Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We investigated biosynthesis, intracellular transport and release of beta-galactoside alpha-2,6-sialyltransferase in a dexamethasone-inducible rat hepatoma cell line. Confluent cells were induced by 10 microM dexamethasone for 24 h, and metabolically labelled with [35S]methionine/cysteine, followed by immunoprecipitation of sialyltransferase and electrophoretic/fluorographic analysis. The 35S-labelled enzyme was synthesized as a 46-kDa precursor, converted to an intermediate 47-kDa form after 1 h, and gradually to a mature form of 48 kDa within the following 3 h. By means of either tunicamycin inhibition of N-glycosylation or cleavage of N-glycans from isolated sialyltransferase using N-glycosidase F, the sizes of the precursor and the mature form were reduced to 41 kDa and 43 kDa, respectively. After a 4-h chase, treatment with endoglycosidase H revealed two distinct molecular forms of sialyltransferase, bearing either two N-acetyllactosamine-type or one oligomannose-type and one N-acetyllactosamine-type N-linked sugar chain. In addition, sialyltransferase became sensitive to neuraminidase digestion after a 4-h chase. The half-life of intracellular [35S]sialyltransferase was estimated at 3 h. A soluble form was detectable in the supernatant, 2 h after the pulse. Only 12% of the initially labelled sialyltransferase was found in the medium after 12 h, while 73% of the enzyme was degraded intracellularly. To characterize a possible intracellular degradation site, we studied intracellular transport in the presence of either secretion-blocking or acidotropic agents or protease inhibitors. Degradation was significantly delayed by all treatments. Our results show that sialyltransferase follows the secretory pathway as a membrane protein and is retained at a late Golgi stage. We suggest that the bulk of sialyltransferase in rat hepatoma cells is diverted to a post-Golgi degradation pathway. This route contrasts with the post-Golgi trafficking of beta-1,4-galactosyltransferase in HeLa cells, which is constitutively secreted [Strous, G. J. A. M. & Berger, E. G. (1982) J. Biol. Chem. 257, 7623-7628].
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PMID:Biosynthesis and intracellular transport of alpha-2,6-sialyltransferase in rat hepatoma cells. 152 30

Detection of the activity of beta-1,4-galactosyltransferase (beta-1,4-GT) in suspensions of viable mouse hepatocytes, the human hepatoma cell line Hep G2, the human colonic adenocarcinoma cell line HT-29, the monocyte-like cell line U937, and human splenic B and T lymphocytes suggested the presence of beta-1,4-GT, in an enzymatically active form, on plasma membranes. The presence of beta-1,4-GT on cell surfaces was also indicated from the effect of trypsinization of live cells, which significantly reduced cell surface beta-1,4-GT activity, but did not affect the activity associated with cytoplasmic membranes. Furthermore, the presence of beta-1,4-GT on the cell surface was demonstrated by indirect immunofluorescence staining of cells with anti-beta-1,4-GT antibody. The detection of radioactivity in immunoglobulins (Ig) and their component chains after incubation with suspensions of intact cells in the presence of Mn2+ and UDP-[3H]-galactose, indicated that Ig molecules were galactosylated. In the absence of UDP-[3H]-galactose, beta-1,4-GT on cell surfaces, or immobilized on Sepharose-4B, formed stable complexes with galactose acceptors, including Ig. The efficiency of binding decreased in the order: J chain > alpha chain > mu chain > polymeric IgA2 > monomeric/polymeric IgA1 > IgM > IgG. Thus, beta-1,4-GT could act as a cell-surface receptor for Ig through a cation-dependent, lectin-like association of the beta-1,4-GT with the carbohydrate moieties of the Ig. This was confirmed by indirect surface immunofluorescence and radiolabeled ligand binding assays. The binding was inhibitable by EDTA, alpha-lactalbumin (in the presence of glucose), GlcNAc, or uridine 3',5'dialdehyde. At 37 degrees C, the apparent affinity constants and association rate constants of interaction between cell surface beta-1,4-GT on glutaraldehyde-fixed HT-29 and U937 cells and alpha 2 chain or monomeric IgA1 were in the range from 7.1 x 10(7) to 4.6 x 10(8) M-1 and from 1 x 10(5) to 3 x 10(6) M-1 s-1, respectively. The dissociation rate constants and half time of dissociation calculated from these data were in the range from 2.1 x 10(-2) to 5.0 x 10(-4) s-1 and from 33 to 1380 s, respectively. The number of alpha 2 or IgA1 molecules bound per HT-29 and U937 cell were in the range from 1.9 x 10(5) to 1.3 x 10(6). The binding of IgA by the cell surface beta-1,4-GT was not associated with internalization or the catabolic degradation of the ligand.
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PMID:Interactions of cell-surface galactosyltransferase with immunoglobulins. 843 5

A human hepatocellular carcinoma cell line, SMMC-7721, was treated with all-trans-retinoic acid (RA) and phorbol 12-myristate 13-acetate (PMA) to induce its differentiation and proliferation respectively. A biantennary sugar chain fluorescently labelled with 2-aminopyridine (PA), GlcNAc beta 1-2Man alpha 1-6(GlcNAc beta 1-2Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4GlcNAc-PA, was used to detect the activity of beta-1,4-galactosyltransferase on the cell surface by HPLC. The results show that the activity of beta-1,4-galactosyltransferase on the cell surface increases when the cell is treated with RA, but decreases when it is treated with PMA, whereas the activities of the whole cell remain stable during the treatments.
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PMID:Effect of all-trans-retinoic acid and phorbol 12-myristate 13-acetate on the activity of human hepatocellular carcinoma cell-surface beta-1,4-galactosyltransferase. 897 76

beta-1,4-galactosyltransferase 1 (beta1,4-GT 1) is localized both in the Golgi complex where it catalyzes the transfer of galactose from UDP-galactose to terminal N-acetylglucosamine forming Galbeta1 --> 4GlcNAc structure, and on the cell surface where it serves as an adhesion molecule. It has previously been reported that the expression of beta1,4-GT 1 was cell-cycle-specific, regulated by cell growth. Transforming growth factor-beta1 (TGF-beta1) could regulate cell G1/S phase transition and modulate cell growth in many types of cells. In this study, we introduced the antisense-TGF-beta1 into SMMC-7721 cell, a human hepatocarcinoma cell line, for blocking its intrinsic TGF-beta1 expression, and changing its cell-cycle, and then analyzed the gene expression of beta1,4-GT 1 together with the beta1,4-GT activity. The result showed that the antisense-TGF-beta1 transfected SMMC-7721 cells (AST/7721) were growth enhanced, with more cells in S phase and less cells in G2/M phase compared with the mock transfected cells (pcDNA3/7721). At the same time, it was found that the gene expression of beta1,4-GT 1 in AST/7721 was decreased to one fifth that of pcDNA3/7721, and the cell surface beta1,4-GT activity was reduced to one fifth of the control, while the total activity of beta1,4-GT was decreased to one half that of the control. The results indicate that suppression of TGF-beta1 expression resulted in change of cell-cycle together with the decreased gene expression of beta1,4-GT 1 and beta1,4-GT activity in human hepatocarcinoma cells.
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PMID:Effect of suppression of TGF-beta1 expression on cell-cycle and gene expression of beta-1,4-galactosyltransferase 1 in human hepatocarcinoma cells. 1089 33