower than was found for the other two proteins. The possibility that sialyltransferase responds to a different monokine compared to the other acute phase proteins is discussed.
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PMID:The acute phase response to inflammation: the role of monokines in changes in liver glycoproteins and enzymes of glycoprotein metabolism. 311 78

Rat peritoneal leukocytes (PEC) were fractionated on Percoll gradients to prepare populations of monocytes/lymphocytes and polymorphonuclear leukocytes; adherent (monocyte enriched) and non-adherent (lymphocytes/polymorphonuclear leukocytes) cells were also isolated from PEC. Cytokines were prepared from PEC and subfractions and injected into rats to induce the acute phase reactants serum alpha 1-acid glycoprotein and sialyltransferase; negative acute phase parameters serum albumin and liver hexosaminidase were also assayed. Monocyte derived cytokines (monokines) mimicked the acute phase response of all four parameters in vivo. The sialyltransferase isoenzyme that responded to monokine was identified as the Gal beta 1----4GlcNAc alpha 2----6 isoenzyme.
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PMID:Studies of monokines as mediators of the acute phase response: effects on sialyltransferase, albumin, alpha 1-acid glycoprotein and beta-N-acetylhexosaminidase. 316 99

Sialyltransferase activity was measured in erythrocyte membranes and in serum in patients with myotonic dystrophy and in matched healthy controls. The reason for assaying this enzyme was to study a possible mechanism behind a previously reported deficiency of glycoprotein-bound sialic acid in the erythrocyte membrane in patients with this disease. No significant differences in sialyltransferase activity with endogenous or different exogenous glycoprotein acceptors were found.
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PMID:Sialyltransferase activity in erythrocyte membranes and serum in patients with myotonic dystrophy. 322 22

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 shown that treatment of S91-C2 murine melanoma cells with beta-all-trans-retinoic acid (RA) results in growth inhibition, enhanced activity of sialyltransferase, and increased glycosylation of a Mr 160,000 cell surface sialoglycoprotein (gp160). None of these effects could be detected in mutant clones (e.g., S91-C154) selected from the S91-C2 cells for resistance to RA-induced growth inhibition. These findings suggest that modulation by RA of gp160 might be related causally to growth inhibition. In this study we examined the possible role of gp160 in growth regulation using specific antibodies to this glycoprotein. Metabolic labeling of S91-C2 cells with either [3H]glucosamine or [35S]methionine revealed that the cells shed into the growth medium a gp160-like glycoprotein, in addition to several other macromolecules. The gp160-like glycoprotein was isolated from concentrated conditioned medium after preparative polyacrylamide slab gel electrophoresis in the presence of sodium dodecylsulfate by excision of the corresponding protein band. Rabbits were immunized with this material and immunoblotting revealed that their sera contained antibodies that bound specifically to gp160 in extracts of untreated or RA-treated S91-C2 cells. Indirect immunofluorescence staining followed by fluorescence-activated cell sorter analysis demonstrated that the anti-gp160 antibodies bound to the surface of both untreated and RA-treated S91-C2 cells and that the treated cells bound more of the antibodies than untreated ones. In contrast, these antibodies bound to the same extent to untreated and RA-treated resistant S91-C154 cells. The growth of S91-C2 cells in the presence of anti-gp160 antibodies in semisolid medium as well as in monolayer cultures was inhibited in a dose-dependent fashion. Fifty % growth inhibition was obtained at an immunoglobulin concentration of 10 micrograms/ml. The growth of cells exposed concurrently to RA and anti-gp160 antibodies was also inhibited strongly in semisolid medium, but the antibodies caused only a small increase in the inhibitory effect of RA in monolayer cultures. No inhibition by the antibodies of either anchorage-independent growth or anchorage-dependent growth of S91-C154 cells, grown in the absence or presence of RA, was observed. These results support the suggestion that cell surface gp160 might be involved in growth regulation in the S91-C2 cells.
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PMID:Growth inhibition of murine melanoma cells by antibodies to a cell surface glycoprotein implicated in retinoic acid action. 355 69

A modified high pressure liquid chromatographic method using lactose (Gal beta 1----4Glc) as an exogenous acceptor has been used to characterize the sialyltransferases known to increase in the serum of colchicine-treated rats. The results show a 10-fold increase of Gal beta 1----4GlcNAc alpha 2----6 sialyltransferase (alpha 2----6 ST), whereas the Gal beta 1----3GlcNAc alpha 2----3 sialyltransferase showed only 1.6-fold increase in the serum after 17 h of colchicine treatment. The sialyltransferase activity in serum using exogenous desialylated, alpha 1-acid glycoprotein as acceptor also showed an eightfold increase. In liver homogenate and Golgi membrane, the sialyltransferase activity when assayed with desialylated alpha 1-acid glycoprotein as acceptor showed a slight decrease after 4 h, but returned to normal level after 17 h. A similar trend was seen when the two transferases were assayed with lactose as acceptor. The antiserum to rat alpha 2----6 ST inhibited the sialyltransferase activity in serum, liver, and jejunal incubation medium. Jejunal sections from rats treated with colchicine for 4 h in presence of heated serum showed a decrease of sialyltransferase, with consequent increase of the alpha 2----6 ST enzyme activity in the medium. This result suggests that intestinal tissue could be a source of increased serum enzyme activity in colchicine treatment.
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PMID:Characterization of serum, liver, and intestinal sialyltransferases from rats treated with colchicine. 358 Jan 69


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